2005

Obes Res. 2005 Apr;13(4):693-702.
Intentional weight loss reduces mortality rate in a rodent model of dietary obesity.
Vasselli JR, Weindruch R, Heymsfield SB, Pi-Sunyer FX, Boozer CN, Yi N, Wang C, Pietrobelli A, Allison DB.
Department of Biostatistics, University of Alabama, Ryals Public Health Building, Room 327, 1665 University Boulevard, Birmingham, Alabama 35294-0022.

OBJECTIVE: We used a rodent model of dietary obesity to evaluate effects of caloric restriction-induced weight loss on mortality rate. Research Measures and Procedures: In a randomized parallel-groups design, 312 outbred Sprague-Dawley rats (one-half males) were assigned at age 10 weeks to one of three diets: low fat (LF; 18.7% calories as fat) with caloric intake adjusted to maintain body weight 10% below that for ad libitum (AL)-fed rat food, high fat (HF; 45% calories as fat) fed at the same level, or HF fed AL. At age 46 weeks, the lightest one-third of the AL group was discarded to ensure a more obese group; the remaining animals were randomly assigned to one of three diets: HF-AL, HF with energy restricted to produce body weights of animals restricted on the HF diet throughout life, or LF with energy restricted to produce the body weights of animals restricted on the LF diet throughout life. Life span, body weight, and leptin levels were measured. RESULTS: Animals restricted throughout life lived the longest (p < 0.001). Life span was not different among animals that had been obese and then lost weight and animals that had been nonobese throughout life (p = 0.18). Animals that were obese and lost weight lived substantially longer than animals that remained obese throughout life (p = 0.002). Diet composition had no effect on life span (p = 0.52). DISCUSSION: Weight loss after the onset of obesity during adulthood leads to a substantial increase in longevity in rats.

Mech Ageing Dev. 2005 Jun-Jul;126(6-7):783-93.
Energy expenditure of calorically restricted rats is higher than predicted from their altered body composition.
Selman C, Phillips T, Staib JL, Duncan JS, Leeuwenburgh C, Speakman JR.
University of Florida, Department of Aging and Geriatric Research, College of Medicine, P.O. Box 100107, Gainesville, FL 32608, USA.

Debate exists over the impact of caloric restriction (CR) on the level of energy expenditure. At the whole animal level, CR decreases metabolic rates but in parallel body mass also declines. The question arises whether the reduction in metabolism is greater, smaller or not different from the expectation based on body mass change alone. Answers to this question depend on how metabolic rate is normalized and it has recently been suggested that this issue can only be resolved through detailed morphological investigation. Added to this issue is the problem of how appropriate the resting energy expenditure is to characterize metabolic events relating to aging phenomena. We measured the daily energy demands of young and old rats under ad libitum (AD) food intake or 40% CR, using the doubly labeled water (DLW) method and made detailed morphological examination of individuals, including 21 different body components. Whole body energy demands of CR rats were lower than AD rats, but the extent of this difference was much less than expected from the degree of caloric restriction, consistent with other studies using the DLW method on CR animals. Using multiple regression and multivariate data reduction methods we built two empirical predictive models of the association between daily energy demands and body composition using the ad lib animals. We then predicted the expected energy expenditures of the CR animals based on their altered morphology and compared these predictions to the observed daily energy demands. Independent of how we constructed the prediction, young and old rats under CR expended 30 and 50% more energy, respectively, than the prediction from their altered body composition. This effect is consistent with recent intra-specific observations of positive associations between energy metabolism and lifespan and theoretical ideas about mechanisms underpinning the relationship between oxygen consumption and reactive oxygen species production in mitochondria.

Laryngoscope. 2005 Mar;115(3):405-11.
Effects of age and diet on rat skin histology.
Thomas JR.
Department of Otolaryngology, Chicago, Illinois, USA.

OBJECTIVE/HYPOTHESIS: To document age-related histologic morphometric changes of rat skin and the effects of calorie restriction on such changes. STUDY DESIGN: Fischer 344 rats of three age groups (young, 4 mo; adult, 1 year; old, 24+ months) were procured from ad libitum (AL) diet and calorie-restricted (CR) colonies of the National Institute of Aging and were used for histologic study. Each study group consisted of six animals. METHODS: Skin samples from the dorsum (DS) and footpad (FP) of these animals were excised and processed for histology with staining techniques for general morphology (hematoxylin-eosin-phloxine) and for differentiation of collagen bundles and elastic fibers (Verhoeff-van Gieson technique). Light microscopic morphometric and stereologic point counting procedures were applied manually to tissue sections to obtain quantitative data on the depth of the epidermis, dermis, and stratum corneum, epidermal nuclear number, and percentage fraction of collagen, elastic fibers, capillaries, and pilosebaceous units. Data were analyzed with two-way of analysis of variance (ANOVA) to determine significant effects of age, diet, and age-diet interaction on these parameters in AL rats and their age-matched cohorts. RESULTS: Significant effects of age, diet, or age-diet interaction were observed in respect of the thickness of epidermis, dermis, stratum corneum of FP, epidermal nuclear number, collagen percentage fraction, and area fraction of capillaries. DS epidermis showed increasing thickness in AL group, but this was reduced in CR rats. A similar trend in DS dermal depth was observed. Fewer capillaries were present in aging CR rats. The DS epidermal nuclear profiles and collagen area fraction also showed effects of diet and age-diet interaction. Aging changes, especially the effect of CR, was more evident in the measured parameters of dorsal skin. No alterations were observed in the distribution of pilosebaceous units and elastic fiber profiles of the skin. CONCLUSIONS: The Fischer 344 rat shows many age-related changes in the skin, some of which are different from data reported in literature. The pattern of aging changes in skin parameters was different in the two groups, suggesting an in influence of CR. CR appears to modify the aging rate of some skin components, and this may be caused by metabolic changes imposed by diet.

2004

Physiol Genomics. 2004 Apr 13;17(2):230-44.
Starvation response in mouse liver shows strong correlation with life-span-prolonging processes.
Bauer M, Hamm AC, Bonaus M, Jacob A, Jaekel J, Schorle H, Pankratz MJ, Katzenberger JD.
Institut fuer Genetik, Forschungszentrum Karlsruhe, 76021 Karlsruhe, Germany.

We have monitored global changes in gene expression in mouse liver in response to fasting and sugar-fed conditions using high-density microarrays. From approximately 20,000 different genes, the significantly regulated ones were grouped into specific signaling and metabolic pathways. Striking changes in lipid signaling cascade, insulin and dehydroepiandrosterone (DHEA) hormonal pathways, urea cycle and S-adenosylmethionine-based methyl transfer systems, and cell apoptosis regulators were observed. Since these pathways have been implicated to play a role in the aging process, and since we observe significant overlap of genes regulated upon starvation with those regulated upon caloric restriction, our analysis suggests that starvation may elicit a stress response that is also elicited during caloric restriction. Therefore, many of the signaling and metabolic components regulated during fasting may be the same as those which mediate caloric restriction-dependent life-span extension.

2001

J Nutr. 2001 Mar;131(3):913S-917S
Calorie restriction in obesity: prevention of kidney disease in rodents.
Stern JS, Gades MD, Wheeldon CM, Borchers AT.
Department of Nutrition, University of California, Davis, CA 95616, USA.

The incidence of end-stage renal disease (ESRD) has risen considerably in the past two decades. This trend is partly due to the alarming rise in the incidence of type 2 diabetes over the same period, which in turn might be linked to the staggering increase in overweight and obesity. If these trends continue, ESRD can be expected not only to cause suffering of ever growing numbers of patients, but also to become an increasing financial as well as logistical burden on the health care system. Therefore, it is imperative not only to gain a better understanding of the molecular, cellular and metabolic mechanisms involved in renal pathology, but also to uncover treatment modalities, including lifestyle changes, that can help prevent and/or slow the progression of kidney pathogenesis. Insights into both of these aspects are provided by animal models of obesity and diabetes. It has long been known that food restriction, more so than restriction of any particular dietary component, can greatly enhance longevity in laboratory rodents. These findings are being extended into a variety of other mammals, including nonhuman primates. These studies have indicated that caloric restriction in nonobese laboratory animals does not primarily affect specific disease processes but rather nonspecifically slows the aging process. In contrast, a growing body of evidence suggests that in genetically obese animals, food restriction can prevent or greatly delay the onset of specific degenerative lesions, in particular glomerulonephritis associated with obesity and diabetes.

Novartis Found Symp. 2001;235:221-30; discussion 230-3
The anti-ageing action of dietary restriction.
Van Remmen H, Guo Z, Richardson A.
Department of Physiology, University of Texas Health Science Center at San Antonio, and South Texas Veterans Health Care System, San Antonio, TX 78284-7756, USA.

Over 60 years ago, McCay's laboratory showed that dietary or calorie-restriction dramatically increased the lifespan of rats. Since then, numerous laboratories with a variety of strains of rats and mice have confirmed this initial observation and have shown that reducing calorie intake (without malnutrition) significantly increases both the mean and maximum survival of rodents. Currently, dietary restriction is the only experimental manipulation that has been shown to retard ageing of mammals. Although mechanism whereby dietary restriction retards ageing is currently unknown, much of the emerging data suggest that the calorie-restricted rodents live longer and age more slowly because they are more resistant to stress and have an enhanced ability to protect cells against damaging agents.

Caloric restriction in rodents is well known to retard the rate of aging, increase mean and maximum life-spans, and inhibit the occurrence of many age-associated diseases. However, little is known about the influence of short-term repeated fasting on longevity. In this study, female (NZB x NZW)F1 mice were used to test the physiological effect of short-term repeated fasting (4 consecutive days, every 2 weeks). The results showed that fasting mice survived significantly longer than the full-fed mice, in spite of the fasting group having a heavier body weight than the control group. Mean survival times for fasting and control mice were 64.0+/-15.3 and 47.9+/-9.4 weeks, respectively. Short-term repeated fasting manipulation was also effective on the prolongation of life-span in autoimmune-prone mice.

Ann N Y Acad Sci. 2000 Jun;908:180-98
Calorie restriction and age-related oxidative stress.
Merry BJ.
School of Biological Sciences, University of Liverpool, United Kingdom.

Calorie restriction (CR) in mammals has been recognized as the best characterized and most reproducible strategy for extending maximum survival, retarding physiological aging, and delaying the onset of age-related pathologic conditions in mammals. The overwhelming majority of studies using CR have used short-lived rodent species, although current work using rhesus and squirrel monkeys will determine whether this paradigm is also relevant to manipulating the rate of primate aging. The mechanism by which restricted calorie intake modifies the rate of aging and pathology has been the subject of much controversy, although an attenuation in the lifetime accumulation of oxidative damage appears to be a central feature. Although the majority of studies have focused on the ability of cells from calorie-restricted animals to scavenge free radicals to explain the slower accrual of oxidative damage with age, it is not established that CR has a consistent effect to upregulate the activity of these enzymes in all tissues. A major effect of calorie-restricted feeding now appears to be on the rate of production or leak of free radicals from the mitochondria. The details of the adaptation and the signaling pathway that induces this effect are currently unknown.

Studies of the multistage nature of hepatocarcinogenesis in the rat have led to the development of models having significant potential application to carcinogenesis in other tissues as well as other species. Whereas the initial and final stages of carcinogenesis-initiation and progression-involve genetic changes and are operationally irreversible, the intermediate stage of promotion is operationally reversible and can be modulated by a variety of environmental factors. Numerous investigations have demonstrated that chronic caloric restriction modifies neoplastic development, primarily during the stage of promotion, so that fewer lesions develop. Short-term fasting of rats, initiated with a nonnecrogenic dose of diethylnitrosamine (DEN) and promoted with 0.05% phenobarbital (PB) for 4 weeks, results in loss of virtually all of the measurable altered hepatic foci (AHF) after two 5-day periods of fasting with an intermediate 2-day period of feeding. This change was accompanied by a marked decrease in bromodeoxyuridine (BrdU) labeling of hepatocytes within AHF together with a significant increase in apoptosis of such cells measured by nick end-labeling. Similar but lesser effects were noted in surrounding, nonfocal hepatocytes. On refeeding, both the numbers and volume percentage of AHF returned within 2 weeks to values seen in nonfasted controls. Administration of PB during the fasting period did not alter these results, although AHF reappeared more rapidly in such animals on refeeding. Nuclear DNA fragmentation was evident in samples of whole liver from fasted animals. During this same period the expression of c-myc mRNA increased 3- to 9-fold, while levels of albumin and insulin-like growth factor I mRNAs decreased significantly. This study demonstrates a model system in which the reversibility of the effects of promoting agents may be rapidly determined and the effects of chemopreventive inhibitors of promotion may be rapidly evaluated.

Connective tissue shows peculiar and complex age-related modifications, which can be, at least in part, responsible for altered functions and increased susceptibility to diseases. Food restriction has long been known to prolong life in rodents, having antiaging effects on a variety of physiologic and pathologic processes. Therefore, the aorta has been investigated in rats fed normal or hypocaloric diet, from weaning to senescence. Compared with controls, caloric-restricted animals showed less pronounced age-dependent alterations such as elastic fiber degradation, collagen accumulation and cellular modifications. Immunocytochemical analyses revealed that elastic fibers were positively labelled for biglycan, decorin, ApoB100 (LDL), ApoA1 (HDL) and elastase and that the intensity of the reactions was time- and diet-dependent. With age, the major changes affecting aortic elastic fibers were increased positivity for decorin, LDL and elastase. Compared with age-matched normal fed rats, caloric restricted animals revealed lower content of LDL, decorin and elastase and higher positivity for HDL. These data suggest that a caloric restricted diet might influence the aging process of the arterial wall in rats, delaying the appearance of age-related degenerative features, such as structural alterations of cells and matrix and modified interactions of elastin with cells and with other extracellular matrix molecules.

The present study was designed to assess the impact of moderate caloric restriction (60% of ad libitum fed animals) on cerebral vascular density and local cerebral blood flow. Vascular density was assessed in male Brown-Norway rats from 7-35 months of age using a cranial window technique. Arteriolar density, arteriole-arteriole anastomoses, and venular density decreased with age and these effects were attenuated by moderate caloric restriction. Analysis of local cerebral blood using [14C]iodoantipyrine indicated that basal blood flow decreased with age in CA1, CA3 and dentate gyrus of hippocampus; similar trends were evident in cingulate, retrosplenal, and motor cortex. Basal blood flow was increased in all brain regions of moderate caloric restricted old animals (compared to old ad libitum fed animals) and no differences were observed between ad libitum fed young and caloric restricted older animals. In response to a CO2 challenge to maximally dilate vessels, blood flow increased in young and old ad libitum fed animals, but a similar increase was not observed in caloric restricted old animals. We conclude that a decrease in cerebral vasculature is an important contributing factor in the reduction in blood flow with age. Nevertheless, vessels from young and old animals have the capacity to dilate in response to a CO2 challenge and, after CO2, no differences are observed between the two age-groups. These results are consistent with the hypothesis that aged animals fail to adequately regulate local cerebral blood flow in response to physiological stimuli. Moderate caloric restriction increases microvascular density and cerebral blood flow in aged animals but tissues exhibit little or no increase in blood flow in response to CO2 challenge. The cause of this deficient response may indicate that vessels are maximally dilated in aged calorically restricted animals or that they fail to exhibit normal regulatory control.

2000

Cancer Res. 1999 Apr 1;59(7):1642-8
Dietary intervention at middle age: caloric restriction but not dehydroepiandrosterone sulfate increases lifespan and lifetime cancer incidence in mice.
Pugh TD, Oberley TD, Weindruch R.
Institute on Aging, University of Wisconsin, Madison 53706, USA.

Dietary manipulations to prevent cancer and other diseases of aging have drawn broad public and scientific attention. One indicator of this interest is that dehydroepiandrosterone (DHEA) supplements are widely consumed by those who hope that this hormone may keep them "younger longer." However, key data to support this belief are lacking. For example, the influence of DHEA treatment on spontaneous cancer and life span in healthy, long-lived strains of mice or rats is unknown. This is in contrast to the situation for caloric restriction (CR), which is known to oppose cancer development and increase maximum life span in rodents. To address this issue, we assigned 300 middle age (12-month-old) male C57BL/6 mice to one of four groups (n = 75 for each group) and evaluated them for longevity and spontaneous disease patterns. Two groups were fed a normal diet (ND), and two others were fed a calorie-restricted diet (RD). One ND group and one RD group were also given 25 microg/ml DHEA sulfate (DHEAS) in their drinking water. Although urine samples from DHEAS-treated mice contained 10-fold more DHEA and DHEAS than did samples from unsupplemented mice, DHEAS administration did not affect body weight, life span, or cancer patterns. The RD lowered body weight by 26% and increased maximum life span by approximately 15%. The incidence of the most prevalent cancer, plasma cell neoplasm, was higher in RD mice (66%) than in ND mice (41%). Thus, DHEAS, as administered here, influenced neither cancer nor longevity at two caloric intakes. In contrast, CR from middle age increased longevity, the age at which tumor-bearing mice died, and the percentage of mice dying with cancers, suggesting that CR may retard promotion and/or progression of existing lymphoid cancers.

1998

J Toxicol Environ Health B Crit Rev. 1998 Jul-Sep;1(3):243-57
Influence of caloric intake on aging and on the response to stressors.
Masoro EJ.
Department of Physiology, University of Texas Health Science Center at San Antonio, USA.

Reducing the food intake of rodents to well below that of ad libitum fed animals increases the life span. This action, which gerontologists often refer to as the antiaging action of dietary restriction (DR), is due to the slowing of the aging processes. DR also maintains most physiological processes in a youthful state and delays the occurrence and/or slows the progression of age-associated disease processes. This antiaging action of DR results from the reduced intake of calories. Reduction of the body fat content does not play a causal role in the antiaging action of DR, nor does reduction in the metabolic rate. Alterations in the characteristics of carbohydrate metabolism and of oxidative metabolism in response to DR have been found that are of such a nature that they could, at least in part, underlie the antiaging action. Several theories have recently been proposed in regard to the mechanisms responsible for the antiaging action of DR, but none has been tested by rigorously designed studies. Of these theories, the one that seems most promising is based on the fact that DR protects rats and mice of all ages against the damaging actions of acute stressors. This protective action against stressors may play a major role in the antiaging action of DR.

1997

Environ Res. 1997;73(1-2):242-8
The physiologic, neurologic, and behavioral effects of caloric restriction related to aging, disease, and environmental factors.
Duffy PH, Leakey JE, Pipkin JL, Turturro A, Hart RW.
Biometry and Risk Assessment, Genetic Toxicology, National Center for Toxicological Research, 3900 NCTR Road, Jefferson, Arkansas 72079, USA.

Little is known about the mechanisms by which acute and chronic caloric restriction (CR) modulate disease, longevity, and toxicity. To study these endpoints, behavioral parameters such as food and water consumption and physiologic parameters such as motor activity, body temperature, metabolic output (oxygen use), and respiratory quotient (RQ) were continuously monitored in 26-month-old male B6C3F1 mice and Fischer 344 rats fed either ad libitum (AL) or a CR diet (60% of AL). Different dietary regimens were used: rodents were (1) chronically food-restricted using daily feeding starting at 14 months of age, (2) chronically food-restricted using alternate day feeding, or (3) abruptly switched from CR to AL (acute CR). The physiologic and behavioral changes seen with chronic and acute CR were consistent across strains and species. Average body temperature, the number of meals, and the ratio of food/water consumption were significantly lower in CR rodents than in AL rodents. Also, the daily range of body temperature, oxygen metabolism, RQ, average water consumption, and motor activity was significantly higher in CR rodents. CR caused the onset of altered neurobehavioral functions such as abnormal water consumption; increases in motor activity, serum corticosterone, and stress proteins (HSP); and decreases in the basal setpoint for body temperature and brain metabolism. These changes strongly suggest that many beneficial effects of CR are controlled by the hypothalamic-pituitary-adrenal axis via hormonal regulation. This study supports the assertion that nutritional status may be a primary factor of consideration in development of safety standards and assessment of risk.

Life-long food restriction is known to slow aging and reduce the rate of occurrence of age-associated disease processes, but the mechanism by which this is accomplished is unknown. In this study we have examined the effect of food restriction on the proliferative response of spleen cells to mitogens and lymphokine production in 6-, 18-, and 30-month-old AL and FR Fischer-344 x Brown Norway (F-344 x BNF1) female rats whose average life span is 137 weeks on an ad libitum (AL) diet and 177 weeks on a food-restricted (FR) diet. In addition, the ability of food restriction to recall antigens was tested in 10-month-old rats by immunizing them with keyhole limpet and hen's egg albumin and measuring proliferative response of draining lymph node cells to these antigens. Our results indicated that the spleen-cell proliferative response to phytohemagglutinin and concanavalin A (Con A) was equal in 6- and 18-month-old rats but declined significantly in 30-month-old AL rats compared to FR rats. Although flow cytometric analyses did not reveal differences for CD4, CD8, and Ig+ cells with age, a significant rise in memory T cells (Ox-22low) in both CD4+ and CD8+ T-cell subset lineage was noted in AL-fed rats at 30 months of age. In FR rats, however, only a minimal shift of naive T cells (Ox-22high) to memory cells was observed. In FR rats, the observed changes in the naive and memory T-cell subsets correlate well with the observed higher levels of the antiinflammatory interleukin-2 (IL-2) and lower levels of the proinflammatory cytokines such as IL-6 and tumor necrosis factor-alpha. The ability of food-restricted animals to recall antigens was lower compared to their age-matched controls, though the proliferative response to T-cell mitogen Con A and superantigen staphylococcal enterotoxin B was higher. These findings indicate that food restriction may selectively act to maintain a lower number of antigen-induced memory T cells with age, thereby maintaining the organism's ability to produce higher levels of IL-2 with age. In summary, the increased cell-mediated immune function noted in aged FR rats appears to be due to the presence of a higher number of naive T cells, which are known to produce elevated levels of the antiinflammatory cytokines, which may in part be responsible for reducing the observed age-related rise in disease.

Mech Ageing Dev. 1997 Feb;93(1-3):87-94
Calorie restriction inhibits the age-related dysregulation of the cytokines TNF-alpha and IL-6 in C3B10RF1 mice.
Spaulding CC, Walford RL, Effros RB.
Department of Pathology and Laboratory medicine, University of California School of Medicine, Los Angeles 90095-1732, USA.

TNF-alpha and IL-6 are generally increased in the sera of aged humans and mice. The dysregulation of these cytokines may be critical in autoreactivity and immune dysfunction. In earlier studies we demonstrated that production of TNF-alpha and IL-6 following in vitro stimulation of peritoneal macrophages by LPS was reduced in old compared to young mice, and that dietary caloric restriction (CR) had no effect on the induction of TNF-alpha in this system. In the present study we examined the effects of age and calorie restriction on the constitutive production of both TNF-alpha and IL-6. Serum levels of both cytokines were significantly higher in old versus young mice. However, in old mice subjected to long term CR the serum levels were comparable to those of young mice. The potential involvement of normalization of TNF-alpha and IL-6 levels in the life extension effect of CR are discussed.

1996

Toxicol Pathol. 1996 Nov-Dec;24(6):742-5
The retardation of aging by caloric restriction: studies in rodents and primates.
Weindruch R.
Department of Medicine, University of Wisconsin, Madison, USA.

Caloric restriction (CR), which has been investigated by gerontologists for more than 60 yr, provides the only intervention tested to date in mammals (typically mice and rats) that repeatedly and strongly increases maximum life span while retarding the appearance of age-associated pathologic and biologic changes. Although the large majority of rodent studies have initiated CR early in life (1-3 mo of age), CR started in midadulthood (at 12 mo) also extends maximum life span in mice. Two main questions now face gerontologists investigating CR. By what mechanisms does CR retard aging and disease processes in rodents? There is evidence to suggest that age-associated increases in oxidative damage may represent a primary aging process that is attenuated by CR. Will CR exert similar actions in primates? Studies in rhesus monkeys subjected to CR and limited human epidemiological data support the notion of human translatability. However, no matter what the answers are to these questions, the prolongation of the health span and life span of rodents by CR has major implications for many disciplines, including toxicologic pathology, and raises important questions about the desirability of ad libitum feeding.

Reproductive ageing in female rodents is accompanied by changes in circulating peptide and steroid hormones leading to irregular, lengthened oestrous cycles prior to loss of fertility. In this study, the effect of ageing is reported on steroid hormone synthesis within individual ovarian follicles and its retardation by restricted feeding for two groups of ad libitum fed animals (114 and 350 days) and two groups of diet-restricted animals (350 and 600 days). Follicles from ad libitum fed animals of 350 days showed a transition in follicular steroid hormone synthesis to release elevated amounts of oestradiol-17beta on all days of the cycle. This age-related change in follicle steroid release was significantly delayed by maintaining animals on a restricted feeding regime, and was not complete even by 600 days of age. This effect of diet as a means to manipulate ageing of the follicular steroidogenic pathways provides a useful system for investigating the control of reproductive ageing in rodents.

Restricting the food intake of mice and rats to well below that of ad libitum-fed animals markedly slows the aging processes. This action is reflected in an increase in longevity, a decrease in the age-associated increase in age-specific mortality rate, the maintenance of the physiological processes in a youthful state even at advanced ages, and the delaying of the onset or slowing of the progression or both of most age-associated diseases. The dietary factor responsible is the reduction in energy (caloric) intake. Many hypotheses have been proposed regarding mechanisms underlying this antiaging action. Hypotheses relating the antiaging action to the retardation of growth and development, the reduction of adipose mass, and the reduction of metabolic rate have been found to be wanting. Two of the proposed hypotheses have some evidence in their support. One involves the altered metabolic characteristics of glucose fuel use and of oxidative metabolism. The other relates to the enhanced ability of the rodents restricted in food intake to cope with challenges, which in turn has been linked to the glucocorticoid system and to the heat-shock protein system.

1995

Toxicol Pathol. 1995 Sep-Oct;23(5):570-82
Longevity, body weight, and neoplasia in ad libitum-fed and diet-restricted C57BL6 mice fed NIH-31 open formula diet.
Blackwell BN, Bucci TJ, Hart RW, Turturro A.
Pathology Associates, Inc., Jefferson, Arkansas 72079, USA.

Groups of C57BL6 mice of each sex were assigned to one of 2 dietary regimens, ad libitum (AL) or dietary restriction (DR), to study effects of food restriction on body weight, survival, and neoplasia. The AL and DR groups were subdivided into a scheduled sacrifice group for examination at 6-mo intervals, and a lifetime group to provide longevity data. Necropsies and microscopic examinations were conducted on 911 animals. In the lifetime group food consumption averaged 33.6 and 34.4 g per week by AL males and AL females, respectively; the DR counterparts were given 40% less. The diet contained 4.35 kcal/g. The average lifetime body weights were 34.8, 26.8, 22.6, and 21.6 g for AL males, AL females, DR males, and DR females, respectively, and their age at 50% survival was 27.5, 26.9, 31.7, and 33.5 mo. Maximal lifespan was increased 18% in DR males and females. Lifetime incidence of tumor-bearing mice was 89% and 86% for AL males and females, versus 64% for each sex of DR mice. Dramatic reduction occurred in female DR mice in lymphoma (9% vs 29%), pituitary neoplasms (1% vs 37%), and thyroid neoplasms (0.4% vs 8%). In males, hepatocellular tumors were reduced to 1% from 10% by DR. In contrast, the incidence of histiocytic sarcoma was increased in DR females and unaffected in DR males. Tumor onset was delayed in DR animals; 87% of all neoplasms in males and 95% in females had occurred in the AL mice by 24 mo, whereas the DR animals had only 52% and 39% of their lifetime incidence, respectively, by that age. This study provided comparative AL and DR data from C57BL6 mice examined randomly at 6-mo intervals (cross-sectional group) in parallel with data from animals in similar cohort that was unsampled and allowed to succumb naturally (longevity group). Dietary restriction reduced the lifetime percentage of tumor-bearing animals and the number of tumors per animal, and delayed the age at onset of most neoplasms.

Clin Geriatr Med. 1995 Nov;11(4):553-65
Role of caloric restriction in the prolongation of life.
McCarter RJ.
Department of Physiology, University of Texas Health Science Center, San Antonio, USA.

Restriction of caloric intake increases longevity, slows the rate of functional decline, and reduces incidence of age-related disease in a variety of species. Most laboratory rodent studies have initiated restriction before puberty, whereas ongoing studies in nonhuman primates utilize restriction in adulthood. The mechanism of action of caloric restriction remains unknown; however, data suggest that cellular functions are altered in such a way that destructive by-products of metabolism are reduced, and defense or repair systems are enhanced by this nutritional manipulation.

1993

Mutat Res. 1993 Dec;295(4-6):191-200
Caloric restriction, aging, and antioxidant enzymes.
Feuers RJ, Weindruch R, Hart RW.
Division of Genetic Toxicology, National Center for Toxicological Research, Jefferson, AR 72079.

The basic mechanisms of aging and its retardation by caloric restriction (CR) remain unclear. One suggested means by which CR could retard aging is based on production of mitochondrial free radicals, and efficiency of their subsequent metabolism. Currently, there is little information concerning the influences of age and CR on the rates of in vivo mitochondrial free radical production. However, evidence for CR-induced modulation of free radical detoxification capacities is mounting. The direction of the influence of CR on free radical detoxification is tissue-specific. These effects are broad and appear to provide positive advantage.

1991

Mech Ageing Dev. 1991 May;58(2-3):139-50
Effect of age and restricted feeding on polypeptide chain assembly kinetics in liver protein synthesis in vivo.
Merry BJ, Holehan AM.
Institute of Human Ageing, University of Liverpool, U.K.

Polypeptide assembly rates during in vivo hepatic protein synthesis were studied as a function of age and restricted feeding in male rats. With ageing the time to assemble the average peptide in the liver of fully-fed rats significantly increased. In young rats maintained on a restricted feeding regime known to retard ageing, the time to assemble the average polypeptide was increased 2.5 times. With ageing the rate of peptide elongation increased so that at 2 years of age the underfed animals assembled peptides at a significantly faster rate than their age-matched controls. The rate of elongation of peptides during hepatic protein synthesis was shown to be directly dependent upon circulating T3 levels rather than the dietary status of the animal. On refeeding young diet restricted rats, polypeptide assembly kinetics did not immediately return to control values although the rate of protein synthesis was significantly increased. Total liver RNA content increased significantly in refed animals allowing for a greater rate of chain initiation to offset the slow rate of chain elongation. A period of 28 days of ad libitum feeding was required before assembly kinetics returned to control values and is probably indicative of a persistent impaired monodeiodination of T4 to T3.

1989

J Gerontol. 1989 Jan;44(1):B20-2
Evidence for the glycation hypothesis of aging from the food-restricted rodent model.
Masoro EJ, Katz MS, McMahan CA.
Department of Physiology, University of Texas Health Science Center, San Antonio.

Glucose has been proposed as a mediator of aging processes by means of glycation reactions resulting in advanced glycosylation end-products, thereby altering protein and DNA function. Testing this provocative concept has a high priority in gerontologic research. In this study, food restriction of rats--a procedure which markedly retards aging processes--was used to test the glycation hypothesis. Food-restricted rats were found to have a sustained plasma glucose concentration and percentage glycosylation of hemoglobin significantly lower than those of ad libitum fed rats. These findings are consistent with and provide support for the glycation hypothesis.

1988

Metab Brain Dis. 1988 Dec;3(4):257-63
Protective effect of fasting upon cerebral hypoxic-ischemic injury.
Go KG, Prenen GH, Korf J.
Department of Neurosurgery, University of Groningen, The Netherlands.

This study was designed to determine the effect of fasting upon cerebral hypoxic-ischemic injury. In the first part of the study the effect of fasting was determined for survival, brain tissue water and kation contents, and blood-brain barrier integrity. In the second part of the study the administration of the substrates beta-hydroxybutyrate (BHB) and glucose has been evaluated regarding their influence upon the effect of fasting. The study used the Levine-Klein model of unilateral carotid occlusion and hypoxia because it mimics clinical situations of ischemia with hypoxia. The data show that fasting did protect rats from developing brain infarction following hypoxia-ischemia. Hypoglycemia seems to be involved in the mitigation of ischemic blood-brain barrier disruption. The plasma glucose level seems to be not the only factor involved in the genesis of the tissue kation changes. Starvation-induced ketosis probably does not play a role in the protection mechanism.

Cancer Invest. 1988;6(6):677-80
Effects of short-term dietary restriction on survival of mammary ascites tumor-bearing rats.
Siegel I, Liu TL, Nepomuceno N, Gleicher N.
Department of Obstetrics and Gynecology, Mount Sinai Hospital Medical Center, Chicago, Illinois.

We studied the effects of short-term dietary restriction on the survival of 3-4-month-old tumor-free and tumor-bearing Fisher rats. The diet-restricted food regimen consisted of alternate day ad libitum feeding followed by alternate day fasting. Diet-unrestricted control rats were fed ad libitum daily. Six tumor-free rats on the diet-restricted regimen compensated for the dietary restriction by an increase in food consumption during the alternate feeding days, and lost an average of only 2-3% of their weight in 13 days. Six tumor-free rats on a daily ad libitum feeding regimen gained an average of 6.8% in 15 days. The above dietary-restricted regimen was initiated 1 week before 24 rats were inoculated intraperitoneally with 15 million Mat 13762 ascites tumor cells. Sixteen of 24 (66.7%) diet-restricted tumor-bearing hosts and 5/24 (20.8%) diet-unrestricted tumor-bearing hosts survived at 9 days after tumor inoculation (p less than 0.005). Twelve of 24 (50%) diet-restricted tumor-bearing hosts, and 3 of 24 (12.5%) diet-unrestricted tumor-bearing hosts, survived at 10 days after tumor inoculation (p less than 0.025). Thus, the survival of tumor-bearing rats was enhanced by short-term relatively mild dietary restrictions. We suggest that relatively mild dietary restrictions should be included in clinical trials designed to inhibit cancer growth and enhance the survival of human cancer patients.

Biochem J. 1988 Feb 15;250(1):303-5
The effects of aging on carbonic anhydrase concentrations in rat liver and skeletal muscle.
Jeffery S, Merry BJ, Holehan AM, Carter ND.
Department of Child Health, St. George's Hospital Medical School, London, U.K.

The isoenzymes carbonic anhydrase II (CAII) and III (CAIII) have been measured by radioimmunoassay in the livers of male and female rats aged from 21 to 800 days. No sexual dimorphism at 21 days was found, but from 50 to 400 days both isoenzymes show sexual differences. From 600 days onwards, these differences are less apparent. CAIII concentrations in two 'fast' fibre muscles and one 'slow' fibre muscle have been determined. There is no sexual dimorphism in muscle, but a wide variation between individuals was observed. Fast muscles show maximal CAIII levels at 800 days, whereas in slow muscle the concentration of the isoenzyme is declining at this time.

Exp Gerontol. 1988;23(4-5):417-27
Effects of chronic dietary restriction on sensory-motor function and susceptibility to stressor stimuli in the laboratory rat.
Campbell BA, Richardson R.
Department of Psychology, Princeton University, New Jersey 08544.

Two sets of experiments describing the effects of chronic undernutrition on sensory-motor function and susceptibility to environmental stressors are described. In the first, Fischer 344 rats between 10 and 12 months of age were placed on an every-other-day feeding regimen. Behavioral tests designed to assess sensory function (auditory and visual thresholds), somato-motor competence (hang time from a horizontal wire, balance on a narrow beam, descent of a wire mesh pole), and sensory-motor integrity (auditory startle) were then conducted every 3 to 6 months. Chronic undernutrition significantly increased life span and increased somato-motor competence but did not affect sensory function or sensory-motor integrity. In the second set of experiments both acute and chronic dietary restriction impaired the ability of young adult Sprague-Dawley rats to effectively thermoregulate in response to a cold environment. Body temperature dropped more rapidly and recovered at a slower rate in the dietarily restricted animals. Fischer 344 rats maintained on a restricted diet for 16 months were similarly impaired. The latter findings suggest that techniques for extending life span based on laboratory animal models may have little relevance to either animals or humans living in their natural habitats where a wide variety of environmental stressors are encountered.

1987

J Gerontol. 1987 Jan;42(1):78-81
Dietary restriction benefits learning and motor performance of aged mice.
Ingram DK, Weindruch R, Spangler EL, Freeman JR, Walford RL.

Female C3B10RF1 mice maintained on either a control (approximately 95 kcal/week) or restricted (approximately 55 kcal/week) diet since weaning were tested in a behavioral battery at 11 to 15 or 31 to 35 months of age (middle-aged vs. aged). Age-related declines observed among control groups in tests of motor coordination (rotorod) and learning (complex maze) were prevented by the restriction regime. In addition, diet restriction increased locomotor activity in a runwheel cage among mice of both ages but did not affect exploratory activity in a novel arena.

J Gerontol. 1987 Mar;42(2):154-9
Rate of aging and dietary restriction: sensory and motor function in the Fischer 344 rat.
Campbell BA, Gaddy JR.

Sensory and motor task performance was assessed at 3 to 4 month intervals in chronically underfed and ad libitum-fed control rats from maturity into senescence. Diet-restricted rats weighed less than controls and lived significantly longer. Diminished body mass improved the underfed rats' abilities to hang suspended from a wire, to maintain balance on a narrow beam, and to descend from a wire mesh pole in a coordinated fashion. Underfed rats, however, lost these abilities at the same rate as did control rats. Undernutrition did not affect the startle response to acoustic stimulation, nor did it influence auditory or visual lead stimulus inhibition of the startle response. Both groups of animals showed progressive, age-related losses of sensory-motor function which proceeded at the same rate in each group. Life-prolonging undernutrition did not appear to retard aging of these simple, reflexive behaviors.

1986

J Nutr. 1986 Apr;116(4):641-54
The retardation of aging in mice by dietary restriction: longevity, cancer, immunity and lifetime energy intake.
Weindruch R, Walford RL, Fligiel S, Guthrie D.

We sought to clarify the impact of dietary restriction (undernutrition without malnutrition) on aging. Female mice from a long-lived strain were fed after weaning in one of six ways: group 1) a nonpurified diet ad libitum; 2) 85 kcal/wk of a purified diet (approximately 25% restriction); 3) 50 kcal/wk of a restricted purified diet enriched in protein, vitamin and mineral content to provide nearly equal intakes of these essentials as in group 2 (approximately 55% restriction); 4) as per group 3, but also restricted before weaning; 5) 50 kcal/wk of a vitamin- and mineral-enriched diet but with protein intake gradually reduced over the life span; 6) 40 kcal/wk of the diet fed to groups 3 and 4 (approximately 65% restriction). Mice from groups 3-6 exhibited mean and maximal life spans 35-65% greater than for group 1 and 20-40% greater than for group 2. Mice from group 6 lived longest of all. The longest lived 10% of mice from group 6 averaged 53.0 mo which, to our knowledge, exceeds reported values for any mice of any strain. Beneficial influences on tumor patterns and on declines with age in T-lymphocyte proliferation were most striking in group 6. Significant positive correlations between adult body weight and longevity occurred in groups 3-5 suggesting that increased metabolic efficiency may be related to longevity in restricted mice. Mice from groups 3-6 ate approximately 30% more calories per gram of mouse over the life span than did mice from group 2. These findings show the profound anti-aging effects of dietary restriction and provide new information for optimizing restriction regimes.

1985

Exp Gerontol. 1985;20(5):253-63
The effects of aging and chronic dietary restriction on whole body growth and protein turnover in the rat.
Lewis SE, Goldspink DF, Phillips JG, Merry BJ, Holehan AM.

Changes in whole body growth, nucleic acids, and protein turnover have been studied in conjunction with ageing and chronic dietary restriction. Normal developmental changes between weaning and senescence included progressive decreases in the fractional rates of growth, protein synthesis, and protein breakdown; the decline in the synthetic rate correlating with decreases in the ribosomal capacity. Dietary intervention was imposed at weaning and involved pair feeding to 50% of the ad libitum food intake. Although this regime slowed whole body growth by retarding the developmental decline in protein turnover, growth was extended into the second and third years of life. The dietary-induced increase in longevity resulting from a retardation of the ageing process(es) appears therefore to be associated with an enhanced turnover of proteins during the major portion of the life span of dietary restricted rats.

J Nutr. 1985 Oct;115(10):1259-66
Chronic food restriction modulates the advance of senescence in the senescence accelerated mouse (SAM).
Kohno A, Yonezu T, Matsushita M, Irino M, Higuchi K, Higuchi K, Takeshita S, Hosokawa M, Takeda T.

The effects of chronic food restriction on grading scores of senescence, deposition of senile amyloid (ASSAM), mean life span and 10th decile were investigated by using animal models for accelerated senescence (SAM-P/1) and for normal aging (SAM-R/1). The experimental groups consisted of control (ad libitum fed), 80% (fed 80% of control intake), and 60% (fed 60% of control intake) groups. The grading score of SAM-P/1 mice was significantly improved in the 60% group, but not in the 80% group, compared to the control group. The grading score of SAM-R/1 mice, however, was significantly less than that in the control group in both the 60 and 80% groups. In SAM-P/1 mice liver, skin and testis, the severity of senile amyloid deposition was significantly less with 40% food restriction (60% group) than in the control group. A restriction of 20% (80% group) had no influence on amyloid deposition. A definite tendency to prolong mean life span (24.3%) and 10th decile (65.9%, mean life span of the last 10th of survivors of a group) was observed in the 60% group of SAM-P/1 mice, but the changes were not statistically significant. In the 80% group of SAM-P/1 mice and also in either restriction group of SAM-R/1 mice, however, such a tendency was not evident. These results indicate that 40% food restriction modulates the advance of senescence in these mice.

1984

Proc Natl Acad Sci U S A. 1984 Mar;81(6):1835-8
Effects of food restriction on aging: separation of food intake and adiposity.
Harrison DE, Archer JR, Astle CM.

Restricted feeding of rodents increases longevity, but its mechanism of action is not understood. We studied the effects of life-long food restriction in genetically obese and normal mice of the same inbred strain in order to distinguish whether the reduction in food intake or the reduction in adiposity (percentage of fatty tissue) was the critical component in retarding the aging process. This was possible because food-restricted obese (ob/ob) mice maintained a high degree of adiposity. In addition to determining longevities, changes with age were measured in collagen, immune responses, and renal function. Genetically obese female mice highly congenic with the C57BL/6J inbred strain had substantially reduced longevities and increased rates of aging in tail tendon collagen and thymus-dependent immune responses, but not in urine-concentrating abilities. When their weight was held in a normal range by feeding restricted amounts, longevities were extended almost 50%, although these food-restricted ob/ob mice still had high levels of adiposity, with fat composing about half of their body weights. Their maximum longevities exceeded those of normal C57BL/6J mice and were similar to longevities of equally food-restricted normal mice that were much leaner. Food restricted ob/ob mice had greatly retarded rates of collagen aging, but the rapid losses with age in splenic immune responses were not mitigated. Thus, the extension of life-span by food restriction was inversely related to food consumption and corresponded to the aging rate of collagen. These results suggest that aging is a combination of independent processes; they show that reduced food consumption, not reduced adiposity, is the important component in extending longevity of genetically obese mice.

1982

Strahlentherapie. 1982 Dec;158(12):734-8
Protective effect of intermittent fasting on the mortality of gamma-irradiated mice.
Kozubik A, Pospisil M.

The effect of 1 to 6 weeks' adaptation to intermittent fasting (alternating periods of 24 h fasting and subsequent 24 h feeding) on the manifestations of radioresistance of mice subjected to whole-body gamma-irradiation was studied. A favourable effect of this feeding regimen on the survival of irradiated animals was observed. The optimal radioprotective effect was achieved in mice adapted to intermittent fasting for 2 to 3 weeks and irradiated after 24 h of food intake. Furthermore, it was shown that the radioresistance of the adapted organism depends on the momentary state of food intake. After renewal of the normal ad libitum feeding the adaptively induced radioresistance decreases.

Science. 1982 Mar 12;215(4538):1415-8
Dietary restriction in mice beginning at 1 year of age: effect on life-span and spontaneous cancer incidence.
Weindruch R, Walford RL.

Lifelong dietary restriction beginning at 3 to 6 weeks of age in rodents is known to decelerate the rate of aging, increase mean and maximum life-spans, and inhibit the occurrence of many spontaneous cancers. Little is known about the effects of dietary restriction started in middle age. In the experiments now reported the food intake of 12- to 13-month-old mice of two long-lived strains was restricted by using nutrient-enriched diets in accordance with the concept of "undernutrition without malnutrition." The mice on the restricted diet averaged 10 to 20 percent increases in mean and maximum survival times compared to the control mice. Spontaneous lymphoma was inhibited by the food restriction.