Intermittent Fasting Can Reduce Cancer Risk and Prolong Life Span
By University of California, Berkeley, A new study has shown that healthy mice given only 5 percent fewer calories than mice allowed to eat freely experienced a significant reduction in cell proliferation in several tissues, considered an indicator for cancer risk. The key was that the mice eating 5 percent fewer calories were fed intermittently, or three days a week.

What is encouraging about the findings is that the reduction in cell proliferation from that intermittent feeding regimen was only slightly less than that of a more severe 33 percent reduction in calories. Until now, scientists have been certain only of a link between a more substantial calorie reduction and a reduction in the rate of cell proliferation.

"Cell proliferation is really the key to the modern epidemic of cancer," said Marc Hellerstein, professor of human nutrition in the Department of Nutritional Sciences and Toxicology at UC Berkeley's College of Natural Resources. Hellerstein is principal investigator of the study.

Cancer is essentially the uncontrolled division of cells, and its development typically requires the presence of multiple mutations. "Normally, a cell will try to fix any damage that has occurred to its DNA," said Hellerstein, "But, if it divides before it has a chance to fix the damage, then that damage becomes memorialized as a mutation in the offspring cells. Slowing down the rate of cell proliferation essentially buys time for the cells to repair genetic damage."

Cell proliferation contributes to carcinogenesis in a number of other ways, as well, collectively termed "cancer promotion."

Studies over the past 70 years have established that substantial calorie reduction - up to 50 percent in some studies - not only can reduce the rate of cell proliferation, it can extend the maximum life span of a variety of organisms, including rats, flies, worms and yeast. The results can be dramatic, with 30 to 70 percent increases in life span reported in the studies.

"Significant caloric restriction is the one and only thing that has been scientifically proven to extend life span," said Hellerstein, who has a joint appointment at UC San Francisco. He noted that while exercise and good nutrition can prevent premature death by disease, they have not been shown to extend a maximum life span.

Cutting calories has also been shown to reduce the development of cancer, enhance insulin sensitivity and lower the risk of heart disease.

Yet, as remarkable as those studies may be, their applicability to a human diet is clearly limited. The researchers refer to an old joke that goes along with the findings on caloric restriction: "It's not that you're living longer, it just feels that way."

No doubt, one would be hard pressed to find people willing to embark on what amounts to a lifetime of food deprivation, so the prospect of a more viable intermittent-feeding pattern is appealing.

"What we found is that it may not be necessary to severely restrict calories to reap some of those health benefits," said Elaine Hsieh, a UC Berkeley Ph.D. student in molecular and biochemical nutrition and lead author of the study. "Cutting just a few calories overall but feeding intermittently may be a more feasible eating pattern for some people to maintain."

The researchers conducted several trials with a control group of mice that ate "ad lib," or freely. They compared the control group with mice that ate 5 percent fewer calories but were fed three times a week with mice that were given 33 percent fewer calories. Trial periods ranged from two weeks to three months.

As expected, the researchers found that mice on the 33 percent reduced calorie diet exhibited significantly decreased proliferation rates for skin, breast and T (lymphocyte) cells. The greatest effect was seen after one month on the regimen, when proliferation of skin cells registered only 61 percent of that for mice fed freely.

The surprising finding came with the results of the more modest 5 percent reduced calorie diet that was fed intermittently. Mice in this group had skin cell division rates that were 81 percent of those for mice fed freely.

In all cases, division rates for breast cells were reduced the most. Mice with the lowest calorie diet had breast cell proliferation results that were only 11 percent of those for the control group mice, and mice fed intermittently had results that were 37 percent of those for the control group.

The researchers said this may be partly related to the reduction in estrogen, which stimulates breast cell division. Tests revealed that the estrus cycle stopped for mice on the lowest calorie diet. The mice fed intermittently, on the other hand, continued to cycle regularly.

Results of the refeeding trials indicated that any weight lost during the calorie restriction period was regained once a normal feeding pattern was resumed.

"Overall, we found that the effects of the diet regimens were rapid and reversible, with cell division rates and weight going back to normal after refeeding," said Hsieh. "Although it's too early to say whether similar results would be seen in humans, this study at least provides some hope that another option to severe calorie reduction exists."

"A five percent reduction in calories would be the equivalent of reducing about 100 calories a day in a human diet," said Hellerstein. In other words, for the mice, intermittent feeding seemed to provide similar gain with a bit less pain than a more restrictive diet.

Hellerstein noted that animals in the wild regularly go through cycles of too much and too little food, though not by choice. Major predators, such as lions, may go days without eating and then binge when they make a successful kill. "It may be normal to have periods where we are not eating," said Hellerstein. "But in domestic life, there generally is continuous access to food."

It goes without saying, however, that there is more to changes in eating patterns, such as fasting, than just the physical effects. Both scientific and anecdotal evidence indicates that eating also can impact one's mental state and emotions.

A recent pilot study of 16 non-obese adults by researchers at the Pennington Biomedical Research Center in Louisiana found that eating only every other day was feasible when the participants successfully followed an alternate-day fasting regimen for three weeks. However, the people also reported feeling hungry and irritable on their fasting days.

The authors of the pilot study said that adding a small meal, fulfilling no more than 20 percent of the day's caloric needs, might just take the edge off and make the feeding pattern more palatable.

Notably, the UC Berkeley study is the first to actually quantify the effects of calorie manipulation on cell division. The researchers did so by using heavy water, which is chemically identical to regular water but is about 10 percent heavier because of an extra neutron.

Hellerstein's laboratory pioneered the use of heavy water as a biological marker for cell proliferation. Because heavy water is incorporated into the DNA of new cells, researchers can compare the mass of DNA from tissues in experimental animals to tissues from control animals. They would know that any differences in DNA mass would be attributed to new cells.

"The significance of this labeling is that it allows researchers to accurately gauge the effects of relatively small changes in diet, such as a five percent reduction in caloric intake," said Hellerstein. "Moreover, humans and animals can safely drink heavy water with no ill effect. Everything we did in our study with mice could be safely replicated with humans." 


Calorie restriction, aging, and cancer prevention: mechanisms of action and applicability to humans.
Annu Rev Med. 2003;54:131-52. Epub 2001 Dec 3.
Hursting SD, Lavigne JA, Berrigan D, Perkins SN, Barrett JC.
Laboratory of Biosystems and Cancer, Center for Cancer Research, National Cancer Institute, Bethesda, Maryland 20892, .

Calorie restriction (CR) is the most effective and reproducible intervention for increasing lifespan in a variety of animal species, including mammals. CR is also the most potent, broadly acting cancer-prevention regimen in experimental carcinogenesis models. Translation of the knowledge gained from CR research to human chronic disease prevention and the promotion of healthy aging is critical, especially because obesity, which is an important risk factor for several chronic diseases, including many cancers, is alarmingly increasing in the Western world. This review synthesizes the key biological mechanisms underlying many of the beneficial effects of CR, with a particular focus on the insulin-like growth factor-1 pathway. We also describe some of the opportunities now available for investigations, including gene expression profiling studies, the development of pharmacological mimetics of CR, and the integration of CR regimens with targeted, mechanism-based interventions. These approaches will facilitate the translation of CR research into strategies for effective human chronic disease prevention.


Caloric restriction and insulin-like growth factors in aging and cancer.
Horm Metab Res. 2003 Nov-Dec;35(11-12):705-11
Sell Ch.
Lankenau Institute for Medical Research, Wynnewood, PA 19096, .

This review examines the influence of a reduction in caloric intake on cancer and longevity. Data indicating that rodents subjected to caloric restriction display lower tumor incidence, reduced susceptibility to carcinogens and extended lifespan is analyzed. The potential role of the growth hormone/insulin-like growth factor type 1 (IGF-I) axis in this effect is discussed as is the evidence that a reduction in growth hormone and/or IGF-I leads to a reduction in spontaneous tumors and susceptibility to carcinogens.


Caloric restriction and cancer.
J Nutr Sci Vitaminol ( Tokyo). 2001 Feb;47(1):13-9.
Kritchevsky D.
The Wistar Institute, Philadelphia, PA 19104, .

In 1909 Moreschi observed that tumors transplanted into underfed mice did not grow as well as those transplanted into mice fed ad libitum. His finding stimulated a decade of research which showed that caloric restriction also affected negatively the growth of spontaneous tumors. Between 1920 and 1940 little work was done in this area, possibly because of limiting methodology. In the 1940s the laboratories of Tannenbaum (Chicago) and Baumann ( Wisconsin) were able to design studies using defined diets and showed that the observed effect was due to caloric content of the diet independently of the source of calories. After another active decade research activity in the calorie-cancer area declined until it was reborn in the 1980s. By the 1980s knowledge of physiology and molecular biology had advanced enough to allow investigators to probe mechanisms underlying the calorie-cancer phenomenon. We now know that caloric expenditure (as work or exercise) will lead to reduced risk. Energy restriction enhances DNA repair and moderates oxidative damage to DNA. Energy restriction reduces oncogene expression as well. Over a half century ago, Boutwell noted that energy restriction in female rats resulted in adrenal hypertrophy and reduced weight of ovaries and uterus. He suggested that energy restriction resulted in "pseudohypophysectomy." We now know that adrenalectomy can negate the effects of caloric restriction. Caloric restriction also affects insulin metabolism and may influence gene expression. These recent observations should help us understand some of the basic mechanisms involved in establishment and proliferation of tumors.


Effect of caloric restriction on age-associated cancers.
Exp Gerontol. 1992 Sep-Dec;27(5-6):575-81.
Weindruch R.

Department of Medicine, University of Wisconsin-Madison 53706.
Caloric restriction (CR) without malnutrition in mice and rats reduces the incidence of spontaneous tumors and delays their appearance while increasing maximum life span. These results depend largely on CR per se, and not on low intakes of fat or other nutrients. Although most studies have tested CR imposed early in life, CR started in midadulthood also retards cancer and aging. The way(s) by which CR impedes cancers remain unclear, but possibilities include less cellular oxidative damage, retarded immunologic aging, hormonal changes, less energy available for cell proliferation, reduced exposure to dietary carcinogens and promoters, enhanced DNA repair, and less carcinogen activation. Far less is known about the relationship between caloric intake and cancer incidence in humans; however, recent findings suggest a positive association for certain cancers.


Dietary restriction, tumors, and aging in rodents.
J Gerontol. 1989 Nov;44(6):67-71.
Weindruch R.
National Institute on Aging, Biomedical Research and Clinical Medicine Program, Bethesda, MD 20892.

A chronic 30-50% restriction of dietary energy intake (but without malnutrition) typically and strongly lowers the incidence of most spontaneous and induced tumors, delays their onsets, and extends maximum life span in rodents. When compared to normally fed controls, animals fed these dietary restriction (DR) regimens show decreased rates of change for most (but not all) age-sensitive biologic indexes studied to date. DR's impact on chemically induced tumors appears to depend more on energy than on fat restriction, and result from less promotion (and not less initiation). The molecular and cellular events underlying these various outcomes of DR are unclear. Viable explanations include less cellular oxidative damage, a retardation in the age-related changes in the immune system, hormonal changes, less exposure to dietary carcinogens and promoters, less energy for tumor growth, less carcinogen activation, and better DNA repair. New findings are consistent with the notion that DR reduces cellular damage mediated by active oxygen. A lower production or higher detoxification rate of active oxygen species, which damages molecules and promotes tumor growth, could explain DR's effects on aging and tumors.


The role of calories and caloric restriction in carcinogenesis.
Hematol Oncol Clin North Am. 1991 Feb;5(1):79-89.
Weindruch R, Albanes D, Kritchevsky D.
Department of Medicine, Universityof Wisconsin, Madison.

Studies in mice and rats show that caloric restriction (CR) without malnutrition lowers the incidence of most spontaneous and induced tumors and delays their onsets. The maximum life spans of rodents and other experimental animals (e.g., fish, spiders, water fleas) are extended by CR. The molecular events that underlie these outcomes remain unelucidated. Although epidemiologic studies have not usually examined the relationship between caloric intake and cancer incidence, recent findings suggest a positive association for certain cancers such as colorectal, breast, and stomach. It is apparent that future studies of diet and cancer in humans must seriously assess the role of calories and energy balance as well as their interaction with the effects of specific nutrients


Nutrition, cancer, and aging.
Ann N Y Acad Sci. 1998 Nov 20;854:371-7.
Dreosti IE.
CSIRO Division of Human Nutrition, Adelaide, South Australia.

The parallel increase in cancer risk with advancing age is well recognized, and several pathophysiological mechanisms common to both conditions have been proposed to explain this interrelationship. The importance of nutrition, both in delaying the aging process and in protecting against cancer is also well recognized, and it is therefore of interest to compare the relative impact several of the more widely studied dietary manipulations may have on each of these conditions. For example, caloric restriction, which putatively reduce oxidative stress and effectively increases life span in animals also seems to reduce the incidence of many cancers, possibly due to diminished mitogenesis. Likewise, oxidative damage to DNA appears to be common to both processes but may be more important in the mitochondria with respect to aging and in the nucleus in relation to cancer. Inadequate dietary folate and impaired DNA methylation status are closely associated with increased cancer risk, and recently defective somatic cell methylation and accumulated genetic instability have been proposed as key mechanisms contributing to senescence. Several other well-established anticancer dietary strategies, which include increased fiber intake and the consumption of more fruits and vegetables, have not been studied extensively in relation to aging, although many of the phytochemicals considered important as chemopreventive agents for cancer may well contribute to delaying the aging process. Although not directly related to nutrition, but nevertheless highly relevant, is the question of physical activity, which has been strongly linked to a reduction in risk of some cancers. Although less is known with respect to exercise and biological markers of aging, physical activity does appear to retard the age-related decline in the muscle strength and in the bone density.


Diet, cancer and aging in DNA mismatch repair deficient mice.
Carcinogenesis. 2002 Nov;23(11):1807-10.
Tsao JL, Dudley S, Kwok B, Nickel AE, Laird PW, Siegmund KD, Liskay RM, Shibata D.
Department of Pathology, Molecular Biology and Surgery, Norris Cancer Center, University of Southern California School of Medicine, Los Angeles, CA 90033, USA.

Diet is an important risk factor for many cancers. High fat/low calcium (HFLC) diets are associated with increased tumorigenesis, whereas caloric restriction (CR) reproducibly increases lifespan and decreases tumors. Mutations are involved in aging and cancer, and different diets may alter mutagenesis. However, a number of repair pathways normally counteract mutations by correcting errors before they can be fixed in the genome. To further understand interactions between diet, aging and cancer, mice deficient in a major repair pathway called DNA mismatch repair (MMR) were fed HFLC, CR or control diets. Mlh1 deficient mice are prone to lymphomas and intestinal adenomas and carcinomas. No significant changes in adenocarcinoma or lymphoma incidence were observed with HFLC or CR diets. Significantly more (2.2-fold) adenomas occurred with HFLC diets although adenoma numbers were unchanged with CR. Only a small increase in lifespan (116% of control) was achieved with CR. In addition, levels of microsatellite mutations in the small and large intestines were unchanged with the different diets. Our studies indicate that MMR deficiency may be epistatic to certain otherwise strong environmental influences on carcinogenesis or aging.


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


Caloric intake, body weight, and cancer: a review.
Nutr Cancer. 1987;9(4):199-217.
Albanes D.

The literature is reviewed for evidence concerning the relation between caloric intake, body weight, and cancer. Convincing experimental data regarding caloric intake and benign and malignant tumor incidence have been available since the 1940s and demonstrate that caloric restriction significantly reduces tumor incidence for a variety of tumor types in several animal models. Some epidemiological investigations provide evidence for a positive calorie-cancer association in humans, although it is difficult (in these studies) to separate the effects of calories per se from those of dietary fat. A larger number of investigations have evaluated body weight alone, and high relative body weight or high caloric intake has been associated with increased risk of cancer of the breast, colon, rectum, prostate, endometrium, kidney, cervix, ovary, thyroid, and gallbladder. In contrast, lung, bladder, and stomach cancers appear to be inversely associated with body weight, and some prospective studies of men demonstrate greater total cancer mortality among lean individuals. However, in their analyses, few of these latter investigations considered the effects of cigarette smoking, antecedent illness, or competing causes of death. While the relations between caloric intake, other dietary macronutrients (e.g., fat), and body weight are complex and require further investigation, a complete review of the data suggests that reducing caloric intake and relative body weight may lead to a considerable decrease in cancer risk in humans.


Caloric restriction perturbs the pituitary-ovarian axis and inhibits mouse mammary tumor virus production in a high-spontaneous-mammary-tumor-incidence mouse strain (C3H/SHN).
Mech Ageing Dev. 1989 Aug;49(2):93-104.
Koizumi A, Masuda H, Wada Y, Tsukada M, Kawamura K, Kamiyama S, Walford RL.
Department of Hygiene, Akita University School of Medicine, .

Dietary restriction (DR) retards aging and extends maximum life span. It is also known to decrease the incidence of hormone-dependent tumors. In the present investigation, we focussed primarily on the influence of DR on the pituitary-ovarian axis, and subsequently on gene expression of the mouse mammary tumor virus. F1 females from the mating of SHN female and C3H male mice were used in this study, since these hybrids display a very high incidence of mouse mammary tumors. The mice weaned at 3 weeks were raised on either a calorically-restricted diet (DR: 50 kcal/week; N = 5) or on a control diet (C: 95 kcal/week N = 5) for 5 weeks. Three C57BL/6J Jcl ad libitum-fed female mice, 8 weeks of age, were used as reference animals since this strain has a very low incidence of mammary tumors. The mean cellular contents of prolactin (PRL) and growth hormone (GH) in the pituitary, as determined by immunohistochemistry, were found to be reduced in mice raised on the DR diet. The decrease in the mean cellular content of PRL (50% of the mean control value) was accompanied by a decrease in the number of lactotrophs (17% of the mean value of control diet mice). However, the decrease in cellular content of GH (53% of the mean control value) was not accompanied by a decrease in the number of somatotrophs (no. of somatotrophs in DR = 103% of mean control value). Histologically, ovaries from DR mice showed many growing and atretic follicles, with few corpora lutea. In contrast, both control-diet and reference (C57BL/6J Jcl) mice showed two or three corpora lutea per ovarian section. In accordance with this finding, DR mice had not established stable estrus cycles by 8 weeks of age, in contrast to both control-diet and reference mice. Since caloric restriction has been shown to decrease mammary tumor virus (MMTV) gene expression, MMTV production was investigated by electron microscopy to confirm the validity of our experimental conditions. In DR or reference C57BL/6J Jcl mice, MMTV particles were rarely found in the mammary gland samples, but were always found in samples from control mice. The development of mammary glands, as indicated by the number of villi or the development of the rough endoplasmic reticulum, was delayed in DR mice. Thus, it was concluded that caloric restriction decreases the number of lactrotrophs, inhibits ovulation and delays mammary gland development. This immature status is considered to be due to perturbations in the pituitary-ovarian axis by caloric restriction.


Diet and carcinogenesis.
Carcinogenesis. 1993 Nov;14(11):2205-17.
Rogers AE, Zeisel SH, Groopman J.
Boston University Schoolof Medicine, Department of Pathology, MA 02116.

In summary there is a wealth of information on dietary and nutritional effects on carcinogenesis in laboratory rodents. Experimental studies based on epidemiological evidence, earlier experimental studies and known or predicted cellular, biochemical and molecular effects of nutrients have produced clear evidence that carcinogenesis in laboratory rodents is influenced by dietary intake of calories, fat, lipotropes (choline, methionine), vitamin A and related retinoids, Se, calcium, zinc, fiber, ethanol and a large number of non-nutrient components of foods. For these substances or groups of substances mechanistic hypotheses supported by experimental data and are leading to further research. The information provided will contribute to understanding of basic processes in carcinogenesis as well as of the specific interactions studied, and should contribute to significant advances in preventive medicine. Restriction of caloric intake of rodents by amounts > 10% over a significant portion of their lifetime reduces tumorigenesis. That level of restriction reduces the rate of growth and maturation, and most experiments in this area employ greater restrictions that virtually abolish growth from a young age. Therefore, the observations are of interest in mechanistic studies, but their applicability to preventive medicine requires better definition of the degree and duration of restriction required for a significant effect and the age at which it must be imposed. Restriction of total fat intake and modifications to increase the intake of omega-3 fats have a reasonably consistent effect on tumorigenesis in rodents but a much less consistently demonstrable effect in humans. Again, the observations in rodents are providing a major stimulus to mechanistic studies. The lipotropes are extremely valuable as tools for investigating mechanisms of carcinogenesis in rodents. Their importance in the epidemiology of human cancer has yet to be demonstrated clearly and is a subject of research at present. The naturally occurring vitamins and minerals, as well as fiber, derive their importance in this context from investigations to explain the consistent epidemiological demonstrations of reduction of tumor risk with increased consumption of fruits and vegetables. The activity of the isolated nutrients as anticarcinogens in rodents has generally not matched the activity expected from epidemiological studies. The anticarcinogenic activity of many of the non-nutrient components of fruits and vegetables is remarkable in particular models, however, as is the activity of natural and synthetic retinoids. At present the results must be interpreted to indicate an important effect of combinations of the whole foods with identification of particular nutrients or non-nutrients in specific cases.(ABSTRACT TRUNCATED AT 400 WORDS)


Prevention of cancer: restriction of nutritional energy intake (joules).
Comp Biochem Physiol A. 1988;91(2):209-20
Hocman G.
Research Institute of Preventive Medicine, Bratislava, 

The reduction of nutritional energy intake (joules) often reduces the incidence of both spontaneous and induced cancers in humans and experimental animals in an approximately dose-dependent manner. 2. To achieve the best preventive effect, the reduction of dietary intake should begin well before the carcinogen insult, should be intense enough (lowering the intake of joules by at least approx. 25-30%) and should last a long time, preferably even life-long. 3. This preventive effect depends upon the strain, sex and age of animals, the kind of carcinogenic insult and also the susceptibility of the target tissue. 4. The mechanism by which the dietary restriction may exert its protective action may involve changes in the hormonal equilibria, influences upon the immuno-surveillance, changes of activities of enzymes involved in carcinogen metabolism and other factors. 5. Since over-eating and the resulting obesity constitutes a pronounced risk factor for the incidence of cancer and other diseases, lowering the nutritional energy intake represents today the simplest, cheapest and most effective way to prevent cancer in the general population.


Effect of caloric restriction on pre-malignant and malignant stages of mammary carcinogenesis.
Carcinogenesis. 1997 May;18(5):1007-12.
Zhu Z, Haegele AD, Thompson HJ.
Division of Laboratory Research, AMC Cancer Research Center, Lakewood, CO 80214, .

Caloric restriction has documented beneficial effects on numerous diseases including cancer, yet the mechanism(s) that accounts for these wide ranging benefits is unknown. Part of the difficulty in defining mechanisms has been the long-term nature of experimental protocols in which these beneficial effects have been observed and the inherent difficulty of investigating mechanisms in such studies. The experiments reported were designed: (1) to determine if caloric restriction would inhibit mammary carcinogenesis in a model for this disease process that is 35 days in duration; (2) to determine if progression from pre-malignant to malignant stages of mammary carcinogenesis was affected by caloric restriction; and (3) to explore whether the effects of caloric restriction were associated with changes in adrenal function. Mammary carcinogenesis was induced in female Sprague-Dawley rats by the i.p. administration of 1-methyl-1-nitrosourea (50 mg/kg body weight) at 21 days of age. Rats were randomized to one of four dietary treatment groups: ad libitum fed, or restriction of food intake to 90, 80 or 60% of the ad libitum intake. Rats were palpated for detection of mammary tumors and all mammary lesions excised at necropsy were histologically classified. Twenty-four-hour collections of urine were obtained at weekly intervals throughout the 35-day experiment. Urine was assayed for corticosterone by direct radioimmunoassay. Caloric restriction resulted in both a dose dependent prolongation of latency to palpable carcinomas (P < 0.01) and a reduction in final incidence of mammary cancer; the dose response was linear (P < 0.05). The percentage of pre-malignant mammary lesions in a group increased with increasing degree of caloric restriction, whereas the percentage of carcinomas decreased (P < 0.05). The level of cortical steroid increased linearly with increasing caloric restriction (P < 0.01) an effect that was not attenuated over time. Poisson regression analyses with the number of cancers per rat as the dependent variable, level of caloric restriction as the independent variable and urinary cortical steroid excretion as a co-variate were performed. These analyses indicated that the variation in cancers per rat, irrespective of the treatment group to which an animal was assigned, could be accounted for by urinary cortical steroid excretion (P<0.05); i.e. urinary cortical steroid excretion was an independent predictor of an animal's carcinogenic response. The data reported in this study support the use of a short term model to study the mechanism(s) by which caloric restriction inhibits mammary carcinogenesis and point to both a stage in the disease process, the conversion of pre-malignant to malignant cells, and a target tissue (adrenal gland) and chemical species (adrenal cortical steroid) that may be involved in mediating the protective effects of energy restriction. These data indicate the feasibility of identifying a chemical basis for the protective effect of caloric restriction that is independent of energy restriction per se and this, in turn, indicates that it may be possible to circumvent the practical problem of implementing a program of chronic energy restriction in human populations, yet still achieve the wide-ranging health benefits of such a program.


The retardation of aging in mice by dietary restriction: longevity, cancer, immunity and lifetime energy intake.
J Nutr. 1986 Apr;116(4):641-54.
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.