Caloric Restriction

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    Caloric restriction (CR), a dietary regimen that reduces calorie intake without incurring malnutrition, has been a subject of scientific study in the context of aging and longevity. This practice is thought to extend lifespan and improve health outcomes in various species, including potentially humans.

    Science Behind Caloric Restriction

    Mechanisms

    Caloric restriction is believed to impact aging through several biological pathways. These include reduced metabolic rate, decreased oxidative stress, improved insulin sensitivity, and activation of cellular maintenance mechanisms such as autophagy.

    Research Findings

    Studies in model organisms, like yeast, worms, flies, and mice, have consistently shown lifespan extension with caloric restriction. Human studies, however, are more complex due to longer lifespans and ethical considerations.

    Effects in Different Organisms

    Positive Effects

    Effects of calorie restriction on the survival rate of laboratory mice (CR=Calorie Restriction).[1]
    Calorie restriction can significantly increase the lifespan of the fruit fly (Drosophila melanogaster).

    Calorie restriction has been studied in model organisms such as Yeast (Saccharomyces Cerevisiae)[2][3], Nematodes (Caenorhabditis Elegans)[4], Fruit Flies (Drosophila Melanogaster)[5], Mice (Mus Musculus)[1], Rats (Rattus Norvegicus)[6], Domestic Dogs (Canis Familiaris)[7] and Non-Human Primates.[8][9][10]

    In many species, not only is the average lifespan of the test animals increased, but also their maximum lifespan. The frequency of age-related diseases correspondingly decreases.[11] The effect of an increase in maximum life expectancy occurs in rodents both when starting the diet in the early life phase (1st to 3rd month), and in the middle life phase (12th month).[8][9] However, if calorie restriction is started in a later life phase of the test animals, such as in the 17th or 24th month of mice, the effect reverses and the lifespan of the test animals is shortened.[12]

    Both in a study with rhesus monkeys[13] by the American National Institute on Aging, and in a study on Drosophila[5], it has been suggested that life extension depends not only on calorie restriction but also on the composition of the diet.

    General Criticism

    Various findings raise doubts about the notion that caloric restriction slows down the aging process, delays the age-related decline in physiological fitness, or extends the lifespan of organisms from different phylogenetic groups.[14] Positive effects of caloric restriction are not universal:

    In fruit flies, positive effects of caloric restriction are not reproduced with careful control of nutrient fractions.[15]

    The increase in lifespan caused by caloric restriction is not even reproducible among different strains of the same species.[14]

    Calorie restriction does not extend lifespan in all mice. In the top graph, a significant effect is observed in C57BL/6 mice ("laboratory mice"), while it is absent in DBA/2 mice ("wild type") below (AL=ad libitum, CR=Calorie Restriction).[12]

    Thus, calorie restriction does not lead to lifespan extension in all mouse strains.[12] In 19 to 27% of the mouse strains studied, a 40% caloric restriction even resulted in a shortened lifespan.[16][17]

    The frequently used C57BL/6 mice tend to become overweight with unrestricted food access (ad libitum). In these animals, the effect of caloric restriction is significant. DBA/2 mice, on the other hand, remain lean even with ad-libitum feeding. In mice from this strain, caloric restriction does not lead to lifespan extension. DBA/2 mice consume more oxygen with the same energy intake than C57BL/6 mice, meaning their metabolic rate is increased – they are poorer "feed converters."[18] It was already observed in earlier experiments that caloric restriction is most successful in mice that gain significant weight in early adulthood.[19] The results of these studies are interpreted to mean that lifespan is more influenced by the balance of energy intake and energy expenditure. Only in test animals prone to overweight or obesity can caloric restriction cause lifespan extension.[20]

    The NIA study on rhesus monkeys found no lifespan extension.[13] In a long-term study conducted at the Wisconsin National Primate Research Center over a period of 20 years on rhesus monkeys, a significantly better health status and a significantly increased lifespan were observed in the group of animals that received a reduced food supply during this period. In this group, 80% of the animals were still alive, compared to only 50% in the normally fed control group. Furthermore, in the animals with calorie restriction, a significantly delayed onset of age-associated diseases such as diabetes, cancer, and brain atrophy, as well as cardiovascular incidents, was observed. The authors of the study conclude that calorie restriction delays the aging process in this primate species.[21][22]

    Benefits of Caloric Restriction

    Research suggests that caloric restriction may offer several health benefits, including:

    • Improved metabolic health
    • Reduced risk of age-related diseases
    • Enhanced brain function and protection against neurodegenerative diseases
    • Possible extension of healthy lifespan

    Potential Risks and Concerns

    Caloric restriction, especially if not properly managed, can lead to:

    • Nutritional deficiencies
    • Loss of bone density
    • Reduced muscle mass and strength
    • Psychological challenges such as food obsession and social isolation

    Guidelines for Safe Practice

    Before starting caloric restriction, it is crucial to consult healthcare professionals. Some general guidelines include:

    • Gradual reduction in calorie intake
    • Emphasis on nutrient-dense foods
    • Regular monitoring of health parameters
    • Adjustment of diet based on individual health needs and lifestyle

    Conclusion

    While caloric restriction shows promise as a tool for extending healthspan and potentially lifespan, further research, especially in humans, is necessary. It is vital to approach this dietary regimen with caution and under medical supervision to avoid adverse effects.

    Todo

    • In fact, it has been shown that caloric restriction increases NAD+ bioavailability by activating the expression of NAMPT (nicotinamide phosphoribosyltransferase, which transforms nicotinamide [NAM] to NAD+ in the NAD+ salvage pathway) [23]

    References

    1. ↑ 1.0 1.1 Weindruch R et al.: The retardation of aging in mice by dietary restriction: longevity, cancer, immunity and lifetime energy intake. J Nutr 1986. (PMID 3958810) [PubMed] [DOI] 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.
    2. ↑ Lin SJ et al.: Requirement of NAD and SIR2 for life-span extension by calorie restriction in Saccharomyces cerevisiae. Science 2000. (PMID 11000115) [PubMed] [DOI] Calorie restriction extends life-span in a wide variety of organisms. Although it has been suggested that calorie restriction may work by reducing the levels of reactive oxygen species produced during respiration, the mechanism by which this regimen slows aging is uncertain. Here, we mimicked calorie restriction in yeast by physiological or genetic means and showed a substantial extension in life-span. This extension was not observed in strains mutant for SIR2 (which encodes the silencing protein Sir2p) or NPT1 (a gene in a pathway in the synthesis of NAD, the oxidized form of nicotinamide adenine dinucleotide). These findings suggest that the increased longevity induced by calorie restriction requires the activation of Sir2p by NAD.
    3. ↑ Lin SJ et al.: Calorie restriction extends Saccharomyces cerevisiae lifespan by increasing respiration. Nature 2002. (PMID 12124627) [PubMed] [DOI] Calorie restriction (CR) extends lifespan in a wide spectrum of organisms and is the only regimen known to lengthen the lifespan of mammals. We established a model of CR in budding yeast Saccharomyces cerevisiae. In this system, lifespan can be extended by limiting glucose or by reducing the activity of the glucose-sensing cyclic-AMP-dependent kinase (PKA). Lifespan extension in a mutant with reduced PKA activity requires Sir2 and NAD (nicotinamide adenine dinucleotide). In this study we explore how CR activates Sir2 to extend lifespan. Here we show that the shunting of carbon metabolism toward the mitochondrial tricarboxylic acid cycle and the concomitant increase in respiration play a central part in this process. We discuss how this metabolic strategy may apply to CR in animals.
    4. ↑ Lakowski B & Hekimi S: The genetics of caloric restriction in Caenorhabditis elegans. Proc Natl Acad Sci U S A 1998. (PMID 9789046) [PubMed] [DOI] [Full text] Low caloric intake (caloric restriction) can lengthen the life span of a wide range of animals and possibly even of humans. To understand better how caloric restriction lengthens life span, we used genetic methods and criteria to investigate its mechanism of action in the nematode Caenorhabditis elegans. Mutations in many genes (eat genes) result in partial starvation of the worm by disrupting the function of the pharynx, the feeding organ. We found that most eat mutations significantly lengthen life span (by up to 50%). In C. elegans, mutations in a number of other genes that can extend life span have been found. Two genetically distinct mechanisms of life span extension are known: a mechanism involving genes that regulate dauer formation (age-1, daf-2, daf-16, and daf-28) and a mechanism involving genes that affect the rate of development and behavior (clk-1, clk-2, clk-3, and gro-1). We find that the long life of eat-2 mutants does not require the activity of DAF-16 and that eat-2; daf-2 double mutants live even longer than extremely long-lived daf-2 mutants. These findings demonstrate that food restriction lengthens life span by a mechanism distinct from that of dauer-formation mutants. In contrast, we find that food restriction does not further increase the life span of long-lived clk-1 mutants, suggesting that clk-1 and caloric restriction affect similar processes.
    5. ↑ 5.0 5.1 Mair W et al.: Calories do not explain extension of life span by dietary restriction in Drosophila. PLoS Biol 2005. (PMID 16000018) [PubMed] [DOI] [Full text] Dietary restriction (DR) extends life span in diverse organisms, including mammals, and common mechanisms may be at work. DR is often known as calorie restriction, because it has been suggested that reduction of calories, rather than of particular nutrients in the diet, mediates extension of life span in rodents. We here demonstrate that extension of life span by DR in Drosophila is not attributable to the reduction in calorie intake. Reduction of either dietary yeast or sugar can reduce mortality and extend life span, but by an amount that is unrelated to the calorie content of the food, and with yeast having a much greater effect per calorie than does sugar. Calorie intake is therefore not the key factor in the reduction of mortality rate by DR in this species.
    6. ↑ C. M. McCay und M. F. Crowell: Prolonging the Life Span. In: The Scientific Monthly 39, 1934, S. 405–414; JSTOR 15813.
    7. ↑ Lawler DF et al.: Diet restriction and ageing in the dog: major observations over two decades. Br J Nutr 2008. (PMID 18062831) [PubMed] [DOI] This report reviews decade two of the lifetime diet restriction study of the dog. Labrador retrievers (n 48) were paired at age 6 weeks by sex and weight within each of seven litters, and assigned randomly within the pair to control-feeding (CF) or 25 % diet restriction (DR). Feeding began at age 8 weeks. The same diet was fed to all dogs; only the quantity differed. Major lifetime observations included 1.8 years longer median lifespan among diet-restricted dogs, with delayed onset of late life diseases, especially osteoarthritis. Long-term DR did not negatively affect skeletal maturation, structure or metabolism. Among all dogs, high static fat mass and declining lean body mass predicted death, most strongly at 1 year prior. Fat mass above 25 % was associated with increasing insulin resistance, which independently predicted lifespan and chronic diseases. Metabolizable energy requirement/lean body mass most accurately explained energy metabolism due to diet restriction; diet-restricted dogs required 17 % less energy to maintain each lean kilogram. Metabonomics-based urine metabolite trajectories reflected DR-related differences, suggesting that signals from gut microbiota may be involved in the DR longevity and health responses. Independent of feeding group, increased hazard of earlier death was associated with lower lymphoproliferative responses to phytohaemagglutinin, concanavalin A, and pokeweed mitogen; lower total lymphocytes, T-cells, CD4 and CD8 cells; lower CD8 percentages and higher B-cell percentages. When diet group was taken into account, PWM responses and cell counts and percentages remained predictive of earlier death.
    8. ↑ 8.0 8.1 Lane MA et al.: Caloric restriction and aging in primates: Relevance to humans and possible CR mimetics. Microsc Res Tech 2002. (PMID 12424798) [PubMed] [DOI] For nearly 70 years it has been recognized that reduction in caloric intake by 30-40% from ad libitum levels leads to a significant extension of mean and maximal lifespan in a variety of short-lived species. This effect of caloric restriction (CR) on lifespan has been reported in nearly all species tested and has been reproduced hundreds of times under a variety of different laboratory conditions. In addition to prolonging lifespan, CR also prevents or delays the onset of age-related disease and maintains many physiological functions at more youthful levels. Studies in longer-lived species, specifically rhesus and squirrel monkeys, have been underway since the late 1980s. The studies in nonhuman primates are beginning to yield valuable information suggesting that the effect of CR on aging is universal across species and that this nutritional paradigm will have similar effects in humans. Even if CR can be shown to impact upon human aging, it is unlikely that most people will be able to maintain the strict dietary control required for this regimen. Thus, elucidation of the biological mechanisms of CR and development of alternative strategies to yield similar benefits is of primary importance. CR mimetics, or interventions that "mimic" certain protective effects of CR, may represent one such alternative strategy.
    9. ↑ 9.0 9.1 Wanagat J et al.: Caloric intake and aging: mechanisms in rodents and a study in nonhuman primates. Toxicol Sci 1999. (PMID 10630588) [PubMed] [DOI] Caloric restriction (CR) increases maximum life span in rodents while attenuating the development of age-associated pathological and biological changes. Although nearly all of the rodent studies have initiated CR early in life (1-3 months of age), CR, when started at 12 months of age, also extends maximum life span in mice. Two main questions face investigators of CR. One concerns the mechanisms by which CR retards aging and diseases in rodents. There is evidence that CR may act, at least in part, by reducing oxidative stress. A CR-induced decrease in oxidative stress appears to be most profound in post-mitotic tissues and may derive from lower mitochondrial production of free radicals. The second issue is whether CR will exert similar effects in primates. Studies on CR in rhesus monkeys (maximum life span approximately 40 years) support the notion of human translatability. We describe the University of Wisconsin Study of rhesus monkeys subjected to a 30% reduction of caloric intake starting at either 1989 or 1994 when they were approximately 10 years old. The data from our study and from other trials suggest that CR can be safely carried out in monkeys and that certain physiological effects of CR that occur in rodents (e.g., decreased blood glucose and insulin levels, improved insulin sensitivity, and lowering of body temperature) also occur in monkeys. Whether oxidative stress in monkeys is reduced by CR will be known by the year 2000, while effects on longevity and diseases should be clearly seen by, appropriately, 2020.
    10. ↑ Weindruch R: The retardation of aging by caloric restriction: studies in rodents and primates. Toxicol Pathol 1996. (PMID 8994305) [PubMed] [DOI] 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.
    11. ↑ Hofer T et al.: Long-term effects of caloric restriction or exercise on DNA and RNA oxidation levels in white blood cells and urine in humans. Rejuvenation Res 2008. (PMID 18729811) [PubMed] [DOI] [Full text] Excessive adiposity is associated with increased oxidative stress and accelerated aging. Weight loss induced by negative energy balance reduces markers of oxidation in experimental animals and humans. The long-term effects of weight loss induced by calorie restriction or increased energy expenditure induced by exercise on measures of oxidative stress and damage have not been studied in humans. The objective of the present study was to compare the effects of 20% caloric restriction or 20% exercise alone over 1 year on oxidative damage to DNA and RNA, as assessed through white blood cell and urine analyses. Eighteen men and women aged 50 to 60 years with a body mass index (BMI) between 23.5 to 29.9 kg/m(2) were assigned to one of two conditions--20% CR (n = 9) or 20% EX (n = 9)--which was designed to produce an identical energy deficit through increased energy expenditure. Compared to baseline, both interventions significantly reduced oxidative damage to both DNA (48.5% and 49.6% reduction for the CR and EX groups, respectively) and RNA (35.7% and 52.1% reduction for the CR and EX groups, respectively) measured in white blood cells. However, urinary levels of DNA and RNA oxidation products did not differ from baseline values following either 12-month intervention program. Data from the present study provide evidence that negative energy balances induced through either CR or EX result in substantial and similar improvements in markers of DNA and RNA damage to white blood cells, potentially by reducing systemic oxidative stress.
    12. ↑ 12.0 12.1 12.2 Forster MJ et al.: Genotype and age influence the effect of caloric intake on mortality in mice. FASEB J 2003. (PMID 12586746) [PubMed] [DOI] [Full text] Long-term caloric restriction (CR) has been repeatedly shown to increase life span and delay the onset of age-associated pathologies in laboratory mice and rats. The purpose of the current study was to determine whether the CR-associated increase in life span occurs in all strains of mice or only in some genotypes and whether the effects of CR and ad libitum (AL) feeding on mortality accrue gradually or are rapidly inducible and reversible. In one experiment, groups of male C57BL/6, DBA/2, and B6D2F1 mice were fed AL or CR (60% of AL) diets beginning at 4 months of age until death. In the companion study, separate groups of mice were maintained chronically on AL or CR regimens until 7, 17, or 22-24 months of age, after which, half of each AL and CR group was switched to the opposite regimen for 11 wk. This procedure yielded four experimental groups for each genotype, namely AL-->AL, AL-->CR, CR-->CR, and CR-->AL, designated according to long-term and short-term caloric regimen, respectively. Long-term CR resulted in increased median and maximum life span in C57BL/6 and B6D2F1 mice but failed to affect either parameter in the DBA/2 mice. The shift from AL-->CR increased mortality in 17- and 24-month-old mice, whereas the shift from CR-->AL did not significantly affect mortality of any age group. Such increased risk of mortality following implementation of CR at older ages was evident in all three strains but was most dramatic in DBA/2 mice. Results of this study indicate that CR does not have beneficial effects in all strains of mice, and it increases rather than decreases mortality if initiated in advanced age.
    13. ↑ 13.0 13.1 Mattison JA et al.: Impact of caloric restriction on health and survival in rhesus monkeys from the NIA study. Nature 2012. (PMID 22932268) [PubMed] [DOI] [Full text] Calorie restriction (CR), a reduction of 10–40% in intake of a nutritious diet, is often reported as the most robust non-genetic mechanism to extend lifespan and healthspan. CR is frequently used as a tool to understand mechanisms behind ageing and age-associated diseases. In addition to and independently of increasing lifespan, CR has been reported to delay or prevent the occurrence of many chronic diseases in a variety of animals. Beneficial effects of CR on outcomes such as immune function, motor coordination and resistance to sarcopenia in rhesus monkeys have recently been reported. We report here that a CR regimen implemented in young and older age rhesus monkeys at the National Institute on Aging (NIA) has not improved survival outcomes. Our findings contrast with an ongoing study at the Wisconsin National Primate Research Center (WNPRC), which reported improved survival associated with 30% CR initiated in adult rhesus monkeys (7–14 years) and a preliminary report with a small number of CR monkeys. Over the years, both NIA and WNPRC have extensively documented beneficial health effects of CR in these two apparently parallel studies. The implications of the WNPRC findings were important as they extended CR findings beyond the laboratory rodent and to a long-lived primate. Our study suggests a separation between health effects, morbidity and mortality, and similar to what has been shown in rodents, study design, husbandry and diet composition may strongly affect the life-prolonging effect of CR in a long-lived nonhuman primate.
    14. ↑ 14.0 14.1 Sohal RS & Forster MJ: Caloric restriction and the aging process: a critique. Free Radic Biol Med 2014. (PMID 24941891) [PubMed] [DOI] [Full text] The main objective of this review is to provide an appraisal of the current status of the relationship between energy intake and the life span of animals. The concept that a reduction in food intake, or caloric restriction (CR), retards the aging process, delays the age-associated decline in physiological fitness, and extends the life span of organisms of diverse phylogenetic groups is one of the leading paradigms in gerontology. However, emerging evidence disputes some of the primary tenets of this conception. One disparity is that the CR-related increase in longevity is not universal and may not even be shared among different strains of the same species. A further misgiving is that the control animals, fed ad libitum (AL), become overweight and prone to early onset of diseases and death, and thus may not be the ideal control animals for studies concerned with comparisons of longevity. Reexamination of body weight and longevity data from a study involving over 60,000 mice and rats, conducted by a National Institute on Aging-sponsored project, suggests that CR-related increase in life span of specific genotypes is directly related to the gain in body weight under the AL feeding regimen. Additionally, CR in mammals and "dietary restriction" in organisms such as Drosophila are dissimilar phenomena, albeit they are often presented to be the very same. The latter involves a reduction in yeast rather than caloric intake, which is inconsistent with the notion of a common, conserved mechanism of CR action in different species. Although specific mechanisms by which CR affects longevity are not well understood, existing evidence supports the view that CR increases the life span of those particular genotypes that develop energy imbalance owing to AL feeding. In such groups, CR lowers body temperature, rate of metabolism, and oxidant production and retards the age-related pro-oxidizing shift in the redox state.
    15. ↑ Lee KP et al.: Lifespan and reproduction in Drosophila: New insights from nutritional geometry. Proc Natl Acad Sci U S A 2008. (PMID 18268352) [PubMed] [DOI] [Full text] Modest dietary restriction (DR) prolongs life in a wide range of organisms, spanning single-celled yeast to mammals. Here, we report the use of recent techniques in nutrition research to quantify the detailed relationship between diet, nutrient intake, lifespan, and reproduction in Drosophila melanogaster. Caloric restriction (CR) was not responsible for extending lifespan in our experimental flies. Response surfaces for lifespan and fecundity were maximized at different protein-carbohydrate intakes, with longevity highest at a protein-to-carbohydrate ratio of 1:16 and egg-laying rate maximized at 1:2. Lifetime egg production, the measure closest to fitness, was maximized at an intermediate P:C ratio of 1:4. Flies offered a choice of complementary foods regulated intake to maximize lifetime egg production. The results indicate a role for both direct costs of reproduction and other deleterious consequences of ingesting high levels of protein. We unite a body of apparently conflicting work within a common framework and provide a platform for studying aging in all organisms.
    16. ↑ C. Y. Liao, B. A. Rikke, T. E. Johnson, V. Diaz, J. F. Nelson: Genetic variation in the murine lifespan response to dietary restriction: from life extension to life shortening. In: Aging Cell. Volume 9, Number 1, February 2010, Template:ISSN, pp. 92–95, doi:10.1111/j.1474-9726.2009.00533.x, PMID 19878144, Template:PMC.
    17. ↑ B. A. Rikke, C. Y. Liao, M. B. McQueen, J. F. Nelson, T. E. Johnson: Genetic dissection of dietary restriction in mice supports the metabolic efficiency model of life extension. In: Experimental Gerontology. Volume 45, Number 9, September 2010, Template:ISSN, pp. 691–701, doi:10.1016/j.exger.2010.04.008, PMID 20452416, Template:PMC.
    18. ↑ Sohal RS et al.: Life span extension in mice by food restriction depends on an energy imbalance. J Nutr 2009. (PMID 19141702) [PubMed] [DOI] [Full text] In this study, our main objective was to determine whether energy restriction (ER) affects the rate of oxygen consumption of mice transiently or lastingly and whether metabolic rate plays a role in the ER-related extension of life span. We compared rates of resting oxygen consumption between C57BL/6 mice, whose life span is prolonged by ER, and the DBA/2 mice where it is not, at 6 and 23 mo of age, following 40% ER for 2 and 19 mo, respectively. Mice of the 2 strains that consumed food ad libitum (AL) had a similar body mass at the age of 4 mo and consumed similar amounts of food throughout the experiment; however, the body weight subsequently significantly increased (20%) in the C57BL/6 mice but did not increase significantly in the DBA/2 mice. The resting rate of oxygen consumption was normalized as per g body weight, lean body mass, organ weight, and per mouse. The resting rate of oxygen consumption at 6 mo was significantly higher in AL DBA/2 mice than the AL C57BL/6 mice for all of the criteria except organ weight. A similar difference in AL mice of the 2 strains was present at 23 mo when resting oxygen consumption was normalized to body weight. Resting oxygen consumption was lowered by ER in both age groups of each strain according to all 4 criteria used for normalization, except body weight in the C57BL/6 mice. The effect of ER on resting oxygen consumption was thus neither transient nor age or strain dependent. Our results suggest that ER-induced extension of life span occurs in the mouse genotype in which there is a positive imbalance between energy intake and energy expenditure.
    19. ↑ Ross MH et al.: Dietary practices and growth responses as predictors of longevity. Nature 1976. (PMID 958413) [PubMed] [DOI]
    20. ↑ Life Extension: Myth of Caloric Restriction Refuted, https://www.aerzteblatt.de/nachrichten/35192/Lebensverlaengerung-Mythos-der-Kalorienrestriktion-widerlegt
    21. ↑ Colman RJ et al.: Caloric restriction delays disease onset and mortality in rhesus monkeys. Science 2009. (PMID 19590001) [PubMed] [DOI] [Full text] Caloric restriction (CR), without malnutrition, delays aging and extends life span in diverse species; however, its effect on resistance to illness and mortality in primates has not been clearly established. We report findings of a 20-year longitudinal adult-onset CR study in rhesus monkeys aimed at filling this critical gap in aging research. In a population of rhesus macaques maintained at the Wisconsin National Primate Research Center, moderate CR lowered the incidence of aging-related deaths. At the time point reported, 50% of control fed animals survived as compared with 80% of the CR animals. Furthermore, CR delayed the onset of age-associated pathologies. Specifically, CR reduced the incidence of diabetes, cancer, cardiovascular disease, and brain atrophy. These data demonstrate that CR slows aging in a primate species.
    22. ↑ rme: Template:Webarchive In: aerzteblatt.de, July 10, 2009.
    23. ↑ Menssen A et al.: The c-MYC oncoprotein, the NAMPT enzyme, the SIRT1-inhibitor DBC1, and the SIRT1 deacetylase form a positive feedback loop. Proc Natl Acad Sci U S A 2012. (PMID 22190494) [PubMed] [DOI] [Full text] Silent information regulator 1 (SIRT1) represents an NAD(+)-dependent deacetylase that inhibits proapoptotic factors including p53. Here we determined whether SIRT1 is downstream of the prototypic c-MYC oncogene, which is activated in the majority of tumors. Elevated expression of c-MYC in human colorectal cancer correlated with increased SIRT1 protein levels. Activation of a conditional c-MYC allele induced increased levels of SIRT1 protein, NAD(+), and nicotinamide-phosphoribosyltransferase (NAMPT) mRNA in several cell types. This increase in SIRT1 required the induction of the NAMPT gene by c-MYC. NAMPT is the rate-limiting enzyme of the NAD(+) salvage pathway and enhances SIRT1 activity by increasing the amount of NAD(+). c-MYC also contributed to SIRT1 activation by sequestering the SIRT1 inhibitor deleted in breast cancer 1 (DBC1) from the SIRT1 protein. In primary human fibroblasts previously immortalized by introduction of c-MYC, down-regulation of SIRT1 induced senescence and apoptosis. In various cell lines inactivation of SIRT1 by RNA interference, chemical inhibitors, or ectopic DBC1 enhanced c-MYC-induced apoptosis. Furthermore, SIRT1 directly bound to and deacetylated c-MYC. Enforced SIRT1 expression increased and depletion/inhibition of SIRT1 reduced c-MYC stability. Depletion/inhibition of SIRT1 correlated with reduced lysine 63-linked polyubiquitination of c-Myc, which presumably destabilizes c-MYC by supporting degradative lysine 48-linked polyubiquitination. Moreover, SIRT1 enhanced the transcriptional activity of c-MYC. Taken together, these results show that c-MYC activates SIRT1, which in turn promotes c-MYC function. Furthermore, SIRT1 suppressed cellular senescence in cells with deregulated c-MYC expression and also inhibited c-MYC-induced apoptosis. Constitutive activation of this positive feedback loop may contribute to the development and maintenance of tumors in the context of deregulated c-MYC.
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