Caloric restriction (CR), undernutrition without malnutrition, remains the only experimental paradigm that has been shown consistently to extend lifespan and slow aging in short-lived species. Decades of research, mostly in laboratory rodents, have shown that CR consistently extends lifespan, reduces or delays the onset of many age-related diseases and slows aging in many physiological systems. In recent years gerontologists interested in CR have focused on two unanswered questions. 1) What is the relevance of this nutritional paradigm to human aging?
Caloric restriction (CR) may retard aging processes and extend lifespan in organisms by altering energy-metabolic pathways. In CR rodents, glucose influx into tissues is not reduced, as compared with control animals fed ad libitum (AL), although plasma concentrations of glucose and insulin are lower. Gene expression profiles in rodents have suggested that CR promotes gluconeogenesis and fatty acid biosynthesis in skeletal muscle. In the liver, CR promotes gluconeogenesis but decreases fatty acid synthesis and glycolysis.
A review of biochemical mechanisms underlying the known approaches to extension of lifespan and/or slowing down of ageing suggests that they all modify balances between generation of active oxygen and carbonyl species and the mechanisms that protect from their damaging effects or repair their consequences. A likely common target of the geroprotector effects of antioxidants, melatonin, and antidiabetic biguanides is the mitochondrial respiratory chain.
Current Opinion in Clinical Nutrition and Metabolic Care
PURPOSE OF REVIEW: The focus of this review is on current research involving long-term calorie restriction and the resulting changes observed in possible biomarkers of aging. Special emphasis will be given to the basic and clinical science studies which are currently investigating the effects of controlled, high-quality energy-restricted diets on both biomarkers of longevity and on the development of chronic diseases related to age and obesity in humans.
Caloric restriction (CR) is the only experimental nongenetic paradigm known to increase lifespan. It has broad applicability and extends the life of most species through a retardation of aging. There is considerable interest in the use of CR in humans, and animal studies can potentially tell us about the impacts. In this article we highlight some of the things that animal studies can tell us about CR in humans. Rodent studies indicate that the benefits of CR on lifespan extension are related to the extent of restriction.
The focus of this review is on current research involving long-term calorie restriction (CR) and the resulting changes observed in physiological and behavioral outcomes in humans. Special emphasis will be given to the first completed clinical studies which are currently investigating the effects of controlled, high-quality energy-restricted diets on both biomarkers of longevity and on the development of chronic diseases related to age in humans.
Current Opinion in Investigational Drugs (London, England: 2000)
SIRT1 (sirtuin 1) is the human ortholog of the yeast Sir2 (silent information regulator 2) protein, which is implicated in lifespan extension in model organisms, such as yeast, worms and flies. It is an NAD+-dependent protein deacetylase with over two dozen known substrates that affect a wide variety of cellular processes, ranging from metabolism, cell cycle, growth and differentiation, inflammation, senescence, apoptosis, stress response and aging.
Ageing can be defined as "a progressive, generalized impairment of function, resulting in an increased vulnerability to environmental challenge and a growing risk of disease and death". Ageing is likely a multifactorial process caused by accumulated damage to a variety of cellular components. During the last 20 years, gerontological studies have revealed different molecular pathways involved in the ageing process and pointed out mitochondria as one of the key regulators of longevity.
Dietary restriction (DR) delays or prevents age-related diseases and extends lifespan in species ranging from yeast to primates. Although the applicability of this regimen to humans remains uncertain, a proportional response would add more healthy years to the average life than even a cure for cancer or heart disease. Because it is unlikely that many would be willing or able to maintain a DR lifestyle, there has been intense interest in mimicking its beneficial effects on health, and potentially longevity, with drugs.
The quest to understand why we age has given rise to numerous lines of investigation that have gradually converged to include metabolic control by mitochondrial activity as a major player. That is, the ideal balance between nutrient uptake, its transduction into usable energy, and the mitigation of damaging byproducts can be regulated by mitochondrial respiration and output (ATP, reactive oxygen species (ROS), and heat). Mitochondrial inefficiency through proton leak, which uncouples substrate oxidation from ADP phosphorylation, can comprise as much as 30% of the basal metabolic rate.