Dietary restriction (DR), the limitation of food intake below the ad libidum level without malnutrition, can extend the mean and maximum lifespan in every organism in which it has been tested, including yeast, worms, flies and rodents. Caloric restriction is the only known non-genetic intervention that robustly extends lifespan in mammals. This regimen also attenuates the incidence and progression of many age-dependent pathologies. DR has also been shown in animal models to slow the progression of, or even prevent entirely, a range of age-dependent pathologies, including cardiovascular disease, multiple types of cancer, several neurodegenerative disorders and diabetes. Short term DR also reduces the risk of coronary disease and stroke in humans.
Numerous independent studies show that dietary restriction does not extend life span when sirtuins are deleted. This result has been shown in multiple organisms, from yeast to flies and even in mice. Moreover, deleting SIRT1, SIRT3, SIRT4, or SIRT5 abrogates various physiological aspects of dietary restriction and fasting, including longevity. In humans, there is also evidence that sirtuins may be involved in mediating the response to dietary restriction and increasing health span. For example, SIRT1 levels increase in humans practicing dietary restriction, and there are strong associations between alleles that increase SIRT1 expression and increased metabolic rate, as well as protection from type 2 diabetes.
People eat less and make different food choices, as they get older. However, lower food intake among the elderly has been associated with lower intakes of calcium, iron, zinc, B vitamins, and vitamin E. Low energy intakes or low nutrient density of the diet may increase the risk of diet-related illnesses. Older adults tend to consume less energy-dense sweets and fast foods, and consume more energy-dilute grains, vegetables, and fruits. Daily volume of foods and beverages also declines as a function of age. Age-related physiological changes of slower gastric emptying altered hormonal responses, decreased basal metabolic rate, and altered taste and smell may also contribute to lowered energy intake. Other factors, such as marital status, income, education, socioeconomic status, diet-related attitudes and beliefs, and convenience likely play a role as well. Many age-related nutritional problems may be remedied by providing nutrient-dense meals through home delivery or meal congregate programs.