still emerging. While calorie restriction has beneficial effects, especially in relation to weight and fat loss, the precise amount of calorie intake and associated fat mass for optimal health in humans is not known. It is conceivable that even moderate amounts of calorie restriction might have harmful effects on certain population groups, such as lean people with low body fat. Non-human primates A calorie restriction study started in 1987 by the National Institute on Aging showed that calorie restriction did not extend years of life or reduce age-related deaths in non-obese rhesus macaques. It did improve certain measures of health, however. These results were publicized as being different from the Wisconsin rhesus macaque calorie restriction study, which also started in 1987 and showed an increase in the lifespan of rhesus macaques following calorie restriction. In a 2017 report on rhesus monkeys, caloric restriction in the presence of adequate nutrition was effective in delaying the effects of aging. Older age of onset, female sex, lower body weight and fat mass, reduced food intake, diet quality, and lower fasting blood glucose levels were factors associated with fewer disorders of aging and with improved survival rates. Specifically, reduced food intake was beneficial in adult and older primates, but not in younger monkeys. The study indicated that caloric restriction provided health benefits with fewer age-related disorders in elderly monkeys and, because rhesus monkeys are genetically similar to humans, the benefits and mechanisms of caloric restriction may apply to human health during aging. Life extension According to scientific reviews, accumulating data suggests dietary restriction (DR) – mainly intermittent fasting and caloric restriction – results in many of the same beneficial changes in adult humans as in studied organisms, potentially increasing health- and lifespan beyond the benefits of healthy body weight. Which protocols of and combinations (e.g. see caloric restriction mimetic and AMPK) with DR are effective or most effective in humans is largely unknown and is being actively researched. A geroscience field of "precision nutrigeroscience" is proposed that also considers the potential need for adjustments of nutritional interventions per individual (e.g. due to differences in genetics and age). The mechanisms of these effects include autophagy and a decline in inflammaging. Intermittent fasting refers to periods with intervals during which no food but only e.g. water and tea/coffee are ingested – such as a period of daily time-restricted eating with a window of 8 to 12