Here, recently published research adds to the weight of evidence to show that firstly even modest levels of reduced calorie intake produce measurable health benefits over the long term, and secondly it is possible to have a high degree of compliance in the study population. The knee-jerk reaction in many quarters to the practice of calorie restriction with optimal nutrition, meaning fewer calories consumed without reducing the intake of vital micronutrients, is that it is too hard. It is certainly true that most people in this age of cheap calories and ever more enticing foods choose not restrict their intake, but that isn't the same thing as "too hard." If you actually take the time to try it out and experiment with dietary options, you'll find that modest calorie restriction is not all that challenging at all.
Caloric restriction (CR), energy intake reduced below ad libitum (AL) intake, increases life span in many species. The implications for humans can be clarified by randomized controlled trials of CR. To determine CR's feasibility, safety, and effects on predictors of longevity, disease risk factors, and quality of life in nonobese humans aged 21-51 years, 218 persons were randomized to a 2-year intervention designed to achieve 25% CR or to AL diet. Outcomes were change from baseline resting metabolic rate adjusted for weight change ("RMR residual") and core temperature (primary); plasma triiodothyronine (T3) and tumor necrosis factor-α (secondary); and exploratory physiological and psychological measures.
Body mass index averaged 25.1 (range: 21.9-28.0). Eighty-two percent of CR and 95% of AL participants completed the protocol. The CR group achieved 11.7%CR and maintained 10.4% weight loss. Weight change in AL was negligible. RMR residual decreased significantly more in CR than AL at 12 months but not 24 months (M24). Core temperature change differed little between groups. T3 decreased more in CR at 12 and 24 months, while tumor necrosis factor-α decreased significantly more only at 24 months. CR had larger decreases in cardiometabolic risk factors and in daily energy expenditure adjusted for weight change, without adverse effects on quality of life.
We conclude that sustained CR is feasible in nonobese humans. The effects of the achieved CR on correlates of human survival and disease risk factors suggest potential benefits for aging-related outcomes that could be elucidated by further human studies.