In the quest to find a way to slow the aging process, there have been two longstanding hypotheses: that we may live longer if our metabolic rate is slower, and that oxidative damage (caused by reactive oxygen species, a marker of inflammation) accelerates our biological aging. Thus, research over the past several decades has worked to understand whether a sustained reduction in calorie intake can slow aging by slowing metabolism and decreasing oxidative stress. While observational studies (and some animal studies) have suggested that calorie restriction increases longevity, there has been very little human clinical trial data available.
A study published in the journal Cell Metabolism, was the first randomized clinical trial to test whether calorie restriction in young healthy people over 2 years could result in health improvements that (the authors postulate) may prolong lifespan.
The trial randomized 34 people to receive a calorie restricted diet (15% reduction in energy intake from baseline) and compared to 19 people following an unrestricted diet. The average age was 40 years, about two thirds were female, and all were healthy, with 42% being of healthy body weight and 58% with slight overweight (by BMI criteria) at the start of the study.
The people in the calorie restricted group lost 8.7kg over two years, whereas the control group gained 1.8kg. In the calorie restricted group, 24 hour energy expenditure dropped by 80-120 kcal more than would be expected by weight loss alone, accompanied by a slight reduction in thyroid hormone levels and reactive oxygen species (a marker of inflammation).
The authors conclude that calorie restriction results in metabolic slowing and reduction in oxidative stress, supporting the above theories of slowing aging. But can we conclude that calorie restriction actually slows aging and prolongs longevity? No. As the authors note, we can’t extrapolate this data to conclude that people who restrict their calorie intake are going to live longer. Also, almost half of the people in this study had a healthy body weight (as defined by BMI) at baseline, and we would not have recommended weight loss in these people (and perhaps not even in those with elevated BMI if they were completely healthy). Further, the obesity paradox suggests that people who carry a little extra weight in their older years may actually live longer, especially in association with chronic medical conditions.
So while weight management is certainly important to maintaining overall health, we are far from finding a ‘cure’ for aging.
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