In humans, there are few randomized controlled clinical trials investigating the effects of caloric restriction in health and ageing. Now, Leanne Redman and her team report the results of a 2-year clinical trial that investigated the effect of caloric restriction in healthy humans. The authors found that caloric restriction of ~15% over 2 years resulted in an average weight loss of 8.7 kg.

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caloric restriction of ~15% over 2 years resulted in an average weight loss of 8.7 kg

In their study, the researchers recruited 53 healthy adults and assigned 34 to the caloric restriction group and 19 to the control group. The caloric restriction group was given a specific diet regime and the control group continued their current diets. During the 2-year study, the team measured the metabolic rate of the participants by various means, including the sleeping metabolic rate (the most robust measurement of human metabolism).

The total body weight of participants in the caloric restriction group was reduced on average by 8.7 kg (70% of which was from body fat), while the control group gained on average 1.8 kg. In addition, the sleeping metabolic rate of participants in the caloric restriction group fell by ~10%, which was beyond what was expected based on the amount of weight loss observed. The authors also reported that participants in the caloric restriction group had reductions in levels of reactive oxygen species and decreases in thyroid activity (reduced levels of T3 and T4), which is a biomarker of decreased ageing.

“The ultimate study into effects of caloric restriction would be one where participants eat a calorie-restricted diet from early adulthood for the remainder of their lives,” concludes Redman. “Such a study is the only way to truly answer the question of whether caloric restriction extends lifespan and improves healthspan in people.”