The practice of calorific restriction as a means to health, improved mental faculties and a longer life is controversial and two recent studies have contributed more fuel to the debate. A study carried out by scientists at the University of Southern California, and published online on January 13th in The Journal of Nutrition, compared metabolic rates in two strains of mice, one genetically engineered to be fat and the other lean. Lifespan of the ‘fat’ strain is increased by calorie restriction whereas that of the ‘lean’ strain is not. When both groups of mice were allowed to eat as much as they wanted, they ate similar amounts and had similar body weights at 4 months old. Later in life, however, the ‘fat’ strain mice were significantly heavier than the ‘lean’ strain mice, a difference linked to lower metabolic rate in the ‘fat’ mice. Only the mice with the lower metabolic rate benefitted from a reduced calorie diet. The study authors conclude that calorie restriction may be pointless – and possibly even dangerous – for non-obese individuals and that, ideally, energy expenditure and energy intake should be in balance.
A second study, published in the Proceedings of the National Academy of Sciences, looked at the effect of calorie restriction and intake of unsaturated fatty acids on cognitive performance in older people. Fifty healthy, normal to overweight subjects, with an average age of sixty, were assigned to one of three groups: 30% calorie reduction, increased intake of unsaturated fatty acids or control. Memory performance was measured before the trial began and after three months. A significant improvement (20%) in verbal memory scores was seen in the group eating fewer calories whereas no significant changes were seen in the other two groups. The improvements in memory correlated with decreases in fasting plasma insulin levels and a marker of inflammation, and were most pronounced in individuals who stuck strictly to the diet. The researchers plan to repeat the study in a larger group of people and also to study the effects of calorie restriction in patients with mild cognitive impairment. It is not clear whether reducing calorie intake would improve memory in lower weight individuals.