Calorie counting off the menu

Thank goodness! It looks like the theory that calorie restriction helps you live longer has been debunked. Researchers at the Charles Perkins Centre have shown that calorie restriction has no beneficial effects on life span in mice - and they say this is probably the case for humans, too.

In fact, the researchers say that not all calories are created equal: protein, fat and carbohydrate have very different effects on food intake, metabolic health, ageing and longevity.

“This research has enormous implications for how much food we eat, our body fat, our heart and metabolic health, and ultimately the duration of our lives,” said Professor Steve Simpson, academic director of the University of Sydney’s Charles Perkins Centre and corresponding author of the study, which was published in Cell Metabolism.

“We have shown explicitly why it is that calories aren’t all the same - we need to look at where the calories come from and how they interact.”

While low-carb, high-protein diets did reduce body fat and food intake in mice, the news wasn’t great for their life span or health: they lived shorter lives and had poor cardiometabolic health.

In contrast, a high-carb, low-protein diet did increase body fat but had better outcomes in terms of life span and cardiometabolic health. Low-protein, high-fat diets were the worst of the lot, the researchers found, with fat content not even reducing food intake.

By examining mice fed a variety of 25 diets, the research team used a state-space nutritional modelling method to measure the interactive effects of dietary energy, protein, fat and carbohydrate on food intake, cardiometabolic health and longevity.

According to the researchers, the results suggest that the life span of animals could be extended by manipulating the ratio of macronutrients in their diet - reportedly the first evidence that pharmacology could be used to extend life span in normal mammals.

“Up until this point, most research has either concentrated on a single nutritional variable, such as fat, carbohydrate or calories, so much of our understanding of energy intake and diet balance is based on one-dimensional single nutrient assessments,” said study co-author Professor David Le Couteur from the Charles Perkins Centre, who is Professor of Geriatric Medicine at Concord Hospital.

“The advice we are always given is to eat a healthy balanced diet, but what does that mean? We have some idea, but in relation to nutritional composition we don’t know terribly well. This research represents an important step in finding out.”

The researchers predict that a diet consisting of 15 to 20% high-quality protein, relatively low in fat and high in good-quality complex carbohydrates will result in good metabolic health and a long life span.