It is not how much you eat, but what you eat that could influence life span, say UK researchers, investigating how calorie quality, not quantity, may dictate longevity, writes Lindsey Partos.
In April, the US Centers for Disease Control and Prevention released a study challenging the conventional wisdom that eating less promotes longevity.
Backing up the study, new research carried out by scientists at the University College London revealed that flies can actually live longer without reducing calories but by eating proportionally less yeast.
Their findings suggest the food industry adage that there is 'no good or bad food, just a good or bad diet' may ring true in the fight against obesity.
Fresh figures released in March show in excess of 200 million adults across the EU may be overweight or obese.
And the number of European kids overweight is rising by a hefty 400,000 a year, according to data from the International Obesity Task Force (IOFT).
"These results make a strong case that calories per se are not the salient factor in prolonging life - at least in fruitflies," say the study authors.
And further, their findings suggest that the dramatic impact of reducing yeast suggests that protein or fat plays a greater role in fly longevity than sugar.
For the latest study, published in the PLoS Biology (3(7): e223), dietary restriction in Drosophila flies involved diluting the nutrients in the fly's standard lab diet of yeast and sugar to a level known to maximise life span.
Since both yeast (which contributes protein and fat) and sugar (carbohydrates) provide the same calories per gram, the authors (William Mair, Matthew Piper, and Linda Partridge at UCL ) could adjust nutrient composition without affecting the calorie count, allowing them to separate the effects of calories and nutrients.
Reducing both nutrients increased the flies' life spans, but yeast had a much greater effect: reducing yeast from control to dietary restriction levels increased median life span by over 60 per cent.
Forty-eight hours after being switched from normal diets to yeast-restricted diets, flies were no more likely to die than flies fed the yeast-restricted diet from the beginning.
In contrast, those switched from the standard restriction diet to the sugar-restricted diet began to die at the same rate as flies on the control diet.