Is shorter life caused by obesity and diabetes?
Excessive sugar consumption correlates with shorter lifespan, which was believed to be the result of obesity and diabetes, diseases related to high sugar consumption, among other causes.
“Just like humans, flies fed a high-sugar diet show many hallmarks of metabolic disease — for instance, they become fat and insulin resistant,” says Dr Helena Cochemé, the principal investigator of the study. “Obesity and diabetes are known to increase mortality in humans, and so people always assumed that this was how excess sugar is damaging for survival in flies.”
Water intake changes lifespan
The new study in fruit flies reveals, however, that there might be something else in play.
“Water is vital for our health, yet its importance is often overlooked in metabolic studies. Therefore, we were surprised that flies fed a high-sugar diet did not show a reduced lifespan, simply by providing them with an extra source of water to drink. Unexpectedly, we found that these flies still exhibited the typical metabolic defects associated with high dietary sugar.”
Uric acid might be the driver of early death
The researchers showed in the study that excess dietary sugar caused the flies to accumulate a molecule called uric acid, the end product from the breakdown of purines. This molecule is prone to crystallise, causing kidney stones to form. Researchers were able to prevent these stones, either by diluting their formation with additional drinking water or by blocking the production of uric acid with a drug. Both methods provided protection against shortened survival associated with sugar-rich diet.
Collaborators from Kiel University in Germany confirmed a similar effect in healthy humans. “Strikingly, just like flies, we found that dietary sugar intake in humans was associated with worse kidney function and higher purine levels in the blood,” says Prof Christoph Kaleta, co-author of the study.
Drinking more water is not enough
Is it ok to eat a lot of sugar if you just drink some extra water?
“Unfortunately not,” says Dr Cochemé, “the sugar-fed flies may live longer when we give them access to water, but they are still unhealthy. And in humans, for instance, obesity increases the risk of heart disease. But our study suggests that disruption of the purine pathway is the limiting factor for survival in high-sugar-fed flies. This means that early death by sugar is not necessarily a direct consequence of obesity itself.”
It still seems that the best course of action is to limit added sugar intake to 10% of daily calorie intake at the most, ideally to 5% of daily calories (6 tsp of sugar) or less.