“That’s three sodas if the rest of your diet is pristine and sugar-free,” said lead author and biologist James S. Ruff. “And those are 12-ounce sodas, not double Big Gulps.”
Sugar-fed females died twice as quickly as control mice, which were fed the same total number of calories. While the sugar-fed males did not die more quickly, they had trouble competing against the control males for mates and were less likely to hold territory and reproduce.
The study was published online Tuesday by the journal Nature Communications.
For the rodents on the sweetened diet, sugar accounted for 25 percent of their total calorie intake. Up to a quarter of Americans consume that proportion of sugar as part of their diets. Previous studies that found harmful effects of sugar consumption tended to use unusually high amounts.
“[Our findings] set a new standard for caution even at low doses of added sugar,” senior author and biologist Wayne K. Potts said.
About 80 percent of substances that are toxic in mice are toxic for people as well, said Potts, so it is likely that the effects of extra sugar could be similar in humans.
The researchers first fed 156 animals either sweetened or normal diets for 26 weeks. They then used a novel lab setup: room-sized mouse barns where the animals could roam free instead of being confined in cages. The goal was to mimic the natural environment.
The scientists used this method because they thought it would be sensitive to the sociological and Darwinian effects of sugar — the mice must struggle for resources and need to be at their fittest to successfully compete. Once in the barns, both groups of mice were placed on the same normal diet. Scientists monitored the mice interactions for 32 weeks.
Overall, Potts and his colleagues found that the sugar-fed rodents, which didn’t look more obese or less healthy than the control animals, were nevertheless “physiologically worse at doing things they need to do on a daily basis.”
Sugar-fed females — but not males — died off sooner than their healthier counterparts, possibly from being too worn out to handle the burdens of reproduction. Many of the mice were nursing one litter while pregnant with another.
For the sugar-fed males, meanwhile, reproductive efforts were hindered by their inability to hold down territory.
A male mouse will typically control a designated area, defending it fiercely from short, intrusive forays by other males. A weakened male mouse will lose territory, along with female attention.
“Females won’t mate with any males that don’t own a territory,” Potts said. The sugar-fed mice held a quarter less area than their counterparts and as a result had an average of five to 10 fewer offspring, as determined by genetic analysis of the litters.
Potts and his colleagues chose a combination of sugars that mimicked high fructose corn syrup, a 50-50 ratio of fructose and glucose. The increase in sugar in the typical American diet in recent decades is largely attributed to higher consumption of high fructose corn syrup.