When mice ate a diet of 25 percent extra sugar - the mouse equivalent of a healthy human diet plus three cans of soda daily - females died at twice the normal rate and males were a quarter less likely to hold territory and reproduce.
This is according to a toxicity test developed at the University of Utah.
"Our results provide evidence that added sugar consumed at concentrations currently considered safe exerts dramatic adverse impacts on mammalian health," the researchers say in a study set for online publication Tuesday, Aug. 13 in the journal Nature Communications
"This demonstrates the adverse effects of added sugars at human-relevant levels," says University of Utah biology professor Wayne Potts, the study's senior author. He says previous studies using other tests fed mice large doses of sugar disproportionate to the amount people consume in sweetened beverages, baked goods and candy.
"I have reduced refined sugar intake and encouraged my family to do the same," he adds, noting that the new test showed that the 25 percent "added-sugar" diet - 12.5 percent dextrose (the industrial name for glucose) and 12.5 percent fructose - was just as harmful to the health of mice as being the inbred offspring of first cousins.
Even though the mice didn't become obese and showed few metabolic symptoms, the sensitive test showed "they died more often and tended to have fewer babies," says the study's first author, James Ruff, who recently earned his Ph.D. at the University of Utah. "We have shown that levels of sugar that people typically consume - and that are considered safe by regulatory agencies - impair the health of mice."
The new toxicity test placed groups of mice in room-sized pens nicknamed "mouse barns" with multiple nest boxes - a much more realistic environment than small cages, allowing the mice to compete more naturally for mates and desirable territories, and thereby revealing subtle toxic effects on their performance, Potts says.
"This is a sensitive test for health and vigor declines," he says, noting that in a previous study, he used the same test to show how inbreeding hurt the health of mice.
"One advantage of this assay is we get the same readout no matter if we are testing inbreeding or added sugar," Potts says. "The mice tell us the level of health degradation is almost identical" from added-sugar and from cousin-level inbreeding.
The study says the need for a sensitive toxicity test exists not only for components of our diet, but "is particularly strong for both pharmaceutical science, where 73 percent of drugs that pass preclinical trials fail due to safety concerns, and for toxicology, where shockingly few compounds receive critical or long-term toxicity testing."
The study was funded by the National Institutes of Health and the National Science Foundation.
A Mouse Diet Equal to What a Quarter of Americans Eat
The experimental diet in the study provided 25 percent of calories from added sugar - half fructose and half glucose - no matter how many calories the mice ate. Both high-fructose corn syrup and table sugar (sucrose) are half fructose and half glucose.
Potts says the National Research Council recommends that for people, no more than 25 percent of calories should be from "added sugar," which means "they don't count what's naturally in an apple, banana, potato or other nonprocessed food. ... The dose we selected is consumed by 13 percent to 25 percent of Americans."
The diet fed to the mice with the 25 percent sugar-added diet is equivalent to the diet of a person who drinks three cans daily of sweetened soda pop "plus a perfectly healthy, no-sugar-added diet," Potts says.
Ruff notes that sugar consumption in the American diet has increased 50 percent since the 1970s, accompanied by a dramatic increase in metabolic diseases such as diabetes, obesity, fatty liver and cardiovascular disease.