A new study from the University of Utah finds mice that consume 'safe' levels of sugar are more likely to die and have fewer offspring.
The increasing prevalence of obesity, diabetes, and metabolic syndrome are creating a health epidemic in the U.S. and many think sugar is at least partially to blame. Research conducted at the University of Utah supports the idea that a high-sugar diet is unhealthy, and in the case of mice, deadly.
"We observed that females that were on the added sugar diet had twice the death rate, had twice the mortality than females that were on the control diet," says lead author Wayne Potts, professor in the Department of Biology. "Males did not have a mortality effect, but males on the added sugar diet had 25% fewer offspring than controls and dominated 25% fewer territories than control males."
Their research differs from previous studies, where animals were fed sugar in very high doses, more than anyone eats in the real world. "People have been working on it a lot, but the primary studies just add fructose to the diet of animals. And to make it easy to see an effect, they add very large quantities of fructose, so that 40, 50, 60 percent of their diet is in fructose. And they get an effect."
To look at a more realistic scenario, he and researcher James Ruff examined the effects on mice of a diet composed of only 25% added sugar. The 50-50 mix of fructose and glucose are the same sugar components in high fructose corn syrup. They found even this lower level of sugar can be deadly.
A diet composed of 25% sugar is considered safe to humans by government regulatory agencies, says Potts. "About 20% of Americans are on this level of sugar intake or higher. It's equivalent to having a very excellent diet with no added sugar, but then three twelve once sodas a day. And it's actually hard to get no added sugar in the rest of your diet if you eat any processed food."
A critical element of their study was that the research team used wild mice, rather than lab mice and let them live in mouse barns so they could freely associate and compete for territory and mates. Previous studies using laboratory mice in cages did not show any effect at lower concentrations of sugar. "These are large room sized habitats where we try to emulate the mouse natural environment," says Ruff
They exposed two groups of mice to different sugar levels throughout their early youth. Following this period, both groups of mice went on the high sugar diet. The difference in diet during the first 6.5 months of life, a period of rapid growth and development, was enough to produce profound long-term effects.
Ruff says they don't know why the sugar-fed females are dying or why the males are failing to reproduce at normal levels. They only found minor differences between the test and control groups after the first 6.5 months. "We saw no difference in body weight, we saw no difference in fasting insulin or fasting glucose, or fasting triglycerides. We had a slight elevation in the sugar-fed animals in terms of total cholesterol, and female mice that were on the sugar- fed diet had slightly slower rates of glucose clearance. But of the two things we got positive findings for, the effect size was relatively minor."
Ruff says the study suggests there may be unknown mechanisms responsible for the decline in health of the sugar fed animals.
The big question remains, does this study have implications for us? Ruff says that an equivalent human study would be extremely difficult to perform, making it difficult to obtain a definitive answer. "This study is equivalent to 75 years of human life. This is lifetime exposure, lifetime performance data," says Ruff.
Nevertheless, Potts says 60-80% of things that are toxic for mice are also toxic for humans. "If a substance poisons a mouse, do you want it in your body? At least before we figure out all of the details?"
Potts and Ruff say they hope this study spurs further research that will eventually help to understand how sugar harms mice, and possibly humans.