(Photo credit: Wikipedia)
If you think it takes a lot of sugar to mess with your body, a new study out in Nature Communications today may challenge that belief. The research reported that when mice were fed a diet of 25% added sugar, the females died twice as often as those fed regular diets, and males were less likely to sire pups and acquire territories. Many studies have looked at what happens when animals are exposed to sugar in very high doses, but this is one of the first to observe it at levels considered “safe” by the powers that be. Though it’s still not totally clear why the mice were dying or otherwise ailing, the authors say the fact that there are lingering questions may not matter so much at all – it’s much more important to pay attention to the study’s overall message. And it’s one that's becoming increasingly hard to ignore.
The researchers fed mice diets consisting of 25% added sugar as soon as they were weaned from their mothers, and tracked them over 32 weeks. It's important to point out that this level of sugar is still what’s considered “safe” by the National Research Council, and is about the equivalent of our eating a healthy diet but adding three sodas on top. In fact, up to a quarter of Americans consume this much added sugar every day.
The mice in the study lived in clever setups known as “mouse barns,” rather than cages, since this replicates their natural environments much more accurately than conventional lab housing. Various aspects of mice’s behavior were tracked – for example, how adept the males were at acquiring territories, how often both sexes reproduced. Of course, their death rates were also of particular interest.
The results were fairly striking: Females who ate the high-sugar diet died at rates twice that of control mice – 35% vs. 17%. The males were much worse at acquiring territories, and they had significantly fewer offspring than control mice (about a quarter fewer in both cases).
But the question, of course, is why the mice were having such health and behavioral problems, and the answer remains somewhat of a mystery. Metabolic markers like insulin levels, triglycerides, and obesity weren’t much different between the two groups, although glucose clearance and cholesterol levels were slightly worse in the sugar-fed females, and the cholesterol levels of sugar-fed males were also a bit worse than in controls.
Study author James Ruff tells me that what may be behind the higher death rate of the females may have to do with their generally higher metabolic demand. “[I]t is likely that female mice have increased mortality as they are in an energetic crucible,” he says. “Specifically, they are both gestating and nursing two separate litters concurrently, which elevates their metabolic rate substantially. Therefore, they may be more susceptible to metabolic disruptions associated with fructose feeding than males.” With the males, it’s less clear, but may have to do with subtle, sub-clinical changes in lipid regulation, he says. But future studies will have to dig deeper into this possibility.
The authors feel strongly that the fact that the underlying mechanisms weren’t totally apparent is not a shortcoming of the study at all. Ruff says that what matters most here is that “human-relevant” levels of sugar were what led to the health problems – unlike most studies that use staggeringly large amounts of sugar – and often, only fructose – to prove the point. “We think it is important to point out that most mechanistic work on sugar-induced toxicity…is done at levels of consumption that are incredibly high, often exceeding 50% of calories (astoundingly often with pure fructose). Researchers often times do this to ‘push the system’ to make mechanistic effects visible and dramatic.”
But, he says, this “push the system” method can be misleading, since the mechanisms occurring with very high doses of sugar may be somewhat different from what’s going on at those that we’re more likely to consume in daily life. And what’s especially important to keep in mind is that you often don’t need high doses of a “drug” – or huge fluctuations in the function of a body system – to effect serious, and perhaps fatal, health issues over the long-term.
“We appreciate that…a study such as ours is a bit unconventional," says Ruff, "but what we have done, where mechanistic labs have failed, is demonstrate that human-relevant levels of added sugar consumption harm mice.” The bottom line, he says, is that “we know that a diet of 25% added sugar harms mice. Therefore, it is likely that it also harms humans, as most substances that are toxic to mice are also toxic to humans.”
More studies will be needed to figure out exactly why the mice were dying, and whether the same things might be going on in us humans as well. In the meantime, says Ruff, “we have to ask ourselves question—if it makes a mouse sick, do we really want it in our body?”
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