The cells that make up our body are outnumbered 10:1 by bacteria residing within us. In fact, we are all carrying around an extra 3 lbs of bacteria at all times . These bacteria, along with the other viruses and fungi in our body, make up our unique ‘microbiomes’. The microbes that inhabit our bodies vary between people, are very stable throughout our lives, and correlate with whether an individual is lean or obese . Our diverse bacterial signatures perform important functions in our bodies that scientists are only now beginning to unravel. Specific bacteria also contribute to risk for various diseases, such as Irritable Bowel Disease (IBD) or colorectal cancer . Recent evidence has shown that different bacteria do not only correlate with disease but may serve as the causative factor.
Earlier this year, Suez et al. at Israel’s Weizmann Institute of Science made an important discovery, published in Science, concerning the effect of non-caloric artificial sweeteners on blood glucose levels via the microbiome . Their findings imply that while many people use artificial sweeteners because they are trying to lose weight or reduce their risk of developing Type II diabetes, these sweeteners may in fact have the opposite effect.
Suez et al. found that mice which were fed a diet high in artificial sweeteners developed increased resting blood glucose levels compared with mice that were not fed artificial sweeteners. Wiping out the gut bacteria with antibiotics abolished this effect, demonstrating that gut bacteria are necessary for the blood glucose response. By performing fecal transplants from mice fed artificial sweeteners to mice that were not fed artificial sweeteners, they demonstrated that the change in gut bacteria alone was sufficient to induce changes in blood glucose levels of mice .
To examine whether these findings held true in humans, 7 healthy volunteers consumed the FDA’s maximal acceptable daily intake of saccharine (5 mg/kg body weight) for 7 days. Over the course of the 7 days the volunteers who consumed saccharine developed a significant increase in resting blood glucose levels relative to control volunteers. They also showed a change in their microbiome profile over the 7-day period .
These findings challenge the idea that calories in vs. calories out are the major determinants of weight gain and subsequent risk for the development of metabolic syndrome. In fact, non-caloric sweeteners may do more harm than good.
These results also underscore the potential value in targeting the microbiome to modulate blood glucose levels either through targeted antibiotics or bacterial transplants.
Tech start-ups have arisen which allow people to investigate their own gut bacterial signatures. Much as companies like 23andMe allow interested people to provide a saliva sample and inexpensively receive personal genome sequencing (although health related results were prohibited by the FDA in 2013), similar companies are providing gut bacterial sequencing services. All you have to do is provide a swab of a fecal sample and companies like μBiome will give you your own bacterial profile, and even tell you how your profile compares to people with different dietary habits, such as vegetarians, vegans, or people who eat a paleo diet.
We will likely hear a lot more about how the microbiome affects health and disease in coming years. For now, it may be wise to skip the diet soda if you are watching your waistline.
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4. Suez, J et al. Artificial sweeteners induce glucose intolerance by altering the gut microbiota. Science. 2014: 514,181–186: doi:10.1038/nature13793