Artificial sweeteners causing glucose intolerance

A new study on artificial sweeteners published in Nature goes a long way toward explaining one of the most puzzling findings about sweetened drinks in recent years: that regular consumption of even diet sodas is associated with an increased incidence of obesity and Type II diabetes. Surely, if the sweeteners have no calories and negligible carbohydrate, this shouldn’t be happening? Surely people should be losing weight? But the national statistics have shown that it is, and they’re not.

According to a news summary in The Scientist (Sugar Substitutes, Gut Bacteria, and Glucose Intolerance), researchers at the Weizmann Institute of Science in Rehovot, Israel, demonstrated that repeatedly consuming zero-calorie sweeteners like saccharin, sucralose and aspartame (e.g., Sweet ‘N’ Low, Splenda, and NutraSweet) increases a person’s glucose intolerance by causing changes to his or her gut bacteria.

The researchers did extensive testing on mice first–fed them artificially sweetened water for several weeks and compared glucose tolerance and gut flora with those of control groups that received either glucose solution or plain water. The experimental mice had much higher rates of glucose intolerance than either of the control groups, including the one that was fed glucose solution.

They also had very different gut bacteria composition, which the researchers thought might be causing the changes in glucose tolerance. Wiping out the gut bacteria of control mice with antibiotics and then repopulating with the gut bacteria from sweetener-fed mice caused glucose intolerance in the normally fed mice.

The researchers repeated their experiments on healthy human subjects, and they got the same dramatic results. The timeframe for measurable changes in glucose tolerance was within as little as six days for one of the tests.

Admittedly, the researchers were dosing their subjects with sweetener concentrations at the highest levels currently deemed safe by the FDA. So if you only consume these sweeteners occasionally and in small quantity–say, chewing sugarless gum once in a while–you might not be causing a drastic change in your gut bacteria or glucose tolerance.

But so many people in the US consume diet sodas and artificially sweetened teas and so on in large quantity on a daily basis that it’s possible they’re coming close to the levels used in these experiments. If you consume even half the maximum defined “safe” daily level, you might well be impairing your glucose tolerance significantly. But there may not be a safe level. There’s no saying what level–if any–of sweetener per day is low enough not to change gut bacteria and raise glucose intolerance–it may be a matter of dose or it may be a matter of how long and how regularly people consume these sweeteners.

Glucose tolerance is a measure of your body’s ability to supply insulin quickly and at the right level whenever you eat or drink something with starches or sugars. Part of the gut’s function is to release glucose into the bloodstream, but