Aspartame May Promote Weight Gain, Study Finds

A Massachusetts General Hospital study found that mice that drank aspartame-sweetened water gained weight.

Researchers found that mice that drank artificially sweetened water blocked a crucial stomach enzyme making the mice more likely to gain weight and develop diabetes.

Researchers explained the enzyme IAP – intestinal alkaline phosphatase – is crucial to preventing obesity and stopping the development of diabetes.

“This enzyme — intestinal alkaline phosphatase or IAP — is very beneficial in terms of preventing obesity and diabetes. So the aspartame, by blocking this enzyme, had its negative effects on the mice,”  explains Massachusetts General and Harvard Medical School Professor of Surgery Richard Hodin, the study’s senior author.

Previous studies have found that aspartame, an ingredient found in many popular sodas, caused an increase in weight gain instead of weight loss. Hodin says this new study illustrates a possible reason as to why so many people gain weight after drinking diet soda.

“There is a lot of evidence that aspartame, as well as other sugar substitutes, don’t work the way they’re supposed to,” Hodin says, “and the reasons for them not working are not very clear.” Theories have included the possibility that artificial sweeteners increase appetite. “But our experiments give at least a likely explanation for why aspartame may not work, and that’s because it blocks this gut enzyme, IAP.”

There are trillions of bacteria living inside the human stomach and Hodin explains the IAP enzyme helps create an environment conducive to a healthy digestive system.

In 2013, Hodin published a study in “Proceedings of the National Academy of Sciences” that revealed feeding IAP to mice on a high-fat diet could prevent the development of metabolism disorders. Phenylalanine is a known inhibitor of IAP enzyme, and is produced when aspartame is digested, which led Hodin and his team to see how the artificial sweetener has an impact on weight-loss.

Researchers examined four groups of mice over the course of 18 weeks. Two groups were fed a normal diet, one receiving drinking water sweetened with aspartame, the other group received regular water. The other two groups were fed a high-fat diet, along with aspartame laced water or regular water. Animals in the normal diet group that received aspartame-infused water gained more weight than those on the same diet that received regular water. In addition, mice receiving aspartame water also had higher blood sugar levels.

“People do not really understand why these artificial sweeteners don’t work. There has been some evidence that they actually can make you more hungry and may be associated with increased calorie consumption. Our findings regarding aspartame’s inhibition of IAP may help explain why the use of aspartame is counterproductive,” says Hodin. “While we can’t rule out other contributing mechanisms, our experiments clearly show that aspartame blocks IAP activity, independent of other effects.”


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