Diet drinks have been in the last decades seen as a substitute for regular sugary drinks as a result of their low-calorie content. However, recent studies have shown that diet soda may not be that effective for people who are trying to shift the pounds. Aspartame sweetener used in most diet drinks in lieu of sugar has been found to prevent weight loss by blocking intestinal enzyme’s activity.
Scientists at Massachusetts General Hospital (MGH) say it’s all to do with sugar substitutes aspartame and found a possible explanation to why the use of the sugar substitute aspartame might not promote weight loss.
"Sugar substitutes like aspartame are designed to promote weight loss and decrease the incidence of metabolic syndrome, but a number of clinical and epidemiologic studies have suggested that these products don't work very well and may actually make things worse," said Dr Richard Hodin, MD, of the MGH Department of Surgery, the lead author of the study published in online in A Applied Physiology, Nutrition and Metabolism.
"We found that aspartame blocks a gut enzyme called intestinal alkaline phosphatase (IAP) that we previously showed can prevent obesity, diabetes and metabolic syndrome; so we think that aspartame might not work because, even as it is substituting for sugar, it blocks the beneficial aspects of IAP."
Researchers show how the aspartame breakdown product phenylalanine interferes with the action of an enzyme previously shown to prevent metabolic syndrome -- a group of symptoms associated with type 2 diabetes and cardiovascular disease. They also showed that mice receiving aspartame in their drinking water gained more weight and developed other symptoms of metabolic syndrome than animals fed similar diets lacking aspartame.
Researchers four groups of mice for 18 weeks. Two groups were fed a normal diet, one receiving drinking water with aspartame, the other receiving plain water. The other two groups were fed a high-fat diet, along with either aspartame-infused or plain water. Animals in the normal diet group that received aspartame consumed an amount equivalent to an adult human's drinking about three and a half cans of diet soda daily, and aspartame-receiving animals in the high-fat group consumed the equivalent of almost two cans.
At the end of the study period, while there was little difference in weights between the weights of the two groups fed a normal diet. However, those on a high-fat diet given aspartame gained more weight than those on the same diet that received plain water.
Also, Aspartame-receiving mice in both diet groups had higher blood sugar levels than did those fed the same diets without aspartame, which indicates glucose intolerance, and both aspartame-receiving groups had higher levels of the inflammatory protein TNF-alpha in their blood, which suggests the kind of systemic inflammation associated with metabolic syndrome
"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, who is a professor of Surgery at Harvard Medical School.
"While we can't rule out other contributing mechanisms, our experiments clearly show that aspartame blocks IAP activity, independent of other effects."
Reference: Inhibition of the gut enzyme intestinal alkaline phosphatase may explain how aspartame promotes glucose intolerance and obesity in mice. Applied Physiology, Nutrition, and Metabolism, 2016; DOI: 10.1139/apnm-2016-0346