The sugar substitute aspartame, used in many diet drinks, encourages weight gain — at least in mice.
A new study, published in Applied Physiology, Nutrition and Metabolism, showed that phenylalanine — a byproduct of aspartame breakdown — interferes with the action of an enzyme previously shown to prevent metabolic syndrome, which is associated with type-2 diabetes and cardiovascular disease.
It also showed that mice receiving aspartame in drinking water gained more weight and developed other symptoms of metabolic syndrome compared with mice just given water.
Phenylalanine inhibits the action of the enzyme IAP (intestinal alkaline phosphatase) which, in a separate study, was found to prevent the development of metabolic syndrome and reduce its symptoms in mice.
The fact that phenylalanine is produced when aspartame is digested led the researchers to investigate the possibility that this could explain aspartame’s lack of weight-loss effect.
The study’s senior author, Richard Hodin, said: ‘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.
‘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.
‘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. While we can’t rule out other contributing mechanisms, our experiments clearly show that aspartame blocks IAP activity, independent of other effects.’
Aspartame has generated huge controversy in the past — studies in the 1990s suggested its consumption might increase cancers in mice. However, large studies found this effect did not translate to humans.
The use of sweeteners in drinks and food has generated health headlines for decades now, and are often used by people trying to lose weight as part of a calorie-controlled diet. However, the evidence of its apparent lack of effectiveness at helping promote weight loss has steadily accrued in recent years and this American-led animal study appears to add further weight to this.
Mice fed aspartame in their drinking water gained more weight than those fed diets lacking aspartame. The reason appears to be that a breakdown product of aspartame called phenylalanine interferes with the action of another enzyme that helps prevent diabetes and obesity.
More work is needed on this but anyone who believes that by simply adding sweeteners such as aspartame to their diet will instantly see the pounds fall off now need to rethink their diet strategy.
Research score: 3/5