Do artificial sweeteners make you thinner or fatter?

photo: krossbow via Flickr

It’s the holiday season, and excess calories are lurking everywhere.   A recent survey by the International Food Information Council found that 70% of American consumers don’t understand that excess calories cause weight gain.  Nevertheless, 70% of respondents also claim they’re trying to eat less sugar.  One strategy for less sugar is more artificial sweeteners.  Do they really help with weight loss?

Think about it this way: if artificial sweeteners helped people lose weight, why do we have an escalating obesity epidemic?  The explosion of obesity pretty much parallels the increased consumption of artificial sweeteners.  Coincidence?  Yet it makes no metabolic sense, if you assume that weight is just about calories.  Artificial sweeteners have no calories, so theoretically, if you substitute a zero calorie soft drink for a 150 calorie sugar-sweetened drink everyday, you cut calories.

Dr. Kelly Brownell of Yale University cites one rat study, which showed that rats fed artificial sweeteners ate more than sugar-eating rats, to support the theory that fake sweet flavors drive eating.  Evidence for this effect in humans is mixed.  One study done in Texas followed several thousand free living people for up to 8 years.  Use of artificial sweeteners and sugar-sweetened beverages was tracked, along with changes in weight.  People who used artificial sweeteners:

  • Gained more weight than people who avoided those sweeteners.
  • Were more likely to be dieting to lose weight
  • Exercised less
  • Consumed fewer calories as carbohydrates or sugar, but more of their calories were from protein, fat and saturated fat.

What can we conclude?  Do artificial sweeteners somehow make you gain weight?   As the study authors noted, there are several ways to interpret the data.  People who consume more artificially sweetened beverages are heavier and more likely to be dieting.  Perhaps dieting is the cause of higher consumption.  Perhaps obesity is promoted by the higher fat diets of artificial sweetener users.  Or perhaps people reward themselves for drinking diet soft drinks by eating rich high calorie foods, and end up gaining weight.

Another possibility: the intense sweetness of artificial sweeteners has a metabolic effect that drives overeating, as shown in the rodent study quoted by Dr. Brownell.  Whatever the explanations for the obesity-artificial sweetener connection, one thing is perfectly clear: use of artificial sweeteners was not linked to lower body weight.  And wasn’t that the point of using them?  The argument for switching to artificially sweetened beverages as a way to lose weigh doesn’t seem convincing.

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