Artificial Sweeteners Linked to Weight Gain

Monday, February 11, 2008 9:49 AM

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Want to lose weight? It might help to pour that diet soda down the
drain. Researchers have laboratory evidence that the widespread use of
no-calorie sweeteners may actually make it harder for people to control
their intake and body weight. The findings appear in the February issue
of Behavioral Neuroscience, which is published by the American
Psychological Association (APA).

Psychologists at Purdue University's Ingestive Behavior Research Center
reported that relative to rats that ate yogurt sweetened with glucose (a
simple sugar with 15 calories/teaspoon, the same as table sugar), rats
given yogurt sweetened with zero-calorie saccharin later consumed more
calories, gained more weight, put on more body fat, and didn't make up
for it by cutting back later, all at levels of statistical significance.

Authors Susan Swithers, PhD, and Terry Davidson, PhD, surmised that by
breaking the connection between a sweet sensation and high-calorie food,
the use of saccharin changes the body's ability to regulate intake. That
change depends on experience. Problems with self-regulation might
explain in part why obesity has risen in parallel with the use of
artificial sweeteners. It also might explain why, says Swithers,
scientific consensus on human use of artificial sweeteners is
inconclusive, with various studies finding evidence of weight loss,
weight gain or little effect. Because people may have different
experiences with artificial and natural sweeteners, human studies that
don't take into account prior consumption may produce a variety of
outcomes.

Three different experiments explored whether saccharin changed lab
animals' ability to regulate their intake, using different assessments –
the most obvious being caloric intake, weight gain, and compensating by
cutting back.

The experimenters also measured changes in core body temperature, a
physiological assessment. Normally when we prepare to eat, the metabolic
engine revs up. However, rats that had been trained to respond using
saccharin (which broke the link between sweetness and calories),
relative to rats trained on glucose, showed a smaller rise in core body
temperate after eating a novel, sweet-tasting, high-calorie meal. The
authors think this blunted response both led to overeating and made it
harder to burn off sweet-tasting calories.

"The data clearly indicate that consuming a food sweetened with
no-calorie saccharin can lead to greater body-weight gain and adiposity
than would consuming the same food sweetened with a higher-calorie
sugar," the authors wrote.

The authors acknowledge that this outcome may seem counterintuitive and
might not come as welcome news to human clinical researchers and
health-care practitioners, who have long recommended low- or no-calorie
sweeteners. What's more, the data come from rats, not humans. However,
they noted that their findings match emerging evidence that people who
drink more diet drinks are at higher risk for obesity and metabolic
syndrome, a collection of medical problems such as abdominal fat, high
blood pressure and insulin resistance that put people at risk for heart
disease and diabetes.

Why would a sugar substitute backfire? Swithers and Davidson wrote that
sweet foods provide a "salient orosensory stimulus" that strongly
predicts someone is about to take in a lot of calories. Ingestive and
digestive reflexes gear up for that intake but when false sweetness
isn't followed by lots of calories, the system gets confused. Thus,
people may eat more or expend less energy than they otherwise would.

The good news, Swithers says, is that people can still count calories to
regulate intake and body weight. However, she sympathizes with the
dieter's lament that counting calories requires more conscious effort
than consuming low-calorie foods.

Swithers adds that based on the lab's hypothesis, other artificial
sweeteners such as aspartame, sucralose and acesulfame K, which also
taste sweet but do not predict the delivery of calories, could have
similar effects. Finally, although the results are consistent with the
idea that humans would show similar effects, human study is required for
further demonstration.