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
"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
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
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.