Fat substitutes used in popular snack foods to help people control weight may have the opposite effect, according to Purdue University research.
"These substitutes are meant to mimic the taste of fat in foods that are normally high in fat while providing a lower number of calories, but they may end up confusing the body," said Susan E. Swithers, professor of psychological sciences. "We didn't study this in people, but we found that when rats consumed a fat substitute, learned signals that could help control food intake were disrupted, and the rats gained weight as a result.
"Substituting a part of the diet with a similar tasting item that has fewer or zero calories sounds like a common-sense approach to lose weight, but there are other physiological functions at work. Tastes normally alert the body to expect calories, and when those calories aren't present we believe the systems become ineffective and one of the body's mechanisms to control food intake can become ineffective."
The findings appear online in the current issue of Behavioral Neuroscience, which is published by the American Psychological Association. This research was funded by the National Institutes of Health. Swithers, as well as co-author Terry L. Davidson, a professor of psychological sciences, are members in Purdue's Ingestive Behavior Research Center. The study also was co-authored by undergraduate student Sean Ogden who graduated this spring.
In this study, laboratory rats received crushed potato chips as a supplement to their diet, and then were divided into two groups that were given either a low-fat chow diet or a high-fat chow diet.
These groups were each split into two smaller groups. One group on each diet was fed a mixture of high-fat chips and the fat-substitute chips, containing olestra, which is a synthetic fat with no calories, while the other group received only regular high-fat chips. The chips were provided for 28 days. Rats maintained on the high-fat chow diet gained more weight and developed more fatty tissue when they were given fat-substitute chips compared to the animals that ate only regular high-fat chips.
"Again we are looking at an animal model, but there are similarities for humans, and based on what we found, we believe that our findings question the effectiveness of using fat substitutes as part of a long-term weight loss strategy," Davidson said.
They also found when the group of rats that had previously consumed both fat substitute and high-fat chips were moved from a low-fat standard chow diet to a high-fat chow diet, they gained more weight.
"What's interesting here is that weight gain occurred regardless of when the rats consumed the low-calorie, fat-substituted chips," Swithers said. "The rationale behind providing both high-fat and olestra chips was to ensure that the animals received similar cues related to the sensory properties of fat, but with different consequences. Without this kind of control, we would not know how they were interpreting the chips as high fat or not."
In past studies, Swithers and Davidson have found that when rats consumed artificial sweeteners, they were more likely to overeat. They believe that a similar disruption of taste-calorie relations may be happening with both artificial sweeteners and fat substitutes.
"When the mouth tastes something sweet or fatty it tells the body to prepare for calories, and this information is key to the digestive process," Swithers said. "This is a reminder to not discount the roles that taste and experience with food play in the way the body's systems work together."
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