Rats fed a high-fat diet gained more weight after eating low-calorie potato chips made with “fake fat”, a synthetic fat substitute designed to taste like fat but without the calories, according to a study due to appear online in the journal Behavioral Neuroscience this week. The findings challenge the notion that using fat substitutes in place of real fats in foods helps people lose weight: they would be better off sticking to low-fat, low-calorie diets, said the researchers.

Lead author Dr Susan E Swithers, a psychology professor at Purdue University in West Lafayette, Indiana, said in a statement that:

“Our research showed that fat substitutes can interfere with the body’s ability to regulate food intake, which can lead to inefficient use of calories and weight gain.”

Swithers and colleagues fed one group of laboratory rats a high-fat diet and the other group a low-fat diet. In addition, half of the high-fat group and half of the low-fat group were also fed normal Pringles potato chips: these are high in fat and high in calories.

The other half of each group of rats was fed the normal high-fat Pringles on some days and on other days they were fed low-calorie Pringles Light chips, which in the United States contain olestra, a synthetic fat substitute that tastes like fat but has zero calories and passes through the body undigested.

The results showed that the rats on the high-fat diet that ate both the high-fat and the fake-fat Pringles ate more food, put on more weight, and gained more body fat than their counterparts on the high-fat diet that were given only the high-fat Pringles.

In fact, even when the researchers stopped feeding them the Pringles, the heavier rats did not shed the extra weight.

In contrast, the rats on the low-fat diet did not experience significant weight gain, regardless of which type of chips they ate.

But, when the researchers swapped those same rats to the high-fat diet, the rats that had eaten both the high-fat and the fake-fat chips put on more weight and body fat than the rats that had only eaten the high-fat chips.

Swithers said these results suggest sticking to a low-fat, low-calorie diet is probably a better way to lose weight than using fat substitutes.

However, she warned results from rat feeding studies don’t always translate to humans, even though we have similar biological responses to food.

Speculating on why they got these results, the researchers said when humans, and other animals like rats, taste food that is sweet or fatty, this sends a signal that the food is likely to be calorie-rich, and triggers the body to respond in preparation to digest it, such as producing more saliva, hormones and changes in metabolism. If the anticipated calories don’t appear, this interferes with that relationship.

In their report, they discuss the principle that energy regulation is a learned process, which is reinforced every time the anticipation of a high-calorie meal (as signalled from the encounter of sight, smell and taste) is followed by the actual cosumption of a high number of calories.

If, on the other hand, the sensory signals that a high-calorie meal is about to be consumed is not followed by the anticipated high number of calories, this “degrades” the link between sensory signals and the learned control of energy regulation.

Thus, they suggest that “… energy and body weight dysregulation are a consequence of a reduced ability to anticipate the actual caloric US [unconditional stimulus] that is produced when normal high-fat and high-energy foods are encountered”.

Swithers and her team reported similar results in an earlier study where rats fed saccharin and other artificial sweeteners also put on weight and body fat.

Swithers said these studies suggest there is “no silver bullet” way to shed excess weight.

“Eating food which is naturally low in fat and calories may be a better route than relying on fat substitutes or artificial sweeteners,” she added.

In their conclusions, the researchers refer to the dramatic increase in the last 30 years in America’s consumption of fat substitutes and artificial sweeteners, a trend that mirrors the simultaneous rise in overweight and obesity.

While a typical interpretation is that people start to eat these products after they begin to put on weight, the researchers instead suggest their results, together with those of previous animal experiments, along with some prospective correlational studies in humans, are consistent with the idea that eating artificial sweeteners and fat substitutes actually contribute to overweight and obesity.

“Fat Substitutes Promote Weight Gain in Rats Consuming High-Fat Diets.”

Susan E. Swithers, Sean B. Ogden, and Terry L. Davidson.

Behavioral Neuroscience, 2011, Vol. 125, No. 4

DOI: 10.1037/a0024404

Additional source: APA.

Written by: Catharine Paddock, PhD