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Science Shows Yo-Yo Dieters Probably Can’t Win

You likely have clients who have been dieting most of their adult lives. A study published in the International Journal of Obesity (2013; doi: 10.1038/ijo.2013.138) shows that there may be a physiological reason why diets could be a poor bet, especially for obese people. Researchers from the University of Adelaide in South Australia discovered that the way the stomach detects and tells our brains how full we are becomes damaged in obese people, but the mechanism does not return to normal once those people lose weight. The authors believe this could be a key reason why most people who lose weight on a diet eventually backslide.

PhD student Stephen Kentish investigated the impact of a high-fat diet on the gut’s ability to signal fullness, and whether those changes revert to normal upon weight loss. Results show that the nerves in the stomach that signal fullness to the brain appear to become desensitized after long-term consumption of a high-fat diet.

The stomach’s nerve response does not return to normal upon return to a normal diet. This means you would need to eat more food before you felt the same degree of fullness as a healthy individual,” said study leader and associate professor Amanda Page from the university’s Nerve-Gut Research Laboratory.

“A hormone in the body, leptin, known to regulate food intake, can also change the sensitivity of
the nerves in the stomach that signal fullness. In normal conditions, leptin acts to stop food intake,” she reported in a university press release. “However, in the stomach in high-fat diet induced obesity, leptin further desensitises the nerves that detect fullness. These two mechanisms combined mean that obese people need to eat more to feel full, which in turn continues their cycle of obesity.”

Page says the researchers are not yet sure whether this effect is permanent. “We know that only about 5% of people on diets are able to maintain their weight loss, and that most people who’ve been on a diet put all of that weight back on within two years,” she notes. “More research is needed to determine how long the effect lasts, and whether there is any way—chemical or otherwise—to trick the stomach into resetting itself to normal.”

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