By Dr. Jack Rutherford
New research from the University of Adelaide in Australia suggests that most people who lose weight on a diet eventually put that weight back on.
The reason has to do with the way the stomach detects and tells our brain how full we are.
The results, published in the International Journal of Obesity, show that the nerves in the stomach that transmit signals of fullness to the brain seem 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,” said study leader Amanda Page of the university’s Nerve-Gut Research Laboratory. “This means you would need to eat more food before you felt the same degree of fullness as a healthy individual,” she added.
The hormone leptin, known to regulate food intake, can also change the sensitivity of the nerves in the stomach that signal fullness.
Under normal conditions, leptin works to limit food intake once the feeling of fullness is achieved.
In an obese stomach, fueled by a high-fat diet consumed over many years, leptin further desensitizes the nerves, meaning that obese people will eat more food until they feel full, which in turn contributes to their continuing cycle of obesity.
The results have “very strong implications for obese people, those trying to lose weight, and those who are trying to maintain their weight loss,” said Page. “Unfortunately, our results show that the nerves in the stomach remain desensitized to fullness after weight loss has been achieved,” she added.
Whether the effect is permanent or just long-lasting is not known.
What is known, however, is that only about 5 percent of people on diets are able to maintain their weight loss, while the vast majority on a diet put all of that weight (and more) back on within two years.
Page says that the next step is to study how long the effect lasts and whether there is a way to get the stomach to reset itself to normal.
The new results support the traditional set-point theory of obesity that suggests that there is a biological set point for body weight.
According to this theory, the hypothalamus in the brain contains centers associated with satiety and hunger.
Physiological signals indicative of glucose concentration, fat cell size, and body weight are sent to the hypothalamus, which are then compared to a “set point,” and an appropriate increase or decrease in feeding behavior occurs.
The theory also proposes that the type of diet can modify the signals sent, which is supported by the new results.
The good news for those trying to lose weight is that exercise also modifies the signals sent, so that feeding behavior can decrease, potentially causing a negative energy balance and weight loss.