A new study claims that yo-yo dieting and repeated bouts of sugar-bingeing could be harmful for the brain and generate overeating.
The Scripps Research Institute researchers said that constant switching between periods of eating sweet and regular-tasting food could activate the brain's stress system and lead to overeat, anxiety, and withdrawal-like symptoms.
"When many people diet, they try to avoid fattening foods that taste good, but ultimately end up going back to their regular eating habits," said senior author Dr. Eric Zorrilla.
"We found that rats cycled in this way between palatable food and less tasty, but otherwise acceptable, food, begin to binge on the sweet food, stop eating their regular food, and show withdrawal-like behaviours often associated with drug addiction. As in addiction to drugs or ethanol, the brain's stress system is involved in each of these changes," he added.
"Our research suggests that this eating pattern leads to a vicious circle. The more you cycle this way, the more likely it is you cycle again. Having a 'free day' in your diet schedule is a risky habit," explained Dr. Pietro Cottone.
For the study, the researchers divided rats into two groups-the first group was fed alternating cycles of five days of regular chow and two days of sweet chow. The second group ate only regular-tasting food. The amount of food consumed was not restricted for either group.
When the diet-cycled rodents were fed regular chow, they put less effort into obtaining the previously acceptable food, ate less, and were more likely to avoid anxiety-provoking situations. When they returned to a diet of sweet food, their anxiety-related behaviors returned to normal, but they ate more than they needed.
The control group showed none of these effects.
The researchers then looked at the involvement of the brain's stress system in underpinning these behaviors-they measured levels of stress-related corticotropin-releasing factor (CRF) mRNA and peptide in an area of the brain known as the central amygdala, which is involved in fear, anxiety, and stress responses.
They found that the diet-cycled group on normal chow displayed five times the control group's levels of CRF. Only when the diet-cycled group was fed sweet food did CRF levels return to normal.
"CRF is a key stress neuropeptide. In observing the activation of the amygdaloid CRF system during abstinence from sweet foods, we understood the causes of recurrent dieting failures," said Cottone.
Zorrilla pointed out that the increase in stress was due to the withdrawal state, rather than to outside factors.
"People will often say they are eating bad foods or fail a diet because they 'are stressed'. Our findings suggest that intermittently eating sweet food changes the brain's stress system so that you might feel stressed, even though nothing that terrible has happened. In other words, you might be self-medicating stress-like symptoms of abstinence with that piece of pie. Or, the adaptations in your brain stress system might make you more reactive to otherwise minor stressors," he said.
The study helps explain how a pattern yo-yo dieting can be established and why it is usually ineffective in promoting weight loss.
The study also underlines the health risks of such an eating pattern, as activation of the brain's stress system has been linked not only to emotional disorders, but also to conditions such as heart disease.
"The findings suggest that frequent dieting with frequent relapse is worse than dieting by itself," said Cottone.
The research is published in an advance, online Early Edition of the journal Proceedings of the National Academy of Sciences (PNAS).