Pizza after a hard workday?

Researchers may have found the key to failed diets, at least in rodents might be the key to losing the weight you gained over Thanksgiving. New research shows that dieting makes the brain more sensitive to stress and the rewards of high-fat, high-calorie treats. These brain changes last long after the diet is over and prod otherwise healthy individuals to binge eat under pressure. Most research on weight loss has focused on tweaking appetite regulation—helping people eat less, get full faster, and have fewer cravings. But once we lose weight, we have trouble keeping it off. Even weight-loss surgery doesn't always help people maintain their more svelte physiques. Maybe, thought Tracy Bale, a neuroscientist at the University of Pennsylvania, the problem is stress. Stress causes the body to release the hormone cortisol, which fuels the blood with energy in the form of sugar, enabling us to flee from potential dangers. Over time, high stress levels lead to chronically elevated cortisol levels that can cause increased appetite and weight gain.

Bale and her co-authors hypothesized that dieting leaves people more susceptible to the chronic stresses of everyday life, making even the strongest dieter yearn for a pint of ice cream or a hot, cheesy pizza. Although one hot fudge sundae won't cause significant weight gain, persistent stress could lead to a pattern of binge or comfort eating that undoes previous weight loss. To test their hypothesis, the researchers cut daily food intake in mice by 25% for 3 weeks, until the rodents had lost about 10% to 15% of their original body weight. This regimen simulates a moderate diet and modest weight loss in humans. After exposure to mild forms of stress, such as loud noises, the hungry mice had higher levels of cortisol in their blood. And their cortisol levels stayed higher longer than in control mice. This indicates that the dieting mice were more stressed and took more time to calm down.