Your Health by Dr. Rallie McAllister

If you've been celebrating the holidays by eating with reckless abandon, you probably won't be surprised to find that you've picked up a few extra pounds and inches. Like most Americans, you may plan to slim down in the New Year.

Most of us know from experience that it's easier said than done. Recent research suggests that the more decadent foods we consume over the holidays, the harder it is to get back into our normal routines of exercising and eating a nutritious diet.

One reason for this phenomenon is that overindulgence in foods that are rich in fat and sugar leads to changes in brain receptors. Scientists at Johns Hopkins University recently reported that bingeing on a high-fat, high-sugar diet increases opioid receptor levels in areas of the brain that control food intake.

Drugs that target opioid receptors in the brain, including heroin and morphine, are known to elicit feelings of pleasure and euphoria. Opioids produced naturally in the body have similar effects.

Most athletes are familiar with the addictive power of natural opioids: They often experience a phenomenon known as "runner's high" after strenuous workouts. Overconsumption of highly palatable foods appears to trigger the same response, producing a type of "binger's bliss" that entices people to continue overeating long after the holiday season is over.

In a study at Scripps Research Institute earlier this year, scientists found that pleasure centers in the brains of rats became progressively less responsive when the animals were given unlimited access to fatty foods such as sausage, chocolate and cheesecake. As these changes occurred, the rats had to eat more to achieve pleasurable sensations.

As a result, the animals developed compulsive eating habits and became obese. The rats continued to overeat even when they had to endure an unpleasant consequence, such as a mild foot shock, in order to keep eating.

The results of previous studies suggest there's another reason we may find it difficult to resume our customary dietary habits after brief periods of overeating. Our brains appear to become less sensitive to the effects of a "stop eating" hormone that normally signals us to put down our forks and step away from the table.

The hormone, known as cholecystokinin (CCK), is released by cells in the gut when fat or protein is eaten.

Penn State scientists found that rats on a high-fat diet were significantly less sensitive to the effects of this hormone than rats on a low-fat diet.

After the rats were given doses of CCK, those on the low-fat diet ate less of a tasty, fat-laden treat. The rats on the high-fat diet, however, didn't adjust their food intake downward in response to doses of the hormone.

Human studies have produced similar results. Although people consuming high-fat diets have higher blood levels of CCK, they tend to be less responsive to its effects.

Because they're less likely to experience feelings of satiety and fullness after meals and snacks, they tend to eat more food and gain more weight.

Unrestrained eating during the holidays may also impair weight loss in the New Year by making exercise more difficult. The results of a recent study revealed that eating a high-fat diet for brief periods can dramatically reduce exercise tolerance and physical endurance.

For the study, investigators at Oxford University switched rats from their standard, low-fat rations to a high-fat diet. After just nine days, the rats on the high-fat diet were able to run only half as far on a treadmill as the rats that continued to receive the standard low-fat feed.

The scientists also found that in little more than a week, the high-fat diet appeared to make the heart much less efficient. After eating a high-fat diet and running on the treadmill, the rats' hearts became significantly bigger in order to pump sufficient blood and oxygen to working muscles.

The results of these studies confirm what most of us have experienced firsthand. After a few weeks of throwing dietary discretion to the wind, resuming our normal, pre-holiday eating and exercising behaviors can be challenging.

With this in mind, it might be wise to decline that second helping of stuffing or an extra slice of pumpkin pie. Eating our favorite foods in moderation during the holidays will make it easier for us to get back on track in the New Year.

Rallie McAllister, M.D. is a family physician, speaker, and co-founder of www.MommyMDGuides.com, a website featuring child-raising tips from trusted doctors who are also moms. To find out more about Rallie McAllister, M.D., and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate Web page at www.creators.com.

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