Ask the Doctors

Dear Doctor: I hate dieting and have been putting off losing these last 12 pounds of baby weight. My husband says I should at least start exercising because it makes your fat healthier. Can this really be true?

Dear Reader: For all the bad press the fat within our bodies receives, it's actually a vital resource. With more than double the calories per gram than proteins or carbohydrates, it's an efficient system for storing energy that helped our ancient (and not-so-ancient) ancestors survive uncertain times. And while we tend to think of body fat in terms of its physical manifestation, as in the bulge of a waistline, it's actually a dynamic nutrient with multiple forms and functions within our bodies.

In addition to being an energy source, fat helps to manage temperature, cushion vital organs, regulate hormone production, build cell membranes and stockpile certain vitamins. It plays an important role in immune function and brain chemistry, as well as many other metabolic processes. Of course, too much stored fat is problematic, and can lead to adverse health consequences, including diabetes, heart disease and metabolic syndrome, to name just a few.

The complex cycle of how the various fats within our bodies are formed, stored, mobilized and metabolized is still not completely understood. (It's only a decade ago that we learned about the existence of "brown fat," which are fat cells within our bodies that burn rather than store lipids.) Now the results of recent studies have shed light on another question that has long puzzled scientists. That is, why do some overweight individuals develop insulin resistance, which is often a precursor to diabetes, and others do not?

One of the problems with stored fat is that it tends to release fatty acids into systemic circulation. This leads to inflammation, which is a common denominator in developing insulin resistance. But it turns out that not everyone who is overweight or obese has the same degree of release of fatty acids. A study last year from researchers at the University of Michigan found that certain individuals, despite being obese, have low rates of fatty acid release, few markers for inflammation and therefore do not develop insulin resistance. But why?

In a second study, the Michigan researchers looked at whether exercise might play a role. When they compared a group of overweight individuals who exercise regularly with a similar group of overweight individuals who did not exercise, they found that the subcutaneous fat of the active group contained more blood vessels. The two groups then took part in a session of aerobic exercise. Post-exercise biopsies of subcutaneous fat revealed that, after that single session, the stored fat in both groups became less "leaky," and this was considered healthier.

While it's important to note that these were both small studies, the results are intriguing. They add to what we already know about the health benefits of exercise and suggest some interesting directions for future study. In the meantime, we agree with your husband that no matter what you're doing with your diet, adding an exercise component to your daily life is a good idea.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

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