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Harvard Commentaries
Harvard Commentaries
Reviewed by the Faculty of Harvard Medical School

Medical Myths Medical Myths

Choosing Your Six-Pack: Abdominal Muscles and Pot Bellies

February 27, 2013

By Robert H. Shmerling M.D.

Beth Israel Deaconess Medical Center

Last reviewed February 27, 2013

You've probably seen the advertisements high over Times Square or staring back at you from magazines: the male model casually displaying his rippling abdominal muscles. What you may not have seen is the effort that goes into getting an abdominal "six-pack," the hours of exercise, and often a careful diet.

If your own six-pack is more of the alcoholic variety, or if you have noticed a spread to your abdomen over time, you may be tempted to begin "crunches," those partial sit-ups that make your abdomen burn with pain, or to order one of those heavily advertised abdominal exercise aids. Before you order that abdominal exerciser from the television commercial or apply for a modeling job, there is something you should know — something your personal trainer, health club, and mail-order fitness videos probably have not mentioned. While exercise is generally a good thing, for most of us, the abdominal six-pack probably won't happen.

The Myth of "Focused Exercise"

It is only logical that if you want to strengthen your arms, exercise your arms; if you want to strengthen your abdominal muscles, do sit-ups. But while exercise directed at one part of the body can certainly strengthen that area and increase the size of those muscles, that does not mean you can shrink an area that you feel is too large (that is, has more fat than you would like) simply by exercising it. The focused exercises for the buttocks, thighs or abdomen commonly recommended to reduce their size will not necessarily lead to those areas getting smaller; in fact, they may get bigger as the muscles enlarge.

Basic Accounting and Biology

Two principles loom large when trying to "sculpt" one's body:

  • Calorie accounting: To lose fat, one must reduce calorie intake and/or increase energy expenditure so that stored fat is used as fuel for the body.
  • Biology is destiny: Fat cells, whether increased in size, number or both, cannot turn into muscle cells.

Reducing the fat accumulation in one area of the body is not easy. The usual measures to lose weight (including reducing calorie intake, increasing exercise or both) may lead to weight loss but not necessarily in a single area. In fact, short of having cosmetic surgery (such as liposuction), you cannot easily choose the area from which the fat will be lost. This is the reason some women notice that their breasts (which are largely composed of fat) get smaller when they diet.

And weight loss is more than just reducing "calories in" compared with "calories out." The difficulty many people have in losing weight probably relates to a well-established phenomenon that seems terribly unfair: As you take in fewer calories, the body's metabolism changes, so that fewer calories are burned with normal body function. In studies of people losing 10% to 20% of their body weight, "calories out" diminished, despite similar activity levels, which slowed further loss of weight.

Given this grim reality, you cannot readily transform an abdomen with excess fat into the physique of your dreams simply by doing lots of sit-ups. You'll lose the fat by diet and/or exercise, and you'll increase muscle mass by exercising those muscles. Of course, there may be other reasons to do sit-ups — for example, strong abdominal muscles reduce the chances of back problems — but shrinking your abdomen is not one of them.

Could It Happen to You?

Still want that abdominal six-pack? If you are starting out with a pot belly, it would likely take hours of exercise each day to lose weight and to strengthen the muscles underneath. It could happen, but there's a reason most of those models are so young: They never had that "middle-age spread" in the first place. In short, it's easier to get the abdominal 6-pack if you skip the beer.

Robert H. Shmerling, M.D., is associate physician at Beth Israel Deaconess Medical Center and associate professor at Harvard Medical School. He has been a practicing rheumatologist for over 20 years at Beth Israel Deaconess Medical Center. He is an active teacher in the Internal Medicine Residency Program, serving as the Robinson Firm Chief. He is also a teacher in the Rheumatology Fellowship Program.

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