Body Fat and Exercise

Myths and misconceptions are abundant surrounding the role of exercise in weight management. Here's a true or false quiz to test your knowledge about body fat and exercise.

If you start an exercise program, you'll lose body fat.

False. To lose body fat, you need to create a calorie deficit for the entire day. That is, you need to burn off more calories than you consume. Exercise can contribute to the calorie deficit, but exercise is often overrated as a way to reduce body fat. Exercise is better used as a tool to help prevent weight gain and to maintain weight loss. Exercise helps relieve stress (which can reduce stress eating), helps you feel good about yourself, boosts your metabolism, and often increases the desire to feed yourself healthfully.

Many people do lose weight by adding exercise. That happens because they start a total health campaign that includes not only adding activity but also subtracting some calories. After they work out, they tend to feel great, they've relieved stress, and they have less desire to unwind after a hectic day by munching through a bag of chips as they might have done before starting the exercise program.

But some of my clients complain to me that they have lost no weight despite hours of working out. That often happens because they are rewarding themselves afterward with generous amounts of calories that replace all they burned off. They may have exercised for 30 minutes and burned off 300 calories, but then they consumed 300 calories of "recovery food" in 3 minutes. Despite popular belief, appetite tends to keep up with your exercise load (except in extreme conditions). The more you exercise, the hungrier you will eventually become, and the more likely it is that you will eat enough to replace the calories you burned off. Nature does a wonderful job of protecting your body from wasting away, particularly if you are already lean with little excess fat to lose (Woo, Garrow, and Pi-Sunyer 1982; Woo and Pi-Sunyer 1985). Another factor that influences the effectiveness of exercise as a means to lose weight relates to the toll of exercise on your total daily activity. Some avid exercisers put all their effort into exercising hard for one or two hours per day but then do little spontaneous activity the rest of the day (Thompson et al. 1995). For example, a group of moderately obese college-age students who participated in a 16-month aerobic exercise program had similar daily energy expenditures before starting and at the end of the program. The students seem to have become more sedentary at other times of the day (Bailey, Jacobsen, and Donnelly 2002). This pattern is common among both casual and serious exercisers, many of whom claim to maintain weight despite their hard workouts.

If you do want to use exercise to promote weight loss, think about doing exercise that builds muscle. Unlike aerobic exercise that burns calories primarily during the exercise session but very few thereafter, strength training builds muscles that boost your metabolism throughout the entire day and night. Muscle tissue actively burns calories. The more muscle mass you have, the more calories you burn.

To lose body fat, do low-intensity, fat-burning exercise.

False. To lose fat, you need to create a calorie deficit for the day. You can do this by adding exercise of any type, eating less, or combining the two. Just be sure that by the end of the day you have eaten fewer calories than you needed. That way, you'll dip into the stored body fat and burn it for energy.

Some people think that the key to body-fat loss is doing fat-burning exercise, or low-intensity exercise that uses more fat than muscle glycogen for fuel. Wrong. Studies have shown that burning fat during exercise does not affect loss of body fat (Zelasko 1995). But because you can sustain low-intensity exercise for longer than you can sustain high-intensity workouts, you can easily burn off more calories in, let's say, 60 minutes of jogging (600 calories) than in 10 minutes of fast running (150 calories).

High-intensity exercise may actually contribute to a lower percentage of body fat (Yoshioka et al. 2001). Research on 1,366 women and 1,257 men suggests that those who did high-intensity exercise tended to have less body fat than those who did lower-intensity fat-burning exercise (Tremblay et al. 1990). The big concern about doing high-intensity exercise relates to the higher risk of injury. If you choose to exercise harder, be sure to exercise wisely—warm up, stretch, and don't do too much, too soon. Keep in mind that you may not enjoy high-intensity activity as much and end up exercising less as a result.

Men are more likely to lose weight with exercise than are women.

True. In terms of evolution, nature wants women to have fat and be fertile; men are supposed to be lean hunters. Given that extreme amounts of exercise can be interpreted as a famine (because of the high calorie deficit), nature seems to work hard to protect women's body-fat stores. In one study of previously sedentary normal-weight men and women who participated in an 18-month marathon training program, the men reported increasing their food intake by about 500 calories per day and the women reported increasing by only 60 calories, despite having added 50 miles per week of running. The men lost about 5 pounds (2.4 kilograms) of fat; the women lost less than 2 pounds (1 kilogram) of fat, despite reporting (with questionable accuracy) a larger calorie deficit (Janssen, Graef, and Saris 1989). Similarly, other studies suggest that normal-weight women fail to lose significant amounts of fat when they add exercise.

In a study of previously sedentary overweight males and females (average age 22 to 24 years) who did fitness exercise five times a week for 16 months with no dietary restrictions, the men lost 12 pounds (5.4 kilograms), and body fat dropped from 27 to 22 percent. They failed to eat enough to compensate for the extra calories burned. The women, however, had no significant weight or body-fat changes; their appetites kept up with their calorie expenditures (Kirk, Donnelly, and Jacobsen 2002). As one of my female clients whined, "I've been running for 10 years, and I still haven't lost one pound." She's not the only one!

To reduce the fat around the stomach and hips, you should incorporate sit-ups into your exercise program.

False. Spot reducing sounds like a great idea. But the truth is that vigorous exercise won't reduce the fat cells in one localized area of your body. When you lose fat, you lose it everywhere, not just from the part of your body you are working most vigorously. Moreover, you need to create a calorie deficit for the entire day to reduce body fat. Muscle movement itself does not result in loss of body fat. For example, the man who did 1,000 sit-ups every day trying to burn off the fat in his abdomen certainly built strong abdominal muscles, but he failed to create a calorie deficit and lose abdominal fat.

If you become injured and are unable to exercise for a week, your muscles will turn into fat.

False. Muscle does not turn into fat, nor does fat turn into muscle. Muscle and fat are separate entities and not interchangeable. Perhaps you've noticed a fat layer on roast beef or pork chops. A similar fat layer occurs in humans. The fat tissue is a layer of fat-filled cells that covers the muscles. Muscle is the protein-rich tissue that performs exercise. When you exercise, you build up muscle tissue. When you consume fewer calories than you expend, you reduce the fat layer.

If you are unable to exercise because of injury or illness, your muscles actually shrink in size. For example, Joe, a skier, broke his leg and was shocked to see how scrawny his leg muscles looked when the cast was removed five weeks later. Once Joe started exercising again, he rebuilt the muscle to its original size. If you overeat while you are ill or injured (as often happens with inactive athletes who are bored, depressed, and hopeful that chocolate-chip cookies will cure all ailments), you will become fatter. I often counsel wounded football players who gain 10 to 20 pounds (4.5 to 9.0 kilograms) after an injury. They continue to eat lumberjack portions although they need fewer calories. The extra fat takes up more space than the muscle, and the players become flabby.

Feeling frustrated and disappointed when you are injured is normal. Share your feelings with others who understand. Think positive, and visualize your injury getting better every day. Find the positive aspect. Time off from exercise can mean more time for friends, family, and other hobbies.

When injured, some very thin athletes do migrate to their natural weight (i.e., the weight they would naturally maintain without rigorous exercise and restricted calories). For example, a 13-year-old gymnast perceived herself as "getting fat" while she recuperated from a knee injury. She was simply catching up and attaining the physique that was appropriate for her age and genetics.

Cellulite is a special kind of fat that appears after a person has repeatedly gained and lost weight.

False. Cellulite is fat that has a bumpy orange-peel appearance and often appears on the hips, thighs, and buttocks. The fat is deposited in pockets just below the surface of the skin. Although much is written about cellulite, little is understood about it. Some medical professionals believe that the dimpled appearance of cellulite may result from restrictions of the connective tissue that separates fat cells into compartments. If you overeat and fill the fat cells, the compartmental restrictions may cause the fat to bulge. Cellulite is more of a problem for women than for men because women have thinner skin and their fat compartments are larger and more rounded. Also, women tend to deposit fat in their hips, thighs, and buttocks, areas in which cellulite appears easily. In contrast, men tend to deposit fat around their waists. A genetic predisposition toward cellulite may exist. If a mother has cellulite, the daughter is likely to acquire it as well. Cellulite generally appears as a person ages because the skin loses its elasticity and becomes thinner.

Did you pass the quiz? If you are exercising primarily to lose weight, I encourage you to separate exercise and weight. Yes, you should exercise for health, fitness, stress relief, and, most important, enjoyment. I discourage you from exercising to burn calories. Under those conditions, exercise feels like punishment for having excess body fat. You'll likely quit your exercise program sooner or later because disagreeable exercise is not fun.

Your job is to find an exercise program that has purpose and meaning so that you will enjoy incorporating some type of exercise into your daily schedule for the rest of your life. Consider these examples:

  • Jim bought a dog and is now walking the dog 3 miles (about 5 kilometers) per day.
  • David enjoys gardening in the summer and walking in the woods in the winter.
  • Gretchen, a busy executive, takes a 30-minute walk at lunch to relieve stress and process her feelings.
  • Sherri commutes to work by bicycle.
  • Kevin joined a marathon training program.

Although exercise without a calorie deficit fails to result in weight loss, we do know that exercise is important for maintaining weight loss and improving health. People who burn off 1,000 to 2,000 calories per week tend to be leaner and healthier than sedentary people. Again, find an exercise program that has purpose and meaning.

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