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EXERCISE & WEIGHT CONTROL: Myths, Truths and Gender Differences

"I'm training for a marathon with hopes of losing weight..."
"Why does my husband shed pounds when he starts an exercise program and I don't???"
"Does exercising with an empty stomach burn more fat?"

Active people commonly link exercise with weight loss. They believe the more they exercise, the more weight they'll lose. Yet, that is not always the case. Many exercisers end up discouraged when they fail to lose weight despite regular workouts. Women, in particular, commonly complain about lack of results from their exercise program. Men, in comparison, seem to simply add on exercise, (subtract beer and fatty foods) and lose weight with ease.

If you are feeling frustrated by a lack of weight loss from your current exercise program, keep reading. This article might help you understand some myths about exercise and weight control.

Myth: Exercise kills your appetite.
Exercise may temporarily kill your appetite, but hunger will catch-up with you within 1 to 2 hours. Appetite is partially regulated by temperature control. Hence, if you feel hot after a hard workout, you may experience a temporary drop in appetite. However, if you are chilled, such as after swimming, you may feel ravenous.

Exercise's effect on appetite varies according to gender. Regularly exercising male rats tend to lose their appetite and drop weight; female rats get a bigger appetite, eat more and maintain weight. Limited human research supports those findings. Post-exercise appetite also varies according to body fatness. Studies with obese women who added moderate exercise to their sedentary lifestyle indicates they did not eat more, hence they lost weight. Diet and exercise studies with men suggest the fatter they were, the more weight they lost (in comparison to their less-fat peers) because they failed to compensate for the calories burned during exercise.

Myth: The more you exercise, the more weight you'll lose.
Often, the more you exercise, the hungrier you get and the more you eat. For example, you may spend an hour on the StairMaster burning off 500 calories, and then devour twelve Oreos (600 calories) in less than six minutes. After a hard workout, your body is hungry. Your soul may also be hungry for a reward. After all, you now deserve a treat for having survived the workout, right...???
Men who add on exercise are likely to lose more weight than do women. In one study with previously sedentary, normal weight men and women who participated in an 18 month marathon training program, the men increased their intake by about 500 calories per day; the women increased by only 60 calories-despite having added on 50 miles/week of running. The men lost about 5 lbs. fat; the women none (Int'l J Sports Med, Vol 10 (S1),1989). Similarly, other studies suggest normal weight women fail to lose fat when they add on exercise...

The effects of exercise on weight loss are complex and unclear. Nature seems to efficiently replenish fat stores of lean athletes and prevent them from wasting away. Lean female athletes, in particular, struggle harder than do males to lose body fat and maintain an even leaner physique. In terms of evolution, Nature wants women to have fat and be fertile; men are supposed to be lean hunters.
Myth: You'll lose weight fastest if you exercise at low intensity (i.e., do " fat burning exercise") on an empty stomach.

"Fat-burning exercise"--a low intensity workout that burns proportionately more fat than carbohydrates (glycogen)--is deemed optimal for weight loss. Aerobic exercisers commonly believe they will lose more body fat if they exercise before eating, because fat will be the predominant fuel. Wrong. For fat/weight control, you need to look at the whole day's calorie balance--not just at what you burn during exercise. If, over the course of the whole day, you create a calorie deficit by burning off more calories than you eat, you'll lose body fat. However, if you consume more calories than you expend (as can easily happen if overeat at night), you'll end up gaining fat.

The biggest benefits of low impact, fat-burning exercise are 1) you are less likely to get injured, and 2) you are able to exercise for longer and thereby burn more total calories. The truth is intense exercise may actually contribute to lower percent body fat. Research on 1,366 women and 1,257 men suggests those who did high intensity exercise tended to have less body fat than those who did lower intensity "fat-burning" exercise. (Am J Clin Nutr. Feb '90)

Myth: Injured athletes gain weight due to lack of exercise.
Weight gained during injury is generally due to overeating, not underexercising. Overeating happens when injured athletes eat lumber-jack portions, regardless of their activity level, and ignore the decreased appetite that accompanies decreased exercise. Injured athletes who sit around bored, lonely and depressed may also find comfort in food (despite discomfort with weight gain).

When injured, some very thin athletes migrate to their natural weight, i.e., the weight they would naturally maintain without rigorous exercise and restricted calories. Although they may perceive this as "getting fat," they may be simply "catching up" and attaining the physique that is appropriate for their genetics.

The bottom line: Nature does an excellent job of defending a healthy weight despite adverse conditions. Given extreme amounts of exercise can be interpreted as a famine (due to the high calorie deficit), "food efficiency " may develop in people who maintain a chronic energy deficit. Women are particularly protected by Nature and fail to lose as much fat as do men (who are supposed to be leaner so they can more efficiently hunt and gather food).

If you are exercising to lose weight, I encourage you to separate exercise and weight. Yes, you should exercise for health, fitness, stress relief and, most importantly, for ENJOYMENT. (After all, the E in exercise stands for enjoyment.) I discourage you from exercising to burn off calories. Under those conditions, exercise feels like punishment for having excess body fat. Grueling exercise fails to get integrated into a life-long, health promotion plan.

Nancy Clark, MS, RD is Director of Nutrition Services at SportsMedicine Associates in Brookline MA. She is author of Nancy Clark's Sports Nutrition Guidebook, Second Edition ($23) and her new Food Guide for Marathoners: Tips for Everyday Champions ($20). Both are available via www.nancyclarkrd.com or by sending a check to Sports Nutrition Materials, 830 Boylston St #205, Brookline MA 02467.