Exercise and weight control: Myths, truths and gender differences

When exercise is something you do to your body, rather than for your body, you'll eventually quit exercising.
"For all the exercise I do, I should be pencil thin!"
"Am I the only runner who has ever gained weight training for a marathon?"
"Why does my husband shed pounds when he exercises and I don't?"

When I listen to athletes complain about their lack of success with losing body fat, I hear abundant frustration: "Why can't I do something as simple as lose a few pounds!" Why? Because weight loss isn't simple and often includes debunking a few diet and exercise myths. Perhaps this article will offer some insights that lead you to weight-loss success.

Myth: You must exercise in order to lose body fat.

To lose body fat, you must create a calorie deficit. You can create that deficit by adding on exercise (which improves your overall health and fitness) or by simply eating fewer calories. For example, sick people commonly lose body fat, but they don't exercise; they create a calorie deficit.

Similarly, injured athletes can also lose fat despite lack of exercise. The story "I gained weight when I was injured because I couldn't exercise" could more correctly be stated "I gained weight when I was injured because I was bored and depressed and I overate for comfort and entertainment."

Myth: The more you exercise, the more fat you lose.

Often, the more you exercise, the hungrier you get, and:

  • the more you eat, or;
  • the more your believe you "deserve" to eat, or;
  • the more you want to eat as a reward for both getting to the gym and surviving the workout.

But if you spend 60 minutes in a spin class and burn off 600 calories only to reward yourself with 12 Oreos (600 calories), you'll wipe out your weight-loss efforts in less than three minutes!

The effects of exercise on weight loss are complex and unclear. A study showed that 56- to 78-year-olds who participated in a vigorous walking program had nearly the same daily calorie needs as those who didn't exercise (2,400 without exercise, 2,480 with exercise).

How could that be? Well, the exercisers napped more and were 62 percent less active throughout the rest of their day than non-exercisers.1

Another study of post-menopausal women found the same results from eight weeks of moderate exercise training. Their 24-hour energy expenditure remained similar from the beginning to the end of the program.2 Bottom line: Eat according to your entire day's activity level, not according to how hard you trained that day.

Myth: If you train for a marathon, your body fat will melt away.

Wishful thinking. I commonly hear marathoners, triathletes and other highly competitive endurance athletes complain, "For all the exercise I do, I should be pencil thin." They fail to lose fat because, like the fitness exercisers described above, they put all of their energy into exercising, but then tend to be sedentary the rest of the day as they recover from their tough workouts.

A study of male endurance athletes who reported a seemingly low-calorie intake found they did less spontaneous activity than their peers in the non-exercise parts of their day.3 Bottom line: Keep taking the stairs instead of the elevator, no matter how much you train!

Alternatively, athletes who complain they eat like a bird but fail to lose body fat may simply be under-reporting their food intake. A survey of female marathoners indicated the fatter runners under-reported their food intake more so than their leaner peers.4

Bottom line: Calories mindlessly eaten while standing or on-the-run count just as much as calories from sit-down meals.

Myth: Couples who exercise together, lose fat together.

In a 16-month study focused on exercise for weight loss, men and women completed an identical amount of exercise. The men lost 11.5 pounds; the women maintained weight.5

In another study of 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 a day; the women increased by only 60 calories -- despite the 50 additional miles of running per week. The men lost about five pounds of fat, whereas the women lost just two.6

What's going on here? Well, a husband who increases his exercise is likely to lose more weight than his wife because he's probably heftier and therefore burns more calories than she does during the same workout. But, speaking in terms of evolution, nature seems protective of women's role as child bearer, making it easier for women to maintain adequate body fat for nourishing healthy babies. Hence, women are more energy efficient.

Obesity researchers at New York's Columbia University suggest a pound of weight loss in men equates to a deficit of about 2,500 calories, while women need a 3,500-calorie deficit.7 No wonder women have a tougher time losing weight than men!

Bottom line

If you're 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; that makes exercise feels like punishment for having excess body fat.

When exercise is something you do to your body, rather than for your body, you'll eventually quit exercising. Bad idea.

Instead of focusing on exercise to lose body fat, pay attention to your calorie intake. Knocking off just 100 calories a day from your evening snacks can theoretically result in a 10-pounds fat loss in a year. Seems simpler than hours of sweating ...

1. Goran, Am J Physiol, 263:E950, 1992
2. Keytel, Int J Sport Nutr, 11:226, 2001
3. Thompson, Med Sci Sports, Exerc 27::347, 1995
4. Edwards, Med Sci Sports Exer, 25:1398, 1993
5. Donnelly, Arch Intern Med, 163:1343, 2003
6. Janssen, Int J Sports Med, 10:S1,1989
7. Pietrobelli Int J Obes Relat Metab Disord, 26:1339, 2002

Sports nutritionist Nancy Clark, M.S., R.D., counsels both casual and competitive athletes in her private practice at Healthworks (617-383-6100), the premier fitness center in Chestnut Hill, MA. Her best-selling Sports Nutrition Guidebook ($23), Food Guide for Marathoners ($20) and The Cyclist's Food Guide ($20) are available at www.nancyclarkrd.com or www.sportsnutritionworkshop.com or by sending a check to PO Box 650124, W. Newton MA 02465.

Copyright 2006 Nancy Clark

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