Exercise and Weight Control: Myths, Truths, and Gender Differences

author : Nancy Clark

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I commonly hear marathoners, triathletes and other highly competitive endurance athletes complain “For all the exercise I do, I should be pencil thin.”

The Athlete’s Kitchen

Copyright: Nancy Clark, MS, RD February 2006

“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 is not simple and often includes debunking a few diet and exercise myths. Perhaps this article will offer some insights that lead you to success with your weight loss efforts.

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. Sick people commonly lose body fat but they do not 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. 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 having both gotten to the gym and survived the exercise session.

But if you spend 60 minutes in a spin class and burn off 600 calories, only to reward yourself with twelve Oreos (600 calories), you quickly wipe out your weight loss efforts in less than 3 minutes.

The effects of exercise on weight loss are complex and unclear. We know among older people (56-78 years) who participated in a vigorous walking program, daily calorie needs remained about the same (2,400 without exercise, 2,480 with exercise). How could that be? Well, the participants napped more and were 62% less active throughout the rest of their day (1).

Another study with post-menopausal women found the same results from 8 weeks of moderate exercise training. Their 24-hour energy expenditure remained similar from the start to the end of the program (2). The bottom line: You have to eat according to your whole day’s activity level, not according to how hard your 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 quite sedentary the rest of the day as they recover from their tough workouts. A study with 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). The bottom line: You need to keep taking the stairs instead of the elevators, 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-report their food intake more than their leaner peers (4). Remember: Calories mindlessly eaten standing up or on-the-run count just as much as calories from meals.

Myth: Couples who exercise together lose fat together.

In a 16-month study looking at exercise for weight loss, men and women completed an identical amount of exercise. The men lost an average 11.5 pounds; the women maintained weight (5)! In another study with previously sedentary, normal weight men and women who participated in an 18 month marathon training program, the men increased their calorie intake by about 500 per day; the women increased by only 60 calories—despite having added on 50 miles per week of running. The men lost about five pounds of fat; the women, two pounds (6).

What’s going on here??? Well, a husband who adds on exercise is likely to lose more weight than his wife because he’s likely heftier and thereby burns more calories during the same workout.  But, speaking in terms of evolution, Nature seems protective of women’s role as child bearer, and wants women to maintain adequate body fat for nourishing healthy babies. Hence, women are more energy efficient. Obesity researchers at NY’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 then do men.

The bottom line

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; that makes exercise feel like punishment for having excess body fat. When exercise is something you do to your body, rather than do 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 10 pounds a year of fat loss. Seem simpler than hours of sweating?

References:

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 dietitian Nancy Clark MS, RD counsels casual and competitive athletes in her private practice at Healthworks (617-383-6100), the premier fitness center in Chestnut Hill MA. Her Sports Nutrition Guidebook ($23), Food Guide for Marathoners ($20) and Cyclist’s Food Guide ($20) all offer additional weight management information. The books are available via www.nancyclarkrd.com or by sending a check to Sports Nutrition Services, PO Box 650124, W Newton MA 02465.

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date: March 5, 2006