Exercise, the cornerstone to weight loss - Tech Brief

American Fitness, Sept-Oct, 2002 by Scott O. Roberts

We have heard the excuses and seen the ridiculous advertisements for weight loss programs. No matter how hard fitness professionals try, consumers are persuaded to try to lose weight through misleading and potentially harmful diet programs. The facts remain--diets don't work and long-term weight loss is almost impossible without regular exercise.

Obesity continues to be a serious health threat for millions of Americans, according to a letter from the Centers for Disease Control and Prevention (CDC) published in the October 4, 2000, Journal of the American Medical Association. Obesity rose 6 percent between 1998 and 1999, affecting all demographic groups and most states. Obesity is defined as having a body mass index (BMI) of 30 or higher. A BMI of 30 typically means an individual is about 30 pounds overweight. Currently, more than half the adults in the United States are overweight (i.e., have a BMI of 25 or higher) and nearly one-quarter are obese.

WHY IS EXERCISE IMPORTANT FOR LONG-TERM WEIGHT LOSS?

Most people who diet to lose weight have done so more than once. This repeated loss and regain of weight is known as weight cycling. A typical weight cycle can range from small (i.e., 5 to 10 pounds) to large (i.e., 50 pounds or more) weight losses and gains. Dieting without exercise results in weight cycling and is detrimental to your resting metabolic rate (RMR).

RMR is the energy required to maintain vital body functions. Your RMR is determined by many factors, including genes and physical activity level. A high RMR means you burn more calories at rest and are less likely to gain weight. When the body perceives a reduction in caloric intake, it responds by conserving energy (i.e., decreasing the resting metabolic rate), therefore, making it easier to regain weight.

Most short-term weight loss via dieting is due to diuresis (i.e., water loss) and loss of lean body mass. During periods of caloric restriction, the body uses stored glycogen for energy (i.e., for each ounce of carbohydrate you store as glycogen, your body simultaneously stores three ounces of water). As carbohydrate stores are depleted, total body water is lost as well, resulting in the rapid weight loss experienced during the first few days and weeks of dieting. With continued caloric restriction, lean muscle tissue is degraded to provide the liver with amino acids to make new glucose.

Studies have proven that exercise combined with a sensible weight loss program results in greater fat loss, maintenance of resting metabolic rate and greater gains in lean body mass--the opposite of what happens when you diet without exercising. Physical activity helps control weight by burning excess calories that would otherwise be stored as fat.

A popular theory that supports the importance of exercise for weight loss claims weight is largely controlled by the hypothalamus--the internal regulating center of our brains. According to the set-point theory, body weight is regulated within a narrow range ( /-10 percent) in adulthood. When a person diets, the hypothalamus lowers the resting metabolic rate to maintain weight, thus having no effect on the set point. Exercise lowers a person's set point, thus readjusting it to a lower body weight. Balancing calories burned through physical activity with calories consumed is the only scientifically proven method for successful long-term weight loss.

CONCLUSION

The University of Colorado established the National Weight Control Registry (NWCR) in 1993. The NWCR's purpose is to identify individuals who have maintained long-term weight loss. To join the NWCR, participants must have lost at least 30 pounds and maintained their weight loss for a minimum of a year. Currently, there are over 2,000 people enrolled in the NWCR. The most powerful commonalities among NWCR clients are the substantial changes in diet and exercise habits employed to lose weight and maintain their new weight. On average, registrants report consuming about 1,400 kcal per day (24 percent calories from fat) and expending about 400 kcal per day through exercise. Walking is the most frequently cited physical activity. The American College of Sports Medicine recommends a daily caloric expenditure of 300 to 500 kcal per day for optimal results during a weight loss program.

REFERENCES

Flegal, K.M., Carroll, M.D., Kuczmarski, R.J., Johnson, C.L. "Overweight and Obesity in the United States: Prevalence and Trends, 1960-1994." Int J Obes. 1998; 22: 39-47.

Fraser, L. Losing It: False Hopes and Fat Profits in the Diet Industry. New York, NY: Penguin, 1998.

Roberts, S.O. "The Role of Physical Activity in the Treatment and Prevention of Childhood Obesity." Pediatric Nursing, 2000; 26(1), 33-42.

Scott O. Roberts, Ph.D., FACSM, FAACVPR, is an assistant professor in the Department of Physical Education and Exercise Physiology at California State University, Chico. His primary area of expertise is Clinical Exercise Physiology. He has authored and co-authored 10 fitness and exercise science books and over a hundred articles and chapters in books. Roberts has contributed three chapters to the Fitness: Theory & Practice textbook, authored two home study courses and contributed numerous articles to American Fitness.