Tell Me Again, Why Am I Exercising?

Billions of dollars are spent each year on diet plans and supplements to help people lose weight. Yet the obesity epidemic in America continues to steadily increase. Adults are consuming far more calories per day than needed. Factors such as bigger portions, convenience of fast food, food choices with higher caloric density and limited access to nutritious foods are to blame.

There is no question that adults need to take in fewer calories and choose healthier foods. A staggering two-thirds of American adults are obese and less than half of them meet the minimum recommendations for exercise. Just how important is exercise in the weight loss predicament? Can I restrict calories alone to reach my ideal weight? To answer these questions we need to first understand how the body's energy equation works.

Burning Calories

There are three primary ways that we use or "burn" calories. The resting metabolic rate (RMR) makes up about 75 percent of the total calories your body uses in a 24-hour cycle. RMR is the minimal caloric requirement needed -- the amount of energy your body would burn if you slept for 24 hours. The other 25 percent of caloric needs is for activity and digestion.

There are many factors that alter the RMR such as age, height, stress and hormone fluctuations, but body composition has the largest impact. Dr. Cheryl Rock, RD, Department of Family and Preventive Medicine at UCSD states, "The biggest contributor to total energy expenditure is the resting metabolic rate, or basal energy expenditure. The major determinant of RMR is the amount of lean body mass."

To increase lean body mass, a person needs to incorporate an exercise regime with cardiovascular activity and resistance training. "Exercise contributes to healthy weight control through two mechanisms -- through increased total energy expenditure and by promoting the retention and increase in lean body mass so that RMR is retained or increased." says Rock.

Just how much exercise is recommended? The Center for Disease Control & Prevention recommends 60-90 minutes of activity daily. Sustained cardiovascular exercise should be gradually increased both in duration and intensity to this 60-90 minute range. Resistance training should be included two to four times per week addressing all major muscles. Consistency is the key to success in any exercise program.

Exercise benefits your body's energy equation in two ways. Short-term -- you burn calories while you do the activity. Long-term -- you add lean body mass, which will increase the amount of calories your body requires at rest. This helps you achieve a healthy weight faster and doesn't require you to starve yourself of nutrients. It also allows you to enjoy life with a fully capable and mobile body.


  1. Center for Disease Control & Prevention, Prevalence of Physical Activity, Including Lifestyle Activities Among Adults -- United States, 2000--2001, MMWR August 15, 2003, 52(32):764--769.

  2. Journal of the American Medical Association. 295(13):1549-55, 2006 Apr 5.

Amy Thompson has served as a group fitness and personal trainer, fitness manager, general manager and fitness director for over 14 years. Amy is also an international presenter and author for the fitness industry in areas of facility design, business development, leadership, fitness and nutrition programming and adherence. She is the lead fitness consultant for the SHAPE Study at UCSD Cancer Center and contributing Fitness Expert for NBC 7/39, KFMB, San Diego Union Tribune, American Council on Exercise and IDEA. Visit her Web site or contact her at

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