Weight loss products are the Holy Grail for the supplement industry. Aside from multivitamins, weight loss is the largest (no fat jokes!) category in terms of sales racking up several billion dollars in 1999 alone. Around the world, the prevalence of overweight and obesity has been steadily increasing over the past fifty years, and studies in developed countries (e.g., the United States, Canada, and Great Britain) suggest that this trend will continue at an alarming rate. Overweight is defined as having a body mass index (BMI) of over 27.0 kg/m2, and obese is defined as a BMI greater than 30 kg/m2 (or about 30 percent above ideal body weight).
Over the past two decades or so (1976 1994), the prevalence of obesity in the American population increased from 12.8 percent to 22.5 percent. Further, in 1999, over half (61 percent) of U.S. adults were classified as overweight or obese (according to the National Health and Nutrition Examination Surveys, or NHANES). The increase in the number of overweight and obese adults is a major health concern because obesity contributes to an increased risk of heart disease, hypertension, diabetes, and some cancers, and is now considered one of the primary risk factors for cardiovascular disease (along with smoking, high cholesterol, hypertension, and sedentary lifestyle).
EXERCISE VERSUS DIET
It is obvious that as we age, we have a tendency to gain weight, particularly fat weight. It is unclear, however, if this age related weight gain is an unavoidable condition. Regular exercise is often promoted as a tool for preventing weight gain and there is good evidence that people who are more active have a reduced risk of gaining weight. In one study, a large group of men were followed over two years. At the beginning of this period, the most active men and those that watched fewer hours of television were less likely to be overweight (it seems that Who Wants to Be a Millionaire contributes directly to obesity). After two years, those who were most active and watched fewer hours of television gained less weight (moral of the story – kill your television). Data from several national surveys (in both the United States and other countries) clearly show that people who maintain higher levels of physical activity are less likely to gain weight, or at least gain less weight than their inactive counterparts.
However, whether exercise is a good tool for promoting weight loss is somewhat controversial. A recent review of studies related to the effect of physical activity in the treatment of adulthood overweight and obesity concluded that adding exercise to a reduction in caloric intake only leads to modest additional weight loss (5 to 7 lb), but that regular participation in exercise is strongly associated with maintenance of weight loss. Thus, although exercise may not be the best approach for initial weight loss, it is an important factor in prevention of weight regain.
So, with most of the available evidence suggesting that physical activity plays a more important role in reducing age related weight gain than in actually promoting weight loss, the obvious question is, “Why is exercise not more effective in promoting weight loss?” The answer is because of the difficulty in promoting a substantial negative energy balance with exercise alone. Negative energy balance is a state in which one expends more energy (calories) than one consumes. To achieve a state of negative energy balance, one must consume fewer calories, expend more energy, or both. This seems like a pretty simple task, but the reality is that most adult Americans do not have a good understanding of the energy value of different foods or exercises. Most people tend to underestimate the caloric value of the food consumed and overestimate the caloric value of exercise.
Calories Burned by Exercise Compared to Those Supplied by Food
Energy (calories) Exercise for 30 minutes” Dietary equivalent
100 Walking, leisurely pace 3/a cup of ice cream
150 Walking, brisk pace 6 Oreo cookies
200 Stationary cycling, easy 3 tablespoons of peanut butter
240 Lap swimming, leisurely 20 potato chips or French fries
240 Aerobic exercise class 1 slice of pizza
300 Lap swimming, vigorous 12 Hershey Kisses
300 Stationary cycling, vigorous 1 fried chicken leg
300 Running, slow pace 1 Burger King cheeseburger
500 Running, fast pace 1 Taco Bell bean burrito with cheese