This video will examine the relationship between exercise, obesity, and weight control. Obesity refers to the excessive accumulation of body fat. The problem of weight control and obesity is very complex and includes many variables including genetic and cultural factors as well as the traditional energy balance equation. I'm sure that you are all aware of the global obesity epidemic. In the United States, the prevalence of obesity has increased dramatically since the 1970s. Over 35% of the adult population, that's more than one third, are considered to be obese. If you include the number of individuals who are overweight, this percentage increases to 75 percent or three in four Americans who are overweight or obese. While these statistics are alarming for many reasons, of greatest concern are the health implications associated with obesity. Shown here are some of the more significant health-related issues including heart disease, type two diabetes, certain cancers, hypertension, and liver disease. Further, the estimated medical cost and loss of work productivity due to absenteeism now exceeds over $200 billion a year. I remind you that obesity is a modifiable risk factor. I thought you might like to take a look at the culprit. Shown here are typical adipose cells where fat is stored. There are many ways to measure and estimate an individual's body composition, including body fatness. Currently, the gold standard is to perform a DEXA or dual-energy x-ray absorptiometry. This imaging system allows for the assessment of total and regional body fat as well as bone density. Based on total body fat, men who have a greater than 25% and women who have greater than 35% body fat would be considered obese. While the most accurate, DEXA instruments are very expensive and are not readily accessible to the general public. Less expensive and more practical for field work, the use of skin fold calipers in conjunction with measurement of hip and waist circumferences can be used to estimate body fat. Other techniques include hydrostatic or underwater weighing, bioelectrical impedance, and air displacement plethysmography. For clinicians and large-scale epidemiological studies, it is convenient to use the body mass index or BMI as an estimate of body fatness. It is simply calculated by dividing your weight in kilograms by your height in meters squared. A BMI of over 25 kilograms per meter squared is considered to be overweight, while a BMI greater than 30 kilograms per meter squared will put one into the obese category. While easy and convenient, the accuracy of BMI in estimating body fatness is a concern. For example, based upon his BMI, when in his prime, Shaquille O'Neal, the professional basketball player was considered to be obese. The BMI did not take into account that a large amount of his overall body mass was in the form of muscle, not fat. From a health perspective not all fat is the same. Upper body fat primarily in the abdominal region puts an individual at a much greater health risk. More specifically, it is the visceral fat located within the abdominal cavity that surrounds important internal organs such as the liver, pancreas, and intestines that provides the greater health risk. Lower body fat which is primarily subcutaneous carries a significantly lower health risks. Here is a cross-sectional CT scan of the abdominal region indicating the visceral fat shown in white surrounding the internal organs and the subcutaneous fat shown in black just below the skin. This individual with a large amount of visceral fat would be at a much higher health risk. Those health risks include the various components of what's known as metabolic syndrome. Metabolic syndrome is a cluster of conditions that includes increased blood pressure, high blood glucose, and abnormal cholesterol or triglyceride levels that all occur together increasing one's risk for heart disease, stroke, and type two diabetes. Weight gain leading to overweightness and obesity occurs when an individual is in a chronic state of positive energy balance. Thus, if the caloric or energy intake exceeds one's energy expenditure over a prolonged period of time, weight gain and fat mass will increase. Such weight gain generally occurs gradually over many years if left unchecked. Weight loss will only occur if a chronic state of negative energy balance can be maintained. This can be accomplished by reducing one's caloric intake or dieting, increasing one's energy expenditure through exercise, or a combination of both factors. Dieting alone can generally produce some weight loss initially, but unfortunately, much of this is from the loss of water, not fat. Over time, the majority of weight loss will be in the form of fat, but also notice that a significant amount of protein is lost usually from skeletal muscle. This is problematic as skeletal muscle is the major contributor to your resting metabolic rate which in sedentary individuals can account for up to 75 percent of the total daily energy expenditure. Thus, dieting alone can reduce one's resting metabolic rate, making it difficult to keep the lost weight off. This is one reason why approximately 90 to 95% of all individuals regain their weight when a weight loss is accomplished by dieting alone. The other component to the energy balance equation is that for total daily energy expenditure. As shown here, one's resting metabolic rate makes up the largest daily contribution – up to 75% of the total. Obviously, for individuals who exercise regularly, the physical activity component will be on the higher side of the 15 to 35% range, thus decreasing the resting metabolic rate contribution toward the lower 60% range. Shown here is just one example, whereby increasing the total daily energy expenditure through physical activity can result in reduced obesity rates. In countries where it is more common to commute to work by walking and biking, the obesity rates are significantly lower. Thus, an inverse relationship exist between the total daily energy expenditure and the rate of obesity. The greater the total daily energy expenditure, the lower the prevalence of obesity. As the number of calories burned during exercise will vary dependent upon the exercise intensity and duration, engaging in exercise alone without decreasing caloric intake may not be sufficient to achieve a constant negative energy balance and thus significant weight loss. A number of overweight and obese individuals who begin an exercise program become frustrated when they don't see any change in their weight after one to three months. Because of their weight and poor fitness levels, these individuals cannot really exercise at higher exercise intensities or for longer durations. As such, the number of calories burned while exercising is relatively small. The optimal method for individuals to achieve and maintain a negative energy balance and thus weight loss is from a combination of dieting and exercise. Shown here is a typical response from using a combination of dieting and exercise for weight loss. These subjects reduced their caloric intake by 500 kilocalories per day while increasing their energy expenditure by 500 kilocalories a day through exercise. On average, they lost two to three pounds a week over the course of six months. Just as importantly, after the first week this weight loss was almost exclusively in the form of fat. The exercise stimulus prevents the muscle loss typically associated with diet alone, also preventing the drop in resting metabolic rate. This greatly enhances one's ability to maintain the weight loss over time. Finally, I must point out that even if overweight and obese individuals do not lose a significant amount of weight while engaging in a regular exercise program, they are still receiving many of the health benefits by reducing the risks for heart disease, diabetes, and some cancers, thereby decreasing their overall risk for all-cause mortality. In summary, the obesity epidemic is a major public health issue worldwide. Elevated levels of visceral fat puts an individual at a greater risk for metabolic syndrome. Dieting alone is not ideal for weight loss maintenance. Both components of the energy balance equation should be adjusted for sustained weight loss and health benefits.
