In a recent study in JAMA, nearly 75% of men and 65% of women between the ages of 25-54 were classified as overweight (BMI>25) or obese (BMI>30). These numbers have dramatically increased in the last 40 years. In response to this rising epidemic, a multibillion dollar weight loss industry ranging from diet companies and supplement manufacturers to diet book authors and obesity doctors has mushroomed. However, we are failing miserably to keep off the pounds or sustain our weight loss. It is a well cited statistic that 90% of people who lose greater than 10% of their body weight, gain it back within 1 year. These results are unsurprising if viewed through the lens of evolution. As I talked about in an earlier post, humans are naturally selected to store energy in the form of fat. The average human stores a 100,000 calories of energy in the form of fat. Energy conservation is the default and in the setting of our cultural milieu of minimally laborious, easily accessible calorically dense food, we will inevitably gain weight.
Additionally, as an isolated variable, obesity is not the best absolute indicator of “poor” health. There is a segment of the population that is defined as overweight, but are nonetheless, metabolically healthy. In one study, the highest rates of mortality were at either ends of the BMI scale, and paradoxically, the “overweight” population had the lowest mortality rate. This is partly because not all fat deposits are deleterious, and therefore, obesity metrics such as BMI are inadequate indicators of poor health in a particular individual. In contrast, decreased cardiorespiratory fitness is a much better marker of poor health and superior predictor of chronic disease. For example, cardiorespiratory fitness is inversely correlated with the development of metabolic syndrome. Obese individuals who exercise regularly are half as likely to die as normal weight individuals who do not exercise. Therefore, considering the difficulty of long term weight loss and even the possible inadequacy of obesity metrics as indicators of chronic diseases or mortality, we should change the goal of primary and secondary prevention from weight loss to a focus on cardiorespiratory fitness and metabolic health.
This change in focus will shift the target from illusive weight loss goals to a more viable goal of improving cardiorespiratory fitness. It is all to common for someone to become disappointed, lose interest, and subsequently stop an exercise regimen because they do not achieve any weight loss. In comparison, easily measurable physical fitness and physiological measures such as muscular endurance, cardiorespiratory performance, balance, flexibility, resting heart rate, and calculated VO2 max are tangible and easily improved (especially for beginners) with moderate intensity exercise regimens. Additionally, this concept of goal setting and achieving can serve as a positive feedback loop with stepwise improvement in fitness. This will not only yield downstream health improvement but can eventually ease the insidious impact of chronic diseases on a population wide basis.
We are at an unprecedented moment in human evolutionary history; at no time in our history, have we gained so much control of our environment and in a blink of an evolutionary eye transformed our communities from caloric insecurity to caloric surpluses. We are able to procure an unprecedented amount of calories with minimal caloric expenditures. By in large this has been beneficial to humanity, however, this has not come without a cost to our health in the form of chronic diseases. Thus far, we have primarily targeted obesity as the intermediary cause of these chronic diseases, but predictably, our “war on obesity” has failed and will continue to fail for the foreseeable future. Components of physical fitness such as aerobic capacity, flexibility, muscular endurance, and balance all yield significant health benefits with or without the accompanying weight loss. In order to make an impact on chronic diseases, medical recommendations, public policy, and the overall health care industry should displace its focus from obesity and weight loss to a target of physical fitness.