In the midst of the obesity epidemic, one of our most important concerns is the association between body mass index (BMI) and the risk of cardiovascular disease (CVD).
However, body weight itself may not be what matters most. Evidence suggests that obesity measures such as BMI, waist circumference, or waist-to-hip ratio, assessed singly or in combination, do not importantly improve prediction of CVD risk when additional information is available on blood pressure, history of diabetes, and cholesterol measures (1).
Putting it differently, measures that promote weight loss without improving CVD risk factors, such as blood pressure, lipids, and markers of insulin resistance and diabetes, will not reduce cardiovascular risk. Similarly, measures that don’t promote weight loss, but do improve these same risk factors, will lower the risk of CVD.
However, most studies do indeed show that weight loss has beneficial effects on CVD risk and losing weight would, therefore, be expected to reduce CVD risk. A randomized trial published 2010 showed that among patients with severe obesity, a lifestyle intervention involving diet combined with physical activity resulted in clinically significant weight loss and favorable changes in cardiometabolic risk factors (2).
Dietary caloric restriction and regular endurance exercise would both be expected to cause energy deficits and subsequent weight loss. In fact, scientific evidence shows that sustained caloric restriction is feasible and promotes weight loss (3). On the other hand, many experts have debated the role of physical exercise as a weight-loss tool.
In his book, Why We Get Fat: And What to Do About It, Gary Taubes goes to great lengths to convince us that, when it comes to losing weight, the role of physical exercise has been highly overrated. He writes; “But the question I want to explore here is not whether exercise is fun or good for us (whatever that ultimately means) or a necessary adjunct of a healthy lifestyle, as the authorities are constantly telling us, but whether it will help us maintain our weight if we’re lean, or lose weight if we’re not. The answer appears to be no.”
In a recent interview with The Guardian, the prominent British cardiologist, Dr. Asseem Malhotra, said: “We know exercising in the right way has many health benefits, but weight loss isn’t one of them. We need to disassociate obesity with exercise altogether. If we’re going to combat obesity, it’s going to happen purely from changing the food environment (4).”
Taubes also quotes Hugo Rony of Northwestern University who already in 1940 wrote: Consistently high or low energy expenditures result in consistently high or low levels of appetite. Thus men doing heavy physical exercise spontaneously eat more than men engaged in sedentary occupations.”
By saying this, Taubes is not necessarily refuting the calorie in/calorie out model. He’s claiming that if we spend many calories, we run the risk of consuming more, resulting in a net effect of zero. Therefore, although exercise burns calories, it does not promote weight-loss.
Now, of course, the calories in/calories out model reflects a very simplistic view on the obesity problem. But, calories aside, is it sensible to downgrade the role of exercise for the treatment of obesity? In my opinion, the answer is no.
A randomized study published 2000 showed that weight loss induced by increased daily physical activity without caloric restriction substantially reduced obesity (particularly abdominal obesity) and insulin resistance in men. Exercise without weight loss reduced abdominal fat and prevented further weight gain (4).
Another randomized trial showed that exercise without caloric restriction was associated with substantial reductions in total fat, abdominal fat, visceral fat, and insulin resistance in women (5).
Weight Management – Caloric Restriction, Exercise, or Both
Edward P Weiss and coworkers recently addressed the question whether the effects of exercise were “additive” to the benefits of weight loss, in a paper published in the American Journal of Clinical Nutrition (6).
The study included 52 overweight men and women who were randomly assigned to one of three treatments, with a weight-loss goal of seven percent over 12-14 weeks. One group consumed a calorie-restricted diet; a second group adhered to an exercise regimen without changing food intake, and the third group followed a combination of calorie restriction and exercise.
The reduction in body weight was similar in all three groups, approximately 7 percent. Fat mass decreased by an average of 15 percent in the three groups; fat-free mass decreased by 2.6 percent in the calorie restricted group and by 1.6 percent in the combined diet and exercise group, with no change in the exercise-only group. This might suggest that exercise can minimize the loss of lean body mass during weight management.
There were similar changes in CVD risk factors in all three groups. Systolic and diastolic blood pressure was decreased, total cholesterol, non-HDL cholesterol, triglycerides, and blood glucose were all reduced. No changes were observed for HDL cholesterol, C-reactive protein, or arterial stiffness. The authors conclude that these changes would be expected to decrease the lifetime risk of CVD from 46% to 36%.
Interestingly, caloric restriction and exercise had the same effect on risk factors and adding exercise to caloric restriction did not increase the benefit. Of course, the CVD risk outcomes between the groups may have been nonsignificant because the study may have been too small to detect such differences.
Obesity and Exercise – The Bottom-Line
The study by Weiss and coworkers suggests that caloric restriction and exercise, either alone or in combination, promote weight loss and have substantial beneficial effects on CVD risk factors.
The authors conclude that a straightforward interpretation of their findings is that “weight loss itself produces a major cardioprotective effect of caloric restriction and exercise and that the benefits do not depend on which approach to weight loss is used.”
However, they also point out that the issue may be more complicated, and address the possibility that the benefit of exercise may also be related to other factors than weight loss itself; “However, because a sedentary lifestyle and poor aerobic capacity are independent risk factors for CVD, exercise provides a benefit that cannot be achieved by using caloric restriction alone, therefore exercise remains a critical component of CVD risk reduction programs.”
It is also important to highlight the fact that dietary interventions not particularly aimed at weight management per se, such as the Mediterranean-style diet, may have beneficial effects on CVD risk factors and clinical events, independent of the effect on body weight (7).
Furthermore, dietary choices that are not particularly aimed at reducing calorie intake, such as low-carbohydrate, high-fat diets may be very useful for weight management (8).
In my opinion, it is important not to degrade the role of exercise for individuals with overweight and obesity. Although some experts have disputed the role of exercise in weight management, the recently published paper by Weiss and coworkers clearly demonstrates that weight loss can be achieved by exercise alone. Furthermore, exercise led to similar reductions in CVD risk factors as caloric restriction.
However, it is important to underscore that although I believe regular exercise should be a part of every weight management program, it does not provide a free pass for unhealthy eating. You can’t outrun a bad diet.