Tammy Chang, University of Michigan and Caroline R Richardson, University of Michigan.
There is a longstanding debate in the research community about the importance of fitness versus diet in health. Are exercise and improving fitness more important than eating well and maintaining a healthy weight?
Some researchers argue body weight does not affect health as long as you are fit, which means your heart and lungs are strong. And national campaigns like Let’s Move are focused on exercise for health without a specific focus on weight loss.
But for people who are obese, losing weight might be more important to their overall health than focusing on fitness. In fact, evidence shows that exercise alone is not an effective way to lose weight. Rather, effective weight loss is mostly about what you eat, though it should also include exercise. (Post continues after video.)
As family physicians, we see obese patients who have heard the message to “just be fit” and have added 10 to 15 minutes of walking to their daily routine or have bought a Fitbit to track their physical activity. We applaud these efforts.
But for many obese people, the message that physical activity is more important than managing weight is not only unhelpful but also not true. When it comes to health and wellness, body weight can matter more than fitness. And of course, for most people, body weight is related to fitness, because excess weight can make exercise much harder.
How are fitness and body weight linked?
Multiple studies have looked at fitness and obesity as two separate entities because they are seemingly separate concepts: one measures how well your heart and lungs work to supply oxygen to your muscles while the other is a measure of your body height and weight. (Post continues after gallery.)
However, the measures of fitness and fatness are both influenced by how much you weigh. Because of the way fitness is calculated, for two people with the same oxygen-transferring power, weighing more typically means lower fitness.
Likewise, what researchers mean by fatness is really body mass index (BMI), a measure of body fat based on height and weight. People are often surprised at what is considered normal weight. To be in the normal weight range, a person who is 5’7″ needs to weigh less than 160 pounds. If this same person weighs over 190 pounds, he or she would be considered obese.
Strictly speaking, obesity does not mean you are automatically unfit. There are obese people who run every day, and then there are thin people who couldn’t run a mile for their life. A muscular individual can also be considered obese, because muscle weighs more than fat, and be very fit.
But these are exceptions, not the rule. Studies show that when someone is categorised as obese, the likelihood of them being fit is very low. So in our society, being obese still generally means lower fitness.