There is a longstanding debate in the research community about the importance of fitness versus fatness in health.
Are exercise and improving fitness more important than eating well and maintaining a healthy weight?
Some researchers argue fatness does not affect health as long as you are fit, which means your heart and lungs are strong.
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 include exercise.
As family physicians, we see obese patients who have heard the message to "just be fit" and have added 10-15 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.
How are fitness and fatness 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.
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.
Strictly speaking, obesity does not mean you are automatically unfit. But 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.
Fatness makes it harder to improve fitness:
For people who are obese, focusing on losing weight is a better place to start than just focusing on fitness. That's because extra weight can make it harder to move, thus harder to exercise. Heavier people need more oxygen to do the same exercise as a healthy-weight person. Some obese people report that even walking can seem tough. Fitness is just harder to achieve if you can't move easily.
Fatness decreases your quality of life:
Studies show that compared to normal weight, fit individuals, unfit individuals had twice the risk of mortality regardless of BMI. But as these studies show, a relatively small proportion of people are fit and obese.
Obesity has been shown to predict diabetes, heart disease, liver disease and a whole host of health problems that may require taking daily pills or having daily injections, or lead to invasive procedures. Even if a higher BMI does not predict earlier death, this does not mean that it "doesn't matter" to your health.
While exercise can and does improve health, for people who have health conditions like diabetes or fatty liver disease, exercise alone won't make a huge difference in reversing these conditions. However, these conditions can be improved or even resolved with weight loss.
For obese people to improve their health and quality of life, it is important to exercise every day, eat healthy food and, most importantly, lose some weight.
Tammy Chang is assistant Professor, Family Medicine, University of Michigan