Fitness vs. Fatness: Is it better to be skinny vs fit?

Is it better to be skinny vs fit? If you’re a couch potato but thin is that okay? Or is being in good shape, even if you have a few extra pounds better for you?

For more than two decades, debate has raged over whether it’s better to be skinny or fit. It was a 1995 study that started it off with its finding that fitness was associated with better health outcomes, regardless of body size. Since then, studies have continued to compare fitness versus fatness.

It’s long been believed that being overweight, or having obesity, means you’re not in good shape. However, this isn’t entirely true. While fitness levels tend to be lower in people with a higher BMI, the two are not mutually exclusive. In fact, one study found over 50% of women with a BMI 31-33 kg/m² had a high fitness level.

The Evolving View of Obesity

Of course, the ideal situation is to be in great shape and be thin. These people have the lowest risk for disease and having an early death. But over 1 in 4 Canadians and 2 in 5 Americans have obesity. At the same time, more than 80% of adults are physically inactive. Therefore, few people fall into the category of being in great shape and thin.

While obesity is defined as a body mass index (BMI) ≥30 kg/m² (overweight ≥25 kg/m²), how we view obesity has changed in recent years. Many medical organizations now consider obesity as a chronic disease. And in 2020, the Canadian guidelines defined obesity not by BMI but as a disease of excess body fat which impairs physical and/or mental health.

Given the challenges with weight loss, there is great interest in how people who are overweight or obese can improve their health. Increasing one’s activity and fitness may play a crucial part.

The Battle: Skinny vs Fit

Some studies have suggested it’s better to be thin rather than active. In one such study, women who were thin yet inactive had a lower chance for early death than those who had obesity and were active. However, in patients with heart disease, being physically active, was more beneficial than having a low BMI. Physical activity reduced the chances of early death even more than weight loss. In both studies, being active was always better than being inactive at the same BMI level.

But those studies looked at physical activity and not fitness. And while the two are related, they’re not exactly the same thing. Fitness is less commonly measured in research because it’s time consuming and requires specialized equipment. However, fitness is one of the strongest predictors of long-term health.

When taking fitness into account, the story seems to be quite different. As expected, in men who were unfit, increasing BMI or waist circumference was associated with a greater chance of early death. However, in those men who were fit, it didn’t seem to matter what size the person was. Effectively, being fit reduced the negative effect of being overweight or obese. Similarly, in adults with diabetes, having a high fitness level reduced the health risk of a high BMI.

And this finding also applies to more than just early death. While overweight and obesity are associated with depression, being fit may be more important. Those people who were fit but obese had a lower chance of being depressed than people who were unfit and lean.

What about those people who have an ideal BMI but aren’t active or physically fit? A review concluded that people who are obese but with a high fitness may actually be healthier than people who are lean and unfit.

Do you need to be skinny to be healthy?

So how is it that obesity is associated with increased chances of disease and early death, yet being in good shape can remove this risk? Is there such a thing as being healthy obese? When it comes to risk for conditions such as diabetes and heart disease, it may be the case.

As a result, scientists have created the term metabolically healthy obese (MHO). These people may be obese but do not have risk factors for heart disease such as high cholesterol, high blood sugar and high blood pressure. It’s likely that being active and in good shape has reduced, or eliminated, these risk factors.

While people who are MHO may have a lower risk for disease than people with obesity and risk factors, being MHO is not without concern. Compared to people at ideal body size with no risk factors, MHO people still had a 50% greater risk for heart disease.

On the other hand, being lean by itself doesn’t ensure one is healthy. A person can be lean and still be at high risk for disease. These people are referred to by terms such as thin on the outside but fat on the inside (TOFI) and metabolically obese but normal weight (MONW). They also tend to have a number of risk factors for diabetes and heart disease, and are in poor shape. This may be due to having more fat around their waist. Together, this puts them at greater risk for heart disease and early death.

The Bottom Line

Both obesity and being out of shape increases your chances for a number of diseases and early death. However, the person who is lean but doesn’t exercise regularly may not be in such good health after all.

Being active and fit is good for you regardless of your body size. And given the challenge of weight loss, focusing on regular activity is a sure way to improve your health make you feel good.

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This post was originally published on March 22, 2018 and updated on February 3, 2021.