Fitness vs. Body Weight: Which is Most Important for Health?

image of overweight young woman jogging in the street. Is being fit more important than body weight as far as health goes?

The news media is full of warnings about the health hazards of obesity – for good reason. Being obese increases the risk of a variety of health problems, including type 2 diabetes, hypertension, and heart disease. It also elevates the risk of at least 13 forms of cancer. We also know that being fit reduces the risk of many of these diseases. For years, scientists have wondered whether the benefits of being fit outweigh the risk of being overweight Now, a new study shows that being physically fit may be more important from a health standpoint than body weight or BMI.

What the Study Showed

Researchers at the Wharton Medical Weight Management Clinics in South Ontario, Canada asked 853 patients to take part in a study. All of the participants were obese to varying degrees from mild to severe. Prior to the study, the participants engaged in a maximal stress test using a treadmill to measure their aerobic capacity, as a marker of fitness level. The researchers also measured other health parameters such as blood glucose, triglycerides, and blood pressure, all of which are linked with metabolic health. The results? Based on treadmill testing, a number of the obese individuals had a high level of fitness – 41% of the mildly obese, 25% with moderate obesity, and 11% with severe obesity. As you’ll soon see, that’s a good thing from a health standpoint.

In the study, researchers noted that even the severely obese individuals had favorable blood glucose, triglycerides, and blood pressure if they were in the highest 80% on the fitness scale. These individuals didn’t seem to suffer from the metabolic issues that plague so much of the Western population. However, obese individuals in the lowest 20% on the fitness scale DID have abnormalities on their metabolic profiles, including abnormal blood glucose and triglycerides that are suggestive of poor metabolic health. Based on these results, it appears that obese people can be metabolically healthy if they’re physically fit – even severely obese individuals.

What makes this study unique is it shows that even severely obese individuals CAN have a high fitness level and a high fitness level is linked with more favorable markers of metabolic health. Previous research suggests that obese individuals are at higher risk of metabolic syndrome, a precursor to type 2 diabetes and heart disease. However, based on this study, having a higher fitness level may mitigate this risk.

How is this study different? Other research has addressed the “fit vs. fat” controversy, but these studies only looked at overweight and mildly obese individuals, not severely overweight individuals. However, they showed that mildly obese individuals who are fit may not suffer the same health risks as unfit individuals and, paradoxically, may have lower mortality than those who are of normal weight. Researchers are still trying to sort through and explain this “obesity paradox.” However, the most recent study focused more on people with more pronounced degrees of obesity and found that fitness may be protective.

As further support for the protective effects of fitness, researchers at Middle Tennessee State University analyzed the results of an additional 10 studies comparing body weight and fitness levels and mortality. The participants were placed into three groups based on their BMI: normal, overweight, and obese and, then, based on the results of fitness testing, divided into a fit or unfit category. After looking at the mortality data, researchers concluded that fitness level was a stronger determinant of whether a person survived or died, over the course of the study, than was body weight or BMI. Unfit people at all BMIs were at higher risk of dying relative to those who had a high fitness level. In fact, normal weight subjects with a low fitness level had double the risk of dying as an obese person who was physically fit. Plus, overweight and obese individuals who were physically fit had a similar mortality rate as normal-weight individuals with a high fitness level.

Fitness Matters

What do these studies tell us? A person’s BMI isn’t the full story. Fitness level is another factor that determines health status and risk of mortality and it may be a stronger predictor than BMI. In other words, fitness trumps body weight. This doesn’t mean that obese people shouldn’t lose weight, but it suggests we should focus more on attaining a higher fitness level. Of course, some obese people find it challenging to get down to ideal body weight. Obesity is a multifactorial condition that’s more complex than “calories in, calories out.” Yet, most obese people still have the capacity to be active.

Fortunately, you don’t have to exercise long and hard to improve aerobic capacity. Relatively brief periods of high-intensity exercise, even 10 minutes if it’s vigorous enough, can improve V02 max. Longer duration, lower intensity exercise such as walking is also effective and may be a better option for someone who’s severely obese. The good news is even small improvements in a person’s fitness level offers substantial health and fitness benefits.

Of course, aerobic exercise is only one aspect of training. The most effective workouts include a combination of aerobic exercise, strength training, and flexibility. Each is important for overall health and fitness. Without strength training, we lose bone and muscle mass at an increasing rate as we age. Without flexibility, we’re limited in the exercises we can do. So, make sure your routine is balanced and includes more than cardio.

The Bottom Line

Body weight and BMI isn’t the full story. Fitness level may be as important or even more important than calculated BMI. We also know that BMI alone is not necessarily a good predictor of health due to differences in body fat relative to muscle.

Unfortunately, not everyone who is obese can get to normal body weight and it may not be necessary if you believe the obesity paradox. Yet, it’s important to be physically fit no matter what your weight. Keep these results in context though. Obese individuals who are physically fit may still suffer from poor metabolic health many years down the line, especially if they stop exercising. Nevertheless, exercise is the most powerful medicine you have to change your physique and mitigate health risks. So, keep moving!



Science Daily. “Study shows benefits of exercise can outweigh health effects of severe obesity”
BMC Obesity, 2018; 5 (1) DOI: 10.1186/s40608-018-0183-7.
Circ Res. 2016;118:1752–70.
MedPage Today. “Low Aerobic Activity Tied to Higher Death Rates in Men”
Progress in Cardiovascular Diseases 56 (2014) 382 – 390.
Diabetes Care. 2012 May;35(5):1021-7. doi: 10.2337/dc11-2407.
American Council on Exercise. “8 Things to Know About Aerobic Capacity (And How to Improve It)”


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