Nutritional Pearl: Can You Be Fit and Fat?

Tom is a 43-year-old overweight man who has had trouble exercising in the past. He tells you that whenever he begins an exercise regimen, he becomes discouraged after several weeks when he fails to lose any weight, and “doesn’t see the point” of continuing.

How do you advise your patient?
(Answer and discussion on next page)

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Answer: Exercise benefits everyone, regardless of body weight.

The controversy continues over whether a person can be considered healthy if their weight is not in the normal range. The problem, of course, is how you define "healthy" and how you define "normal weight."

Much of the research has defined "normal weight" in terms of body mass index (BMI), with "normal" being a score of 20-25, "overweight" a score of 25-30, and "obese" 30 and up. But BMI isn't particularly accurate for whole groups of people, including children, the elderly, people who are extremely muscular (have low levels of body fat), and others. Waist to hip ratio is another score that may actually be more useful than BMI as a measure of healthy weight.

"Healthy" is most often defined in terms of cardiovascular or metabolic health, including cholesterol scores and blood pressure along with glucose levels and insulin response.

The Research

A team of researchers in Toronto, Canada looked at the interaction between weight and fitness, but took an unusual approach to the definition of "healthy": they looked at VO₂ max. This is the measure of the maximum rate of oxygen (usually in liters per minute) utilized by an individual during exercise and is considered a good measure of aerobic capacity, with higher levels of aerobic capacity indicating higher physical fitness. For the most accurate results, it's tested using an exercise cycle or a treadmill and sophisticated equipment, so it's a fairly expensive test to perform.

For their study, the team recruited 853 people from those attending Wharton Medical Clinic, a weight and diabetes management clinic in Toronto, Canada. These men and women all had a BMI of at least 32. Every participant received a VO₂ max score via a treadmill test and had their blood pressures tested along with a standard blood panel, which included cholesterol scores and glucose scores.

The authors defined "unfit" versus "fit" in terms of the participants' VO₂ max score: those scoring below the 20th percentile for their age and sex were considered "unfit," while those scoring in the 21st percentile and above were considered "fit." The participants' relative fitness was then correlated with their BMI, waist circumference, and blood test results.

The Results

You might be surprised to learn that 41% of those with "mild" obesity (a BMI between 30 and 35) were considered fit, as were 25% of those with "moderate" obesity (BMI between 35 and 40) and 11% of those with "severe" obesity: a BMI 40 and over. Indeed, those who were fit but classified as severely obese had glucose levels and cholesterol scores, along with blood pressures, that were not statistically significantly different from those who were fit and had only mild obesity.

What’s the Take-Home?

More than anything else, this should be taken to underscore the benefits of exercise for everyone, regardless of body weight. The current recommendation is for a minimum of 150 minutes of moderate exercise per week: that's just 30 minutes of walking 5 days per week, and yes, walking through the parking lot counts. The benefits of fitness may not fully outweigh the risks of being overweight—this study compares those who are severely overweight with those who are moderately overweight, not those of clinically normal weight—but it's clear that it makes a significant difference in heart health.

Reference:

Do K, Brown RE, Wharton S, et al. Association between cardiorespiratory fitness and metabolic risk factors in a population with mild to severe obesity [published online January 31, 2018. BMC Obesity. doi 10.1186/s40608-018-0183-7