Fit or Thin: Which is more important??

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February 2, 2017

In the media and in medical literature, there are debates about which is more important for a long healthy life, being fit or being thin. There isn’t a simple answer, so I’d like to thank my colleagues for debating these points with me recently. For sure, FITNESS is VERY important. Fitness – being able to perform well on a treadmill test – proves that all systems are go. Not only do the muscles have the strength and endurance they need to keep you active, but the heart and lung function are good enough to support that activity. The impact of WEIGHT on longevity, on the other hand, is more of a grey issue.

In medicine, measurements related to weight usually refer to the BMI – the weight in kilograms divided by (the height in meters) squared – i.e., weight in relationship to height.

Here’s a link to a site with a BMI calculator, with more information about the usefulness of the BMI itself:

As an example, given a height of 5’3”, a weight of 115 calculates out to a BMI of 20, 140 pounds makes your BMI 25 and 170 pounds on the same 5’3” frame gives a BMI of 30. A BMI of 18.5-25 is considered ‘normal’, 25-30 ‘overweight’, while 30-35, 35-40 and >40 are different levels of ‘obese’.

By looking at someone, you can generally state that their BMI is on the low side or on the high side.  However, studies reaching conclusions based on BMI have to be carefully analyzed. Obesity (BMI > 30) has increased dramatically from 1960 through 2000, but death rates didn’t increase as much. Why not? Likely due to more aggressive and effective management of blood pressure, cholesterol and diabetes. Does that make the high BMIs OK? My answer is no – because the side effects and the financial cost of the medicine are tremendous and the DISABILITY associated with the increased weight, especially in the older population are very significant. And, in fact, that disability has increased over time, relative to normal-weight adults.

In general, a higher BMI is associated with more health issues. However, a major problem with using BMI as a measure is that it doesn’t account for build (narrow vs broad frame) and it doesn’t look at where the weight is concentrated (in large muscles vs fat in the belly vs fat in the thighs). Looking at the BMI alone can give you a false impression of a person’s health status.

Someone with ‘normal’ weight, for instance, can have a narrow frame and a protuberant abdomen. Abdominal or CENTRAL OBESITY is much more highly associated with high blood pressure, high cholesterol, and type two diabetes. Someone with lots of their weight in the belly has a higher likelihood of illness than someone who is bulked up with muscle, even though their BMIs might be the same. To account for this difference, some studies (e.g. Padwal, et al and Sahakyan et al) have shown that increased waist circumference is associated with increased mortality. A ‘high’ waist circumference is generally defined as over 35” in women and over 40” in men. By other studies, this higher risk associated with obesity can be counteracted, at least to some degree, by a better level of fitness.

With effective medication, people may not die as prematurely from their weight-related illnesses as they would have in the past, but in general, they don’t get around as easily as their normal-weight counterparts and they have higher health-related costs. I am concerned that when medications lower the BP, cholesterol and sugar, people are less motivated to exercise as a different way to achieve those same goals. Regular exercise, leading to improved fitness, is really the ticket to a longer, more active, life. It should be considered as part of the prescription. Take your statin, your BP and diabetes medication, and exercise 30 minutes most days.

Even for those in the ‘normal weight’ category by BMI (~ 20-25), fitness counts. Being normal weight and ’unfit’ is associated with twice the mortality of normal-weight fit adult.

Obesity has surpassed smoking as the #1 cause of PREVENTABLE disease and disability. Why are we talking about this? Because if you’re in a position to alter your nutrition or exercise status, NOW is the time to start. No matter your age, if you would like to be running around ten years from now, you’ve got to be moving NOW. Don’t get stuck on not being able to lose weight, or what your waist circumference is, just check with your doctor, and if it’s OK, keep moving. Aim for a higher fitness level by gradually increasing the duration and/or intensity, as approved by your personal physician. Think of it as a marathon, not a sprint. Slow and steady without injuries wins the race!


McAuley, et al. AJM 129(9): 960 – 965. Sept 2016.

Padwal R, Leslie WD, Lix LM, Majumdar SR. Relationship Among Body Fat Percentage, Body Mass Index, and All-Cause Mortality: A Cohort Study. Ann Intern Med 2016; 164:532.

Sahakyan KR, et al, Normal weight central obesity: implications for total and cardiovascular mortality. Ann Intern Med. 2015; 163(11): 827-835.