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While Body-Mass Index isn't the worlds most accurate indicator, it does correlate quite nicely with body fat, as the graph below shows.

BMI vs Body Fat %

One of the uses of BMI in this case, is that a high BMI is generally considered to be correlated with poor health outcomes, especially cardiac problems. However, it is common for people to point to athletic outliers as an indication that BMI is flawed.

However, even with a high-weight and a low body fat, the heart still has to do more work to pump body through a larger frame. As such, is there any research that looks at the link between individuals with a high-BMI and low body fat, and health?

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  • I don't think your question makes sense. You mean, does being a short muscular person (heavy, but low fat), have an increased risk then a taller muscular person? – user7050 Mar 17 '14 at 5:21
  • @LazyMan No the question is more along the lines of: Are there health differences between two people, of the same height and body fat percentage, but with one being "obese" and one being "normal" according to BMI? – user2861 Mar 17 '14 at 5:23
  • But its more along the lines of "does a high BMI correlate with poor health outcomes, regardless of body fat make up"? – user2861 Mar 17 '14 at 5:24
  • A high BMI is 'generally related with poor health outcomes' because people generally don't have high mass/low BF%. Only certain athletes share these characteristics (e.g. strength athletes, bodybuilders) which makes the application of the BMI for these people pretty absurd. There are adjusted BMI scales for strength athletes or paralyzed people, though, which just goes to show how arbitrary this whole BMI business is. – user8119 Mar 17 '14 at 7:40
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    @LarissaGodzilla That's the question, is there a study that looks at the correlation between BMI and health outcomes AND ALSO controls for body composition. – maxywb Mar 17 '14 at 18:47
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To the best of my ability, I've not been able to find a study that thoroughly looks into this issue. However, BMI is a poor indicator in and of itself for a multitude of reasons. I'll enumerate some of them: (a) visceral fat is far worse than subcutaneous fat in terms of health. (b) too little fat is also bad for your health, but the odds of your BF% entering the into the essential fat levels is rather small and requires extreme effort or starvation. (c) heart health depends on more than just body fat, Cholesterol levels, stress and cortisol levels, additionally, the amount of cardio that you do has a profound effect on heart health. So, you could have a high BMI a 10% body fat and be a high risk of heart attack. Furthermore, regardless of what the tissue is, any addition of vascular tissue results in greater strain and work that the heart must overcome in order to pump blood through your body. In terms of heart health, BMI is poor indicator as it tells you little more than what you could learn from a mirror. If you're concerned about health, and heart health, consult a physician to have them do a cardiac stress test and run bloodwork. For example, congestive heart failure occurs

As for orthopedic health, BMI correlates better and has a great possibility of causation due to the fact that body mass is among the largest contributors to orthopedic issues after diet, exercise, and genetics (Joint problems). Too much mass and your body will be overstressed, too little mass and your bones will be weaker due to decreased stress loads resulting in less calcium being transferred into the bones (Osteoporosis).

TL::DR: regardless of composition, increased mass results in greater work on the body. Greater persistent work causes greater stress, greater waste, etc. The problem comes with finding balance between exercise and muscle gains (hypertrophy) and inactivity (atrophy). Generally, inactivity is worse for your health than too much body mass. Ultimately, any concerns you have regarding health is best suited for a doctor who can run tests and make objective evaluations in addition to subjective evaluation.

This answer is based largely off of my experience as a paramedic and being a biomedical engineering student with a minor in pre-med. I apologize for not being able to come up with a definitive study, but I suspect there aren't many since high muscle low fat people aren't nearly the health concern as obesity and high fat people.

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Okay, Cardiac risk can't be weighed on BMI alone. There are many factors at play here. When assessing Cardiac health, most physical fitness uses VO2max. The higher the VO2max, the better the cardiac function. This can be assessed at home just by taking your (resting heart rate/maximum peak heart rate)*15. Your max peak heart can be found by 220-age=max peak heart rate. This measurement tells how effective your Cardiac system is supplying oxygen to the body. The higher your VO2max, the healthier your Cardiac system is. Body builders do have strong hearts; however, there VO2max isn't increased. Bodybuilders due have strong hearts, but the changes in the heart muscle isn't for VO2max. Steriods builds muscles quickly. Unfortunately, the left side of the heart becomes more muscular as well resulting in reduced fill volume. Generally, Body builders using growth hormones and steroid usually results in diastyolic heart failure. If the heart can't fill enough, it can't eject enough. Runners generally have a high VO2max where the heart muscle is built stronger to eject more blood efficiently supplying the body of oxygen quicker. A high VO2max mean your heart doesn't have to work hard to supply your body. Most large muscular men that live long like Arnold Schwartzneggar, Dwyane Johnson, etc usually have one thing in common, they RUN. The running is what saves there heart by keeping the VO2max up. So, there you go, the science behind the madness. If I missed anything or managed to have something incorrect, please fill free to correct me. I am always learning as well.

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