The example of Jim Fixx is used to point out that health, fitness, and body composition are three completely separate entities. All three interact; meaning that one's health can affect one's fitness, but that one's health is not the same as one's fitness. The same is true with body composition. Being able to run up and down a soccer field without getting tired does not make one healthy, and neither does a single digit body fat percentage. This has been seen in several epidemiological studies.
A 2012 study published in the European Heart Journal found that obese folks who had similar blood pressure, cholesterol levels, blood sugar levels, and exercise habits to their normally weighted peers were at no higher of a risk for developing or dying from a heart attack. The implication of this research is that body composition is not as significant of a risk factor for heart disease and cancer as the aforementioned variables.
On the other hand, a 2012 study published in the Journal of the American Medical Association found that diabetics of a normal weight were nearly twice as likely as obese diabetics to die in a given year (1.5% compared with 2.8%). This finding held true even when taking into account risk factors such as high blood pressure, high cholesterol levels and smoking.
This is not to suggest being obese is healthy. The point I am trying to make is that body composition exists independent of health. Fitness and health have a similar relationship; they interact but are independent of each other. There is also epidemiological data to support the independence of their relationship.
A 1990 study published in the journal Medicine and Science in Sports Exercise examined the relationship between weekly energy expenditure through aerobic exercise and hypertension and cardiovascular disease. The subjects were divided into six groups: 0 calories expended (group 1), 1-399 calories expended (group 2), 400-899 calories expended (group 3), 900-1499 calories expended (group 4), 1500-2499 calories expended (group 5), and 2500+ calories expended (group 6). Group 1 and group 6 had the highest rates of both hypertension and cardiovascular disease, suggesting that at some point aerobic exercise stops being beneficial for one's health.
More recent data seems to bolster this suggestion. Research presented in June 2012 at the American College of Sports Medicine found that those who ran at a 7 minutes/mile pace or more than 20 miles/week were at a higher risk of mortality than those who ran at a 10 or 11 minutes/mile pace or 10-20 miles/week.
In the confusing world of health, fitness, and body composition, the three terms seem to have taken on the same meaning. This is incorrect, as all three terms are independent of each other. Accordingly, it would be helpful for each term to be defined. My favorite definitions for each are as follows:
Health: A state of complete physical, mental and social well-being and not merely the absence of disease.
Fitness: Physiologically being able to handle challenges above rest.
Body Composition: The proportion of muscle, bone, and fat in a human body.
Now that the above terms have been given separate definitions, they can be treated appropriately. Don’t run hundreds of wind sprints each week if you are trying to better your health. Don’t attempt a six pack if your goal is minimizing disease risk factors. Health, fitness, and body composition are not the same thing!
Sifferlin, Alexandra. "Can You Be Fat and Fit." Time. N.p., 5 Sept. 2012. Web. <http://healthland.time.com/2012/09/05/can-you-be-fat-and-fit-or-thin-and-unhealthy/>.
Park, Alice. "‘Obesity Paradox’: Why Being Thin with Diabetes Is a Dangerous Combo | TIME.com." Time, n.d. Web. 8 Aug. 2012. <http://healthland.time.com/2012/08/08/obesity-paradox-why-being-thin-with-diabetes-is-a-dangerous-combo/>.
Quinn, TJ, HW Olson, WD Van Huss, and HA Sprague. "Caloric Expenditure, Life Status, and Disease in Former Male Athletes and Non-athletes." Medicine and Science in Sports Exercise (1990): n. pag. NCBI. Web. <http://www.ncbi.nlm.nih.gov/pubmed/2287250>.
Reynolds, Gretchen. "Moderation as the Sweet Spot for Exercise." Well. The New York Times, n.d. Web. 6 June 2012. <http://well.blogs.nytimes.com/2012/06/06/moderation-as-the-sweet-spot-for-exercise/>.