Impact of BMI on Health

What is the optimal or ideal body weight? It depends on how you define it. The optimal body weight for an Olympic weight lifter, Sumo wrestler, or professional football lineman is well above a body mass index (BMI) of 30, at least in terms of athletic success. However, in terms of health and longevity, men who compete successfully in these sports have only about one-half of the life expectancy when they retire (usually in their 30s) as does the average man in the U.S. or Japan.

If we define optimal or ideal body weight as that at which longevity is greatest, and the risk of common chronic diseases is lowest, a BMI close to 20 appears to be ideal.

Higher BMI equated to a higher risk of disease

A recent follow-up study of 123,000 people found that the risk of heart disease, colon cancer, gallstones, stroke, and diabetes all increased as the BMI rose above the 18.5 to 22 range.1 Compared to those with a BMI in the “normal” range (18.5 to 24.9), those with a BMI above 35 were about 20 times as likely to develop type 2 diabetes.

Other studies have found that the risk of other cancers, osteoarthritis, polycystic ovarian syndrome, and asthma all increase with increasing BMI. Data from the American Cancer Society’s Cancer Prevention study found that all-cause mortality increased with increasing BMI above 21 up to age 75 years.2

Aging and BMI

An important question that has not been answered in humans is whether or not intentional weight loss will slow the aging process and/or prevent degenerative diseases. The latter seems likely because weight loss reduces many of the risk factors associated with the development of chronic diseases such as heart disease, stroke, and diabetes. Dyslipidemia, insulin resistance, elevated C-reactive protein levels, and hypertension have all been shown to improve with weight loss. In all species of mammals studied, the aging process itself has been shown to slow down and life span increased significantly when calorie intake is reduced.3 This is in fact the only proven way to increase the life span in animals. Interestingly, in some genetically fat rodents, calorie restriction increases life expectancy compared to genetically thinner rodents who consume more calories.

Whether or not reducing calorie intake in middle-aged humans would slow the aging process and prevent degenerative diseases seems likely but remains to be proven. Part of the problem in proving this is that very few people lose weight when placed on a calorie-restricted diet. Calorie-restricted diets work in animals because they are locked in cages and have no way to get more food.

The Bottom Line:

Current research suggests that thinner is better but even modest amounts of weight loss have now been shown to reduce the risk of developing diabetes in people at high risk. Blood lipids and other CVD risk factors begin to improve with as little as 5-10 lbs of weight loss, although greater losses usually lead to more dramatic improvements. Ideal or optimal weight from a health and longevity perspective is likely to be the lowest weight a person can achieve with a healthier diet and exercise program.

By Dr. James J. Kenney, Ph.D., FACN.

References:

1. Field AE, Coakley EH, Must A, et al. Impact of overweight on the risk of developing common chronic diseases during a 10-year period. Arch Intern Med 2001;161:1581-6

2. Stevens J, Jianwein C, Pamuk ER, et al. The effect of age on the association between body-mass index and mortality. N Engl J Med 1998;338:1-7

3. Morrison SD. Nutrition and longevity. Nutr Rev 1983;41:133-42

Do You Know Your BMI?

BMI stands for body mass index. It is a ratio between height and weight. BMI is a helpful tool to assess patients because the index is simple, correlates to body fat, and applies to both men and women. A BMI of 25 to 29.9 is considered overweight while 30 or above is considered obese.

Although the BMI is useful for creating guidelines for healthy adults (ages 20 to 65 years), it does not apply to athletes, infants, children, adolescents, pregnant or breastfeeding women, and adults over 65 years of age.

How do you lower your BMI?

The answer is twofold. First, eat a low-fat, near-vegetarian diet that consists mainly of whole foods that are low in calorie density so you feel full on fewer calories. These include fruits, vegetables, whole grains, legumes, nonfat dairy, and lean poultry or fish. For example, choose oatmeal and other whole-grain cereals instead of bagels, Danish, or sweetened cereals. Choose salads, baked potatoes, low-fat bean soup, or low-fat stir-fry dishes instead of deli sandwiches, hamburgers, and other high-fat, high-processed fare.

Second, exercise consistently. Shoot for at least 30 minutes of aerobic exercise on most days of the week and add in a couple of days of resistance exercise such as calisthenics, exercise bands or weights.

More articles on BMI:

Keys to Long Term Weight Loss Success

BMI Makeover

Do You Know Your BMI?

National Weight Loss Registry Findings

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