The Human Beast

Why we do what we do

So you think that losing weight will make you healthy. Think again!

Weight loss far more dangerous than we think

There are many earnest claims that if a person gets thin, they will be healthy. This is the premise of a messianic reality TV show. Research findings on the subject got badly mangled in translation to popular media, however.

To begin with, thin people have more health problems and shorter life expectancy as we have known for a long time thanks to Metropolitan Life Insurance data. Thin is definitely not equivalent to healthy. So why the false belief that skinny people are healthy?

How the weight-loss-for-health craze began
Being underweight (body mass index < 18.5) is a risk factor for disease compared to normal weight (18.5-25) but this connection got swept under the rug of history. One reason is that there are not many underweight people around in developed countries. On the other hand, there is an epidemic of obesity (body mass index, BMI > 30) thanks to insufficient physical activity and a high-fat, low-fiber diet. Calculate your BMI here.

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The excess poundage is accompanied by diabetes, high blood pressure, kidney disease and related problems known as "the metabolic syndrome," all of which reduce life expectancy.

The grim truth about weight loss
If excess weight reduces life expectancy, does losing weight improve health? A review article published in 2007 (1) that summarized 40 years of research produced an extremely guarded endorsement of weight loss: "There is some evidence that intentional weight loss has long-term benefits on all cause mortality for women and more so for diabetics. Long-term effects especially for men are not clear and need further investigation."

In recent years, the research literature appears to be converging on a consensus that weight loss is bad with the possible exception of specific groups such as diabetics and the morbidly obese. This, of course, is exactly the opposite of what the public, and their physicians, are saying and doing.

Here are the conclusions from two major studies published in 2009 (2) and 2010 (3)..

"Weight loss is associated with excess mortality among normal, overweight, and mildly obese middle- and older-aged adults. The excess risk increases for larger losses and lower initial BMI [body mass index]. These results suggest that the potential benefits of a lower BMI may be offset by the negative effects associated with weight loss. Weight gain may be associated with excess mortality only among obese people with an initial BMI over 35." So weight loss is bad for most of us (below severe obesity) and weight gain has trivial effects on longevity.

"Weight loss of 15% or more from maximum body weight is associated with increased risk of death from all causes among overweight men and among women regardless of maximum BMI." Increased mortality rates ranged from 46% - 170%.

One reason that weight loss increases mortality may be the use of unsafe methods, such as severe calorie restriction, or stimulant drugs, including nicotine. Risks include diabetes, high blood pressure, osteoarthritis, and strokes. Another reason is that weight losers often have widely fluctuating weight that is a risk factor for heart disease (4).

Why does weight gain have trivial effects on life expectancy for all but the severely obese? One possibility is that physicians have become more skilled at treating the metabolic syndrome using improved drugs and procedures. Another is that it is natural to gain some weight with age. Finally, it may be that there is individual variation in the amount of body fat that is healthy.

What to do
Weight loss may be risky but it need not be. The safest method of weight loss is through an active lifestyle. Instead of subtracting years like other weight loss methods, regular physical activity improves health and longevity. We know because people who live long are physically active (5) and because lack of fitness is a key risk for heart disease the leading cause of death (6).

Indeed the metabolic syndrome may be entirely reversible via improved lifestyle. When ten diabetic overweight urban Aborigines from Derby, Western Australia, spent seven weeks living as hunter gatherers, they lost an average of 18 pounds (about a tenth of their body weight) and there was a remarkable improvement in their blood sugar (7).

Forget about weight and appearances. Focus on leading a healthy lifestyle more consistent with how our forager ancestors lived with plenty of activity and a sensible diet. Weight, appearance, and health, will take care of themselves.

1. Poobalan, A. S. (2007). Long-term weight loss effects on all cause mortality in overweight/obese populations. Obesity Review, 8, 503-513.
2. Myrskyla, M. & Chang, V. W. (2009). Weight change, initial BMI, and mortality among middle- and older-aged adults. Epidemiology, 20, 840-848.
3. Ingram, D. D. & Mussolino, E. E. (2009). Weight loss from maximum body weight and mortality: The Third National Health and Nutrition Examination Survey Linked Mortality File. International Journal of Obesity, 34, 1044-1050.
4. Wannamethee, S. G. et al. (2002). Weight change, weight fluctuation, and mortality.
Archives of Internal Medicine, 162, 2575-2580.
5. Yates, L. B., et al. (2008). Exceptioinal longevity in men. Archives of Internal Medicine, 168, 284-290.
6. Myers, J., Prakash, M., Froelicher, V., Partington, S., and Atwood, J. E. (2002). Exercise capacity and mortality among men referred for exercise testing. The New England Journal of Medicine, 346, 793-801.
7. O'Dea, K. (1984). Marked improvement in carbohydrate and lipid metabolism in diabetic Australian aborigines after temporary reversion to traditional lifestyle. Diabetes, 33, 596-603

Nigel Barber, Ph.D., is an evolutionary psychologist as well as the author of Why Parents Matter and The Science of Romance, among other books.

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