Losing Weight Has Hidden Health Benefits

Summarized by Robert W. Griffith, MD
June 4, 2004

Introduction

Chronic inflammation can be present for long periods in people without them being aware of it, although there are blood tests to demonstrate it. Its presence, however, puts one at increased risk of coronary artery disease, heart attack, stroke, diabetes, and death. And it's more common in older, overweight people. A new study reported in the American Journal of Clinical Nutrition has examined the effects of diet-produced weight loss on some of these tests for chronic inflammation. Here's a summary of the publication.

What was done

Older people with a BMI of 28 or above (i.e. overweight or obese), with X-ray evidence of knee osteoarthritis, were enrolled in the study. After full baseline examinations, including blood tests, they were randomly allocated to one of four groups:

1. Diet-induced weight loss - targeting a 5% weight loss maintained throughout the 18-month study
2. Exercise - 3 days-a-week aerobic and resistance exercises for 1 hour
3. Diet-induced weight loss as in 1. plus the above exercise program
4. Control group - monthly meetings with advice on healthy lifestyle

The relevant blood tests for chronic inflammation, done at baseline, 6 months and 18 months, were: C-reactive protein (CRP), interleukin 6 (IL-6), and soluble tumor necrosis alpha factor (S-TNF-α).

What was found

Of 316 volunteers who entered the study (73% of them were women), 80% completed it satisfactorily. Those in the weight-loss group lost an average of 5.7% of their weight and reduced their BMI by 2.0 during the 18 months. In the weight-loss plus exercise group, people lost 4.4% of their baseline weight and reduced their BMI by an average of 1.5.

The effect of diet-induced weight loss on the blood tests was compared with the results in the subjects who didn't diet, i.e. groups 1 and 3 versus groups 2 and 4. There was a significant reduction in CRP levels in the weight-loss groups, whereas exercise (groups 2 and 3 versus groups 1 and 4) didn't produce a similar effect. The CRP was reduced more in men than in women.

Similarly, there was a significant reduction in IL-6 levels in the weight-loss groups, compared with the other two groups; again, there was no effect of exercise on this test. The reduction was greater in non-white than in white subjects, but men and women behaved the same in this respect.

One fraction of S-TNF-α - designated S-TNFR1 - showed a significant reduction in the weight-loss groups, although the other fractions failed to show such an effect; again, this reduction was more marked in non-whites than in whites.

What does this mean?

The results of this study show that weight loss induced by dieting, with and without an exercise program, reduced overall inflammation in older, overweight adults. This represents another benefit of weight loss - one less obvious than looking better, feeling better, and being less likely to develop high blood pressure and a heart attack, but nevertheless an important plus. It's somewhat surprising that exercise didn't have a similar effect on these tests of chronic inflammation, given its good effects on the other benefits mentioned.

An interesting finding was that an individual's weight loss didn't link closely with her CRP and IL-6 reduction; this suggests that there may be another mechanism at work. For instance, reduced energy intake might be responsible for the lowered markers for inflammation; this might be an explanation for the increased life-span seen in animals with strict dietary restriction.

Whatever its mechanism of effect, it's clear that diet-induced weight loss is a good thing; in addition to the obvious benefits on appearance, mobility, blood pressure, heart attack and cancer risk, and overall mortality, a reduction in chronic inflammation is certain to be helpful in many of these areas, as well as in others.

Source

• Diet-induced weight loss, exercise, and chronic inflammation in older, obese adults: a randomized controlled clinical trial. BJ. Nicklas, W. Ambrosius, SP. Messier,  et al., Am J Clin Nutr, 2004, vol. 79, pp. 544--551

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