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Update on Obesity: Partial Answers to Heavy Questions

Dr. Rosen brings us: Update on Obesity: Partial Answers to Heavy Questions

When I speak with obese patients in my clinic, I spend a lot of time talking about diet, exercise, and the risks and benefits of drug therapy or surgery. In the end, patients have to decide for themselves which path to pursue, based on personal preferences, financial resources, and cultural mores. My job, I believe, is to present the available data in a digestible manner, so that informed choices can be made. For many of the most pressing questions about obesity, however, there is simply not enough data available to help patients make informed decisions. Some help arrived recently, however, in the form of two new studies just published in the New England Journal of Medicine.

The first of these studies addresses the notion that it is OK to be heavy—as long as you are physically fit. Many people have noted that body mass index, or BMI, is a very imprecise way of estimating “fatness.” If you take a bunch of people with the same height and weight, and thus the same BMI, you will find very different amounts of muscle and fat. This observation led to studies showing that some men with a high BMI but who were very physically fit had the same risk of death as lean men. This fueled the “fat but fit” movement, which encouraged people to focus less on losing weight and more on getting sufficient exercise.

Researchers at the Harvard School of Public Health decided to take a look at the “fat but fit” hypothesis, using data from the a very large community health study known as Nurses Health Study. This study has compiled detailed information on the health and well being of around 120,000 nurses since 1976, and it represents one of the most detailed and best validated sources of information we have on many different aspects of women’s health. Researchers found that the lowest risk of death was seen in women who were lean and who reported a high degree of physical activity. Women who were lean but who were physically inactive had about a 50% increase in the risk of premature death. A similar increased risk was seen in women who were overweight but who reported a high degree of physical activity. The highest risk, as you might predict, was seen in women who were both overweight and physically inactive, who were two-and-a-half times as likely to die as lean, physically fit women.
When the news of this result hit the popular press, the headlines read “physical fitness is no substitute for leanness,” or “fat but fit is not enough—patients need to lose weight as well as keep active.” While not inaccurate, these blurbs only tell half the story. The results of this study say that exercise and leanness have independent effects on mortality, which means that it’s also true that it’s not enough to be skinny; people need to exercise in order to get the maximum health benefit.

This study had several limitations, such as using self-reported measures of weight and physical activity. Even in an anonymous survey, people may tend to underestimate their weight and overestimate the amount of time they spend exercising. This would tend to make exercise look less beneficial, and could confound the current results. Putting that caveat aside for a moment, it still looks likely that exercise and weight loss are both required for maximum health benefit.

Ok, you say, I can go to the gym a little more often, but how am I going to lose a significant amount of weight? Exercise itself will help a little, as will dieting. A few patients can squeak some benefit out of one of the existing anti-obesity medications. In the best case scenario, these avenues typically result in 5-10% weight loss, which means that a 300 lb. person might still weigh 270 lbs. after a rigorous program of weight loss. Of course, that most folks don’t achieve a sustainable 5-10% weight loss, and this doesn’t take into account the side effects seen with current weight loss drugs.

For most severely overweight people, surgery remains the only viable option at present for truly significant weight loss. This recognition has led to an explosion in the number of gastric surgery operations in the U.S., up to about 100,000 in 2003 alone. Despite the increasing popularity of this approach, little information exists about either its long-term safety or its benefits.

Now, new data are available from Swedish researchers who have followed a group of obese patients for ten years after their gastric surgery. While still significantly obese, these patients on average weighed a bit less than the typical American patient for whom such surgery is recommended. A variety of operations were employed, including gastric bypass, gastric banding, and vertical gastroplasty. The results show that two years after having surgery, patients had lost an average of 23% of their body weight, but by ten years most had regained some weight and were now down only 16% from their pre-operative weight. The best results were seen with the most invasive forms of surgery, and the fact that many people still regain some weight is disappointing. Still, these results are better than those seen with other weight loss remedies, which typically provide much lower benefit for shorter durations.

In addition to weight loss, surgery provided significant benefits in terms of a reduced incidence of diabetes, and lower blood pressure, triglycerides, and uric acid levels, although cholesterol was curiously unaffected. As expected, the beneficial effect on these parameters was greater at two years than at ten, probably reflecting the fact that some of the weight had been regained at the later time point.

So, why don’t we universally recommend weight-loss surgery? Well, for one thing, there is still a fairly high rate of complications in the immediate post-operative period, including respiratory problems, infections, blood clots, and even death. In the Swedish study, the post-operative mortality was fairly low at 0.25%, but this reflects the fact that they used highly experienced obesity surgeons in specialty centers, and even then there was a death rate of one in four hundred. That’s pretty high considering that most of these patients were reasonably healthy (albeit obese) ate the time of their surgery. It has to be borne in mind that even though we know that obese people have a higher risk of premature death than lean folks, no conclusive study has yet shown that any intervention for obesity (including surgery) can reduce that risk. That’s a pretty serious caveat, and should give patients and physicians who are considering this option pause.

So what can we conclude from all this? Well, I would say that while exercise is not likely to cause significant weight loss by itself, it does contribute to a reduced risk of death, and should be prescribed for all obese patients in whom it is not specifically contraindicated. While physical fitness does not substitute for leanness, neither does leanness substitute for physical fitness, and increasing activity is something almost everyone can do right now. For those with significantly elevated BMI, it is reasonable to consider gastric surgery, which is still the only effective method to profoundly reduce body weight over time. It is reasonable to expect that such surgery will help with insulin resistance, hypertension, and some elevated blood lipids, although it is not formally proven yet that any of that will help an obese person live longer. As you can tell, there’s still a lot yet to learn.

Reference:
Sjostrom L, Lindroos AK, Peltonen M, Torgerson J, Bouchard C, Carlsson B, Dahlgren S, Larsson B, Narbro K, Sjostrom CD, Sullivan M, Wedel H. Lifestyle, diabetes, and cardiovascular risk factors 10 years after bariatric surgery. Swedish Obese Subjects Study Scientific Group. New England Journal of Medicine. 2004; 351(26):2683-93.
Hu FB, Willett WC, Li T, Stampfer MJ, Colditz GA, Manson JE. Adiposity as compared with physical activity in predicting mortality among women. New England Journal of Medicine 2004; 351(26):2694-703.