Most of us think obesity is bad. We tend to associate it with negative lifestyle habits, diabetes, heart disease and other chronic disorders.
The recent obesity epidemic has been highlighted by the media, health professionals and many scientists.
In the general population, obesity is associated with increased mortality and risk for cardiovascular disease. Weight reduction is considered a priority for those who are overweight or obese, regardless of whether they are otherwise healthy or have an underlying chronic disease.
However, obesity has followed the human being for thousands of years, probably due to evolutionary reasons. Individuals who are able to store energy are more likely to survive periods of famine.
We therefore might ask ourselves whether obesity is always bad. Could there be health benefits associated with obesity? Are there conditions in which it is better to be overweight or obese, rather than normal weight?
Obese people have a higher frequency of cardiovascular risk factors such as high blood pressure, lipid disorders, and diabetes. Therefore, these individuals are at higher risk for cardiovascular disease and death.
Weight reduction is usually associated with improved risk profile. Therefore, guidelines on primary prevention of cardiovascular disease generally recommend weight loss for overweight or obese individuals. These recommendations have also been extended to patients with known cardiovascular disease.
Obese or overweight people who have suffered a heart attack or a stroke are almost always recommended to lose weight in order to improve health. But, it appears that the scientific support for such an approach is weak. In fact, some epidemiological studies indicate that obesity may be protective in disease settings such as diabetes, kidney failure, heart failure, atrial fibrillation and coronary artery disease. This has lead scientists to propose a phenomenon termed the obesity paradox.
Earlier this month a Swedish study linking the obesity paradox to patients with acute coronary syndrome was published in the European Heart Journal. The Swedish scientists extracted data from a large registry of Swedish patients undergoing coronary angiography.
Patients with at least one significant narrowing of a coronary artery were selected for analysis. Patients were divided into nine different BMI categories. Mortality in these subgroups was compared during a maximum of three years follow-up.
The underweight group (BMI > 18.5) had the highest mortality. Patients with modest overweight (BMI 26.5 – 28) had the lowest risk for mortality. When BMI was studied as a continuous variable, the adjusted risk for mortality decreased with increasing BMI up to 35 and then increased, indicating a U-shaped curve. Although this is an observational study, the authors consider their data to substantially strengthen the concept of an obesity paradox.
Let us look at what an obesity paradox implies. If you are a healthy obese person, epidemiological data indicates that your risk of developing lipid problems, type – 2 diabetes, high blood pressure and heart disease are increased. Furthermore, weight reduction will likely reduce your risk. However, if you have a chronic disease, such as coronary artery disease, kidney failure, heart failure or diabetes, studies indicate that being overweight or obese is associated with a better survival than if you are normal weight or underweight. However, keep in mind that the U-shape of the curve implies that with severe obesity (BMI > 35), prognosis becomes worse.
Does an obesity paradox mean that it is wrong to recommend people with chronic disease to lose weight? We don’t know that, because a hidden protective factor in obese individuals does not necessarily have to be the obesity in itself. In fact, such a factor might be something else, something that just happens to travel with obesity.
However, recommending weight loss for people with established chronic disease seems to lack scientific support. Despite that, the European Society of Cardiology and the American College of Cardiology/American Heart Association recommend a BMI of <25 in their guidelines of secondary prevention strategies. This recommendation may need reevaluation.
Experts still debate whether there is an obesity paradox or not. Possibly, obese patients are younger and healthier when diagnosed with their chronic disease. Thus, they could be at an earlier stage of their disease and therefore have a better prognosis.
One possible mechanism behind a protective effect of obesity could be related to the catabolic state that develops in many chronic diseases. In such conditions, the body needs more energy than under normal condition, and a caloric reserve could be helpful. If caloric reserve is limited, there is risk for malnutrition, although body weight is normal.
Genetic factors may also be involved. It is possible that thin people who develop diabetes or heart disease may have a stronger genetic predisposition than those who are obese and develop the same disease. Thus, thin people may develop a more aggressive underlying disease due to genetic reasons.
Most of the studies on the obesity paradox have relied on BMI. However, BMI does not tell the whole story when it comes to obesity. For example, BMI does not take into account factors such as metabolic function and muscle mass. BMI does not reflect physical fitness. In fact, it may be healthier to be fat and fit, than thin and unfit.
Furthermore, there exists a phenomenon called “normal weight obesity” or “metabolically obese normal weight”. Patients with “normal weight obesity” have normal body weight but metabolic abnormalities of the same kind as seen in obese people, such as insulin resistance and high levels of triglycerides. To make things even more complicated, some obese people do not have the metabolic abnormalities generally associated with obesity.
Dr. Robert Lustig , a pediatric endocrinologist at The University of California, has suggested that obesity in itself is not the main problem. Hypertension, insulin resistance, type-2 diabetes, lipid problems and heart disease are not caused by the obesity itself, “although obesity travels with those diseases”.
Obesity might just be a marker for a phenomenon generally termed the metabolic syndrome. In fact almost 20 percent of obese people have a normal cellular metabolism and a normal life expectancy. On the other hand, about 40 percent of people with normal weight have metabolic disturbances that may reduce their life expectancy. According to professor Lustig “nobody dies of the obesity per se….they die of the diseases that come from the metabolic dysfunction”.
Therefore, using BMI as a marker of obesity and metabolic dysfunction may be misleading. Possibly the obesity paradox is not a paradox at all. It might be due to an oversimplification of the relationship between BMI, metabolic dysfunction and disorders that travel with obesity, such as high blood pressure, insulin resistance, lipid problems and nonalcoholic fatty liver disease. Using BMI as a sole marker for obesity and metabolic dysfunction therefore needs reevaluation.
However, if the obesity paradox is a real phenomenon, we have to reconsider our views on overweight and obesity in people with chronic disease. In many cases we might even have to recommend against weight loss.