How much truth is there to the obesity paradox?

The term “obesity paradox” was first used in a medical publication back in 2002 in which US researchers at the Cardiovascular Research Institute in Washington DC described their observations of patients with coronary heart disease. Contrary to their initial assumptions, they came to the conclusion that patients with excess weight and obesity exhibited a much lower risk of dying within one year following a vascular intervention than those patients of a normal weight. 

In the years that followed, similar results were reproduced in other studies involving patients with heart conditions, metabolic disorders and tumours. As such, these observations contradict the established school of thought that excess weight constitutes a key risk factor in the development of a variety of diseases and that it adversely impacts the progression of such diseases. 

Proponents of the paradox argue, for example, that people with overweight have greater energy reserves, which may be beneficial when fighting debilitating conditions such as tumours. It is also thought that higher blood lipid levels can have a protective effect, as they can bind and neutralise bacterial toxins and also promote the synthesis of anti-inflammatory steroid hormones. Furthermore, fat deposits are particularly useful in protecting older people against broken bones due to falls and can thus reduce their risk of mortality. An additional argument is that people with excess weight receive intensive medical care and monitoring at an early stage, which could improve their prognosis compared to that of patients with a normal weight. 

Critics see the obesity paradox as the result of distortions and misinterpretations. They claim that it has mainly been shown in observational studies in which conclusions were drawn about the participants’ risk of disease, their disease progression and their mortality on the basis of data gathered about their level of health and lifestyle. In such studies, however, it is possible to confuse cause and effect. Weight loss and cachexia are often found in the advanced stages of many illnesses. At the start of an observational study, it may be the case that patients exhibit a normal weight because they have already experienced disease-related weight loss. The survival advantage of people with overweight may therefore be based on the fact that, on average, they are healthier than those people with normal weight/underweight at the time of the data being gathered. Likewise, the body mass index is frequently used to measure the person's nutritional condition. But as it is based solely on body weight and height, it provides imprecise information in this regard. It does not say anything about the makeup of the body. A healthy individual with high muscle mass and a normal body fat percentage may be categorised as overweight in terms of BMI, whereas a person who is already experiencing muscle atrophy, but who has a high body fat percentage, may be classed as having a normal weight.

An increasing number of studies in recent years have refuted the obesity paradox. This is particularly true for studies that do not just consider BMI, but that also factor in other criteria for assessing state of nutrition, such as waist circumference and the waist-to-hip ratio. Such studies indicate that overweight and obesity significantly increase the risk of disease. Some studies have also shown that patients with overweight do not exhibit a survival advantage, but that, on average, they contract disease earlier than people with a normal weight.

We now know that no general protective effect can be attributed to overweight, even though it may offer such an effect in individual cases. Mild excess weight, for instance, may offer benefits in tumour patients about to undergo chemotherapy, as it may offset the weight loss often caused by the treatment programme. 

Generally speaking, however, normal weight is desirable in order to reduce personal risk of disease. Leading specialist bodies usually state normal weight as the aim in the event of illness, but advise against extreme weight loss in cases of overweight and obesity. 

To sum up, we now know that the obesity paradox only makes sense on the surface and should be regarded as debunked.