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Arguments Against Obesity As A Disease #2: Inconsistent Relationship Between Body Fat And Health



scatterplot variationYesterday, in my brief series on the pros and cons of calling obesity a chronic disease, I addressed the issue of BMI as a poor definition of obesity (understood here as “abnormal or excess body fat that affects health”).

Another common argument I hear from those who do not support the notion of obesity as a chronic disease, is that there is an inconsistent relationship between body fat and health.

This is no doubt the case.

Indeed, whether or not your body fat affects your health depends on a range of factors – from your genetic predisposition to certain “complications” to the “nature” of your body fat, factors that cannot be captured or assessed by simply stepping on a scale.

Often, this variability in the relationship between excess body fat and its impact on health, is used to argue against a “causal relationship” between the two. This argument is often presented along the lines of, “If obesity is a disease, how come I don’t have diabetes?”.

Where the direct impact of excess body fat on health should be evident,  is when the amount of excess fat poses a direct “mechanical” problem that impedes physical functioning. This impact, however, is likely to vary from one person to the next.

A good example of this, is obstructive sleep apnea, where an increase in pharyngeal fat deposition is directly and causally related to the airway obstruction. The causal relationship of pharyngeal fat and the symptoms is directly evident by improvement in symptoms following surgical removal of the excess fat (an operation that is seldom undertaken due to possible complications and redeposition of fat). There is also substantial evidence that significant weight loss (such as induced by bariatric surgery) results in a dramatic improvement in apnea/hypopnea index and sometimes even in complete resolution of the problem.

Yet, not everyone with excess weight develops obstructive sleep apnea. One of the factors that explains this variation, is the anatomical dimension of the pharyngeal space, which varies significantly from one person to the next. So, just how much excess fat in the neck region results in symptoms (if any) will necessarily be highly variable. This is not an argument against the relationship between excess body fat and obstructive sleep apnea, it is just the expected variation between individuals that is evident in many diseases.

Likewise, when the amount of excess fat impairs the body’s capacity to perform essential functions (from mobility to performing simple tasks of personal hygiene), it is not a matter of “opinion” whether obesity is the cause of the problem. There is however variation in how people perceive these “limitations” as limitations, which explains why there may well be considerable variation and inconsistncy in the objective vs. subjective impact of excess body fat on physical functioning.

The relationship between excess or abnormal body fat and metabolic problems is perhaps less easy to understand but biologically as evident. Thus, there is an almost linear relationship between the presence of visceral fat and the risk for diabetes. This risk is greatly amplified in individuals with a family history of diabetes. Thus, the amount of visceral fat necessary to impair glucose homeostasis varies from one person to the next and depends on other factors including beta-cell capacity to produce insulin.

Note that I said “visceral” fat rather than body fat. This is because subcutaneous fat appears to have little (if any) effect on diabetes risk and may even be protective. Thus, it is not the total amount of body fat but rather its location and biological function that determines its effect on metabolic disease. Therefor, it is easy to see why there would be an inconsistent relationship between body fat (or even cruder measures such as BMI) and risk for diabetes.

There is also considerable evidence that the metabolic effects of excess body fat can be substantially modified by cardiorespiratory fitness (“fat but fit” vs. “lean but unfit”). This is in part because although exercise does not necessarily reduce overall body fat, it appears to have a very specific effect on visceral fat. Moreover, increased muscle mass appears to neutralise some of the metabolic consequences of excess body fat. While all of this is true, it does not negate the fact that visceral fat remains one of the key drivers of metabolic risk, even if there remains substantial variations in how much this risk translates into severe health problems for a given individual.

Even more difficult to understand is the relationship between excess body fat and its impact on mental health. This is particularly difficult because the emotional impact of excess weight also very much depends on the social context. Clearly, the impact of body shape and size on health and well-being will be different across societies that are more or less accepting of larger bodies.

Nevertheless, social context does not obviate the fact that excess body fat can significantly affect mental health in a given individual living in a given societal context. Indeed, there are numerous instances where the “environment” defines or amplifies the effect of biological variations on health. The most extreme example I can think of would be a peanut allergy. While this may have no impact whatsoever on the health of someone living in a nut-free environment, it can be fatal to someone living in a society where peanuts are found in almost every dish (e.g. Thailand).

Thus, despite variation in the relationship between body fat% or BMI and health, including the fact that this relationship may vary depending on societal or environmental context, is not really an argument against obesity as a disease.

All that matters for the definition of obesity as a chronic disease is whether or not a person’s physical, emotional or functional health is affected by excess or abnormal body fat – that this varies between individuals is only to be expected.

Indeed, the impact of many diseases on health can be substantially modified by environmental factors or social context (e.g. diabetes, heart disease, depression) – this does not prevent us from calling them diseases.

Similarly, the actual impact of many disease on an individual’s health can vary widely between individuals – this does not make them more or less of a disease.

In fact, I would claim that there is an “inconsistent” relationship between virtually every disease and morbidity and mortality at the level of the individual – from depression to cancer, from pneumonia to Alzheimer’s.

Thus, inconsistencies in the relationship between body fat and its impact on health across a population, does not speak against the notion that when excess or abnormal body fat negatively affects a given individual’s health, it should be considered a chronic disease.

@DrSharma
Berlin, Germany

 

3 Comments

  1. Yes, me again. 🙂

    Although obesity is a risk factor for obstructive obesity, isn’t there a significant percentage of people, especially men, of all weights, who develop it due to a “lantern jaw”? Anecdotally, I know a bunch of thin men who have developed it. Some have fixed the issue through jaw surgery. (Ow.)

    Although of course exercise is the best thing for metabolic fitness for everyone, isn’t part of the reason that it can help reduce the risk of T2DM that it improves insulin reception, which in turn reduces insulin resistance, which can reduce the risk of developing the disease?

    And, again, probably preaching to the choir: Sure, societal environment can greatly affect the mental health of fat people, such as the work of the Rudd Center has shown, and may perpetuate and/or exacerbate the issue, such as studies that have found links to bullying with extra weight.

    One of the base tenets of the HAES movement I like is the idea that people need to like themselves, because those that do are more likely to want to care about their health and develop healthier habits. Depression and self-loathing can cause you to more easily give up or think, Why bother?

    Yet this is perceived to be the same thing as, “If you tell fat people they can like themselves, you’re telling them that it’s ok to be fat, and that’s wrong.”

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  2. Nobody with diabetes, heart disease or depression is completely healthy. If they were, they would not have gone looking for a diagnosis. In contrast, many people with BMIs over 30 feel (and are) absolutely fine. Their quality of life and lifespans are / will be completely normal. They have not gone looking for a diagnosis. The diagnosis has been forced on them based on their height/weight ratio. How is that a disease?

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    • This is explained in my previous post – obesity is only a disease when your body fat affects your health – if it doesn’t, you don’t have the disease, if it does, you’re not healthy – it’s really that simple.

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