Can You Be Healthy at Any Size?

Would it surprise you to learn that Americans have been debating "healthy at any size" for nearly 50 years¹? During this half-century of weight-related dissension, both sides amassed substantial evidence in support of their positions. Yet, on a societal level, we somehow appear to remain as far from a consensus as ever. Is a resolution even possible?

Let's put the evidence to the test, with you in the roles of judge and jury. Specifically, let's examine arguably the three strongest science-based arguments for and against the "healthy at any size" concept and let you decide which is more persuasive.

Firstly, identify which way you may already be leaning on this complicated topic. Which of the following statements strikes you as most true?

1). Research unequivocally shows that overweight and obesity are important risk factors for the top five leading causes of death in the U.S.— cardiovascular diseases, cancer, COVID-19, dementia, and diabetes. For this reason, "healthy at any size" is a social movement, not science. Universal screening and treatment of overweight and obesity in both youth and adult populations are vital despite some adverse consequences that may occur. The public health consequences of excess weight are simply too important to ignore.

2). Research clearly shows that body weight and body mass index (BMI) values are poor indicators of individual health. Worse, when weight and BMI are used as a proxy for a person's health status, numerous and substantial harms can result. These include those associated with mental health and eating disorders, discrimination and bias, and the mass prescription of weight loss treatments that are often unnecessary and usually ineffective. The cure is worse than the disease.

Now that we know on which side of the debate you may already be leaning, let's examine the evidence to learn whether it reinforces or changes your initial position.

Arguments against and for healthy at any size.

Argument 1: Body-fat and health.

Against: Excess body-fat is demonstrably unhealthy. The higher a person's BMI, the higher their risk of heart disease, stroke, diabetes, dementia, and 13 different forms of cancer^2. Further, when people with obesity (BMI≥30) are compared to people with normal BMI values (BMI between 18.5 and 24.9), the former have much higher rates of metabolic diseases. Lastly, clinical trials demonstrate that losing body-fat lowers the risk of all these health conditions, indicating a causal relationship between excess body-fat and impaired health.

For: There are two simple arguments that defeat the premise that body-fat is inherently unhealthy. The first is biological sex differences. Biological women, on average, have significantly higher body-fat levels than biological men. If body-fat was unhealthy, women should experience higher rates, for example, of cardiovascular disease than men. Yet the reverse is true. The second argument is a rare condition called lipodystrophy (a type of disease affecting body-fat tissue). People with lipodystrophy usually have excessively low levels of body-fat yet have excessively high rates of metabolic diseases. Instead of obesity or body-fat, what the science really shows is unhealthy is visceral fat (that is, fat in the liver, pancreas, muscles, and other internal organs)³, not the benign subcutaneous fat mostly captured in the mirror and by BMI values.

Argument 2: Body-fat measurement.

For: The single biggest problem with using body-fat to determine a person's health is how it is usually measured. The BMI is a crude tool designed for population-level estimation. But it was nevertheless adopted for individual-level body-fat estimation in healthcare settings despite many empirically demonstrated shortcomings. Meta-analyses analyzing the accuracy of the BMI in a clinical setting, for example⁴, show that it misses fully 50 percent (half) of patients with excess body-fat as assessed by gold-standard body composition measures. BMI values are known to be confounded by sex, age, ethnicity, and body composition—arguing for nuance—yet BMI values are instead routinely used to make black-and-white diagnoses. BMI supporters argue that it is a convenient screening measure and that we should accept its limitations. Yet, for nearly all patients, BMI is the only tool their providers use to determine a patient's body-fat levels. Based on the flaws of the BMI, it is no wonder that up to a third of patients with BMI-defined obesity are found to be metabolically healthy.

Against: The limitations of the BMI are real and important, but they are not an argument against measuring and treating excess body-fat. Quite the opposite. For all its imperfections, the value of the BMI for detecting excess body-fat and predicting health risks is supported by decades of research, making it one of the most cost-effective measures in all of medicine⁵. The BMI likewise spares patients the time, costs, and even radiation exposure involved with more precise bodyfat tests (such as DEXA scans). The fact that providers can easily estimate body-fat levels using the BMI to offer evidence-based treatments is of great benefit to most patients. Further, studies show that when more precise measures of body-fat are used, they even more strongly predict health risk⁶. Criticism of the BMI, therefore, is a red herring: body-fat levels, measured crudely with the BMI or precisely with imaging, are important risk factors for health outcomes.

Argument 3: Bodyfat and social consequences

Against: Screening for and treating overweight and obesity are fundamentally the same as for other medical conditions. For example, screening for and treating diabetes and cancer are also standard practice. But like weight, both can produce stress, and stigma and involve unpleasant treatments. Yet few would argue we should ignore diabetes and cancer. Providers would of course prefer that there were no downsides to addressing weight-related concerns. However, they also realize that nearly all healthcare involves tradeoffs of benefits and risks. The benefits of weight-related care, for most people, exceed the risks.

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For: As the prevalence of overweight and obesity has risen in the U.S., so have the social consequences. With >40 percent of U.S. adults now meeting criteria for obesity based on their BMI, and nearly 20 percent of youth, this means that millions of people are exposed to discrimination in their schools, workplaces, and healthcare settings, stigma in their careers and relationships, and vulnerability to eating disorders and other weight-related mental health conditions⁵. For this reason, it is more important than ever to de-emphasize the focus on weight loss and BMI and shift the conversation, both inside and outside of healthcare settings, towards the promotion of health and quality of life.

Verdict: The debate over healthy at any size may rage eternal. By understanding the arguments on each side, however, you may appreciate that this debate serves the purposes of 1) increasing awareness of the potential downsides of weight-related care; and 2) simultaneously warning us against the risk of throwing the baby out with the bathwater.