Since the World Health Organization declared a global obesity epidemic in 1997, weight has played a dominant role in the conversation about health and wellness. At the intersection of physical and mental health, influenced by a heady mix of public health, sociology, economics and culture, the increase in average weight through the 21st century is a topic of passionate debate. The crux of the argument usually comes down to one fundamental question: is it possible to be fit and fat? We know that normal weight is by no means a guarantee of wellbeing, but is excess fat an absolute sign of poor health?

The media has entered the fray. In 2015 alone, the Huffington Post declared: ‘Yes, it’s possible to be obese and healthy (sort of).’ Forbes told us that healthy obesity ‘is mainly a myth’. Salon asserted that healthy obesity might not exist at all, while Slate countered: ‘It’s time to stop telling fat people to become thin.’

On one side of the conversation stands most of the medical community, emphasising that obesity is inherently unhealthy, and that managing weight is key to health. On the other are proponents of the Health at Every Size and fat-acceptance movements, who claim that obesity is not a major concern; they argue instead that health is independent of body weight, and that the ‘war on obesity’ may be more damaging than obesity itself. Further clouding the debate on whether obesity can be healthy is the recently identified ‘obesity paradox’ – the idea that obesity may actually be protective in some circumstances or populations, for instance, among the elderly or those with chronic disease.

The two sides seem to agree on only one set of facts: after decades of steady increase, the overall prevalence of obesity in the United States finally held steady between 2004 and 2012 at 35 per cent; body weight in the US today is higher than at any time in the past, but the relentless increase has at least come screeching to a halt. These facts are based on a value called the body-mass index, or BMI – derived from weight divided by height squared in metric units. BMI is a centuries-old epidemiological tool designed to assess obesity rates at the level of a population. But because it is a quick and easy way to assess a healthy body state, it was adopted as a standard diagnostic tool for individual patients. It does not consider distribution of fat, type of fat, muscle tone, age, sex, or even big bones. In spite of these flaws, healthcare professionals continue to use BMI as a guideline. A BMI of 20-25 is considered ‘normal’, and anyone larger or smaller is automatically counselled to achieve a healthier weight.

In 2009, the Lancet reported that mortality increased about 30 per cent for every five-point increase in BMI above the normal range. In their interpretation of the data, the study authors estimated that obese individuals with a BMI between 30 and 35 would see median survival reduced by 2-4 years; at a BMI of 40-45, median survival is reduced by 8-10 years. Obesity is generally understood as a risk factor for heart disease, stroke, cancer, and diabetes, as well as an increase in overall mortality. Excess body weight also increases stress on joints and internal organs.

Given these concerns, it’s easy to understand why so many people have celebrated the plateau in BMI. Unfortunately, that news has buried the lead: BMI may not be the best measure of obesity.

Your percentage of body fat and waist or abdominal circumference are far more reliable personal indicators of health outcomes than BMI. For example, central obesity, measured by waist circumference, is a more accurate determinant of personal risk and shows an even stronger correlation with poor health outcomes. Also known as visceral obesity, it is considered more dangerous than peripheral obesity (that is, in the extremities) because it indicates that the extra adipose tissue is surrounding your vital organs – practically applied, this means that a thin person with a beer gut may have far more dangerous health risks than a fit person with a high BMI. And while it is true that the average BMI in the US has remained constant at 28.8, both waist size and abdominal obesity have actually continued to increase. According to the Centers for Disease Control and Prevention, the average waist size for American women and men is currently 37.5 and 39.5, respectively.

But all of this is relevant only if you accept obesity as a legitimate health concern. Those who argue against this idea point to the Metabolically Healthy Obese (MHO) – patients who have excess weight but whose biomarkers seem to indicate the health of an individual of ideal weight. Some have argued that if an obese individual is negative for the known metabolic risks associated with increased mortality – hypertension, high fasting blood sugar, low levels of HDL (good) cholesterol and high levels of triglyceride fats in the bloodstream – then life expectancy should be the same as a normal-weight counterpart. If you can be healthy and obese, the argument goes, we should stop harping about weight altogether.

It is a tantalising hypothesis, but what does the evidence show? To find out, Australian researchers followed a group of metabolically healthy obese participants over the course of five to 10 years. Despite initially normal biomarkers, the team reported in a 2013 issue of Diabetes Care that their subjects were more likely than non-obese control patients to develop metabolic abnormalities and diabetes. One-third of the participants who began the study as metabolically-healthy obese had become ‘unhealthy’ obese by the time the study ended. Younger people and those with low central obesity (indicated by a smaller abdominal circumference) were more likely to sustain metabolically-healthy obesity over time. But for a significant percentage of participants in the study, ‘healthy obesity’ was a transient state, a precursor to the development of medical abnormalities.

Some studies indicate that the metabolically-healthy obese have no increased risk of mortality, but these have tended to follow subjects for less than a decade. Contrast that with an article published in 2015 in the Journal of the American College of Cardiology addressing the course of metabolically-healthy obesity over two decades. Researchers found that after 20 years, roughly half of those who were initially metabolically-healthy obese adults had become unhealthy obese. The lead author, Joshua Bell, explains: ‘Even obese adults who appear to be metabolically healthy have a substantially greater risk for developing type 2 diabetes and cardiovascular disease compared with healthy, normal-weight adults. There is also a strong tendency for healthy obese adults to progress to unhealthy obesity (the highest risk group) over time. Excess fat is itself a metabolic dysfunction, with strong links to insulin resistance. Some obese adults may have a more favourable fat distribution and are considered relatively healthy, but the number of obese adults who can maintain an optimal balance of fat stores in the long-term is not high.’

Americans seem to have access to a Weight Watchers in every town centre and face a steady slew of Jenny Craig ads on TV

Others argue that we may even be using the wrong metabolic lab ranges for the healthy obese. A 2014 study in the Journal of the American College of Cardiology lowered the diagnostic bar by looking specifically at coronary artery calcification in asymptomatic and metabolically-normal individuals of all weights. Obese participants had higher rates of subclinical coronary artery disease than their normal-weight counterparts. By relying on the same normal ranges for obese and normal-weight individuals, we may be missing early signs of disease.

It is undeniable that healthy obesity is far better for you than unhealthy obesity. The ‘healthy’ obese live longer, get sick less often, and are more physically active than their unhealthy-obese counterparts. No one disputes that it is better for you to have low blood pressure and normal blood glucose levels; the question, fundamentally, is whether obese individuals with normal lab values are as healthy as normal-weight individuals with comparable values. The answer, at least according to the majority of biomedical research, is that they are not.

And even if the metabolically-healthy obese had the same quality and quantity of life as their normal weight counterparts, they account for a minority of obese patients. The same can be said of the obese elderly and chronically ill who benefit from the ‘obesity paradox’, in which extra weight may be protective. These individuals are anomalies. Public health cannot be framed around the outliers; rather, the focus must be on the majority. And the truth is that for the majority of obese individuals, excess body mass is a costly health concern.

The high price of obesity goes well beyond personal health. As rates of obesity climb, so does health care spending. By some estimates, 20 per cent of health care costs in the United States are attributed to obesity. A recent study by the Brookings Institution in Washington, DC, suggested that the societal cost of obesity could add up to trillions.

In the face of the growing epidemic, the medical establishment and a bankable diet industry have jumped on to the weight-loss bandwagon. Americans seem to have access to a Weight Watchers in every town centre and face a steady slew of Jenny Craig ads on TV, yet the problem remains entrenched.

On the surface, the solution appears simple: health care professionals could just tell people to eat less and exercise more; stop buying McDonald’s and cook some vegetables. Get away from the television and go for a run outside. Have one potato chip instead of five.

These are obvious (and, in some circumstances, valid) recommendations. Unless obesity is secondary to another medical issue, reducing calorie intake and increasing calorie expenditure should lead to weight loss — that arithmetic is simple and verifiable.

Some in the Health at Every Size movement argue that weight is not a modifiable factor, and that we should no longer consider it changeable

But these suggestions are easier said than done. A recent study published in the American Journal of Public Health tracked the weight of more than 270,000 adult men and women between 2004 and 2014. Researchers found that only 0.5 per cent of obese men and 0.8 per cent of obese women were able to attain and maintain a normal body weight. They concluded that once an individual becomes obese, it is very difficult to return to a healthy body weight. Indeed, persistent dieters stuck in a pattern of weight cycling, or ‘yo-yo dieting’, might be altering their hormones and altering their sense of hunger, some research suggests.

Furthermore, even if weight loss works, it is important to consider what kind of weight an individual is losing: fat loss decreases mortality but loss of lean muscle weight may have the opposite effect. And how is that weight being lost? A person could technically lose weight on a steady diet of pizza and french fries, but this would do little to improve overall health.

Citing the myriad studies suggesting that weight loss is often unsustainable or meaningless, some in the Health at Every Size movement argue that weight is not a modifiable factor, and that we should no longer consider it changeable. More reasonably, what it means is that we have no real way of managing weight yet, not that our BMI is part of our manifest destiny. Nevertheless, given these known challenges, and in light of the cultural and psychological issues at play, some question whether weight should be a part of the health conversation at all.

Americans are raising a generation of adults who have been overweight and obese since childhood. They carry with them not only the physical effects of obesity but, for some, a lifetime of discrimination and abuse related to their weight. And there is no apparent end in sight. The California psychologist Deb Burgard, an expert in the treatment of eating disorders, argues that the major health risk for the obese comes not from excess adipose tissue but from the treatment that the overweight often receive – emotional abuse, delivered by everyone, from well-meaning friends and family, to doctors and strangers on the street.

Our cultural response to obesity is the spectacular failure of body-shaming and stigmatising weight, a cruel and dehumanising attitude that reduces people to their body size. To the people who shame others under the guise of helping: if fat-shaming children or stigmatising overweight adults worked, the prevalence of obesity would have dropped years ago. Issues of health are between patients and health care providers. Weight discrimination does not serve to increase weight loss or shame people into thinness, and may, in fact, cause people to gain more weight. Any programme focused on healthy behaviours and weight must emphasise the importance of loving and respecting the body you have.

‘So we have to ask: is there value in focusing on weight at all?’ Burgard said. ‘Even if the data show a disparity between the health of people at a higher and lower weight, why do we define this as a risk factor located in the body – rather than evidence of a health disparity due to weight bias, economic inequality, racism, lack of access to competent health care, etc?’

She speaks with a conviction and passion that come from years of experience working with individuals who are often silenced and judged only on the basis of their appearance. Her point sticks, blunted by data that do, in fact, show a health disparity between people of different weights – and on the other hand, strengthened by research showing a strong connection between chronic stress and health.

So I reach for middle ground. Can we both be right? Can’t we recognise obesity simultaneously as a risk factor located in the body and a magnet for social stress? Obesity is more prevalent in minority populations, those of low socioeconomic status, and other vulnerable groups. These vulnerabilities reflect the fact that, for many, obesity comes down to lifestyle and surroundings. People who live close to a supermarket that sells fresh foods (and have the space and time to prepare it) are more likely to have a normal BMI; proximity to convenience stores has the opposite effect. People who live in ‘walkable’ neighbourhoods with accessible, well-maintained sidewalks have lower BMIs and rates of obesity. Living next to a highway or on a street without a sidewalk is associated with increased levels of obesity. Access to a safe outside space increases physical activity. These are very basic ideas – it’s not rocket science.

Diet and exercise will both play a role in the fight against obesity, though people keep debating which matters more. In March of this year, there was an enormous amount of coverage given to an editorial in the British Journal of Sports Medicine that declared: ‘You cannot outrun a bad diet.’ The authors placed the blame for the obesity epidemic squarely on the shoulders of the food industry and unhealthy diets. The article was temporarily retracted before being reissued with a stated conflict of interest; the authors had declined to acknowledge that they were both involved in the diet industry. But that does not mean it was entirely wrong. A bad diet – high in salt, trans fats and sugar — cannot be outrun, no matter what Coca Cola wants you to believe. Although it is possible to maintain a healthy weight on a high-fat diet, society’s tendency to ‘super-size’ constantly challenges such restraint. And even if you could keep serving size down, being thin doesn’t exempt you from the effects of poor nutrition.

You can be thin and still have the same health risks as someone who is obese

A healthy diet may not make up for a lack of physical activity, either. A 2012 study in Obesity found that high levels of cardiorespiratory fitness can help counteract some of the dangerous effects of increased adiposity, thereby decreasing cancer mortality. Increased physical activity is also associated with improved quality of life, independent of weight and body size. The obesity epidemic in the US can be blamed on both Americans’ relatively sedentary lives and their unhealthy diets. No need to pick just one.

‘I’m not sure why the question always focuses on whether obesity is sustainable or not, when the real issue should be: “This is where we’re at now. How can we promote health for everybody?”’ says Harriet Brown, an associate journalism professor at Syracuse University in New York State and the author of Body of Truth, a book about our cultural obsession with weight. ‘Even if you could show in theory that it’s not healthy to be obese in the long term, it still doesn’t mean that getting thin is the solution to everything.’

She is absolutely correct. Getting thin isn’t a panacea. In fact, you can be thin and still have the same health risks as someone who is obese. People who fall into this category eat unhealthily, fail to exercise, and have abnormal lab values, but are blessed with a fast metabolism or helpful genetics, and effortlessly maintain an optimal BMI. The ‘thin obese’ – metabolically-abnormal but optimal-weight individuals – are seldom involved in the discussion, but they should be. Thin people can be unhealthy too, but that doesn’t mean we should ignore weight.

Somewhere along the line, someone made the decision to wage our health war on fat. This was an unfortunate choice because, in reality, health is not only about size – it’s about nutrition and physical activity. The term ‘obesity epidemic’ is ubiquitous and certainly makes for a catchier headline than ‘a high prevalence of unhealthy behaviours associated with an increased national body mass index’, but it misses a key point in our discussion about health. There is an epidemic of unhealthy behaviours, and an elevated BMI is simply the most obvious marker.

The scientific research largely supports the medical community’s perspective – healthy obesity is unlikely to be maintained long-term and excess adipose tissue contributes to many dangerous medical conditions. The history of the obesity epidemic, however, lends some support to the challengers: the current war on obesity – which frequently focuses on weight loss as treatment – is a failed effort.

the psychological impacts of discrimination are profound, but professionals cannot deny a major medical issue because society is cruel

The solution is not to reframe obesity as superfluous, but rather to seek a new approach to a decades-old problem. We need to focus on treating and preventing obesity, not only through intensive weight-loss regimes for individuals, but by attacking the root cause: the behaviours that are damaging to your health, no matter what your size.

Deb Burgard cautions against what she calls the ‘harmful paradigm’ that obesity is a health condition. We are ‘sending people down a road pursuing weight loss when it is very likely to fail and is emotionally abusive’, and when ‘the person will have to experience weight regain’, she says. ‘Weight gain is our body healing from that insult of an unnatural catabolic state.’

I counter that, just because we do not have an effective way of maintaining long-term weight loss, does not mean we should pretend it is not a health goal. Ignoring obesity as a health risk is irresponsible – the psychological impacts of fat shaming and discrimination are profound, but health care professionals cannot deny a major medical issue because society is cruel.

Recent findings suggest that more than one-third of obese Britons classify themselves as merely ‘overweight’. It helps no one – not the doctors, nor the patients, nor their families – when we allow people to delude themselves, and to redefine the relationship between weight and health. We may have reached a new normal, but that doesn’t change the optimum. On the other hand, reducing all of health to a mathematical formula of ‘weight over height squared’ is absurd.

So where does that leave us? As a culture, we must embrace different body types and accept that a person’s weight and waist circumference are not a commentary on their worth. Governments and societies must address the social deficits that contribute to obesity – poverty, food deserts (districts with no ready access to fresh, healthy and affordable food) and lack of exercise spaces – to empower people to take care of their own health. In the long run, the medical community must find ways to help people stay healthy through lifestyle fixes, medical interventions, or both, regardless of their size.