Is it possible to be “fat but fit”? The debate is making headlines yet again, with supporters of body positivity trends welcoming any new suggestion that excess body fat may not be harmful. For evidence, they typically point to studies which suggest people with obesity can be “metabolically healthy,” with no signs of high blood sugar, high cholesterol, type-2 diabetes or heart disease.

In October 2023, at the annual meeting of the European Association for the Study of Diabetes, Professor Matthias Blüher, a leading expert in obesity at the University of Leipzig and the Helmholtz Centre in Munich, referenced data that suggests a large volume of people may have this kind of “metabolically healthy obesity.” His comments triggered a range of gleeful newspaper columns celebrating the news that you can be “fat but fit”.

But few journalists reported that Professor Blüher also pointed to other data which showed that the so-called “healthy obese” still have a higher risk of ill health, including a 50% greater risk of heart disease. “Even in the absence of other cardiometabolic risk factors, increased fat mass and adipose tissue dysfunction contribute to a higher risk of Type 2 diabetes and cardiovascular diseases,” he concluded. “Therefore, weight management and recommendations for weight loss are still important for people living with metabolically healthy obesity.”

Fit and fat fallacy

It’s the latest example of a recurring series of skirmishes around the “fat but fit” debate, in which studies and comments are cherry-picked to fit the news agenda. And this harmful messaging is one reason why Dr Rishi Caleyachetty – a doctor at University Hospitals Coventry and Warwickshire and an Honorary Associate Professor at Warwick Medical School – decided to research the issue.

Dr Caleyachetty is an expert in obesity, diabetes and cardiovascular health, the Chair of the Junior International Committee for the Royal College of General Practitioners and a member of the UK All-Party Parliamentary Group’s Obesity Strategic Council.

In 2017, he published research which exploded the ‘fat but fit’ myth. In contrast to other researchers, he followed the health of people with obesity not at one set point in time but over the course of around 5.4 years. By looking through this longer-term lens, he discovered that people with obesity who had no signs of metabolic abnormalities had little cause to celebrate, because on follow-up they faced a 49% higher risk of cardiovascular disease, a 7% higher risk of cerebrovascular disease and a 96% higher risk of heart failure compared to people of normal weight with no metabolic abnormalities. In other words, the negative health effects of their obesity just hadn’t caught up with them yet. But as the years ticked by, those serious health risks inevitably and inexorably soared.

On publication Dr Caleyachetty announced: “So-called ‘metabolically healthy’ obesity is clearly not a harmless condition and the term should no longer be used in order to prevent misleading individuals that obesity can be healthy.”

Data and denial

Dr Caleyachetty’s work has been backed up by other robust studies. One paper published in the European Heart Journal, which followed 520,000 subjects in ten countries, found that being overweight increases the risk of heart disease by 26-28%, even if you have normal blood pressure, blood sugar and cholesterol.

And a 20-year study by University College London revealed that among the number of “healthy obese” with low cardiometabolic risk factors, 31.8-35.8% were deemed “unhealthy obese” after 5 years, and 34-48.1% became “unhealthy obese” after 20 years.

As a GP, Dr Caleyachetty also recognises the toxic impact of weight-based stigma and the importance of nurturing a patient’s self-esteem. But he doesn’t believe that the promotion of the “fat but fit’’’ myth is a helpful approach to take. Here he discusses the nuances of obesity and explains how best to address this dangerous issue.

What inspired your research into the so-called “metabolically healthy obese” and the ongoing “fat but fit” debate?

I actually started my research into the “metabolically healthy obese” because of the ongoing conversations in the media and in policy circles. And I thought that we should try to clarify a few things and push the conversation forward. And the key point from that research is that even if you’re metabolically healthy, at that point in time – with no presence of diabetes, hyperlipidemia (high cholesterol) or hypertension (high blood pressure) – if your BMI (body mass index) is in the obese range, you’re more at risk of developing some form of cardiovascular disease outcome, compared to someone who is normal weight and metabolically healthy.

The point is that we shouldn’t be waiting for these conditions – diabetes, hypertension, hyperlipidemia – to develop before we do things. And that’s the problem. I think that sometimes the conversation is that an individual can be obese but because they don’t have these other medical problems [yet], that is okay.

And I think that’s potentially missing the point. As a medical professional, excess body fat, to the point where you’re in the obese range, is associated causally with certain co-morbidities: diabetes, hypertension, hyperlipidemia and some musculoskeletal problems. There is an association with cardiovascular disease and certain cancers as well. So most medical professionals would not be encouraging weight gain, and they would certainly be talking about weight reduction, but in a healthy way.

How did your research differ from other papers which have suggested that it is possible for people to be “metabolically healthy obese”?

We used the largest contemporary cohort design – around 3.5 million people were tracked or followed up, versus a smaller number of individuals who were assessed at one moment in time. This was based on linked GP electronic health records. Previous studies used inconsistent definitions of metabolic health. And we looked at a (wider) range of cardiovascular disease outcomes, such as heart attack, stroke, heart failure and peripheral vascular disease.

Excess body fat also changes the mechanical properties of the lungs and chest wall leading to asthma or asthma-like symptoms”

Dr Rishi Caleyachetty

Why does body fat – and particularly abdominal fat – have such a negative impact on human health?

Body fat has several anatomical, metabolic and physiological effects. For example, weight gain over time is distributed to body compartments, and this mechanical load has major effects on the hip, knee and ankle joints, making obesity a risk factor for the development of osteoarthritis and joint degeneration. Excess body fat also changes the mechanical properties of the lungs and chest wall, due to fat deposits in the mediastinum, or abdominal cavities, leading to asthma or asthma-like symptoms.

Excess body fat is accompanied by increases in macrophages, or immune cells, in adipose tissue, which secrete proinflammatory cytokines [signalling molecules that promote inflammation]. This contributes to insulin resistance, which is known to increase risk of cardiometabolic disease. Also with excess body fat, liposomes in hepatocytes [liver tissue cells] can increase in size [steatosis], which can lead to nonalcoholic fatty liver disease [NAFLD], steatohepatitis [liver inflammation], and cirrhosis [scarring of the liver].

Based on your own clear research, and your work as a GP, what are your thoughts on the Health At Every Size movement? This movement helps to fight weight-based stigma but overtly rejects weight-loss as a health goal.

I think that with anyone who has a health problem or chronic disease, it’s important that they’re not stigmatised for having that health problem or disease. And so in that way, I’m pretty for this movement. So that’s a plus side.

Society sometimes discriminates against particular illnesses. In the past, it used to be HIV or AIDS. And obesity is one of those chronic diseases where people face prejudice from school to adulthood. People are called names. There is evidence of less job opportunities for people who are obese. So there’s a lot to address with stigma and discrimination in this area. And if stress eating is one of the behaviours that people who are obese do, if they are stressed from stigmatisation and discrimination, it will make weight loss or maintaining their weight more challenging.

We can appreciate that any stigma or discrimination is not good for a person’s mental health and potentially their physical health. The evidence is quite substantial now. It is recognised by major international health organisations, including the WHO [World Health Organization] and the CDC [Centers for Disease Control and Prevention]. But it’s quite difficult actually to reconcile this idea being pushed that excess weight, or more specifically excessive body fat, to the point where people are obese, is not harmful.

I’m all for any way to help support patients to lose weight, but we must also address the other lifestyle factors, and any kind of psychological trauma that people have encountered”

Dr Rishi Caleyachetty

As doctor, how would you help a patient to lose weight?

It’s understanding what the cause is. Some people just talk about diet and physical activity. But there are other reasons why people can be obese: hormonal issues like polycystic ovary syndrome (PCOS), or rare conditions like Cushing’s. It is not about immediately thinking about a person’s inability to control their diet or to partake in physical activity. There could be trauma in their childhood that leads them to cope by eating.

It is essentially understanding the individual in front of you, working with them to improve whatever aspect is necessary, whether it’s from a psychological point of view, or if they’re stress eating, or if they’re not very health literate, in which case you need to explain or refer them to other health professionals to talk about diet. Or maybe they need to be in a group for physical activity.

There are other things to consider. People lead busy lives. They don’t have access to healthy food. We have a cost of living crisis. Fruit and vegetables are quite expensive. You have to know how to prepare them. So it’s multifactorial.

Weight loss is hard but would it be harmful for people to think it is impossible?

It is very challenging to lose weight. Some patients lose weight and regain the weight quite quickly, if they’re not fully supported. But there have been intervention studies from America, India and Europe which demonstrate that weight loss is possible, although it requires sometimes intensive dietary change and physical activity. There are also new medications that have come on the market – GLP1 drugs – which has shown some promise in weight loss as well.

If you walk into a supermarket right now, the cheapest things you can buy are probably things which have got high fat, high carbohydrate and high salt content”

Are these exciting new weight-loss drugs a magic bullet for obesity?

I’ve been asked about these drugs by colleagues who’ve wanted to lose weight. Some people have been ordering them online, without a doctor’s prescription, which we don’t recommend. They’ve been prescribed a lot, to the point where patients with Type-2 diabetes don’t have access to this medication as well. But the trials have shown that they are effective for weight loss. I think that it is a good medication to use, in conjunction with lifestyle changes. But that has to be explained adequately to patients. And doctors and health professionals need the time to do that with patients.

We’ve had previous weight loss medications before like Orlistat. The uptake wasn’t so high because of the side effects. I’m all for any way to help support patients to lose weight, but we must also address the other lifestyle factors, and any kind of psychological trauma that people have encountered. So I wouldn’t consider it a magic bullet. It would be quite dangerous to think of it in that way. It was the same with bariatric surgery. A lot of people were suggesting that that was going to be a magic bullet. But there are issues with bariatric surgery: you can actually gain weight following bariatric surgery, and you do still have to follow certain dietary restrictions.

What changes in obesity treatment would you like to see in the future?

There are not enough resources in primary care to manage all the people living with obesity. And that could mean, for example, nurse practitioners who specifically deal with chronic diseases including obesity… We don’t have enough research in universities and medical schools on sustainable interventions for people living with obesity. I think bariatric surgeons would also say that they are underfunded.

But we’re talking about the same things over and over again. So, for example, increasing access to healthy foods where you work and in supermarkets. These are all population-wide things that we talk about a lot. It’s really the first line in terms of prevention. But if you walk into a supermarket right now, the cheapest things you can buy are probably things which have got high fat, high carbohydrate and high salt content.

And people need to know how to cook fruits and vegetables. There is the [healthy] Mediterranean diet but first you need to buy the ingredients, then you need to know how to prepare them and then you have to have the time. So it’s multifactorial.

I feel that we will probably have this same conversation in ten years. And from my work with an APPG (All-Party Parliamentary Group), it’s always a struggle to get the right policy decisions made on improving our food environment and physical environment.