91É«ÇéƬ

IF, LIKE me, you put on a few pounds during the pandemic lockdowns, you may not be looking forward to your next doctor’s visit in case they ask you to step on the weighing scales.

91É«ÇéƬcare staff assess whether people are overweight by calculating their body mass index (BMI), a measure of weight that takes height into account. Those whose BMI is judged too high may be given diet advice sheets or recommended a website, app or slimming clubs.

The link with lockdown is particularly cruel as also tell us that being overweight puts people in greater danger from covid-19. So anyone concerned about the next coronavirus variant may well feel pressure to follow their doctor’s orders.

Most of us would accept that we are being given good advice, whether or not we manage to follow it. But there are reasons to think that such recommendations aren’t based on good evidence – and might well be wrong.

It is uncontroversial that people who are very heavy die younger than those who are slim, succumbing earlier in life to conditions such as heart attacks and strokes. They are also more likely to find walking difficult, to get out of breath more easily and to have joint pain.

What is less clear is just where the red line is between being a healthy weight and the danger zone. The standard advice in most high-income countries is that anyone with a BMI of 25 or more is overweight. It is unclear exactly where this figure stems from, but it seems to have been cemented into the medical orthodoxy by a report from a .

Yet there is a good deal of evidence to suggest we should place the cut-off for being overweight a bit higher – perhaps at a BMI of 30 or even more. The question marks over the 25 to 30 bracket are important because it accounts for about half of those who would be medically advised to lose weight in most high-income countries.

The doubts first came from an analysis by researchers at the US Centers for Disease Control and Prevention in 2005 that used a from a regular government-run nutrition survey. They found that people whose BMI is between 25 and 30 had a lower death rate over the period of time studied than people whose BMI was in the supposedly ideal range of 18.5 to 25.

The findings were highly controversial, but several other pieces of research have investigated the question, and in other countries too. While some disagreed with the 2005 conclusion, the majority concurred, as shown by a summarising 97 such studies.

This year, a Chinese study confirmed the finding in people over 80 – the age range when most people die. Although the weight categories used don’t correspond exactly to those in the UK, this found that even people who would be classed as mildly obese, with a BMI over 28, had a lower death rate than those classed as having a healthy weight, with a BMI between 18.5 and 24.

Even the link between weight and covid-19 danger seems to be overstated, because that a raised risk only kicks in at BMIs of 35 and over. Yet most health bodies continue to give the outdated message that if our BMI gets above 25, we weigh too much and should do something about it.

Another key question is how people should go about trying to lose weight, if that is their goal. For decades, doctors have said we should cut out fat from our diet, for instance by using reduced-fat dairy products, avoiding butter and oils in cooking and, increasingly, swerving red meat.

But more recently, randomised trials of different diet approaches have found that aiming for a low-carbohydrate and high-fat diet is as good as a low-fat diet for losing weight and keeping it off, and doesn’t cause heart attacks either.

Another alternative is fasting diets, where people intersperse periods of normal eating with bouts of consuming very little. Fasts are usually either for two non-consecutive days of the week or between 8.00pm and midday.

Some believe this works because it regularly flips the body into relying on a different metabolic pathway, others because it simply nudges people into eating less. Either way, it does seem to help some people – and yet it also goes against the usual medical advice not to skip breakfast. It may be that different kinds of dieting suit different people better. But again, this isn’t the impression you would get from most medical sources of advice on healthy eating.

So while I hugely respect the staff of my primary care practice, who have provided sterling service to my family during the pandemic, if they ask me to step on any scales, I will politely decline.

Ìý