Researchers think we should consign Body Mass Index calculations to the bin.
Researchers think we should consign Body Mass Index calculations to the bin.
We are obsessed by weight and as long as our weight stays roughly the same, who cares about that tightening waistband? It’s the all important number on the scales that counts. And who can blame us? Our GPs are similarly obsessed. Who hasn’t been asked to step on that monstrous machine in their doctor’s office?
“Just hop on the scale for me will you?” It’s less a request than a command.
If yours is between 18.5-24.9, you can breathe a sigh of relief. You are a “normal” healthy size. More, and you’re too fat. Less, you are underweight. Anything above 30 is considered obese.
It’s the gold standard measure used by GPs in our midlife health check and to decide whether we should be offered operations – or not – as a high BMI can lead to complications. Except now experts aren’t so sure it’s even worth the paper it’s written on.
A new Italian study is ringing alarm bells – and it’s far from the first time experts have questioned the measure.
Scientists at the University of Tor Vergata found that BMI failed to spot around a third of obese people. The study of 4800 adults aged 40-80, found 38 per of men and 41 per cent of women were categorised as obese using a BMI calculation.
But when participants’ body fat levels were scanned, 71 per cent of men and 64 per cent of women were in the obese bracket.
The study authors suggest lowering the marker for obesity to 27 – but should we actually consign the BMI index to the bin?
In fact, BMI was never meant to be a measure of individual health. It was created more than 200 years ago by a mathematician, Lambert Adolphe Jacques Quetelet, simply to work out the weight of the average man. But it was then co-opted many years later, in 1972, by physiologist Ancel Keys, who devised the term body mass index (BMI), and proposed it as a quick and easy way to measure obesity in the general population, to assist the government in allocating resources.
BMI is only useful if you’re very overweight or very underweight
The big problem with BMI is that it is that it fails to look at what that weight is made up of. Is it fat or is it muscle? There’s a big difference when it comes to our health.
But it still has its merits, explains Dr Esther Fox, a clinical specialist and director of Mount Kelly Physiotherapy Centre. “BMI picks up either end of the spectrum: very underweight people who are very frail, and very overweight people. A high BMI has been correlated with heart disease, cancer and other metabolic diseases.
“But there’s a grey area in the middle, at around 25 to 27, because it doesn’t take into account body composition.” A super-fit bodybuilder can be categorised as obese, or, as in the Italian study, people aged from 40-80 – whose heavier muscle mass has started to decline but lighter body fat has increased – slip through the net.
Why body fat percentage is a more accurate measure of health
If we simply go by our weight, without taking our body fat percentage (BFP) into account, or indeed where that fat is deposited, we might be lulled into a false sense of security.
Evidence shows high body fat is linked to higher prevalence of heart disease and other metabolic disorders such as Type 2 Diabetes. While extra muscle tissue can improve your health.
The extra fat we carry can make the body produce more cholesterol and triglycerides, while having more muscle makes us burn up glucose that could turn to fat. Fox says: “High levels of lipids in your bloodstream will fur up the arteries. If you have too much glucose in your blood, that’s toxic for your cells. Having a lot of muscular tissue actually acts as a glucose sponge.”
A measure of 25 per cent body fat percentage is considered obese for men and 30 per cent for women.
Forget regular scales - body composition scales can tell you more about your body fat percentage. Photo / 123rf
How to find out your body fat percentage
A Dexa scan delivers gold-standard accuracy with measurements of bone density, lean mass and body fat percentage.
If you don’t want to shell out, good old-fashioned callipers can provide a decent estimate, but their accuracy will depend on the skill of the person administering the test. Body composition scales are often a better measure. They provide not only body fat measurements but also muscle mass, BMI, hydration levels and metabolic age. The scales compare your data to others of similar age and sex, and the benefit is that you can track a pattern rather than spend money to get a one-off view.
Fox says: “They are not entirely accurate, but they will give you a good idea about your body fat levels.”
Michael Baah, a personal trainer, adds: “Scales are a tool to keep an eye on where you are heading. If you are going in the wrong direction, they are going to tell you.”
Where they also beat callipers is in giving a visceral fat measurement. This is fat which sits in the abdominal cavity around your central organs.“Visceral fat is a type of fat that can be more detrimental to health than subcutaneous fat, which doesn’t have such a metabolically active role,” explains Dr Charlotte Norton, the chief medical officer of The Slimming Clinic. “It’s vital to provide cushioning but too much of it can have an inflammatory effect.
“The term we use to describe that is ‘sick fat’. Fat cells become sick in themselves and start releasing pro-inflammatory chemicals, which means people who carry extra weight around their belly could be more at risk of vascular disease, heart disease and Type 2 diabetes.”
Waist measurement is a better gauge of health than BMI
Waist measurement alone can give an indication of increasing visceral fat levels – above 35ins in women and 40ins in men is considered high risk. The UK’s National Institute for Health and Care Excellence (NICE) also recommends using a waist-to-height calculation (waist measurement divided by height). A ratio of 0.5-0.59 shows increased risk and above 0.6 high risk. Similarly, a waist-to-hip ratio is also a good indicator of risk. The WHO categorises abdominal obesity as 0.85 in women and 0.9 in men.
A 2022 study from Oxford University looking at health data from adults aged 40-70 found that the risk of heart attack increased by four per cent for every extra centimetre on the waistline.
The common sense test: the mirror
As well as the tape measure, we can also employ common sense. Kirsten Whitehouse, a women’s fitness expert, says: “Most of us deep down know whether we are obese or not. We should all ask ourselves, ‘How do I feel? Can I walk for 10 minutes and still hold a conversation?’”
Baah agrees. “Are your clothes fitting or do you fill them out a bit more? How do you look in the mirror? How do you feel when you walk up the stairs? If you want to go deeper, get your bloods checked.”
Blood tests, which can be done at your GP surgery, can give more detailed information on cholesterol and triglyceride levels and blood sugar. In the UK these are usually offered every five years as standard as part of the over-40s health check.
Our ethnicity also plays a part in how vulnerable we are to disease and should always be considered by medics and personal trainers, especially as some ethnic groups are more likely to put on weight around their middle. Current NICE guidelines advise: “People with a South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean family background are prone to central obesity and their cardiometabolic risk, [a group of risk factors including high blood sugar, raised blood pressure and low good cholesterol], occurs at a lower BMI.”
What action do our experts advise we should take once we’ve established our body fat percentage and visceral fat levels are too high? “I like to keep things very simple. If you’re eating more than your body can actually burn, you’re naturally going to put on weight,” Baah says. “Calorie deficit should always be the number one go-to.”
“Eat lean protein, freshly prepared foods, and a lot of different colours, and no processed carbs,” Whitehouse advises. “Then you need a balance of cardiovascular exercise to help drop overall body fat, and resistance training which will help build muscle mass.”
