Sat, Jul-22-23, 08:13
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Plan: Muscle Centric
Stats: 238/153/160
BF:
Progress: 109%
Location: UK
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Do we really need to calculate our BMI? The new science of healthy weight
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Do we really need to calculate our BMI? The new science of healthy weight
Research now shows that other measurements are more accurate, says Charlotte Lytton
The body mass index (BMI) has been the go-to global metric for weight management and health for the past half-century. But while it remains the starting point of all NHS treatment for weight-related conditions, last month the American Medical Association (AMA) announced it would be moving away from using the BMI, as measuring your waist circumference provides a more accurate insight into the risk of developing diabetes, high blood pressure and certain cancers.
Meanwhile, this month researchers from Tel Aviv University found that up to a third of people with a BMI that technically falls within the healthy range were in fact overweight, with the study’s lead author, Professor Yftach Gepner, concluding that measuring your body-fat percentage would be a much better health indicator than the BMI.
First devised by a Belgian astronomer 200 years ago to tally the size of the average man (before being retooled as an obesity metric in 1972), the BMI’s formula of weight divided by height squared (18-24.9 = healthy, 25-29.9 = overweight and 30 and over = obese) was based on the measurements of white European men. Though subsequently adjusted to include averages for women, BMI has proven far less effective for people of some ethnicities and age groups because it is too blunt a tool to distinguish what weight really means for different people.
Take uber-fit types and athletes. Due to the BMI’s failure to differentiate between muscle and fat, Arnold Schwarzenegger in his bulging bicepped prime would be classified as obese, while a report published in the British Medical Journal Heart found that two thirds of rugby forwards in last year’s Six Nations Championship had a BMI over 30, which makes them — according to the BMI, at least — obese.
“Most of us are not rugby players,” points out Giles Yeo, professor of molecular neuroendocrinology at the University of Cambridge and author of Why Calories Don’t Count. So for the most part, the principle that “the higher the BMI, the more fat we tend to carry” does ring true. But while the BMI’s overarching categories can quickly define who might be in need of help, for many individuals, the results simply do not apply. “I wouldn’t say using it on an individual basis is next to useless,” Yeo says. “But I think it should be used as only one of the measurements.”
As well as being unable to drill down into individual results, the standard BMI categories don’t reflect the health risks of non-white patients. While a white person with a BMI of 24.9 would be considered healthy according to the BMI’s scale, experts say that there is a far higher likelihood of an Asian person developing a weight-related illness when their BMI edges past 23.
Researchers are still trying to understand why this might be, with one possible explanation being that South Asian people, in particular, have especially high levels of body fat and are more susceptible to abdominal obesity. The NHS’s online BMI calculator does acknowledge this to a degree, advising those from Bangladeshi, Chinese or Pakistani backgrounds that they run a “high risk of health issues” when their BMI reaches 27.5 (rather than 30).
Still, given the confusion, would we be better off binning the BMI, then?
Checking waist circumference may well be the best substitution — not least where cost and simplicity are concerned, says Yeo, as it’s the “cheapest and most impactful thing that you could do [to gauge your health] immediately”.
The objective here is to measure visceral fat — the kind that is harder to see, and wraps itself around your organs, raising the risk of health conditions such as type 2 diabetes and heart disease. “If you’ve got a big bum, for example, but a relatively skinny waist, you’re going to be fine, broadly speaking. But if you’ve got a big waistline yet have a relatively low BMI, then that’s bad for you,” Yeo explains.
A number of studies have found that our waist measurement is more effective than the BMI, in terms of weight management. A 2019 paper from Imperial University found that waist size was a better predictor of heart attacks among both men and women. Another study of 44,000 women over 16 years, published in the journal Circulation, found that women who reported the highest waist sizes had almost double the risk of dying from heart disease than those with the smallest measurements, as well as being at a higher risk of death from all other causes (with the risk steadily increasing for every extra inch they carried around their waist).
The British Heart Foundation advises that for men, a waist circumference below 37in qualifies as low risk (with over 40in classed as “very high”). For women, under 31.5in is low risk while 34.6in or over is “very high”. Last year, the National Institute for Health and Care Excellence (NICE) suggested that a waist circumference of half your height was an equally useful calculation. Waist-to-hip ratio — where your waist circumference is divided by your hip circumference — can also be used to measure the same thing, with 0.81-0.85 being a healthy result (moderate risk) for women and 0.96-1 for men.
Some studies suggest that neck circumference may be an even better indicator of obesity than waist measurements, as this can show that excess fat is being stored in the upper body, which has been linked to increased likelihood of obesity and coronary artery disease. A 2021 paper published in Clinical Epidemiology and Global Health found it to be an “efficacious tool for screening obesity with good sensitivity and specificity”, noting too that it was “less invasive than measuring waist [as the neck is typically exposed and requires no movement of clothing], and less cumbersome than assessing BMI”. A neck circumference of over 35cm for men and over 32cm for women “should be considered the cut-off point for overweight/obesity”, according to a 2018 cross- sectional study involving eight US universities, including West Virginia University, Florida, and Kansas State.
For those looking for a BMI equivalent with more specialised results, the ABSI (a body shape index) may also prove a useful calculation — combining waist circumference with your sex, height, age and weight to calculate premature mortality risk. Devised in 2012 by the father-and-son team Jesse Krakauer, an endocrinologist, and his son Nir, an assistant professor of civil engineering, it can also predict the risk of cancer, cardiovascular disease and diabetes. A score of 1 means you’re at average risk of death for your age (less than that means a below-average risk profile; above equates to the reverse — you can check yours at omnicalculator.com/health/a-body-shape-index).
For those really looking to investigate their fat distribution and what risks it may bring, a DEXA (dual-energy X-ray absorptiometry) scan is considered the gold standard, Yeo says. They are available in hospitals and private clinics, starting from about £95, and may be particularly useful for older people, as BMI’s calculation often underestimates their levels of body fat by not taking into account the decline in muscle mass we experience as we age.
However you measure it, women’s body fat percentage should be no more than 35, and men’s under 27, explains Chika Anekwe, an obesity doctor at Massachusetts General Hospital Weight Center and instructor at Harvard Medical School, while lean muscle should account for 60-90 per cent of your body mass (depending on gender and level of athleticism).
Ultrasounds, too, can be a valuable tool for fat analysis — particularly when it comes to detecting non-alcoholic fatty liver disease (NAFLD), a range of conditions caused by a build-up of fat in the liver, such as cirrhosis, high blood pressure and kidney disease. NAFLD is closely associated with obesity and can also present in those with a regular BMI, says Saira Hameed, consultant endocrinologist at Imperial College London and author of The Full Diet.
“Fatty liver disease is at the root cause of many metabolic illnesses and is strongly associated with insulin resistance.” She adds that it “can usually be reversed in the early stages” (with lifestyle and dietary changes) — so early detection can provide that necessary first step.
“It’s going to take a lot of time for the consensus to actually move towards the use of more specific measurement tools [for weight-related conditions],” Anekwe says. In the interim, then, getting your tape measure out is likely the most accurate — and cheapest — guide to what your weight means for your health.
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https://www.thetimes.co.uk/article/...eight-v63kcqwmk |
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The exam chair automatically weighed me… No one in US is changing BMI anytime soon after that equipment expense!
Must ask the logic behind all the built-in weighing devices, I thought maybe to avoid transcription errors from scale to records, since the weight is recorded to the 1/10 of an ounce. This nurse did warn me when she would weigh me, but it has also been done discreetly. It has been years since I went to the Dr Westman's clinic; he didn’t have any of this space age furniture, but did use a Professional version of a bio impedance scale.
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