THE BODY MASS index (BMI) calculation, which is nearly 200 years old, might need to be updated for modern health assessments. In our weight-obsessed society, many overlook the tightening waistbands as long as the number on the scale remains steady. However, this focus on weight and BMI might need to be found. BMI, calculated by dividing weight in kilograms by the square of height in meters, categorises individuals into underweight, normal, overweight, and obese. Despite its widespread use by GPs and the NHS, recent studies suggest it may not be as reliable as once thought.
The Flaws of BMI
A new Italian study from the University of Tor Vergata indicates significant flaws in BMI as a health measure. The study, involving 4,800 adults aged 40-80, found that BMI failed to identify about a third of obese individuals. Specifically, while 38% of men and 41% of women were categorised as obese based on BMI, body fat scans revealed that 71% of men and 64% of women fell into the obese category. The study’s authors suggest lowering the obesity marker from 30 to 27, but this raises the question: should we discard BMI altogether?
Dr Esther Fox, director of Mount Kelly Physiotherapy Centre, acknowledges BMI’s utility at the extreme ends of the spectrum—identifying very underweight and very overweight individuals. However, she notes, “There’s a grey area in the middle, at around 25 to 27, because it doesn’t consider body composition.” This oversight can misclassify muscular individuals as obese and older adults with declining muscle mass but increasing body fat as healthy.
Body Fat Percentage: A More Accurate Measure
Relying solely on weight without considering body fat percentage (BFP) or fat distribution can lead to false assumptions about health. High body fat, rather than high weight, correlates more strongly with heart disease and metabolic disorders such as Type 2 Diabetes. Conversely, muscle mass benefits health by burning glucose that could otherwise convert to fat. Dr Fox explains, “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 acts as a glucose sponge.” The criteria for obesity based on body fat percentage are 25% for men and 30% for women. This method provides a clearer picture of health risks than BMI.
Measuring Body Fat Percentage
A Dexa scan is the gold standard for the most accurate body fat measurement, providing detailed insights into bone density, lean mass, and body fat percentage. However, it can be costly, around £200. More accessible options include body composition scales, which, though not as precise, offer valid estimates of body fat, muscle mass, BMI, hydration levels, and metabolic age. These scales allow for tracking changes over time, which can be more informative than a one-off measurement.
Waist Measurement: A Simple, Effective Tool
Waist measurement alone can indicate increasing visceral fat levels, which is more dangerous than subcutaneous fat. A waist size above 35 inches in women and 40 inches in men is considered high risk. Dr Charlotte Norton, chief medical officer of The Slimming Clinic, notes, “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.”
NICE recommends a waist-to-height ratio (waist measurement divided by height). A ratio of 0.5-0.59 indicates increased risk, and above 0.6 signifies high risk. Similarly, a waist-to-hip ratio is a reasonable risk indicator, with the WHO categorising abdominal obesity as 0.85 in women and 0.9 in men. A 2022 Oxford University study found that each additional centimetre on the waistline increased heart attack risk by 4% in adults aged 40-70.
Practical Advice
Common sense and simple tools can also help assess health. Kirsten Whitehouse, a women’s fitness expert, suggests self-assessment questions like, “How do I feel? Can I walk for 10 minutes and still hold a conversation?” Personal trainer Michael Baah advises, “Are your clothes fitting, or do you fill them out 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 blood checked.”
Blood tests, available through GPs, provide detailed information on cholesterol, triglyceride levels, and blood sugar, typically part of the NHS health check for those over 40. Ethnicity also influences disease vulnerability, with certain ethnic groups more prone to central obesity and associated risks at lower BMIs. NICE guidelines highlight this, advising specific consideration for individuals of South Asian, Chinese, Middle Eastern, Black African, or African-Caribbean backgrounds.
Conclusion
Action is crucial. If you’re eating more than your body can burn, you will naturally put on weight. Calorie deficit should always be the number one go-to. “Eat lean protein, freshly prepared foods, many different colours, and no processed carbs. Then you need a balance of cardiovascular exercise to help drop overall body fat and resistance training to help build muscle mass.”
