Why India's new obesity guideline must look beyond BMI

In 2019, as an obesity medicine practitioner, I was happy to see that the Government of India announced the 'Fit India Movement'.

Seven years later, we are about to set up the National Obesity Guideline – it's a welcome and needed step – given that NFHS-6 found nearly 43% of urban Indian women are now overweight or obese and a significant proportion suffer from metabolic syndrome as a consequence of obesity. This warrants such an obesity guideline as an urgent step to be taken now rather than later.

To treat any problem – first we have to measure it and grade it. How do we measure and grade obesity? By BMI – worldwide. However, the gap in measuring obesity by BMI is that it can't tell muscle mass from fat mass, and the two behave differently. Two people with the same BMI and gender can have different lean body mass and consequently a different metabolic profile.

This is the reason India adopted a lower BMI limit than the Western nations, not just because BMI cannot separate fat from muscle, but because Indians carry more body fat, and more of it is visceral, at any given BMI than Western populations do. The WHO pointed out this issue in the Asian population about twenty years ago, setting the Asian BMI action point at 23 instead of 25 for overweight and 27.5 instead of 30 for obesity.

There's an additional point to be settled—whether men and women should have the same BMI cutoff. Women naturally carry more body fat than men (25% vs 15%) owing to reproductive physiological requirements, and they typically weigh about 5 kg less than men of the same height and age. Devine's widely used ideal-body-weight formula puts this gap at 4.5 kg. At a height of 160 cm, that represents nearly two BMI points, making a strong case for setting women's BMI action points about two points lower than men's (21 vs 23). 

A relatively fresh Chinese study of about 4,600 adults found that the BMI cutoff that predicted metabolic issues was lower for women than for men. The gender-adjusted BMI is not a standard practice anywhere in the world, including India, and is not followed in India's current guidance; however, this deserves testing in Indian data before the benchmark is finalised.

None of the above discussion means that BMI shouldn't be considered; it means that BMI alone isn't enough and needs a rider. A rider – the waist-to-height ratio – can on its own predict metabolic outcomes better than most measurements; an untrained man with a BMI of 23 and a waist-to-height ratio of 0.6 needs immediate intervention, while an athlete with a BMI of 25 and a waist-to-height ratio of less than 0.53 is considered in good shape. 

The BMI and the waist-to-height ratio tell very different stories – one is looking at the envelope, while the other is looking at the contents.

Lessons from experience

I have spent the last seven years treating obesity and associated metabolic disorders as a speciality, across more than 5,000 patients in Noida and Rishikesh. I have built my own classification system for this specific reason – a single cutoff such as BMI was never able to capture the whole picture, which has been in front of my eyes all the time.

The obesity guideline ICMR is about to finalise has a real chance to set up a correct benchmark, not just a borrowed concept from the West, but a truly multi-layered benchmark such as gender-adjusted BMI combined with the waist-to-height ratio. That's a better guideline to write than a single number. It's also the kind that would work better in actual clinical practice and lower the burden of metabolic diseases such as diabetes and hypertension.

The author is a consultant physician and obesity specialist based in Rishikesh and Noida. 

 

The opinions expressed in this article are those of the author and do not purport to reflect the opinions or views of THE WEEK.