metaboliq
BMI tells you how heavy you are for your height. BMR tells you how many calories your body burns lying still for a day. Rohan, 34, weighs 78 kg at 172 cm, so his BMI is 26.4 and his BMR about 1,690. The first says his weight is above the healthy range for an Indian man; the second is where his calorie target starts.
You get BMI by dividing weight in kg by height in metres squared, and on Indian cut-offs risk starts to rise at 23. BMR usually comes from the Mifflin–St Jeor equation, which uses weight, height, age and sex. A common mix-up is to treat BMR as the amount to eat, when it covers only the resting part of the day. Neither number can see fat or muscle, which is why a waist measurement adds so much to both.
How do you calculate BMI?
BMI = weight in kilograms ÷ (height in metres × height in metres). Ancel Keys gave it the name in 1972, after comparing several weight-for-height indices in large groups of men and settling on this one.
Rohan, 34, writes software in Bengaluru, weighs 78 kg and is 172 cm tall. Convert his height to metres, 1.72, and square it: 1.72 × 1.72 = 2.96. Then 78 ÷ 2.96 = 26.4.
Anjali, 45, teaches in Jaipur, weighs 68 kg and is 158 cm. Square 1.58 to get 2.50, and 68 ÷ 2.50 gives about 27.2. Neither is a real patient; swap in your own weight and height.
If you know your height in feet and inches, multiply the total inches by 2.54 to get centimetres first. Five feet four is 64 inches, or about 163 cm. The formula is the same for men and women and for adults of every age. What changes is how the result is read.
Sources: [1]
What BMI is healthy for Indians?
The international bands put a healthy BMI at 18.5–24.9, overweight at 25–29.9 and obesity at 30 or above. In 2004 a WHO expert consultation reviewed the evidence for Asian populations. It found that a large share of Asians had a high risk of type 2 diabetes and heart disease at BMIs below 25.
The consultation kept the international bands but suggested extra action points at 23, 27.5, 32.5 and 37.5 for Asian countries to use. Indian experts went further. A 2009 consensus statement led by Anoop Misra set the normal range for Indian adults at 18–22.9, overweight at 23–24.9 and obesity at 25 or above.
On those cut-offs Rohan's 26.4 and Anjali's 27.2 both fall in the obesity range, though an international chart would call them only overweight. That gap matters, because Indians tend to carry more fat, and more of it round the middle, at the same BMI.
The same Indian consensus added waist limits: 90 cm for men and 80 cm for women. A tape measure round the navel adds a great deal to a BMI.
How do you calculate BMR?
Most calculators use the Mifflin–St Jeor equation, built in 1990 from measured resting energy in 498 adults. For men: BMR = 10 × weight in kg + 6.25 × height in cm − 5 × age + 5. For women, replace the final + 5 with − 161.
For Rohan: 780 + 1,075 − 170 + 5 gives 1,690 calories a day. For Anjali: 680 + 987.5 − 225 − 161 gives about 1,280. David Frankenfield's 2005 review compared the common equations and found Mifflin–St Jeor came within 10% of the measured value in more people than any other.
Indian bodies may run a little lower than the equations expect. When Sinha and Kurpad's team measured young men in Bengaluru, the international equation they tested overestimated BMR by about 6.5%. Treat any calculated BMR as an estimate, not a measurement.
BMR is not the same as the calories you need. Multiply it by an activity factor, from 1.2 for a desk-bound day upwards, to get total daily energy use. The Bengaluru men's measured factor was about 1.35, lower than many charts assume.
Why can two people with the same BMI have different BMRs?
Lean tissue drives BMR, and BMI has no way of seeing it. Alexandra Johnstone's team in Aberdeen measured BMR in 150 adults. Fat-free mass, mostly muscle and organs, explained 63% of the differences between people, fat mass 6% and age just 2%.
Take two women, each 65 kg and 160 cm, so each has a BMI of 25.4. Priya is 28 and does squats and push-ups at home twice a week. Her aunt is 52 and has not exercised in years. On the formula alone, Priya burns about 120 calories a day more, purely because of age. Her extra muscle likely adds more again, and the formula cannot see that.
BMI misses fat in the same way. A 2010 meta-analysis from the Mayo Clinic pooled 32 samples and found standard BMI cut-offs caught only about half the people whose measured body fat was high.
Indian doctors see this so often it has a nickname, the thin-fat Indian: a normal BMI with enough fat round the liver and belly to push up sugar and cholesterol.
What do BMI and BMR look like side by side?
Rohan, 34, 78 kg, 172 cm, desk job in Bengaluru. BMI 26.4, which is obesity on Indian cut-offs and overweight on the international chart. BMR about 1,690 calories. Daily burn at a 1.35 activity factor, about 2,280. Starting target, about 1,750–1,800 calories, with a 90 cm waist as his line to get under.
Anjali, 45, 68 kg, 158 cm, schoolteacher in Jaipur, on her feet half the day. BMI 27.2. BMR about 1,280. Daily burn at 1.35, about 1,730. Starting target, around 1,300–1,350, plus a 20-minute walk after dinner, with 80 cm as her waist line.
Sameer, 29, 70 kg, 175 cm, plays football three evenings a week. BMI 22.9, normal on both charts. BMR about 1,650, and a daily burn closer to 2,560 with an activity factor of 1.55. His weight is already in range, so for him the numbers mainly guide how much to eat on training days.
Meena, 52, 58 kg, 152 cm, retired and rarely walks far. BMI 25.1. BMR about 1,110. At 1.2 her daily burn is about 1,330, so a big calorie cut would leave very little food. Adding movement and protein is likely to help her more than eating much less.
Can you raise your BMR?
Yes, mostly by adding or keeping muscle. Two or three strength sessions a week, whether at a gym or with bodyweight moves at home, and enough protein at every meal are the main levers.
Protein also costs more energy to digest than carbohydrate or fat, so a higher-protein plate nudges daily burn up a little. A katori of dal, a bowl of curd, some paneer, eggs, chicken or fish at each meal is a sensible Indian pattern.
Very low-calorie crash diets work the other way. They take muscle along with fat, and the body responds by burning less. Eating too little for too long is one of the surest ways to end up with a lower BMR than you started with.
BMR falls as weight comes off, and faster if muscle goes with the fat, which is why a diet that worked in March often stalls by June. Herman Pontzer's team pooled measured energy use from thousands of people; once body size was allowed for, daily burn barely changed between 20 and 60. So the slowdown is mostly muscle, and muscle can be kept. At Metaboliq, where doctors aim for up to 20% of body weight lost with muscle kept, that means protein at every meal and strength work from the first week. It starts with a home blood test and a doctor's review of the results.
Thyroid hormone sets the pace too. In the Aberdeen study, thyroxine explained part of the leftover variation in men. If BMR seems very low for your size, with tiredness and feeling cold, a thyroid test is worth doing.
How should you use BMI and BMR together?
Start with BMI and waist to see where you stand. On Indian cut-offs, a BMI of 23 or more, or a waist above 80 cm for women or 90 cm for men, is worth acting on.
Then use BMR, multiplied by an honest activity factor, to set a first calorie target. Weigh yourself at the same time each morning for three weeks and compare weekly averages. If the average does not move, your real burn is lower than the estimate.
Recalculate both every five kilos or so. BMI will fall, which is the point. BMR will fall too, so the calorie target needs trimming, or activity needs adding, to keep progress going.
Keep a third number alongside: how many squats or stairs you can manage. If that improves while BMI drops, you are probably keeping muscle, which keeps BMR from falling faster than it has to.
Sources: [3]