metaboliq
What metabolism means, in calories
Metabolism is all the energy your body uses in a day.
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It has three parts: the energy you burn at rest, the energy spent digesting food, and the energy you use moving.
Klaas Westerterp at Maastricht University, who has spent a career measuring this, describes the split. The resting part, your basal metabolic rate, is usually the largest share for people who are not very active. Digesting a mixed diet costs another 5% to 15%, more when the meal is high in protein. Activity, from a gym session to pacing during phone calls, makes up the rest and varies the most between people.
The resting part is mostly organs at work. Using standard values, the heart and kidneys burn about 440 kcal per kilo a day, the brain 240 and the liver 200. Muscle burns about 13 and fat about 4.5. Muscle is the one tissue you can add to, and you can easily lose it, so it decides most of what changes.
Sneha, 33, an HR executive in Bengaluru, is a composite of the readers who write to us. She eats less than her flatmate, gains weight more easily, and has decided she was born with a slow metabolism. The rest of this page tests that idea against what the research shows.
Is a slow metabolism real?
People do differ, but mostly for reasons you can measure.
Sources: [3]
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In one study of 150 adults, lean mass explained most of the difference in resting metabolic rate between them.
Alexandra Johnstone's team at the Rowett Institute in Aberdeen measured the basal metabolic rate of 150 adults several times each. Fat-free mass explained 63% of the variation between people, fat mass 6% and age 2%. Once body make-up was accounted for, sex made no significant difference, and 26% remained unexplained. Part of that unexplained share is the small, real variation people call a fast or slow metabolism.
So Sneha's flatmate, who plays badminton four evenings a week and carries more muscle, probably does burn more at rest. Some of the difference may simply be luck. But the biggest single factor is one Sneha can change.
It is also worth checking the eating side honestly. Tea with sugar, a few biscuits, a handful of namkeen and the extra helping at dinner are easy to forget. Writing down everything for one week, including the biscuits with chai, is a humbling exercise, and many readers find it more useful than any calculator.
Does metabolism slow down with age?
Between 20 and 60, hardly at all. That surprises almost everyone, including Sneha, who had read that metabolism drops every decade after 25.
Sources: [4]
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The best evidence is a 2021 study in Science led by Herman Pontzer at Duke University. His team pooled energy measurements on 6,421 people, from babies eight days old to adults of 95, all made with doubly labelled water, the most accurate method for real life. Once body size was accounted for, babies burned the most, about 50% more than adults around their first birthday. From about 20 to 60 the line was flat, and it stayed flat through pregnancy. Only after 60 did it begin to drop, slowly.
So when a 35-year-old gains weight, the cause is almost always something other than age. Sneha's college days involved walking across a large campus, badminton most evenings and a hostel mess that served dinner at 8. Now there is a desk, a two-hour commute on Outer Ring Road and food delivered at 10 pm. Her metabolism did not change; her life did.
After 60 the decline is real but gentle, and losing muscle makes it steeper, which is why strength training matters more with every decade.
- 20-60years of steady metabolism
Crash diets slow your metabolism, sometimes for years
This is the one real, measurable slow-down most dieters create themselves.
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Cut food hard and fast, and the body lowers its energy use by more than the weight lost would explain.
Michael Rosenbaum and Rudolph Leibel at Columbia University spent decades on this. After weight loss, energy use falls further than the smaller body predicts, and much of the gap is in the energy spent moving: the body becomes more efficient, fidgets less and burns fewer calories for the same tasks.
The most striking example is the American television contest The Biggest Loser. Erin Fothergill's team measured 14 contestants six years after the show. They had lost 58 kg on average, and their resting rate had dropped by 610 kcal a day. Six years later they had regained 41 kg, yet their resting rate was still 704 kcal below where it started, and 499 kcal below what their size predicted.
Few Indian dieters go to those extremes, but the pattern shows up in smaller ways after every soup-only fortnight or 800-calorie wedding diet. A slower loss, with protein and strength training, triggers much less of this.
- 499kcal below size-predicted rate
Thyroid: the medical cause worth ruling out
An underactive thyroid really does slow metabolism, and it is common in India, especially in women. A TSH blood test answers the question.
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A study across eight Indian cities, led by Dr A G Unnikrishnan, tested 5,360 adults and found an underactive thyroid in 10.95%, in 15.86% of women and 5.02% of men. About a third of those cases, 3.47% of everyone tested, had no idea until the study's blood test.
The classic signs are tiredness, feeling cold when others are comfortable, dry skin, constipation, puffy eyes and heavier periods. The weight it causes is usually modest, a few kilos. A review in the Indian Journal of Endocrinology and Metabolism notes that treating an underactive thyroid moves weight only a little, and that obesity itself can push TSH slightly up.
Sneha has been feeling cold in an office where everyone else is fine, and her mother has hypothyroidism. Her TSH came back raised, and a doctor is now treating it. Her weight will still need the rest of this page, but the tiredness should lift.
Everyday movement is the part you control most
The energy you spend outside the gym, walking to the chai stall, standing on the metro, climbing stairs, even fidgeting in meetings, differs more from person to person than any other part of metabolism.
Sources: [9]
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James Levine at the Mayo Clinic showed how much it matters. He overfed 16 volunteers by 1,000 kcal a day for eight weeks and measured where the extra energy went. Two-thirds of the rise in what they burned came from this everyday, non-exercise movement, and it explained a tenfold difference in how much fat they put on. The people who stood up more, paced and fidgeted stored the least.
Sneha's week shows the gap. Her flat is in HSR Layout, her office is in a tech park on Outer Ring Road, and on a normal day she goes from bed to cab to lift to desk and back, with her phone telling her she managed about 2,800 steps. She now takes her one-to-one calls walking round the floor, climbs the four floors to her desk, and walks the last kilometre home from the metro. None of it feels like exercise. Her step count has roughly tripled.
A phone pedometer is all you need. Note your average for a week, then add about a thousand steps a day each week until walking is simply part of how you live.
| Before | After | |
|---|---|---|
| Office floor | Lift | 4 floors of stairs |
| Calls | Seated | Standing, walking |
| Commute | Door to door | 1 stop early |
- 2/3of extra burn from everyday movement
How to speed up a slow metabolism
Sneha's plan, in the end, had nothing exotic in it.
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She lifts, she eats protein at every meal, she walks more, and she stopped the fortnight-long soup diets that she used to start every January.
The lifting matters most. Gary Hunter's group in Alabama put women on the same diet until each had lost about 12 kg. The women who did resistance training kept their lean mass and their resting energy use; the women who only walked or jogged, or did nothing, lost some of both. Two or three sessions a week of squats, lunges, push-ups against a wall and rows with a band are enough to start, and a gym can come later.
Protein helps twice over. Digesting it uses more energy than carbohydrate or fat, and Heather Leidy's review found higher-protein meals keep people fuller. Eggs, besan, dal, curd, paneer, fish and chicken all count.
Skip the metabolism boosters. The capsules and detox teas on sale have little evidence of changing anything you would notice. At Metaboliq the aim we set with members is "Lose up to 20% of your body weight — and keep your muscle". Results vary; your doctor decides what is right for you. Holding on to muscle is the thing that stops a diet slowing your metabolism. The plan starts with a home blood test, TSH included, that a doctor reads with you.
45+ markers, one home blood test
- HbA1c
- Thyroid test
- Fasting insulin
- HOMA-IR
- Fasting blood sugar
- Lipid profile
- Liver function test
- Kidney function test
Every source, in full (11)
[1] Westerterp KR. Diet induced thermogenesis
Nutrition & Metabolism, 2004. Daily energy expenditure has three parts: basal metabolic rate, diet-induced thermogenesis and activity. A mixed diet costs 5 to 15% of daily expenditure to process, more when it is high in protein, which also adds to fullness.
Read the source[2] Wang Z, et al. Specific metabolic rates of major organs and tissues across adulthood: evaluation by mechanistic model of resting energy expenditure
American Journal of Clinical Nutrition, 2010. Uses resting rates of about 13 kcal per kilo a day for skeletal muscle and 4.5 for fat tissue, against 200 for the liver, 240 for the brain and 440 for the heart and kidneys.
Read the source[3] Johnstone AM, et al. Factors influencing variation in basal metabolic rate include fat-free mass, fat mass, age, and circulating thyroxine but not sex, circulating leptin, or triiodothyronine
American Journal of Clinical Nutrition, 2005. In 150 adults, fat-free mass explained 63% of the differences in basal metabolic rate between people, fat mass 6% and age 2%; sex made no significant difference once body make-up was counted, and 26% stayed unexplained.
Read the source[4] Pontzer H, et al. Daily energy expenditure through the human life course
Science, 2021. In 6,421 people measured by doubly labelled water from 8 days to 95 years of age, size-adjusted energy use peaks about 50% above adult values at around one year, declines to adult levels by about 20, stays stable from 20 to 60, even in pregnancy, then declines.
Read the source[5] Rosenbaum M, Leibel RL. Adaptive thermogenesis in humans
International Journal of Obesity, 2010. After weight loss, energy expenditure falls by more than the change in body mass and composition predicts, with much of the difference in the energy spent on physical activity.
Read the source[6] Fothergill E, et al. Persistent metabolic adaptation 6 years after "The Biggest Loser" competition
Obesity, 2016. Fourteen contestants lost 58 kg on average and their resting rate fell 610 kcal a day; six years later they had regained 41 kg, yet resting rate was still 704 kcal below baseline and 499 kcal below what their size predicted.
Read the source[7] Unnikrishnan AG, et al. Prevalence of hypothyroidism in adults: an epidemiological study in eight cities of India
Indian Journal of Endocrinology and Metabolism, 2013. Of 5,360 adults tested in eight Indian cities, 10.95% had hypothyroidism (15.86% of women, 5.02% of men), and 3.47% had it undetected until the study's blood test.
Read the source[8] Sanyal D, Raychaudhuri M. Hypothyroidism and obesity: an intriguing link
Indian Journal of Endocrinology and Metabolism, 2016. Overt hypothyroidism is linked with modest weight gain; a raised TSH can follow obesity rather than cause it; treating overt hypothyroidism has at most a modest effect on weight, and thyroid hormone has no supported role when the thyroid is normal.
Read the source[9] Levine JA, Eberhardt NL, Jensen MD. Role of nonexercise activity thermogenesis in resistance to fat gain in humans
Science, 1999. When 16 adults were overfed by 1,000 kcal a day for eight weeks, two-thirds of their rise in energy use came from non-exercise activity, and it explained a tenfold difference in how much fat they stored.
Read the source[10] Hunter GR, et al. Resistance training conserves fat-free mass and resting energy expenditure following weight loss
Obesity, 2008. In 94 women losing about 12 kg, those who did resistance training kept their fat-free mass (46.9 to 47.2 kg), resting energy expenditure and strength; those doing aerobic training (45.4 to 44.4 kg) or no exercise (47.9 to 46.4 kg) lost fat-free mass and resting energy use.
Read the source[11] Leidy HJ, et al. The role of protein in weight loss and maintenance
American Journal of Clinical Nutrition, 2015. Reviews the evidence that higher-protein meals increase reported fullness and reduce later intake compared with meals matched for energy but lower in protein.
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