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Why your TDEE drops as you lose weight

The diet didn't stop working. Your body got smaller, and the numbers moved with it.

Written by AdnanUpdated 7 min read

Your TDEE drops as you lose weight because a smaller body needs less energy to run and to move, because you tend to move less when you eat less, and because your metabolism adapts a little to the deficit. For a 40-year-old man who goes from 100 kg to 90 kg, maintenance falls by about 155 calories a day from body size alone. That is why progress slows, and why you should recalculate with the TDEE calculator after every 4–5 kg (about 10 lb).

The four reasons

  1. Less body to maintain. BMR depends mostly on body size. Lose weight and BMR falls.
  2. Less body to move. Walking and climbing stairs cost less energy when you are lighter.
  3. Less everyday movement. In a deficit, people tend to fidget, stand and walk less, often without noticing.
  4. Adaptive thermogenesis. Your body becomes slightly more efficient, so energy use falls a little more than weight loss alone predicts.

Eating less also means burning a little less digesting food, which shaves off a few more calories.

Worked example

40-year-old man, 180 cm, moderate activityAt 100 kg his BMR is about 1,930 and his TDEE about 2,992. At 90 kg, BMR is about 1,830 and TDEE about 2,837. If he kept eating 2,492 calories (his original 500 deficit), his deficit would shrink to about 345 calories, before any change in daily movement.

How big is metabolic adaptation?

For typical dieters it is modest. The most-cited large effect comes from a 2016 study of 14 former contestants on the TV show The Biggest Loser. They lost an average of about 58 kg in 30 weeks, and their resting metabolic rate fell by about 610 calories a day by the end of the competition. Six years later it was still about 700 calories below their starting level. That is an extreme case of very rapid, very large weight loss, and it isn't what most people should expect from a steady diet. It does show that the body pushes back against weight loss.

Hall and colleagues showed in 2011 that the old "3,500 calories per pound" rule overstates long-term weight loss because it ignores these changes. The NIH Body Weight Planner models them more realistically.

What to do about it

  • Recalculate after every 4–5 kg lost, using your current weight.
  • Keep daily movement up. A step goal stops everyday activity quietly falling.
  • Keep lifting and eat enough protein to protect muscle, which supports your BMR. See how much protein you need.
  • Take planned breaks. A week or two at maintenance can ease hunger and fatigue on a long diet.
  • Adjust in small steps: 100–150 calories at a time.

Is it really a plateau?

Water swings can hide fat loss for one or two weeks. Before changing anything, check that your weekly average hasn't moved for at least 2–3 weeks, and that your food logging is still accurate. How to track and adjust your calories shows how to read the trend.

Recalculate with your current weight.

Open the TDEE calculator

Frequently asked questions

Why has my weight loss slowed down?
As you lose weight, your body burns fewer calories. You have less mass to maintain and move, you may move less without noticing, and your metabolism adapts a little. The same intake becomes a smaller deficit, so progress slows.
Is metabolic damage real?
Metabolic adaptation is real: energy use can drop a bit more than weight loss alone predicts. But 'damage' overstates it for most people. The large, lasting effects reported in some studies came from extreme weight loss, such as in The Biggest Loser contestants.
How do I get past a weight loss plateau?
Check your food tracking first. Then recalculate your TDEE for your current weight, lower calories by 100–150 or add daily walking, and keep protein and strength training high. A planned week or two at maintenance can also help if you are worn out.
Will my metabolism recover after dieting?
Much of the drop is simply because you are smaller, and that part stays as long as you weigh less. Hunger and energy usually improve after a period at maintenance. Strength training helps you keep the muscle that supports your metabolism.

Keep reading

Track and adjustKnow when to change your target.How big a deficit?Sizing the gap.Maintenance calculatorFor diet breaks.

Sources

  1. Hall KD, Sacks G, Chandramohan D, et al. Quantification of the effect of energy imbalance on bodyweight. Lancet. 2011;378(9793):826–837. PubMed 21872751
  2. Fothergill E, et al. Persistent metabolic adaptation 6 years after "The Biggest Loser" competition. Obesity. 2016. doi:10.1002/oby.21538
  3. National Institute of Diabetes and Digestive and Kidney Diseases. Body Weight Planner. niddk.nih.gov
  4. Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241–247. PubMed 2305711