How many calories are in a pound of fat?
About 3,500 calories. That’s where the old rule comes from: eat 500 calories a day less and lose a pound a week. It works for the first weeks, then overshoots, because a smaller body burns less. In seven closely watched weight loss studies, people lost about 20 pounds where the rule predicted about 28.
Where 3,500 comes from
Fat tissue is about 87% fat, plus water and cells. A pound of it holds roughly 3,500 calories. The figure fits people carrying a lot of fat best, and it overstates the loss for leaner people.
Why the rule overshoots
As you lose weight, you burn less: there’s less of you to move and keep warm. So the same diet makes a smaller gap each week. It’s like saving from a paycheck that shrinks a little every month. Spend the same, and you save less each time.
A 2011 model from NIH scientists gives a better rule of thumb. Every 10 calories a day you cut, for good, takes off about 1 pound in the end. Half of that comes off in about a year and nearly all of it by about three years.
| Cut for good | Where you end up | After about a year |
|---|---|---|
| 100 calories a day | about 10 pounds lighter | about 5 pounds lighter |
| 250 calories a day | about 25 pounds lighter | about 12 pounds lighter |
| 500 calories a day | about 50 pounds lighter | about 25 pounds lighter |
What to do
- Use the 3,500 rule for the first month, then expect the pace to slow.
- Re-set your calories every 10 to 15 pounds, with the calories to lose calculator.
- Judge by the trend, since a single week mixes in water.
3 sources
- Hall, What is the required energy deficit per unit weight loss?, International Journal of Obesity, 2008pmc.ncbi.nlm.nih.gov
- Thomas et al., Can a weight loss of one pound a week be achieved with a 3500-kcal deficit? Commentary on a commonly accepted rule, International Journal of Obesity, 2013pmc.ncbi.nlm.nih.gov
- Hall et al., Quantification of the effect of energy imbalance on bodyweight, The Lancet, 2011pmc.ncbi.nlm.nih.gov
