"I ate in a calorie deficit but didn't lose weight."
No, you did not.
Jeremy Ethier ran a small metabolism experiment using astronaut-grade accuracy.
What he found was that out of 9 people, not one had a fast or slow metabolism. Everyone burned almost exactly what their body weight predicted.
The most interesting part he found was that most people underestimated how much they ate by 500–1,000 calories a day.
A skinny guy who couldn't gain weight guessed 2,000. He was actually eating 3,300. An overweight girl who wanted to lose weight guessed 1,800. She was at 3,000.
Not one had an abnormal metabolism. Every single one had a tracking problem.
Studies actually show people underestimate their daily calorie intake by 20–50%, with the gap widest among those who need accuracy most.
People are not broken, but their tracking is. Fix that and the math takes care of itself.
y’all this video is so interesting