Why am I gaining weight on a calorie deficit?

Common reasons

1. You may be eating more than you think. Studies that measure food intake precisely find most people underestimate what they eat, often by a lot. Cooking oils, drinks, snacks and weekend meals are easy to miss. Weighing food for a week or two can help.
2. The scale is showing water, not fat. Body weight can swing by a few pounds from day to day because of salt, carbohydrates, hormones (such as the menstrual cycle), constipation or starting a new exercise routine. Look at the trend over several weeks.
3. Your body is adjusting. As you lose weight, your body burns a little less energy, and a calorie amount that worked at first may stop working. This is normal, not a broken metabolism.
4. Medicines can play a part. Some medicines can cause weight gain, including steroids, insulin, some diabetes pills, some antidepressants and some mental health medicines. Don't stop any medicine, but ask your doctor.
5. Sleep and stress matter. Short sleep and ongoing stress are linked to more hunger and eating more, which can quietly undo a deficit.
6. Sometimes it's a medical condition. An underactive thyroid, fluid build-up from heart, kidney or liver problems, or (rarely) hormone disorders can cause weight gain. See a doctor if you gain weight quickly, have swelling in your legs or belly, feel short of breath, or gain weight you can't explain.

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