A fat person has more cells than a skinny one. Cutting weight cuts the number of cells. Otherwise a fat person would have gargantuan fat cells if cell count never changed.

u/#wrong

However, the number of fat cells stays constant in adulthood in lean and obese individuals, even after marked weight loss, indicating that the number of adipocytes is set during childhood and adolescence.

https://www.nature.com/articles/nature06902

The above study used a combination of two unique procedures:

1. The scientists were able to determine the age of fat cells in the body by measuring the incorporation of radioactivity from the atmosphere into the DNA of the fat cells.

2. They compared the mass of the fat cells in relation to the full amount of adipose tissue in a extremely large number of human subjects whose body weights varied widely.

The scientists found that people who have obesity produce approximately twice as many new fat cells annually as lean people. They also found that fat cell death happens at twice the rate among people who have obesity, compared to lean people. Even if the people with obesity they studied lost a significant amount of weight, their total number of fat cells in the body remained constant, but the size of individual fat cells fell substantially.

https://www.medicalnewstoday.com/articles/106343#1