People with obesity have more fat circulating in their blood at rest, and their bodies are breaking down and re-storing fat at a faster rate than people without obesity.

Insulin reduces fat burning in the blood the same way in obese and lean people, but obese people still burn more fat overall because their bodies are burning fat stored inside cells — not just from the blood.

Obese people re-store more fat inside their cells at rest, and insulin doesn’t slow this process down as much as it does in lean people.

When healthy adult men eat a large mixed meal high in fat, their blood free fatty acid levels rise slowly and peak after 6 hours. When they eat a meal with 75 grams of pure fat, their free fatty acid levels rise faster, peak at 4 hours, and stay high at 6 hours. The type of fat in the meal affects when and how much free fatty acid appears in the blood.

In people with obesity who don’t have diabetes, fat cells still respond normally to insulin — the high fat levels are just because they have more fat tissue, not because their fat cells are broken.

In people with obesity, insulin doesn’t reduce fat release from fat tissue as well as it does in lean people — but if you account for how much fat they have, insulin works just as well.