Even though the whole-food sandwich had a bit more protein (which burns more calories), that alone couldn’t explain why it burned almost twice as many calories — so the processing must be the real reason.

Consuming whole foods increases postprandial energy expenditure compared to isoenergetic ultraprocessed foods due to higher digestive effort and reduced thermodynamic efficiency.

Whole-food sandwiches have way more fiber — like 3 times more — which might make your body work harder to digest them and absorb fewer calories.

The sandwich made with real bread and cheese has about three times more fiber than the one made with white bread and processed cheese — and that extra fiber might make your body work harder to digest it.

Your body keeps burning calories longer after eating a sandwich made with real ingredients than one made with processed stuff — about an extra hour.

Processed foods are easier for your body to break down because they’re stripped of fiber and nutrients — so your body doesn’t have to work as hard, which means fewer calories burned.