After eating a meal high in carbohydrates, men with overweight or obesity process glucose for energy less efficiently than men with normal body weight.

Even though obese people have higher blood sugar after eating carbs, their bodies still break down and use the sugar from those carbs just as well as lean people do.

When healthy young men ate the same number of calories but swapped carbs for fat for just three days, their body’s response to sugar changed—blood sugar went up, insulin came out slower, and a gut hormone went up.

People with obesity tend to have higher insulin levels when fasting and their blood sugar spikes more after eating carbs, but their bodies still use the sugar from those carbs just like lean people do.

Men who are overweight or obese release more insulin after eating a high-fat meal than men with normal weight, even when their blood sugar levels rise the same amount, suggesting differences in how their bodies regulate insulin that are not due to blood sugar changes.

After eating just three days of mostly fatty food instead of carbs, healthy young men had higher blood sugar spikes when they drank a sugary drink, meaning their bodies handled sugar less efficiently.