When people don't eat for 3 days, their body burns calories at a slightly higher rate for about a day and a half, then returns to normal levels.

When men and women don't eat for 3 days, men tend to have higher levels of blood pressure, blood flow to arms, calorie burning rate, and stress hormones than women, but both sexes respond similarly to fasting.

When people don't eat for 3 days, their heart rate goes up, increasing from about 62 to 69 beats per minute, with most of the increase happening within the first day and a half.

When people don't eat for 3 days, their blood sugar levels drop significantly, from about 4.5 to 3.1 mmol/L.

When people don't eat for 3 days, their insulin levels drop significantly, which is part of the body's adaptation to fasting.

When people don't eat for 3 days, their body starts using more fat for energy, which can be seen in a drop in the respiratory exchange ratio from 0.80 to 0.72.