The body uses energy/calories from food to function. It takes approximately eight hours after the last meal for food to be digested, and for nutrients to be absorbed. After this, the body enters a fasting state until the next meal. During this period, the body uses its stores of carbohydrates (stored in the liver and muscle). Once the carbohydrate stores are used up, fat stores are used as a source of energy.
Eating a balanced meal at Suhoor and Iftar will allow the body stores to be replenished, and once these are used up, the body will gradually switch from carbohydrate stores to fat stores for energy.
There is a misconception that if one misses Suhoor, it will result in weight loss. This can be counterproductive, as over a longer period of fast the body thinks it is in starvation mode and the body is less likely to breakdown fat stores for energy and over time will switch to breakdown of muscle protein. After missing Suhoor, many also feel like they deserve a feast at Iftar, resulting in overeating of high fat and sugary foods, which they would not have done if they had a well-balanced Suhoor in the first place.