Fruits are also carbohydrate, but are closer in nature to sugar than most vegetables. They lack protein, but they are good sources of a number of other nutrients. Fructose, the sugar found in fruit, is many times sweeter than processed sugar, so it gives you more sweetness per calorie than high-sugar desserts. But there are experts who believe that we eat too much protein already, and not nearly enough carbohydrate. Everyone accepts that eating too much fat is harmful.
Carbohydrates are important to the body in many ways.
It is, for example, the only energy source the brain can draw upon. Too little carbohydrate and the brain cannot function properly. When you exercise heavily, you tend to use up carbohydrates, so you need to eat enough to fuel both your exercise and your nervous system. Carbohydrates also combine with fat in the biochemical cycle that produces energy to fuel the muscles. Therefore, very low or zero carbohydrate diets tend to be self-defeating, because they inhibit the metabolism of fat.