Villi (singular villus) are small, finger-like structures in the small intestine. They help to absorb digested food. However, they cannot absorb undigested food. When villi absorbs the food, it breaks down proteins, fats and carbohydrates into protease, lipase and amylase. The villi also increases the surface area of the intestinal walls. A higher surface area allows more nutrients to be broken down. An increased surface area helps the nutrient molecules to travel a much less average distance, so the effectiveness of diffusion increases.