The human body mainly takes starch from grains. Proper amount of starch does not make people fat, but slowly decomposes into glucose through digestive juice in the intestine, and glucose is the only energy source for brain work. The brain needs to consume 100 ~ 150 grams of sugar every day. These sugars come from 400 ~ 500 grams of food intake, and the brain even needs 600 grams when working hard. Stop eating staple food and rely entirely on protein and vegetables to provide energy, which will easily lead to low blood sugar and insufficient brain energy supply, and people will feel tired and unable to concentrate on their work.