Sometimes food also supplies an agent or chemical that aids in the metabolism of other nutrients. Such foods act by changing the ecology within the human body. Many of the old time remedies stress food avoidance as well as specifying what to eat. For example, the ancient Indian practice of Ayurveda, is mainly based on diet control. As you can learn by referring to the section on Ayurveda in HolisticOnLine , foods are classified as either helping or hurting the three doshas, the governing pricnciples under which all living being are classified in Ayurveda.
Many people are allergic to some foods such as chocolate, lactose etc.
Similarly some people get constipation from excessive high intake of fiber. Diabetes patients, especially Type 2 diabetes, need to watch out what they eat especially food containing sugar. People with heart disease need to control the intake of foods containing high amount of fat and cholesterol. These are all common sense diet therapies. Diet and Cancer A study conducted by the National Cancer Institute has concluded that as much as 90 percent of all cancer in humans have been attributed to environmental factors, including diet.