Ayurveda says that poor digestion is the root cause of many diseases. However, modern doctors rarely ask about diet and digestion. Why is digestion so important in Ayurveda?

Ayurveda talks a great deal about digestion and Agni. Agni means gastric fire, enzymes, and metabolism. 

A healthy strong digestive fire (Agni) is really important for maintaining health. If your digestive fire (Agni) is low, then food will not be digested properly and undigested food will create toxic metabolic waste. These undigested waste products create Ama - an Ayurvedic term for toxins. According to Ayurveda, these toxins (Ama) are the root cause of all disease. Toxins (Ama) are very sticky by nature and clog up the internal channels in the body. Toxins accumulated in the body weaken the immune system over time and we become vulnerable to infections; they adversely effect our digestion and eventually can lead to more serious problems. 

As you can see, low digestive fire (Agni) and excess production of toxins (Ama) in the body is the main reason that we get sick according to Ayurveda. This is why Ayurveda puts a great emphasis on maintaining healthy functioning of digestion and elimination.