Many great Doctors from ancient times have known it, within and without Ayurveda, but humans, unlike all other animals are constantly working against it. Aulus Cornelius Celsus wrote in Da Medicina that "above all things everyone should be acquainted with the nature of his own body".
Most creatures are naturally and instinctively acquainted with their physical bodies, you can watch dogs eat grass when they feel sick for example. They know, without thinking too hard about it, what they should or shouldn't eat, when they are hungry and above all when to stop eating.
Humans on the other hand have that great gift of intelligence, but it is not always accompanied by wisdom, and it can override our all important intuition. Know thyself, don't trip up on desires, or think about things too much, or be too persuaded by media or doctors (even Ayurvedic ones!) If you are hungry; eat, if you are full; stop eating. If someone tells you to eat something which makes you feel bad in your body (not in your head) listen to yourself. Only you can truly know your own body.
Remember you could be addicted to some things, which could give your body some bad symptoms when you give them up. Like sugar or other simple carbohydrates, like chocolate or coffee, if you stop eating these things which you are addicted to you could feel worse for a few days or even weeks, but in the long term you will feel better. Know the difference between a food craving that is intuitive and one that is an addiction.
Learn that heavy feeling in your body from drinking too much milk, or that sour hunger from alcohol, or a light, buzzing from sugar or how your stomach feels like you've eaten a brick when what you've really eaten is something deep fried.
Learning and developing this intuitive response to your physical body is crucial, more important than anything you can learn in your head about disease pathways or doshas or diets. As Hippocrates put it "It is more important to know what sort of person has a disease than to know what sort of disease a person has."