The idea is we are a certain body type. I've copy and pasted this bit for you:
The first step towards eating for your Ayurvedic constitution is to find out what your constitutional type or dosha is. If you haven't done so already, please take this quiz.
Once you know what your Ayurvedic dosha is, you can balance it by learning what foods support you and what foods can further aggravate your dosha.
The following general guidelines can help you get started. An Ayurvedic physician can help you further tailor your diet towards your individual constitutional type.
In Ayurveda, the five elements of space, air, earth, fire and water make up everything in the universe including the human body. These elements come together to create three different constitutional types or doshas known as Vata, Pitta and Kapha.
If air and space were the predominant energies present during your birth then you are Vata in nature, if water and earth were predominant, you are Kapha and if fire and water were predominant then you are Pitta.
Knowing your dosha can help you understand what activities, foods, and lifestyle elements can support and nurture your health and what can cause imbalance.
The most accurate way of learning your constitution is to visit an Ayurvedic doctor. He or she can conduct a physical examination including pulse assessment and can tell you what your dosha is and provide specific recommendations. Many people are a combination of two doshas.
http://altmedicine.about.com/cs/2/a/ayurveda.htm
You will be able to find reading matter without visiting a specialist. Hope this helps.