Many Rastas eat limited types of meat in accordance with the dietary Laws of the Old Testament; they do not eat shellfish or pork. Others abstain from all meat and flesh whatsoever, asserting that to touch meat is to touch death, and is therefore a violation of the Nazirite oath. (A few make a special exception allowing fish, while abstaining from all other forms of flesh.) However, the prohibition against meat only applies to those who are currently fulfilling a Nazirite vow ("Dreadlocks Priesthood"), for the duration of the vow. Many Rastafari maintain a vegan or vegetarian diet all of the time. The purpose of fasting (abstaining from meat and dairy) is to cleanse the body in accordance to serving in the presence of the "Ark of the Covenent".
Usage of alcohol is also generally deemed unhealthy to the Rastafarian way of life, partly because it is seen as a tool of Babylon to confuse people, and partly because placing something that is pickled and fermented within oneself is felt to be much like turning the body (the Temple) into a "cemetery".
In consequence, a rich "alternative" cuisine has developed in association with Rastafari tenets, eschewing most synthetic additives, and preferring more natural vegetables and fruits such as coconut and mango. This cuisine can be found throughout the Caribbean and in some restaurants throughout the western world.
Some of the Houses (or "Mansions" as they have come to be known) of the Rastafari culture, such as the Twelve Tribes of Israel, do not specify diet beyond that which, to quote Christ in the New Testament, "Is not what goes into a man's mouth that defile him, but what come out of it". Wine is seen as a "mocker" and strong drink is "raging"; however, simple consumption of beer or the very common "Roots Wine" are not systematically a part of Rastafarian culture this way or that. Separating from Jamaican culture, different interpretations on the role of food and drink within the religion remains up for debate. At official state banquets Haile Selassie would encourage guests to "eat and drink in your own way".
I got this from Wikipedia, they explain it more than I can.