Lifestyle modification is one of the risk factor for cardiovascular diseases.Fastfood plays a very important role in the lifestyle modification. Nowadays fast food is one of the essential foods in our day today life mainly in urban areas[12].In this paper, a discussion is made on how much intake of fastfood will lead to heart diseases and the threshold value for the fast food eaters using fuzzy rule based system is studied. Finally the threshold value for fast food eaters is detected.