Butter is in fact considered to be a low GI food along with fruits, green leafy vegetables, nuts, breads, meats, yogurts, milk, and even soy milk. These days lots of people are on low GI diets because it is extremely healthy.
GI stands for glycemic index which has to do with how much glucose is released in the body when certain foods are digested. It is important to stick with low GI foods as much as possible because too much glucose in the body can cause all sorts of problems. Beans and legumes are especially healthy for a number of reasons, but also because they are considered to be low GI foods. Butter is among these foods and although it contains quite a bit of fat, it still releases a minimal amount of glucose in the body when it is ingested.