They lose weight without having to control portion sizes by just following the guidelines in the program. Initially, it takes a while for your body to get used to it and get over the cravings for fat, but your taste does change and you do not crave the fat, and you adapt to the diet. The important thing is making sure you get adequate calories and adequate fiber. Commonly people have to eat more frequently following this program, because of it being so low in fat. Some vegetarians choose not to eat any animal products, or any product derived from any animal, such as avoiding honey.
Some vegetarians refer to themselves vegetarians and are just avoiding red meats.
The Ornish Program includes egg whites, and nonfat dairy products, as being optional to help with better compliance and adherence to the program. And I would be concerned about getting enough fiber and calories. Most of us are not used to eating so frequently. Again, I would emphasize whole grains, adequate beans and soy, and whole fruits and vegetables, and I would recommend eating every two to four hours. It seems so massively overused in all processed foods.