Conjugated linoleic acid (CLA) is a popular weight loss supplement. Milk, which is high in saturated fat, is the best food source for CLA. Milk from grass-fed cows contains more CLA than milk from grain-fed cows. Researchers from Harvard University studied the relationship between CLA in fat cells and the risk of heart attack in people living in Costa Rica, a country where most cows are grass-fed. People with the highest levels of fat cell CLA had the lowest risk of heart disease. The CLA content of milk more than compensated for its high levels of saturated fat.