Beginning in October, more than 13,000 McDonald's restaurants in America will use a new kind of cooking oil. McDonald's aims to make its French fries and other fried foods healthier. The change will not affect the taste or the number of calories in the food. But by changing the cooking oil, McDonald's says, it hopes to cut by nearly half the amount of trans-fatty acids(转换脂肪酸) in French fries and reduce the amount of saturated fats(饱和脂肪) by 16 percent. Scientists believe that trans-fatty acids and saturated fats raise cholesterol(胆固醇) levels and increase the risk of heart disease. McDonald's new step is important because McDonald's is an industry leader and other fast-food chains and food processors may follow the lead. For McDonald's, the action comes at a time when Americans are becoming more and more concerned about obesity(肥胖) is an increasing pressure on food companies to offer healthy food to consumers. After three years of study, McDonald's officials say they are switching oil that is lower in saturated fats and trans-fatty acids. McDonald's says the change will not cause higher coats for consumers. Though there is some change, scientists say that the amount of trans-fat in foods at McDonald's and at other fast-food companies is still important. The main idea of the text is ______.