The main ingredient of cereals and beans is starch, which also contains a certain amount of protein, but the fat content is generally low. In natural food ingredients, starch and protein have no fragrance, and fat is the main source of fragrance, so cereals and beans have only a slight fragrance, or almost no fragrance. In order to increase the aroma of cereals and enhance their taste, the most common way is to add fat. For example, fritters, fritters, biscuits, instant noodles, bread, and other staple foods all add more fat during processing and cooking. The fat content in the fat is almost 100%, so they contain more fat. Fat is not only delicious, but also can provide more calories. For example, the steamed bun made of 100 grams of flour is 160 grams, providing 1?506 kilojoules (360 kilocalories) of calories, and the weight is 162 grams after fritters, providing up to 2 calories. 620 kJ (626 kcal). Moreover, fat is emptied in the stomach more slowly than starch or protein, so these staple foods with fat are both "delicious" and "starved". However, it is emphasized that the main purpose of eating a good staple food is to reduce the intake of calories and fat, so these staple foods that are rich in fat and are rich in fat are not recommended.

　　In the production of the food industry, in order to achieve shortening (such as shortbread bread, shortbread, pastry, baked goods), extend the shelf life (such as instant noodles, biscuits) and save costs (such as deep-fried dough sticks, For the purpose of fried twist, french fries, etc., "partially hydrogenated vegetable oil" is widely used at present, referred to as hydrogenated oil for short. The so-called "hydrogenation" is to open the double bond of the unsaturated fatty acid molecule in the vegetable oil and add a hydrogen atom, so that the double bond becomes a single bond, and some unsaturated fatty acids become saturated fatty acids. Hydrogenated oil is more stable than ordinary vegetable oil, is not easily damaged by oxidation, and has the characteristics of shortening. However, during the hydrogenation process, trans isomerization of double bonds is easy to occur. Most of the unhydrogenated parts are trans fatty acids. Therefore, hydrogenated oil products contain more (10% to 30%) trans fatty acids.

　　 The so-called trans fatty acids refer to fatty acids with hydrogen (H) on both sides of the double bond according to the molecular spatial structure. The opposite is "cis-fatty acids", that is, fatty acids with hydrogen (H) on the same side of the double bond. In natural foods, almost all unsaturated fatty acids are cis fatty acids, and trans fatty acids are few and far between.

　　 Now, more and more people know that trans fatty acids are harmful to health. When the intake of trans fatty acids is large, it can increase the blood low-density lipoprotein cholesterol (LDL-C), reduce the high-density lipoprotein cholesterol (HDL-C), and increase the risk of coronary heart disease. Some studies believe that trans fatty acids cause more atherosclerosis than saturated fatty acids in animal oil. The study also found that trans fatty acids can be transported to the fetus and infants through the placenta and breast milk, and affect their growth and development; trans fatty acids are also associated with increased risk of breast cancer, dementia, diabetes, obesity and other diseases.

　　 Since 2000, the United States has recommended that consumers throughout the country reduce their intake of trans fatty acids to reduce the incidence of cardiovascular disease. In the dietary guidelines published in August 2004, the daily average intake of trans fatty acids was advised to be less than 1% (2-3 grams) of total calories. In December 2006, New York City enacted a law prohibiting all restaurants in the city from using fats containing trans fatty acids. my country currently has no relevant laws and regulations to regulate the use of trans fatty acids in food, and there are no relevant standards that restrict this. Although the processed foods sold today are not labeled with the content of trans fatty acids, consumers can still find trans fatty acids from the food ingredients list: if they contain "shortening oil", "hydrogenated vegetable oil", "partially hydrogenated vegetable oil", " "Margarine", "dairy creamer", "milk fat" and other ingredients, then the food contains trans fatty acids.

　　In addition to hydrogenated vegetable oils, ordinary vegetable oils can be over-heated or repeatedly fried to produce trans fatty acids, so fried or fried staple foods will contain more trans fatty acids. According to the Announcement No. 4 of the Ministry of Health in 2005, starchy foods (staple foods) are prone to produce acrylamide when cooked at high temperature (>120°C). Animal experiments show that acrylamide is a possible carcinogen. The ordinary frying or frying temperature is far above 120℃. In addition, under the high temperature of frying, animal foods rich in protein and fat may also produce trace amounts of heterocyclic amines and polycyclic aromatic hydrocarbon carcinogens. To this end, the Ministry of Health recommends avoiding cooking starchy foods for a long time or at high temperatures as much as possible, and changing the eating habits of fried foods and high-fat foods.