Studies have shown that the saturation of dietary fatty acids is an independent factor regulating serum total cholesterol (TC) levels.
The composition of fatty acids in food is very complex, usually consisting of 12-22 carbon atom chains, which can contain 0-6 double bonds (unsaturated bonds). The effect of fatty acids on blood lipids should depend on the length of the carbon bond and the number and position of the unsaturated bonds.
Saturated fatty acids (SFA) play the following roles in human metabolism:
- Energy supply: Saturated fatty acids are an important source of energy in the human body, similar to gasoline in a car. They are oxidized and decomposed in the body to produce energy for various physiological activities.
- Influencing the hormone system: Saturated fatty acids have a certain impact on the hormone system, such as insulin-like growth factors (IGF), also known as growth factors. IGFs are a class of factors that promote cell growth and have metabolic effects similar to insulin.
- Affecting cholesterol levels: Excessive intake of saturated fatty acids can increase blood cholesterol levels. Experimental research has found that after eating a large amount of saturated fatty acids, the activity of HMG-CoA reductase in the liver increases, resulting in increased cholesterol synthesis.
- Distribution in different foods: Saturated fatty acids are commonly found in animal-based foods in the average diet, such as meat, eggs, and dairy fats. These foods are usually accompanied by high cholesterol content.
- Affecting serum TC: There are differences in the effects of different carbon chain saturated fatty acids on serum TC. It is generally believed that saturated fatty acids with fewer than 12 carbon atoms and those with 18 or more carbon atoms have no impact on serum TC.
It should be noted that although saturated fatty acids play a certain role in human metabolism, excessive intake can lead to increased cholesterol levels and increase the risk of cardiovascular diseases. Therefore, appropriate intake of saturated fatty acids is necessary, and a balanced fatty acid intake ratio should be maintained in the diet.
Second, Monounsaturated Fatty Acids (MUFA):
Monounsaturated fatty acids are fatty acids containing a single unsaturated bond. Research has shown that they have a lowering effect on serum total cholesterol (TC) levels. Monounsaturated fatty acids can significantly reduce serum low-density lipoprotein cholesterol (LDL-C) and TC levels without gender differences. Additionally, they can increase serum high-density lipoprotein cholesterol (HDL-C) levels. Although the lowering effect of monounsaturated fatty acids on serum TC levels is less pronounced than that of polyunsaturated fatty acids, they still have some cardiovascular protective effects.
Monounsaturated fatty acids in the diet mainly come from oleic acid. Olive oil contains up to 84% oleic acid, followed by peanut oil (56%), corn oil (49%), and sesame oil (45%). Studies have shown that the serum TC levels in populations from the Mediterranean region (such as Greece, Italy, etc.) are lower, which may be related to their high consumption of olive oil in their diet.
In conclusion, monounsaturated fatty acids have certain benefits in reducing cholesterol and maintaining cardiovascular health. Appropriately increasing the consumption of oils rich in monounsaturated fatty acids, such as olive oil, peanut oil, and corn oil, helps improve the dietary structure and reduces the risk of chronic diseases. However, it should be noted that excessive intake of oils can still lead to obesity and the development of chronic diseases. Therefore, maintaining a balanced and diverse intake of fats is crucial.
Third, Polyunsaturated Fatty Acids (PUFA):
Polyunsaturated fatty acids are fatty acids containing two or more unsaturated bonds. They can be divided into two types based on the number and position of the double bonds.
Linoleic acid is an essential fatty acid for humans. It can reduce serum total cholesterol (TC) levels and is recommended to partially replace saturated fats in the diet to improve the dietary structure, which has shown good results. Research has shown that after replacing saturated fats in the diet with polyunsaturated fats, serum TC and low-density lipoprotein cholesterol (LDL-C) levels are significantly reduced; polyunsaturated fats can significantly decrease serum triglyceride (TG) levels.
Linoleic acid is mainly found in plant oils, with sunflower seed oil containing 66%, followed by soybean oil (51%), cottonseed oil (48%), and sesame oil (41%). Currently, the effects of dietary monounsaturated and polyunsaturated fats on serum TC are different from those of saturated fats, mainly due to different metabolic pathways. However, it has not yet been fully confirmed that the degree and intensity of influence on different blood lipid components are consistent. The mechanism by which these unsaturated fats reduce serum TC has not been fully elucidated.
Food sources of alpha-linolenic acid (ALA), a type of polyunsaturated fat, are mainly from fatty fish, which contain eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA).
The content of ALA in plant oils is very low, with only 6.5% in soybean oil, and the abundant linoleic acid in plant oils cannot be converted into EPA and DHA in the body. Recent studies have proven that w-3 polyunsaturated fats can mainly reduce serum TG levels and increase serum high-density lipoprotein cholesterol（HDL-C）levels, while reducing serum TC levels through decreasing very low density lipoprotein (VLDL). The serum TC, TG, LDL-C, and VLDL-C levels of the Inuit people in Greenland are low, and it is believed to be related to their long-term reliance on fish as their main food source.
Unsaturated fats are high-calorie nutrients, and excessive intake can lead to overweight and obesity. Moreover, since the human body cannot produce enough lipase to promote their hydrolysis and absorption, it can also cause indigestion, nausea, and other adverse reactions. Unsaturated fats, such as the w-3 series of polyunsaturated fats, are very susceptible to oxidation and may pose a risk of lipid peroxidation. Therefore, it is not recommended to excessively increase the intake of unsaturated fats in the diet.
It is important to maintain a balanced diet and consume a moderate amount of unsaturated fats, as they offer various health benefits when consumed in appropriate amounts. Consuming a mix of saturated and unsaturated fats in moderation can help maintain a healthy lipid profile and reduce the risk of cardiovascular diseases.
To minimize the potential risks of excessive unsaturated fat intake, focus on incorporating a variety of healthy fats into your diet, such as those found in avocados, nuts, seeds, and olive oil. Incorporating fatty fish rich in w-3 fatty acids, like salmon, sardines, and mackerel, can provide health benefits without the risk of excessive intake, as these foods also contain essential nutrients like vitamins and minerals.
Remember that a well-balanced diet should prioritize nutrient diversity and moderation, ensuring that you consume enough healthy fats, along with proteins, carbohydrates, and other essential nutrients. Consult a healthcare professional or registered dietitian for personalized dietary guidance that suits your specific needs and lifestyle.
