The function of fatty acids has been clarified through epidemiological surveys, intervention studies, and animal tests. In this section, as a result of this substantiation, we will introduce items which are supported by numerous nutritionists and which are reasonable for an actual diet. At the same, food products you should remember that food products are not medicine and immediate effects cannot be expected. Also, insufficient consumption of fatty acids creates the concern for deficiency-related symptoms; however, when observing the current amount of fat consumption, there is no need to worry about deficiencies.

1) Essential fatty acids
Fatty acids are an essential substance for maintaining a healthy human body. In particular, "essential fatty acids" refer to fatty acids that cannot be synthesized in the human body and therefore must be obtained from foods (polyunsatured fats such as linoleic acid and a-linolenic acid). It is known that EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) are synthesized in the human body from the metabolism of a-linolenic acid. However, it is difficult to synthesize a sufficient amount and it is preferable to also obtain these essential fatty acids from food.

2) Saturated fatty acids
Many people may believe that saturated fatty acids are fatty acids that have an adverse effect on health. A large amount of saturated fatty acids are contained in animal fats. Also, animal fats contain large amounts of cholesterol, which makes it preferable to suppress consumption of animal fats to reduce cholesterol consumption. This contributes to the negative image towards saturated fats.
Saturated fatty acids contained in vegetable oil are evaluated as described below.

Regarding the effect on fluctuations in cholesterol, in addition to increasing LDL (otherwise known as "bad cholesterol"), saturated fatty acids also increase HDL ("good cholesterol"). Therefore, saturated fatty acids are important for maintaining the proper ration between HDL and LDL. The negative effects such as the rise in LDL are thought to occur due to excessive consumption. Although the Dietary Reference Intakes for Japanese (2020) states that excessive consumption does not directly impact the onset of cardiovascular disease and death, it does clearly impact the important risk factors of blood total cholesterol and LDL cholesterol in both adults and children. As such, it is considered necessary to set a target amount for consumption. However, studies showing the existence of a clear threshold between the two are scarce, and there is insufficient scientific evidence to decide the extent of the limit on intake of saturated fatty acids.

Furthermore, recent research has given rise to the theory that there is no relationship between the consumption of saturated fatty acids and the occurrence of coronary heart disease, strokes, and cardiovascular disease. This can also be applied to other fatty acids, but there may not be any significance in seeking to attribute the cause of diseases to a single dietary constituent.

3) Monounsaturated fatty acid: Oleic acid
Oleic acid is one piece of evidence for the healthiness of olive oil. People living in Mediterranean regions have a low occurrence of coronary heart disease despite eating large amounts of food and drinking large amounts of wine. There is the theory that the health of these people is maintained by olive oil; in other words, by the large amounts of oleic acid contained in olive oil. Regarding the cholesterol behavior of oleic acid, it decreases LDL without decreasing HDL. This selective effect on cholesterol reduction has led to many people strongly advocating the health benefits of oleic acid. In turn, this has created the theory that olive oil is good for health.
Currently, oleic acid is normally evaluated as listed below.

Today, the selective effect of oleic acid on decreases in cholesterol is becoming increasingly viewed as a gentle fatty acid that does not increase LDL, rather than being viewed as only reducing LDL. This perspective is taken by the by the 2010 and subsequent editions of the Dietary Reference Intakes for Japanese (DRI). Also, the 2020 edition states that “since it is not yet clear how and to what extent monounsaturated fatty acids can contribute to (or become a risk for) the prevention of major lifestyle-related diseases, we did not set a target amount for monounsaturated fatty acids.” Also, some people are of the opinion that, when compared to the effect of consuming oleic acid alone, the effect of reducing LDL can be heightened by consuming oleic acid together with the linoleic acid that will be discussed later in this section. Furthermore, since oleic acid is a substance with high oxidation stability in this body, it can be said that it is best always consume the proper amount of oleic acid.
Note that the health benefits of Mediterranean are not attributable to olive oil alone; instead, it should be viewed as the synergistic effect of cuisine made by preparing fresh fish and vegetables with olive oil, garlic, pepper, and other seasonings.

4) Polyunsaturated fatty acids (n-6 fatty acids)
n-6 fatty acids include linoleic acid and y-linolenic acid. Almost all n-6 fatty acids consumed by Japanese people are linoleic acid. The evaluation of linoleic acid has changed greatly with the passage of time. Japanese people have the ethnic trait of high occurrence of dyslipidemia and diabetes. One factor in this occurrence is cholesterol, so it is important to maintain healthy level of cholesterol. Therefore, there were times in which consumption of strong linoleic acid was espoused as necessary in order to decrease cholesterol. However, observation and animal testing has shown that consuming large amounts of linoleic acid also decrease good cholesterol. It has also been shown that arachidonic acid, a metabolite of linoleic acid, produces eicosanoids that cause inflammation and may lead to cancer. This has damaged the reputation of linoleic acid.
Currently, linoleic acid is evaluated as described below.

An essential fatty acid.
There are expectations that linoleic acid intake may prevent coronary artery disease.
Although linoleic acid reduces cholesterol, a large amount of consumption also decreases HDL.
There is concern that consuming large amounts may lead to inflammation, etc.
Insufficient consumption will cause skin disorders.

However, in some ways, the evaluation for linoleic acid as described above arose in order to emphasize the effect of a linolenic acid and oleic acid. The majority of negative evaluation for linoleic acid comes from phenomena observed when feeding in large amounts during animal experiments. For example, the generation of eicosanoids which cause inflammation occurred when providing linoleic acid at 12% or more of feed weight. Also, anti-inflammatory substances are also produced at the same time, and it has been observed that there is an antagonistic relationship. The current consumption of linoleic acid by Japanese people is currently at an energy ratio of about 6% to 7%. This level is far from excessive consumption, so there is no need to worry about the production of inflammatory substances.
Furthermore, in regards to the relationship with cancer, the Dietary Reference Intakes for Japanese (DRI) (2010) make the following statement denying the relationship between linoleic acid and cancer: "Previously, there was concern that an increase in the amount of linoleic acid consumed would increase the risk of cancer; however, meta-analysis shows that, at the very least, there is no relationship with breast cancer, stomach cancer, or prostate cancer." However, due to subsequent valuation and verification, the description about the association with cancer has been deleted from the 2020 edition. Therefore, it should be recognized that consuming appropriate amounts of linoleic acid will not cause any health problems.

5) Polyunsaturated fatty acids (n-3 fatty acids)
n-3 fatty acids are essential fatty acids. In addition to the a-linolenic acid which is the most widely known n-3 fatty acid, other commonly recognized types include EPA and DHA, which are contained in large amounts in fish. n-3 fatty acids are evaluated as listed below.

Japanese people mainly obtain n-3 fatty acids in the form of EPA and DHA from fish. Among vegetable oil, soybean oil and rapeseed oil contain a-linolenic acid. Other oils which contain large amounts of a-linolenic acid are linseed oil and perilla oil. However, these oils include three double bonds and are therefore prone to oxidation. This results in problems such as being poorly suited for cooking with heat and the inability to withstand long-term storage. The Dietary Reference Intakes for Japanese (DRI) (2010) emphasize that consuming a certain amount of linolenic acid is necessary in order to avoid disease from insufficiency (occurrence of dermatitis, etc.). However, there is no proof that consuming large amount will increase the efficiency, and the DRI does not discuss consumption above the necessary level. No related changes have been made to the 2020 edition. On a different note, there is a theory that DHA is a fatty acid that will make people more intelligent. However, while problems such as decreased memory have been observed in the event of insufficiency, consuming large amounts of DHA will not make people more intelligent.

6) Balanced consumption of fatty acids
Until this point, we have discussed the characteristics of fatty acids. No types of vegetable oil are made from a single fatty acid. Instead, oils contain various types of fatty acids which function in harmony in order to achieve a synergistic effect. It is not possible to independently consume linoleic acid, oleic acid, or a-linolenic independently. Therefore, it should be recognized that balanced consumption of these fatty acids will increase effects and alleviate defects. Moreover, vegetable oil is an ingredient for cooking. Therefore, there is no such thing as a diet that contains excessive or insufficient amounts of vegetable oil. Instead, the amount consumed changes depending on the type of food being eaten and the cooking methods used. Table 6 shows the recommended amount (target and approximate amounts) of consumption for each type of fatty acid according to the Dietary Reference Intakes for Japanese (DRI) (2020)

Now, about how much fatty acids are actually consumed by Japanese people? There is no clear answer to this question. However, the amount of fatty acids consumed can be estimated from current conditions for food consumption according to the National Health and Nutrition Survey. These estimates are shown in Table 7. On average, the fatty acid consumed most by Japanese people is monounsaturated fatty acid (mainly oleic acid). This is followed in order by saturated fatty acids, n-6 fatty acids (mainly linoleic acid), and n-3 fatty acids (mainly a-linolenic, EPA, and DHA). Some people may warn against excessive consumption of linoleic acid. However, when looking at current conditions, it is clear that such warnings are unfounded.