一Japan Oilseed Processors Association is a nonprofit industry organization comprised of companies involved in the production and processing of vegetable oils.

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Vegetable Oil and Nutrition

(3) Function of fatty acids

(3) Function of fatty acids

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.

Myristic acid, palmitic acid :Increases cholesterol. Accelerates hardening of the arteries.
Stearic acid :Neutral in changes of cholesterol.

When a minimum amount of consumption continues, there is a heightened risk of lifestyle diseases such as an increased incident rate of cerebral hemorrhage.

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. However, according to the Dietary Reference Intakes for Japanese (DRI) (2010), there is a lack of definitive proof to make this judgment. The DRI shows cases in which a decrease in the amount of saturated fatty acids consumed was observed to reduce LDL cholesterol and to reduce the morbidity rate from arteriosclerosis, etc. Consequently, it is though that "a diet high in saturated fats will incite diseases such as myocardial infarction or diabetes." On the other hand, as explained above, insufficient consumption also has a negative effective. Accordingly, lower limits and upper limits have been set in order to discourage excessive consumption and insufficient consumption. At the same time, when determining the cause for the heightened rate of cerebral hemorrhage due to insufficient consumption, it is impossible to clearly distinguish between only the deficiency of saturated fatty acid consumption and the effect of insufficient consumption of animal protein. Therefore, the conclusion was reached that saturated fatty acids should be obtained from meat and dairy products. For that reason, instead of consciously trying to control the amount of saturated fatty acid consumption, it should be recognized that appropriate consumption of animal protein will also keep consumption of saturated fatty acids at an appropriate level.

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.

Cholesterol :Does not increase LDL and does not decrease HDL
 (the cholesterol lowering effect is weaker than polyunsaturated fatty acids).

It has been indicated that consuming large amounts of oleic acid may create the risk of coronary disease, so caution is required toward excessive consumption.
Oleic acid is stable towards oxidation and suppresses the occurrence of peroxide in the body.

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 also taken by the Dietary Reference Intakes for Japanese (DRI) (2010). 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.
Although linoleic acid reduces cholesterol, a large amount of consumption also decreases HDL.
There is concern that consuming large amounts may lead to inflammation and cancer.
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 oleic acid and a linolenic 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." Linoleic acid is an essential fatty acid that cannot be synthesized in the human body. 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.

An essential fatty acid.

a-linolenic acid :Prevention of arteriosclerosis, improvement of serum lipids, improvement of immune response, prevention of cancer.
EPA :Prevention of thrombosis, decrease of serum triglycerides, anti-inflammatory properties, prevention of cancer.
DHA :Improved brain/nerve function, anti-inflammatory properties, prevention of cancer.

Has a high degree of unsaturation and is prone to generating peroxides.

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. 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 of consumption for each type of fatty acid according to the Dietary Reference Intakes for Japanese (DRI) (2010).

Table 6: Recommended amount of consumption for fatty acids (for adults aged 18 years or older)
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Source: Dietary Reference Intakes for Japanese (2010) (MHLW)

Note: As "an amount at which almost no people in a certain group shows signs of deficiency," the approximate amount is shown as the amount consumed per day. A recommended consumption amount is not given due to a lack of scientific basis. The target amount is "an amount which should be target in order to prevent lifestyle diseases" and is shown as a ratio of total calories consumed per day.

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.

Table 7: Conditions for consumption of fatty acids by Japanese people
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Source: National Health and Nutrition Survey (MHLW)
Note: The values in the table were estimated by the JOPA based on the state of food consumption according to the National Health and Nutrition Survey.

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