Every bite you eat is responsible for your brain

After the various fatty acids in food enter the human body, they will selectively concentrate in specific organs and tissues. For example, linoleic acid (n-6 fatty acid) is enriched in the liver, skin, and muscles, and DHA (n-3 fatty acid) is enriched in the brain, retina, and nervous system.

These two fatty acid families cannot be converted into each other, but they share a set of elongation enzymes and desaturases during metabolism, so they form a competitive inhibition effect with each other. It is particularly important to maintain a balance of n-6/n-3 in the diet.

The Nutrition Society once recommended that the reasonable ratio of n-6 to n-3 is 4 to 6.

The 2015 National Nutrition and Health Monitoring Dietary Survey found that the national average n-6/n-3 PUFA ratio of adult dietary intake in China was about 8.6 , with great differences between different regions. For example, the ratio in Nanjing may be as high as 12.7 , while in Zhejiang it is lower, at about 6.5 [1].

The imbalance in n-6/n-3 intake caused by dietary structure is one of the common dietary problems of Chinese residents [2]. Severe imbalance may be closely related to mental retardation, Alzheimer's disease and other diseases.

01

The contrast between n-3 and n-6 ​​in the modern diet

Vegetable oils are the main source of fatty acids, and their type has a significant impact on the composition of dietary fatty acids. Among urban residents in my country, 64.3% of n-6 fatty acids and 46.5% of n-3 fatty acids come from vegetable oils[1].

The problem is that n-6 oil (high in linoleic acid) is very common now, while n-3 oil (high in linolenic acid) is relatively rare.

Classification of edible oils by fatty acids

In 2011, the linoleic acid intake of men and women in China was 19.8 g/d and 17.2 g/d , respectively [3], while the recommended intake is only about 11.6 g/d (based on 2600 kcal/d) [4].

Therefore, under normal diet conditions, the supply of linoleic acid is sufficient and even exceeds the body's needs.

In contrast, the sources of n-3 fatty acids are limited, with only a few oils (flaxseed oil, perilla seed oil, walnut oil) as sources. In addition, some deep-sea fish, algae, and nuts rich in n-3 do not seem to be frequent guests on our tables.

The result is that the intake of linoleic acid is much higher than that of α-linolenic acid, so the balance always tends to produce ARA, while the synthesis of EPA and DHA is inhibited, resulting in a state of deficiency of n-3 fatty acids.

The deficiency of n-3 is not only closely related to the risk of chronic diseases such as cardiovascular disease and diabetes, but also leads to dysfunction of the nervous system, including decreased vision and anxiety. Some of these "symptoms" belong to the advanced functions of the brain and are often not easy for us to detect and perceive.

02

Your Brain Needs n-3

Compared to other animals of similar size, humans have the largest brains of any species. The brain is complex, sophisticated, and responsible for higher mental functions such as learning, comprehension, and emotional stability.

The composition of the mammalian brain is very different from that of other organs. The lipids in the brain are mainly composed of special highly unsaturated fatty acids, especially DHA. DHA is the most unsaturated fatty acid found in mammalian tissues. High levels of DHA play an extremely important role in maintaining the integrity and fluidity of nerve cell membranes and maintaining the cognitive function of the brain.

The loss of DHA due to various reasons such as age may be related to a variety of elderly diseases related to learning and memory. It can be seen that DHA may not determine the upper limit of your IQ, but it may determine the lower limit of your IQ.

03

Your body needs n-6

Among skin lipids, n-6 fatty acids have functions that cannot be replaced by other fatty acids.

Without n-3, the body (weight and height) may still grow and develop normally and reproduce normally, but without n-6, it will not work.

People first discovered the existence of essential fatty acids because of pathological skin damage, and the disease can be quickly cured by supplementing n-6 fatty acids in the diet.

04

n-3 and n-6: one gains, the other loses

These two fatty acid families share the same enzyme system when synthesizing long-chain polyunsaturated fatty acids.

Reference 5

After all, the number of enzyme resources is limited, so the two fatty acid families will compete for the use of enzymes. If one of them is too strong, it will inhibit the normal metabolism of the other.

The following two pictures can reflect this competitive relationship.

Left: As the intake of n-3 α-linolenic acid increases, the n-6 metabolic line is inhibited, and its precursor linoleic acid accumulates because it cannot be metabolized, and the number of corresponding intermediate metabolites decreases;

Right: Vice versa, when linoleic acid intake is high, the n-3 line is suppressed.

Reference 6

The following picture may be more intuitive. Through the analysis of ten natural populations, it was found that the contents of two fatty acid families in plasma showed a negative correlation trend.

Reference 6

It can be seen that a reasonable ratio must be maintained between them to ensure peaceful coexistence and meet the needs of our body and brain.

Therefore, "balance" is very important, especially the two essential fatty acids: linoleic acid and alpha-linolenic acid.

Strictly speaking, DHA is not an essential fatty acid. Our human body can synthesize it through α-linolenic acid under normal circumstances. However, the synthesis efficiency is very low and may not reach the amount we need on a daily basis. Especially for people in special physiological or pathological conditions, such as infants, pregnant women or sick people, DHA may become a "necessity". Sometimes DHA is also said to be a "conditionally essential" fatty acid.

On February 14, 2020, my country issued the "Diagnosis and Treatment Plan for Severe and Critical Cases of Novel Coronavirus Pneumonia (Trial Second Edition)", which specifically reminded critically ill patients to pay attention to the nutritional supplementation of DHA and EPA | Reference 7

Source: National Health Commission of the People's Republic of China

Reference intake of dietary fatty acids for Chinese residents | Reference 4

For these special groups, in addition to ensuring the supply of α-linolenic acid through a reasonable diet, they should also supplement foods rich in DHA. Adults should also consciously increase their DHA intake in their diet to avoid laying the hidden dangers for the occurrence of brain diseases in the elderly.