Why are there few fish in the northern lakes and how is it useful for food? How is an imbalance in omega-3 and omega-6 polyunsaturated fatty acids associated with cardiovascular disease? Mikhail Ivanovich Gladyshev, Corresponding Member of the Russian Academy of Sciences, Head of the Laboratory of Experimental Hydroecology of the Institute of Biophysics, FRC KSC SB RAS answered these and many other questions to the digital edition “Scientific Russia”.

─ It is generally accepted that there are a lot of fish in the North. Is it really so?

I would argue that this is a popular misconception. There is a lot of fish in the North until you start catching it: the northern Arctic ecosystems are oligotrophic in nature, that means that they have very low production. If you come to the northern lake, where no man's foot has stepped, then during the first fishing there will indeed be a lot of fish, but you need to understand that this fish has been growing for many years, and having caught it once, the next year such a rich catch is already not possible.

In northern lakes with clean transparent water, there can be no high production by definition. These lakes can grow a high biomass of fish but fish grows slowly in such lakes with little food. After catching big fish, the lake will reach this large biomass only after many, many years.

Northern low-productive lakes must be exploited with extreme caution in order to exactly calculate how much fish we can take from it in a certain period of time.

- Are there still lakes and rivers untouched by man in Russia in the North, in particular in the Krasnoyarsk Region?

There are a huge number of lakes and rivers untouched by man. Remember the famous Taimyr reserve, where, by definition, nothing can be touched. There are hundreds of thousands of lakes in the Arctic and there is more water than land in the tundra, for example, in the polar tundra, there is generally more water than land. Of course, in the North there are countless lakes and rivers, but they are all oligotrophic and low-productive.

─ Do you think fish must be present in the human diet?

Yes, and this is due to the balance of polyunsaturated fatty acids (PUFAs), omega-3 and omega-6.

From omega-6 ARA, for example, thromboxanes of the second series are synthesized, which constrict blood vessels and increase platelet aggregation, that is, increase blood pressure, or prostaglandins of the second series, which trigger the recovery response. And from its counter-regulator, EPA, acids of the omega-3 family, namely, endohormones, are synthesized, which have the exact opposite effect: they dilate blood vessels, reduce platelet aggregation, that is, blood pressure, and have an anti-inflammatory effect.

The human genotype is initially tuned to a one-to-one ratio of omega-3 to omega-6. It is with this balance that our body functions normally; in this case inflammation and pain do not kill us, but, on the contrary, heal our organism, in particular, from infections.

It is important to note that in the human body, especially in that of Caucasian race representatives, ARA and EPA, and another important regulator from the omega-3 family, docosahexaenoic acid (DHA), are very poorly synthesized from biochemical precursors, which are short-chain omega-6 and omega-3 acids, and we must definitely get ARA, EPA and DHA from food.

─ And if a person, for example, does not eat meat, but eats only seafood, fish, then these problems of imbalance of omega-3 and omega-6 will not affect him?

You are absolutely right. By the way, on earth, in terrestrial food, these acids are not present, because plants synthesize only short-chain acids with 18 carbon atoms. And long-chain omega-3 acids with 20 and 22 carbon atoms, EPA and DHA, are synthesized only by some types of microalgae, then they are transferred along the food chain to fish, being accumulated there. So, fish is the main source of EPA and DHA for humans.

─ What about flaxseed oil, which is often advised to be consumed for omega-3s?

All terrestrial plants are unable to synthesize EPA and DHA, the precursors of endohormones. Flaxseed oil, like, for example, rapeseed and camelina, contains only 18-atom alpha-linolenic acid from omega-3; it is a precursor of eicosapentaenoic acid. In principle, we can synthesize eicosapentaenoic acid from this acid, but our synthesis is ineffective and covers only 5% of the body's physiological need in long-chain acids! Therefore, the World Health Organization and a number of scientific medical societies in different countries recommend for the prevention of cardiovascular diseases a daily intake of one gram of eicosapentaenoic and docosahexaenoic acid, which is found only in fish. It is simply absent in the oil of terrestrial plants. When you come to the pharmacy and see the pills named “Omega-3-acids”, you should ask: “What kind of acids are these? How many carbon atoms are there? " If it is 18-atomic alpha-linolenic acid, it simply won't work. But if it is eicosapentaenoic and docosahexaenoic acid, then everything is fine.

─ It turns out that linseed oil and the like are not suitable. What about fish oil? How can we find the fish oil on the counter which would meet our need in EPA and DHA?

Eicosapentaenoic and docosahexaenoic acids, precursors of endohormones, are not found in the fat that comes from fish. Fish oil is a storage nutrient called triglycerides, non-structural storage components.

If the fish oil which flows from fish is collected and sold in a capsule form, this does not mean that it is an omega-3 acid. But they can be made in a special way, with capsules containing the high required daily dose of EPA and DHA, and of course, they cost a lot of money. And it is easier, for example, to eat 40 grams of saury, where a can of this fish contains 5 daily doses of EPA and DHA, than buying such pills. In addition, human digestibility of EPA and DHA obtained with fish meat, for example, with such canned saury, is 3 times better than the digestibility of acids contained in pills.

If you do decide to buy fish oil from a pharmacy, then please note that eicosapentaenoic and docosahexaenoic acids must be there.

I believe that fish consumption should be promoted. It is known that in Russia almost half of deaths are associated with cardiovascular diseases. At the same time, it has been proven that receiving EPA and DHA, which are found in fish meat, together with food, can reduce mortality from cardiovascular diseases by at least 35%.

Meat and hamburgers themselves are not poisonous, but in order to avoid harm, this meat in the diet needs to be balanced with fish. If a person eats, for example, 40 grams of saury or 50 grams of herring per day, he will have a physiologically optimal balance of omega-3 and omega-6 PUFAs that ensures health.


Source: Scientific Russia