Benefits and Risks of Fish for Health: Analysis of 40+ Studies | PRO7fitness.com

Fish is considered a healthy product, and nutritionists recommend including it regularly in the diet for everyone who cares about their health.

The benefits of fish are explained by its content of protein, vitamins, and minerals, as well as essential omega-3 fatty acids, known for their exceptional role in the human body.

However, consuming seafood is associated with certain risks.

The potential harm of fish to human health is explained by the presence of toxins in it, primarily of anthropogenic nature, which enter the water as a result of human industrial activity (mercury, polychlorinated biphenyls, dioxins), as well as parasites, worms, antibiotics, etc.

Some types of toxins pose a particular danger to children and pregnant women (more precisely, their fetus), due to their ability to irreversibly disrupt the process of forming a growing organism.

Not all types of fish are equally dangerous. Among them, there are those that accumulate significantly more toxins or are more susceptible to infection by parasites and worms than others.

The degree of danger is determined by the conditions of cultivation (seas, oceans, or farms) and storage, position in the food chain (predators are more harmful), geography of habitat (the degree of chemical pollution of the oceans varies in different regions), etc.

Thus, we have a classic dilemma characteristic of modern dietetics: on one hand, the product (fish) is incredibly beneficial due to its naturalness and richness in micro and macroelements; on the other hand, it carries a fairly high risk of harm to health as a consequence of environmental pollution and other factors.

In this article, we will discuss what scientific research says about the benefits and harms of fish, and also determine what is more reasonable: a complete refusal to consume fish due to potential harm or consumption despite the risks to gain advantages from its beneficial properties.

Benefits of Fish

Let’s start with the health benefits of fish.

But don’t rush to conclusions.

Practice shows that reading scientifically supported positive information about certain products, especially those we like, greatly stimulates our appetite for these products.

Read to the end and make an informed decision. No, no, it’s not that bad, but a certain degree of caution will be required.

1 Fish – a source of dietary protein

Fish is a source of high-quality protein with a complete amino acid profile. It also has a low content of saturated fats.

Thanks to these two facts, it is included in the list of most popular natural protein products used by athletes for gaining and maintaining muscle mass, alongside poultry, red meat, and dairy products.

Fish is also on the list of permitted products in many effective diets for weight loss (in the “without harm to health” category), as it provides important micro and macro elements, the risk of deficiency of which increases during calorie restriction, and is a source of protein.

During weight loss, nutritionists recommend slightly increasing the proportion of protein in the diet for the following reasons:

• it helps to avoid loss of muscle mass, which is very likely under calorie restriction (many people “lose weight” by losing muscle mass without realizing it);
• protein-rich foods have a higher satiety index (compared to carbohydrates and fats), meaning they better satisfy appetite during meals and suppress the desire to snack between meals;
• protein foods require more energy for digestion (compared to fats and carbohydrates), which increases the number of calories burned at rest.

At the same time, it should be noted that consuming animal protein in very large amounts can be dangerous to health.

Scientists say that regular consumption of large doses (especially with a lack of plant foods) increases the risk of kidney stones, cancer, and leads to decreased bone density.

Fish is a source of dietary protein; because of this, it is widely popular in bodybuilding for gaining muscle mass and is also recommended by nutritionists for weight loss.

2 Fish is rich in vitamins and minerals

Fish is a good source of certain vitamins and minerals. Among them are vitamins A and D, B12, thiamine (vitamin B1), riboflavin (vitamin B2), niacin (vitamin B3), vitamin B6, and minerals such as iron, magnesium, phosphorus, potassium, selenium, and others.

Fatty types of fish are generally characterized by high levels of vitamin D and omega-3 unsaturated fatty acids: a deficiency of both of these micronutrients is one of the most common vitamin and mineral deficiencies worldwide.

The risk of vitamin D deficiency is particularly high for those living in latitudes with a low number of sunny days per year (Russia is among them).

Among other benefits of this vitamin, we will mention just one, relevant for athletes: it is a natural testosterone booster. Scientific studies indicate a clear relationship between low testosterone levels in the blood and a deficiency of vitamin D in the body.

At the same time, statistics show that vitamin D deficiency is observed in 40% of the US population ²². It is unlikely that the situation in Russia is significantly different.

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To illustrate the benefits of fish as a source of valuable macro and microelements, the table below presents the nutritional values of several of the most common types of fish found in our stores.

Note the abundance of microelements, as well as the significant differences in their quantitative content in different types of fish.

The table shows that a small portion of mackerel and salmon is sufficient to meet the daily requirement for vitamin D.

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The same applies to vitamin B12, the deficiency of which is very common among vegetarians and vegans, while fish is on the list of its best natural sources.

Fish contains a wide range of vitamins and minerals, including vitamin D, the risk of deficiency of which is very high among half of the residents of Russia. It is important to understand that the quantitative content of vitamins and minerals varies among different types of fish.

3 Fish – one of the best sources of essential omega-3 fatty acids

Omega-3 fatty acids are nutrients that are sometimes compared in importance for the normal functioning of the body to vitamins, although in the strict sense of the word, they are not.

According to scientific research, omega-3s support brain and cardiovascular health, counteract inflammatory processes, reduce the risk of heart disease and hypertension, help (and protect) in the fight against depression and other mental disorders, and are vital for the normal development of the fetus during pregnancy.

At the same time, the “essential” in the name of these fatty acids implies the necessity of regular intake through food.

This is related to the official recommendation to consume fatty fish such as salmon, mackerel, herring, sardines, and others at least twice a week, which are some of the best natural sources of omega-3.

The benefits of fatty fish are explained by their high content of essential omega-3 fatty acids, which have numerous health advantages.

4 Benefits for the heart and blood vessels

Epidemiological studies of large groups of people indicate that fish consumption is associated with a lower risk of heart attack, stroke, and death from any cardiovascular diseases ^1,14-18.

One of them postulates the following:

“Regular consumption of fish once a week reduces the risk of cardiovascular diseases by more than 15%.”

The most likely explanation for the benefits of fish for heart health is seen in the increased intake of omega-3 fatty acids along with it.

Omega-3 positively affects cholesterol levels in the blood (the level of “good” high-density cholesterol increases, while “bad” low-density cholesterol decreases), reduces the risk of thrombosis and triglyceride levels in the blood – all of which are factors for cardiovascular health.

Regular consumption of fish reduces the risk of heart disease and death from all cardiovascular diseases

5 Fish is good for the brain

As is known, the human brain loses its function with age, and very often elderly people develop senile dementia, one manifestation of which is Alzheimer’s disease.

According to scientific data  regular consumption of fish reduces the speed of neurodegenerative processes and the risk of dementia. The likely reason, again, lies in omega-3 fatty acids ¹⁹.

Scientists talk about a correlation between the mass of gray matter in the brain, which is responsible for memory functions, information processing, and consciousness, and the amount of omega-3 in the diet ²⁰.

This is what concerns elderly people.

For healthy adults, for whom age-related issues are not yet relevant, consuming fish can also be beneficial due to its ability to positively influence mental health.

Research indicates that people who regularly consume fish are significantly less prone to depression. And again – thanks to omega-3 fatty acids.

Over the past 150 years, there has been a significant change in the human diet. The predominance of omega-6 fatty acids over omega-3 has become a factor contributing to the development of inflammatory processes in the body, which accompany many modern diseases, including depression, and cause them.

Consuming omega-3 in the form of supplements or natural products rich in them helps in the fight against depression and other mental disorders, as well as significantly enhances the effectiveness of their medical treatment ²¹.

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Fish is good for brain health. Its regular consumption reduces the risk of depression and other mental disorders, slowing down neurodegenerative age processes

6 Other beneficial properties of fish

Among other beneficial properties of fish are the following:

• benefit for vision: consuming fish once a week reduces the risk of degenerative retinal diseases – the leading cause of vision loss in old age – by ~50% ^23,24;
• benefits for sleep: regular consumption of fish improves sleep quality, one of the reasons for its disruption that scientists cite is a deficiency of vitamin D and omega-3 ^25,26;
• reduction of the risk of autoimmune diseases, including type 1 diabetes ²².

Harm of Fish

The issue of the harm of fish and other seafood, which is periodically and increasingly raised by the media and discussed by scientists in their academic circles, hidden from the public eye, mainly lies in the global pollution of the world’s oceans with chemical waste, leading to the accumulation of various toxins in fish and other seafood.

Among the chemical substances, mercury, polychlorinated biphenyls (PCBs), and dioxins pose the greatest danger.

But this is not the only problem.

For fish, as for any other animals, a high level of parasitic infection is characteristic. In fish farms, antibiotics are used to combat them, which inevitably end up in the fish meat.

To illustrate the overall picture of the potential harm of fish, the table below shows the likelihood of infection and contamination of the most popular species.

The data is obtained based on laboratory tests of samples from various regions of the world’s oceans. Source – FDA (Food and Drug Administration – the main regulatory body in the USA for food, dietary supplements, and medications) ³⁵.

*Scombrotoxin (histamine)* – a toxin that forms in fish when storage conditions are violated immediately after catch.

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1 Mercury

Mercury is a heavy metal that is toxic to the human body, especially during the period of formation and active growth.

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Most likely, everyone has already heard about the problem of mercury content in fish and other seafood, but the answers to the following questions remain unclear:

• How dangerous is mercury to humans and who is in the high-risk group?
• Is all fish dangerous or only certain types?
• Can the concentration of this metal in fish be minimized by choosing specific cooking methods?

According to scientific data, today the entire world’s ocean (rivers, lakes, seas, and oceans) is contaminated with mercury to some extent.

It enters these bodies of water both as a result of natural processes (volcanic eruptions, forest fires) and human industrial activities (coal burning at power plants, gold mining, chlorine production, etc.).

According to information from the FDA website ⁷:

“Almost all fish contains mercury.”

For most people, consuming fish and seafood contaminated with mercury does not pose a serious health risk.

The concentration of mercury in some types of fish and shellfish is higher than in others, which can pose a risk to the development of the nervous system of the fetus during pregnancy or small children.

The risk of harm from mercury contained in fish is determined by its concentration in the fish (which varies among different species) as well as the frequency and amount of consumption.

Therefore, the FDA recommends that women who plan to become pregnant, pregnant women, nursing mothers, and small children consume only those types of fish that have low mercury content.

Fish species with high mercury content: shark, king mackerel, swordfish, marlin, Pacific tuna, and others.

Fish species with low mercury content: salmon, shrimp, sardines, flounder, tuna.

The issue of mercury content in fish is discussed in detail in the article Mercury in Fish: Risks. Scientific Research.

It provides data on the types of fish that accumulate the most and the least mercury, discusses methods for removing it from the body and from fish, and offers recommendations for seafood consumption to avoid harm from mercury.

How dangerous is mercury in fish?

Side effects observed with mercury accumulation in the body include paresthesia (tingling sensations on the skin, burning sensations, “crawling” sensations on the skin), ataxia (disruption of coordination and the consistency of movement of various muscles), and impaired mental and neuromuscular development in children ³².

Mercury inhibits the action of antioxidants, leading to an increase in the concentration of free radicals in the body, which are a known factor in the development of cancer diseases.

At very high concentrations of mercury in the body, death may occur.

One of the main and widely discussed reasons for the harm of fish in the media is the mercury content in it. Today, the entire world’s ocean is contaminated with this metal, which has the property of accumulating in the tissues of living organisms, including fish.

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2 Polychlorinated biphenyls (PCBs) and dioxins

Dioxins and polychlorinated biphenyls (PCBs) are highly toxic chemicals that rank among the top ten most dangerous chemicals for the environment, characterized by high stability.

Despite some differences in chemical structure, dioxins and PCBs are most often understood to refer to the same class of toxins.

PCBs and dioxins were widely used in the past in various industries, including electronics, as heat transfer fluids and hydraulic fluids, as plasticizers and pigments in the production of paints and rubber products, for bleaching paper, in the production of pesticides and polyvinyl chloride plastics, and more. ^28,32

PCBs are tasteless and odorless.

After the discovery of the high toxicity of polychlorinated biphenyls to the environment, their production and use were banned in the USA in 1979, and then worldwide. However, it is evident that they may still be present in products manufactured before the ban was implemented.

Industrial products that may contain PCBs ²⁸:

• transformers and capacitors;
• electrical equipment, including voltage regulators, switches, circuit breakers, bushings, and electromagnets;
• oil used in engines and hydraulic systems;
• old electrical devices or appliances containing capacitors for printed circuit boards;
• fluorescent lamps;
• cable insulation;
• thermal insulation materials, including fiberglass, felt, foam;
• adhesives and tapes;
• oil-based paints;
• minting;
• plastics;
• carbonless copy paper;
• floor finishes.

As a result of improper waste disposal of products containing dioxins and PCBs, their illegal use, leaks from electrical transformers, and the incineration of these wastes, they enter the environment, atmosphere, and the world’s oceans.

In the human diet, estimates suggest that sources of PCBs and dioxins in food are distributed as follows: beef, chicken, pork (~34%), dairy products (30%), vegetables (22%), fish and seafood (9%), eggs (9%) ^32,33.

And in the table below, the approximate content of PCBs and dioxins in food products is presented.

* 1 pg = 1-12 g

Note the record holder – fish fillet from freshwater farms (!).

The maximum dose of PCBs and dioxins considered safe and not recommended to exceed is 1-4 pg per kilogram of body weight per day. That is, for a person weighing 70 kg, this is 70 – 280 pg per day.

Based on this, the recommended total amount of ocean fish (pork, beef, chicken, etc.) per day should not exceed 212-848 g.

The data was obtained in 1995 from selective testing in a laboratory of 110 products from supermarkets in the USA. Naturally, the results of such checks are a function of time and geography: the situation may be different in other countries and most likely improves over time (very little improves over time in our world).

PCBs and dioxins are resistant to degradation and circulate for a very long time: atmosphere, soil/water, atmosphere. They are even found in snowy regions significantly distant from emission sources.

PCBs and dioxins accumulate in plants and animal bodies, including fish. Just like with mercury, they accumulate in the body of fish and other animals due to their ability to dissolve in body fat and their long elimination period.

The longer an animal lives and the higher it is in the food chain (the more predatory it is), the greater the concentration of toxins in its body.

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Health hazards of PCBs and dioxins from fish

PCBs and dioxins cause a wide variety of side effects.

They are carcinogenic to animals, affecting their immune, reproductive, nervous, and endocrine systems, and also have toxic effects on the liver.

Studies on humans also confirm the potential carcinogenic nature of these chemicals and non-carcinogenic effects characteristic of animals (harm to immunity, sexual function, etc.) ^29,31.

According to recent studies in populations of people exposed to constant dioxin exposure, the ratio of male to female births shifts towards females ³⁰.

In humans, PCBs and dioxins accumulate in fatty tissues, so with regular intake into the body even in small doses the overall content in the body can over time reach dangerous levels.

This property is called “bioaccumulation.”

The half-life of dioxins in the human body is 8-15 years ²⁹.

The potential harm of fish to humans can be explained by the accumulation of dioxins and PCBs – highly toxic chemicals, the source of which is human industrial activity. The longer a fish lives and the more predatory it is, the more toxins it contains.

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3 Antibiotics

Fish, like any other animals, can get sick. The causes of diseases can be bacteria, fungi, parasites, viruses, or poor water quality.

In the case of fish population diseases, the producer incurs huge losses, so it is natural that medications are used for treatment and prevention. Just like in humans.

Among the medications used, there are those that are more harmful and less dangerous for humans who subsequently eat such fish.

– Is it safe to eat fish (aquaculture) raised on farms that were treated with antibiotics?

Here’s what the FDA (Food and Drug Administration) has to say about this:

“The FDA is responsible for protecting consumer health and must ensure the safety of food products on the shelves. Part of the approval process for antibiotics used in aquaculture fish farming is the obligation of the producers (farms) to provide the FDA with information that products made from such fish are safe for humans.” ²⁷

It is clear that there are many “buts” in this formulation. If the aquaculture producer is reputable and honestly fulfills the obligations imposed by the FDA, then it is likely that their product can be considered relatively safe.

But usually, none of the consumers know how reliable the information provided to the FDA by the producer is, or if it is provided at all.

It also states that there are antibiotics that are safe for humans, conditionally safe, and dangerous.

Which of them was used by the salmon producer that is currently on your table – no one can say.

Pay attention to the table above regarding the potential harm of fish and seafood: antibiotics have been found in all types of aquaculture.

Antibiotics are used to treat and prevent fish from various diseases. Among them, there are both safe for humans and those that pose potential harm.

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4 Worms and parasites

Parasites are living organisms that live off other organisms and usually to the detriment of the latter. Their carriers can be any animals, including cats, dogs, humans, and of course, fish.

The presence of parasites in fish is as natural as insects on plants.

They pose a danger when consuming raw fish, as well as seafood that has not undergone deep freezing or sufficient heat treatment (see below).

Parasites can also live in marinated, salted, dried, and smoked fish ³⁹.

The harm from parasites is significantly lower than that from pathogenic bacteria, which are present in almost all food products ³⁶.

Roundworms or nematodes are the most characteristic parasites of marine fish. They are sometimes referred to as “mackerel worms” or “cod worms” due to their high frequency of occurrence in these fish species.

The most well-known representatives of roundworms that can live in humans include: ascarids, pinworms, trichinella, hookworms, and dracunculus. Their eggs enter humans when personal hygiene rules are not followed, along with contaminated food and water.

The fight against parasitic nematodes involves expelling them from the host’s body using medications.

There is a great diversity of roundworms: from 24,000 species (studied) to 1 million in total, according to scientists’ estimates ³⁷. They live in soil, lakes, rivers, and seas and cause diseases in plants, animals, and humans – nematodoses.

The spectrum of human disease symptoms is very broad, as these parasites inhabit various organs and tissues, ranging from blood vessels to the eyes, brain, and lymph nodes.

Freshwater fish, such as trout and salmon, which spend part of their lives in freshwater, can be carriers of the tapeworms Diphyllobothrium. These are whitish worms of a flabby constitution that resemble a chewed ribbon ³⁷.

Real-life examples

I remember how one time my ecologist friend told me the results of his own research on freshwater fish for parasite infection.

He and his colleagues caught fish from the Braslav Lakes in Belarus, which are considered some of the cleanest and are sometimes called “Blue Lakes” due to the extraordinary crystal color of the water.

The result of their experiment was impressive: a thorough analysis showed an average of about 20 parasites in each fish…

Well, for those who still doubt that “there are worms in fish” – here are a few amateur videos from YouTube about parasites in sushi, pike, crucian carp, perch, and of course, salted herring…

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How to avoid harm from parasites in marine and freshwater fish?

The likelihood of finding parasitic worms and their larvae in raw fish, especially those that have been salted or subjected to insufficient heat treatment, is very high.

Consuming such fish can lead to the transfer of live worms to humans.

How dangerous is this?

It depends on the type of parasites.

Most of them CANNOT adapt to human hosts and after consuming such fish are digested and expelled without consequences ³⁶.

– Are parasites in fish destroyed during cooking?

Yes, when cooked properly, they do not pose a health risk to humans. “Proper” cooking means cooking at a temperature of at least 60 ⁰C for at least 15 seconds ³⁶.

Parasites are also destroyed by deep freezing at a temperature of -20 ⁰C and below for 7 days ³⁶.

Home refrigerators are not suitable, as they provide a minimum temperature of no lower than -18 ⁰C.

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What are the dangers of parasites in fish? Symptoms of infection

Symptoms of parasitic infection are not always obvious and can sometimes resemble food poisoning, pneumonia, or anemia ⁴¹.

The most characteristic symptoms include:

• itching in the anal and vaginal areas;
• abdominal pain;
• weight loss;
• increased appetite (you need to feed both yourself and them);
• intestinal obstruction;
• diarrhea and vomiting, which can ultimately lead to dehydration;
• sleep disturbances;
• worms in vomit or stool;
• anemia;
• muscle or joint pain;
• general malaise;
• allergy;
• fatigue;
• nervousness;
• and ultimately even – death.

For example (to scare a little), here is a medical report that reveals some details about what it is like to “carry worms” ³⁹:

“A 43-year-old woman was admitted to the emergency department in Edmonton (Canada) with acute diarrhea and vomiting, and she was diagnosed with gastroenteritis (inflammatory disease of the stomach and small intestine).

The symptoms of the disease were eliminated; however, after 8 weeks, the patient returned to the clinic complaining of persistent diarrhea that had not stopped yet. Otherwise, she was healthy.

Prior to this, she had not traveled to exotic countries.

She was prescribed the following tests: a complete blood count; including vitamin B12 levels; liver function tests and lipase tests (an enzyme that breaks down fats); tests for hepatitis A, B, and C; and a stool test for the presence of eggs and parasites.

However, the next day, before the tests were conducted, the patient brought a flatworm measuring 75 cm to the clinic. She took it to the laboratory, where it was identified as a segment of the tapeworm Diphyllobothrium latum.

The other tests were within normal limits, except for the levels of certain antibodies.

During the interview, the patient described herself as a sushi lover who consumes it regularly.

Parasites (worms) are present in almost every fish. The likelihood of their presence in raw, salted, marinated, smoked, or dried fish is very high. They are destroyed by deep freezing and heat treatment.

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BENEFITS vs HARM of fish: to eat or not?

It is clear that fish, on one hand, carries undeniable health benefits for humans, while on the other hand, it poses potential harm due to the accumulation of toxins and the presence of antibiotics, parasites, worms, etc.

What to do?

What seems to be the right solution: to completely exclude it from the diet to avoid harm, or to continue eating it to not miss out on a source of health-beneficial omega-3s, vitamins, minerals, and dietary protein?

Let’s see what scientists say about this.

Researchers from JAMA Networks provide the following assessment of the issue ²:

“The harm from mercury found in fish should not be a concern for most men and women.

Mercury poses a danger when it enters the developing bodies of children and fetuses.

Therefore, pregnant women, women who plan to become pregnant, or those breastfeeding their children, as well as very young children, should avoid consuming four types of fish that contain high levels of mercury: shark, swordfish, king mackerel, and tilefish.

The levels of dioxins and polychlorinated biphenyls in fish, including aquaculture, are very low, comparable to levels in meat and dairy products. Compared to the health benefits, the risk of harm from these chemicals is very low and should not influence anyone’s decision to consume fish.”

According to the data from these same authors, tuna, salmon (both wild and farmed), and shrimp have low mercury content and are relatively harmless.

Considering the health benefits, the advantages of consuming fish outweigh the risks of harm.

This conclusion is supported by the results of an intriguing mathematical analysis of the risks of NOT consuming omega-3 fatty acids found in fish, and the potential harmful substances, including carcinogens, consumed along with it ^32,34:

“For 100,000 people, consuming farmed or wild salmon is associated with a risk of 24 versus 8 deaths from cancer due to the toxins present in fish.

At the same time, consuming omega-3 with salmon will lead to a reduction in the number of deaths from cardiovascular diseases by 7,125 deaths.

The cardiovascular health benefits outweigh the cancer risk by 100-370 times for farmed salmon and by 300-1000 times for wild.”

The risk of harm from PCBs and dioxins in fish can be significantly reduced (by 12-40%), if you avoid consuming the fish’s belly, skin, and other fatty body parts, which accumulate toxins ³².

However, it is precisely in the fatty parts of the fish that the highest amounts of omega-3 are found…

Scientists are convinced that the benefits of consuming fish outweigh the harm from not consuming it, even considering the risks associated with the presence of chemical toxins, parasites, and antibiotics.

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Conclusion

So, let’s summarize:

• all fish are infected and contaminated to some extent;
• to minimize the harm from the chemical toxins present in fish, choose species that are not predators and are smaller in size;
• avoid consuming fish fillets;
• remove the fatty parts of the fish, where the most toxins accumulate;
• do not consume raw, smoked, dried, or salted fish that has not been heat-treated, as it may harbor parasites;
• cook fish thoroughly (at a temperature of at least 60 ⁰C for 15 seconds) to kill parasites;
• most of the beneficial properties of fish are related to its omega-3 content; a similar positive effect can be achieved by taking omega-3 supplements in capsules, in the production of which, as a rule, all harmful substances are removed. This means that it is quite possible to do without fish.