Introduction

There is a growing concern about how the food you digest affects your body and how to maintain a healthy digestive system. Your digestive system plays an important role in breaking down food into nutrients for the body to use for energy, growth and repair. Issues in the digestive system can cause a depletion of nourishment and prevent your body from functioning as normal.

Fatty fish are speculated to have many benefits when digested, from helping support cognitive function to anti-inflammatory properties around the body. One example of a fatty fish is mackerel, which is found to be an excellent source of protein and micronutrients such as vitamin B12, vitamin D, and omega-3 fatty acids. Mackerel is known to be rich in omega-3 fatty acids, particularly EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid).

What is mackerel?

Mackerel is a fast streamlined fish found in dense shallow water that moves in a group together in the warmer months. They feed on zooplankton and small fish, such as sand eels, and are identifiable by their vertical lines on the upper sides.¹ The Atlantic mackerel, also known as the scomber scombrus, is the most common mackerel found but there are many other types of mackerel around the globe.

What are Omega 3 fatty acids?

Omega-3 fatty acids are polyunsaturated fats, also known as the “good fats”. They play a crucial role in forming the cell’s outer layer responsible for providing structural support, determining what enters or leaves the cell and interactions between other cells. 

Role of omega-3 fatty acids in digestive health

Ingesting omega-3 fatty acids is seen to have a positive effect on the gut microbiome, changing its composition and promoting the growth of beneficial bacteria to enhance the digestion of food, regulate the inflammatory response in the gut and strengthen the intestinal barrier² as well as the promotion of mucosal integrity.³ By extension, this will prevent intestinal damage and reduce the risk of a “leaky gut”, where bacteria and toxins from your intestines leak into the bloodstream. Furthermore, its anti-inflammatory properties can aid against inflammatory bowel disease (IBD)⁴ such as Crohn’s disease and ulcerative colitis.

What is the gut microbiome?

The gut microbiome is responsible for supplying nutrients, synthesising vitamin K and being able to carry out vital biochemical pathways for metabolising nondigestible carbohydrates such as resistant starch or cellulose.⁵ In addition, intestinal bacteria also compete for nutrients and attachment sites, preventing harmful bacteria (pathogenic) from being able to attach and potentially enter the intestinal epithelial cells. Antimicrobial compounds are also produced, known as bacteriocins, which inhibit the growth of the bad bacteria and this minimises the risk of toxin release and protects your digestive system.

Role of protein content for digestive processes

Proteins are synthesised from amino acids and are used to make molecules such as enzymes and hormones but are also used to aid in the repair and maintenance of tissues. Digestive enzymes made from amino acids support the digestive system in breaking down food into smaller molecules for absorption and the muscles involved are crucial for the movement of food through the digestive tract. Mackerel is highly protein-dense, providing a lot of protein for the body when broken down and digested.

Vitamin B12

Mackerel happens to be known as one of the best sources of vitamin B12 (cobalamin), so incorporating it into your weekly dinner plan will help prevent a vitamin B12 deficiency due to our diet being its only source. Vitamin B12 binds to proteins in food and is released once the food is broken down to then combine with a protein called intrinsic factor for further digestion through the small intestine. 

As vitamin B12 is utilised by bacteria in the gut microbiome, it also can affect the composition of bacteria present, affecting the balance of the complex system in place.⁷ Additionally, vitamin B12 acts as a cofactor for many enzymes, assisting them in their function as a catalyst in processes in the body. In addition, vitamin B12 is known to be essential for creating red blood cells.

Vitamin D

Another vitamin associated with a healthy digestive system is vitamin D, which supports and regulates the immune response in the gut. Vitamin D also contributes to maintaining the gut microbiome and the intestinal barrier’s integrity by regulating tight junction protein expression responsible for protecting against inflammatory and infectious pathogens.⁸ Eating mackerel accounts for the majority of the vitamin D intake you need daily, so it can be beneficial if you struggle to have enough through your diet or do not get enough sun exposure.

In terms of deficiency, vitamin D deficiency is commonly present in up to 95% of people with IBD and the level of vitamin D present is seen to correlate with the severity of IBD.⁸ Coinciding with this, administering vitamin D has been seen to decrease the severity of IBD, particularly Crohn’s disease.⁹ Therefore, maintaining healthy levels of vitamin D, possibly by eating mackerel, can help with regulating the inflammatory response in the digestive system.

Things to consider when incorporating mackerel into your diet

Considering there is a concern about how much mercury is in fish, the Atlantic mackerel, Pacific chub mackerel, and Spanish mackerel are all low in mercury and can be eaten in two portions a week. However, bigger fish such as the King mackerel have a higher mercury content and should be avoided, as suggested by the Food and Drug Administration (FDA).¹⁰ Toxic effects of mercury can occur on the nervous, digestive and immune systems, and lungs, kidneys, skin and eyes.¹¹ It is especially detrimental to a child's development in the womb so should be considered. This is why it is important to differentiate the fishes that have lower mercury and those that have a higher amount of mercury. Thus, having selected mackerel is safe to consume in moderate amounts.

Summary

In conclusion, eating mackerel has a wide range of positive effects on the body, but particularly can benefit and maintain a healthy digestive system. The gut microbiome is strongly influenced by the foods we eat, so providing the essential nutrients for reducing inflammation and strengthening the digestive system's defences, will help to reduce the risk of gastrointestinal issues such as IBD from occurring. It is important to opt for the smaller mackerel and avoid the King mackerel to utilise the benefits of mackerel without the adverse effects of ingesting a high amount of mercury.

FAQs

What other benefits are there with eating mackerel?

As mentioned previously, mackerel has a high omega-3 fatty acid content, which is linked to a variety of health benefits to the body, not just the gut. Omega 3 is known to prevent heart disease and reduce blood pressure, as well as lower your cholesterol levels through lowering your triglyceride levels. This happens through accelerating the breakdown of triglycerides, which in turn reduces the risk of atherosclerosis and reduces the risk of heart attack or stroke. Omega 3 also increases the high-density lipoprotein (HDL)¹³ that helps remove fat or cholesterol from your bloodstream, thus further reducing the risk of cardiovascular disease and blood clots. Furthermore, cognitive function and mental performance have been found to improve in people with higher omega-3 in their blood, even showing a reduction in the onset of dementia and mental deterioration.^14,15 However, this is suggested in more of an older population rather than the younger, healthier population. 

Mackerel also contains a high level of selenium (Se), a mineral that can activate Se-dependent enzymes for protective function against oxidative damage.¹⁶ This is seen to protect reproductive health by reducing oxidative stress. It also promotes thyroid health, as selenium is converted into selenoproteins that help regulate your thyroid hormones.¹⁷

How much is a portion of mackerel?

Around 140g is a portion of mackerel.¹⁸

Can I still have mackerel if I am pregnant?

It is recommended to have fish such as Mackerel, that are low in mercury, as they are found to have a positive effect on the baby’s cognitive development¹⁰ and linked with a lower risk of preterm birth or a premature birth.¹²

Can eating too much mackerel be bad for you?

Oily fish such as mackerel have a higher level of pollutants than other types of seafood, so eating two portions a week is the maximum recommended amount for:

• Girls
• Women who want to get pregnant
• Women who are pregnant or breastfeeding

This is due to the pollutants being able to build up in the body and affect the future development of the baby.¹⁸