More robust immunity through ancestral eating habits

A healthy defence system doesn't just appear out of nowhere. It is shaped by the constant interplay between digestion, diet and the body's own defences. Science on microorganisms and immune responses shows that old eating habits were often smarter than we thought: what you eat influences how your defences respond, partly thanks to the vitamins, minerals and natural compounds in raw or minimally processed food.

Research into evolution-inspired dietary patterns helps us better understand this link between the digestive tract and the immune system. Many people today eat more refined sugars and heavily processed foods, while their intake of fermentable fibre, organ meat and fermented foods is declining. Research shows that people who eat plenty of unprocessed foods, such as fish, vegetables, fruit, nuts or legumes, often show fewer signs of low-grade inflammation than people on a diet full of processed ingredients.

Gut and immunity: the central hub

More than two thirds of all our immune cells reside in or near the abdominal organs. The gut wall, for example, contains a lot of lymphoid tissue, together with cells specialised in recognising danger. While this barrier is open to vitamins and sugars, it keeps harmful invaders out. Bacterial diversity plays a key role in these cardinal functions: what grows there, and how much, influences how tight the defence is.

Diet is very important here. Bacteria in the gut ferment the fibre from root vegetables, vegetables, fruit and old-fashioned grains into short-chain fatty acids. One example is butyrate, which is thought to help maintain a firm gut lining and to regulate how immune cells respond.

A Stanford study found that regularly eating fermented foods (think yoghurt or sauerkraut) for ten weeks increased the diversity of gut bacteria. Various substances in the blood that indicate inflammation also decreased. Research suggests that when more, and more diverse, microorganisms live in the gut, the immune system often responds in a more stable way.

All over the world, fermentation has played a central role in nutrition for centuries. In Europe people ate sauerkraut, while kimchi became popular on the Korean peninsula. Japan had miso and natto. In Ethiopia, injera flatbread is a staple of meals. Fermented cassava is used in many African dishes. The Caucasus knew raw kefir as part of its traditional food culture. Through these products, people regularly consumed live microorganisms. Organic acids are formed during fermentation, as are bioactive compounds that can change the gut flora.

Micronutrients and traditional food

Traditional food is known for its rich nutrient content. Herbs and shellfish are naturally rich in nutrients. Organ meats provide concentrations of vitamins that are not found in processed meat. Proteins from eggs play a role in bodily processes in ways that are often underestimated. Beef bone broth contains a wide variety of nutrients.

Vitamin A

Vitamin A contributes to the maintenance of normal mucous membranes, such as those in the airways and gut, which form a protective layer between the body and the outside world. Egg yolk and liver supply plenty of retinol; of all everyday foods, liver contains by far the most of this vitamin. Vitamin A also contributes to the normal function of the immune system.

Vitamin D

Acting as a prohormone, vitamin D interacts with both the innate and the adaptive immune system: many immune cells carry receptors for it. Vitamin D contributes to the normal function of the immune system. Everyday sources used to include cod liver oil, fish liver and oily fish. Research has repeatedly found an association between low vitamin D levels in the blood and a higher incidence of respiratory infections.

Zinc

Zinc contributes to the normal function of the immune system and has a role in the process of cell division. It is also involved in the messages that cells exchange and influences how quickly certain proteins can do their job. Of all foods, oysters contain by far the most zinc. Beef liver and kidneys are also good sources.

Iron, selenium and copper

Dishes such as liver and shellfish are excellent sources of iron, selenium and copper. Iron, selenium and copper contribute to the normal function of the immune system, and selenium also contributes to the protection of cells from oxidative stress. Iron contributes to normal oxygen transport in the body, but an imbalance can disrupt the body's defences. When an infection occurs, the body automatically adjusts how much iron is released. This adaptation ("hypoferraemia of inflammation", or "nutritional immunity") happens through built-in systems that prevent bacteria from profiting from excess minerals.

Omega-3 fatty acids

Seafood such as oily fish, mussels and oysters contains the omega-3 fatty acids EPA and DHA, which are being studied for their role in the body's resolution of inflammation.

Ancestral foods of interest to immunologists

Here are a few examples of age-old foods that enjoy the keen interest of immunologists.

• Bone broth: it contains glycoproteins, as well as building blocks such as glycine and proline. Glycine and proline are building blocks of collagen in tendons, skin and cartilage, and they are released from the bone material during long simmering.
• Kefir or yoghurt: fermented dairy products contain active bacteria. Live cultures are crucial.
• Pickled and fermented vegetables such as sauerkraut, kimchi and gherkins.
• Berries contain many substances that interact with gut bacteria.
• Garlic and onions contain sulphur compounds that inhibit bacteria in lab tests.
• Turmeric has been studied for its effects on inflammatory signalling.
• Honey has been on the table for centuries, not only as food but also to make products keep longer. Honey contains vitamins, minerals, enzymes and polyphenols (including flavonoids and phenolic acids), and it inhibits the growth of bacteria and fungi, which is why it was used for preservation.
• Seaweed contains plenty of iodine. It also contains special fibres that gut bacteria can use as food, which they break down into compounds that affect digestion.
• Seeds and nuts. These provide zinc and selenium together with vitamin E.

Colostrum

After birth, mammalian young first receive colostrum. Regular mother's milk follows later and differs greatly in composition due to specific components. Colostrum has a twofold function for the newborn: nutrition and building up immunity. The latter happens through concentrated antibodies (the immunoglobulins IgA, IgG and IgM), white blood cells and growth factors. The result is so-called passive immunity in the calf or child; at the same time, the gut microbiota is established, which in turn benefits growth.

Conclusion

A more robust defence doesn't come from one magic ingredient: it stems from a diverse way of eating. Research on the gut flora, the body's responses to injury or invaders, and vitamins supports this view. Returning to the diet of the past fits in with this. What was everyday fare centuries ago often matches surprisingly well with what our cells need now more than ever.