Winter Diets: Supporting Our Immune System

 
 
 

Article by Emilia Fish, BSC MSC ANUTR

There is lots of talk surrounding how our diet may affect our risk of getting ill, and it is important to point out at the start that there is no way to “boost” our immune system, and that there are no miracle supplements or foods which prevent illness. However, having an adequate diet providing us with a balance of all the nutrients we need can help support the healthy functioning of our immune system (1, 2).

The Immune System:

Our immune system is made up of a network of biological processes which protect us from illness (3). It is made from various organs, cells, and proteins and has three main tasks (4):

  • To fight disease causing germs, such as bacteria and viruses, and remove them from our body.

  • To recognise and neutralise harmful substances.

  • To fight disease causing changes in our body, such as cancerous cells.

There are two sub-types. Firstly, the innate immune system, which is a fast, non-specific response, providing general defence against harmful substances. Secondly, the adaptive immune system is a specific response, but its activation is delayed. In this response, our body makes a protein called antibodies which are used to identify and neutralise foreign substances, including pathogenic bacteria and viruses. Our adaptive immune system develops memory against pathogens after a first confrontation so that its response is much faster upon a second encounter with that same pathogen (3, 4, 5).

Our Diet And Immune System:

As previously shared, there is no way to “boost” our immune system; however, eating a balanced diet that provides adequate nutrients can support good immune functioning (5, 6). Please note, research continuously evolves in this field; the evidence discussed is up-to-date as of publication and is meant to be considered in terms of a whole diet.

Dietary Pattern

A poor overall nutrient status has been associated with inflammation, and oxidative stress, which can negatively affect our immune system (2). Therefore, following a dietary pattern such as the Mediterranean diet, which has been shown to have antioxidant and anti-inflammatory properties, may help support our immune system's healthy functioning. The Mediterranean diet is rich in plant foods, including whole grains and extra virgin olive oil, contains a moderate amount of fish, dairy and poultry and limited red and processed meat (3, 6).  

Sources of protein

Dietary protein deficiency has been associated with impaired immune functioning. This may be because amino acids (the building blocks of protein) play an important role in regulating the activation and growth of certain immune cells and producing antibodies and other substances that help remove germs (7).

There are 20 amino acids, 9 of which are essential. The term “essential amino acids” means we cannot make them in our body and therefore must consume them through our diets. Animal and animal products are good protein sources as they provide us with all 9 essential amino acids, as do soy products and quinoa. While most other plant-based protein sources do not contain all 9 essential amino acids on their own, we can consume all of them through eating a variety of plant-based foods rich in protein such as nuts, seeds, and legumes – we call these complementary proteins; and the key is variety (8)!

Oily fish

The impact of Polyunsaturated Fatty Acids (PUFAs) on our immune system has been recognised for a long time, with research specifically focussing on omega-3 PUFAs. These are α-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). ALA is found in nuts and seeds, whereas EPA and DHA are found in oily fish. Research has shown that omega-3 fatty acids can modulate our immune system, have anti-inflammatory properties, and specific effects on certain immune cells (5, 9).

It is recommended for most adults to aim to include 2 portions of fish per week, one of which is oily. This is different if you are pregnant/ trying to conceive/ breastfeeding/ with certain types of fish; you can find out more about the recommendations here. It is great to include oily fish, not just for omega-3 PUFAs, but also because they are a great source of micronutrients too, including vitamins A and D, the B vitamins, iodine, iron, selenium, and zinc (10) – many of which may also contribute to the normal functioning of our immune system (2, 3, 11)!

The gut microbiome

Our gut microbiome plays a vital role in supporting our health, and one of its functions is regulating our immune system (12, 13, 14). Did you know, approximately 70% of our immune system is located in our gut (15)? Therefore, it is important to support a beneficial composition of our gut microbiome, which we can do by (16):

  • Aiming to eat at least 30g of fibre per day by eating a variety of plant-based foods such as fruits and vegetables (aim for at least 5-a-day), choosing wholegrains where possible, and by including beans and legumes, nuts, and seeds.

  • Adding fermented foods into our diets.

  • Including probiotics and/ or prebiotics.

Remember, we don’t have to do everything, and that it is important to find balance, and include things we enjoy. For example, if you do not enjoy fermented foods, it is OK to not have them and instead focus on adding things to your diet you do enjoy!

Micronutrients

Many micronutrients are involved with the normal functioning of our immune systems, such as vitamins A, B6, B12, C and D, and minerals iron, folate, selenium, and copper. It is encouraged to eat a balanced diet, including a variety of foods which will provide adequate amounts of all the nutrients we need (2, 3, 11, 17).

There has been lots of talk about vitamin D and the immune system. Vitamin D has several functions within our body, including a role in our immune system (18). As such, a rapid review was conducted in December 2020 on the best available scientific evidence we have so far by NICE, PHE and SACN. It was “concluded that there is currently not enough evidence to support taking vitamin D solely to prevent or treat COVID-19” (19). However, vitamin D plays an essential role in our health, working with calcium and phosphorus to support healthy bones, muscles, and teeth. While dietary sources include oily fish, cod liver oil, meat, egg yolk, and some fortified breakfast cereals, our primary source of vitamin D is sunlight. During the Autumn and Winter months in the UK, the sun is weaker, and therefore children over the age of one, and adults are advised to take a 10microgram supplement of Vitamin D a day (20). You can find more about the recommendations here.

Lifestyle:

Besides food, many other factors also contribute to our health (21, 22), including:

  • Keeping hydrated. It is recommended to aim for 6-8 glasses (1.5-2L) of fluid a day, focussing on water, but coffee, tea and fresh juices all contribute too (23, 24).

  • Limiting alcohol consumption and quitting smoking. It is recommended to drink no more than 14 units per week, which should be spread across 3 days or more, and to try and include a few alcohol-free days (25, 26).

  • Maintaining good sleep hygiene. It is recommended for adults to have between 6 to 9 hours a night and a regular bedtime schedule (27).

  • Keeping moving. Including physical activity in our routines can help support our overall health and well-being. Try and find what you enjoy: dancing, strength training, gardening, hiking, and so much more (28)!

  • Managing our stress levels. This may be through adding a walk, yoga, stretching, baking, or calling a friend into our routines to take time for you (29).

Summary And Tips:

  • Aim to eat a balanced, varied diet.

  • Support a beneficial microbiome composition.

  • Think about lifestyle factors.

  • Try planning an idea of some meals you will enjoy for the week; this can help us see an overview of the balance of our diet.

  • For specific nutrition needs, please follow the dietary recommendations from your accredited Nutritionist, or Dietitian, GP or other healthcare professional. Other resources available to you include the NHS, British Nutrition Foundation and British Dietetics Association websites.

This blog post was written by Emilia Fish, a Registered Associate Nutritionist with a BSc in Food Science and Nutrition and MSc in Clinical and Public Health Nutrition. She is a Dietetic Assistant who has worked with several accredited Nutritionists and Dietitians and enjoys sharing evidence-based nutrition and recipes on @nutritionnourishment. Emilia shares others nutrition journeys and expertise on her podcast, The Nutrition Nourishment Podcast.

Resources:

  • BDA. Healthy Eating: Food Fact Sheet (30).

  • NHS. What is the Mediterranean diet (31)?

  • The Vegan Society. Nutrients (32).

References:

 
 
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