To help keep our immune system on track this winter, many of us would benefit from taking a closer look at our lunch box or dinner plate before reaching for the medicine cabinet or the supplement isle. The science is clear that poor diet is a major cause of an impaired immune system, increasing a person’s risk of infection and decreasing the ability of the body to fight infections.(1, 2) Here’s the evidence on the role of diet and immunity and why legumes may be the missing weapon in your arsenal fighting against infection this winter.
Immune responses are fuelled by diet
The immune system is a complex system that protects against infection. While this system is functioning at all times, the presence of a virus or harmful bacteria increases the activity of the system in order to mount an immune response. During such times, the immune system places an increased demand on the body and it is ultimately our diet that must supply the proteins, fats, vitamins and minerals that the immune system requires to respond optimally to ward off or fight infection.(2, 3)
As we enter the winter months, sustaining a nutrient-rich diet is an important step towards building a strong immune system and guarding against common infections like colds and the flu. For many Australians, the first step towards achieving a nutrient-rich balanced diet is to enjoy a wider variety of plant foods, particularly vegetables and legumes, instead of nutrient-poor discretionary foods (like cakes, biscuits, chips, sweetened beverages). The most recent National Nutrition Survey found that over one-third (35.4%) of Australians’ energy intake came from discretionary choices, while only 6.8% of Australians reporting meeting the recommended 5 daily serves of vegetables and only 4.5% of people ate legumes (also classified as a vegetable) on the day of the survey(4, 5). Enjoying a wider variety of plant foods, particularly vegetables and legumes more often will help to ensure a constant supply of the components essential for a healthy immune system including vitamin A, D, E, and B vitamins, zinc, iron, iodine and selenium(2, 3).
Boosting immunity with legumes
As well as delivering essential nutrition, our diet also impacts on the balance of bacteria in our digestive system which plays an important role in our health and immune function. One way to improve the balance of bacteria in the gut is by providing a top of up of live beneficial bacteria, known as ‘probiotics’, which can be found in in fermented foods including cultured dairy products, some fermented milks and capsules. Probiotics have been found to support the immune system in a number of ways, including by helping to create a physical barrier that protects against infection and also by producing a range a compounds that can act directly to inhibit infection.(2)
While probiotics have received lots of attention, there is now emerging evidence that ‘prebiotics’ have the potential to induce the same or even enhanced immune effects, acting through similar mechanisms to probiotics.(2, 6-9) Prebiotics are special types of dietary fibres that ferment in the digestive system and are abundant in legumes (such as peas, chickpeas, lentils and beans), as well as whole grain and high-fibre grain foods containing wheat, rye, barley, oats, brown rice and certain fruits and vegetables.(6, 10) It is this fermentation that helps to feed the beneficial bacteria in the digestive system, improving the composition and/or activity of probiotics (already in the digestive system or consumed) which produce protective components and confer health benefits.(9) Enjoying a range prebiotic-containing foods within a balanced diet may help to support the balance of bacteria and potentially improve immune function.(2, 9)
The bottom line
Whole diets feed our immune system to fight and avoid common infections like cold and flu. The Australians Dietary Guidelines provide recommendations for Australians to meet nutrient requirement of macronutrients and micronutrients that are essential for immune function and resistance to infection.(10) Legumes are one nutrient-rich plant foods with lots of potential to bring balance back to Australian diets that may also enhance immune health through the delivery of essential nutrition and a prebiotic effect – an increase in the balance of beneficial bacteria in the digestive system provides a range of health benefits including improved immune responses.
1. Katona P, Katona-Apte J. The Interaction between Nutrition and Infection. Clinical Infectious Diseases. 2008;46(10):1582-8.
2. Calder PC. Feeding the immune system. Proceedings of the Nutrition Society. 2013;72(03):299-309.
3. Calder PC. The Importance of Nutrition to Healthy Immune Function. Wellmune; 2013.
4. ABS. Australian Health Survey: Nutrition First Results - Foods and Nutrients, 2011-12. Australian Bureau of Statistics, 2014.
5. GLNC. Secondary Analysis of the National Nutrition and Physical Activity Survey 2011-2012 Unpublished: 2014.
6. Muir J. Conference Presentation: What are the risks/benefits of fermentable carbohydrates? The FODMAP story. [4/4/13]. Available from: http://www.glnc.org.au/4th/events/ilsi-presentations/
7. Lomax AR, Calder PC. Prebiotics, immune function, infection and inflammation: a review of the evidence. The British journal of nutrition. 2009;101(5):633-58.
8. Bird AR, Conlon MA, Christophersen CT, Topping DL. Resistant starch, large bowel fermentation and a broader perspective of prebiotics and probiotics. Beneficial microbes. 2010;1(4):423-31.
9. Gibson GR, Probert HM, Loo JV, Rastall RA, Roberfroid MB. Dietary modulation of the human colonic microbiota: updating the concept of prebiotics. Nutrition research reviews. 2004;17(2):259-75.
10. NHMRC. Australian Dietary Guidelines: Providing the scientific evidence for healthier Australian diets 2013 [cited 2015 January]. Available from: http://www.nhmrc.gov.au/guidelines-publications/n55.