This week’s post was written by Zoe Cooke, a first year student of the Bachelor of Applied Science and Master of Dietetic Practice at La Trobe University.
Zoe has been an ethical vegan for six years, for the wellbeing of humans, animals, and the planet alike. Zoe promotes a vegan lifestyle and shares plant-based recipes through her blog and Instagram account. Zoe has a particular interest in whole food, plant-based nutrition and the effect it has on human health, and she aims to incorporate this interest into her future studies, research, and practice as a dietitian when she graduates.
Winter is finally upon us, and with its arrival also comes the dreaded cold and flu season. Luckily, there are a number of steps you can take to boost your immune system and reduce your susceptibility to infection, including:
1. Increase your intake of phytonutrients
There is good evidence that phytonutrients found in plant-based foods such as fruit, vegetables, nuts, seeds, whole grains and legumes are able to boost our immune system . Phytonutrients are bioactive compounds produced by plants to protect themselves from the environment, pathogens, and pests. Plants contain tens of thousands of different phytonutrients, such as:
- Carotenoids: found in yellow-orange coloured fruits and vegetables such as carrots, sweet potatoes, pumpkin and mangoes;
- Flavonoids: found in kidney and black beans, berries, beetroot and eggplant;
- Lignans: found in sesame, sunflower and flax seeds, mushrooms, oats and whole-grains;
- Isoflavones: found in soy beans, green beans and mung beans;
- Isothiocyanates: found in Brassica family vegetables such as broccoli, Brussels sprouts, cauliflower, kale and cabbage.
Aim to include a rainbow of fruits and vegetables every day, as different colours in these foods corresponds to different antioxidants. For example, sweet potato, carrots and pumpkin get their bright orange colour from the carotenoid phytonutrients they contain. Try adding grated carrot to your morning porridge, and swapping a sandwich at lunch for a soup packed with winter vegetables and beans.
2. Ward off bacteria with ginger and garlic
Ginger and garlic are widely used in many parts of the world not only to flavour food, but also to prevent and treat bacterial and fungal infections in traditional medicine. The antioxidant and antimicrobial properties of ginger can be attributed to the phytonutrient gingerol (2), and allicin in garlic (3).
Add freshly sliced ginger to black tea for a kick, and try adding freshly-minced ginger and garlic to a vegetable stir-fry.
3. Eat more mushrooms
The body’s greatest contact with the outside world is via the mucous membranes that line the digestive tract. The body produces antibodies to protect these membranes such as immunoglobulin-A (IgA), which flags foreign substances for destruction by the immune system (4).
Daily intake of mushrooms is thought to contribute to the immune responses that result in the secretion of IgA antibodies, and in turn, boost immunity by reducing the entry of pathogens across the mucous membranes and into the body (4).
Add sliced mushrooms to a lentil Bolognese pasta, or try a hearty mushroom risotto.
4. Get enough vitamin D
Vitamin D is well known for its ability to enhance calcium absorption in the body, but less recognised for its ability to influence the activity of the immune system. Vitamin D receptors are present on almost all immune cells and have been found to regulate both the innate and adaptive immune system (5).
Vitamin D is primarily obtained from the synthesis of vitamin D3 in the body when the skin is exposed to the sun’s UV rays. Dietary sources (on a plant-based diet) include mushrooms exposed to UV light (marketed as ‘vitamin D enriched’) and fortified foods, such as certain soy milks.
5. Up your intake of prebiotics and probiotics
Prebiotics are dietary fibres found in an array of plant-based foods which provide a food source for our hard-working gut bacteria (6). Prebiotics are found in foods such as wheat, rye, garlic, onions, broccoli and cauliflower, and are also formed when starchy foods such as rice and potatoes are cooked and cooled (known as ‘resistant starch’, as it resists digestion and absorption in the small intestine).
‘Probiotics’ refers to foods containing live organisms, such as cultured yoghurts, fermented vegetables such as kimchi and sauerkraut, natto (a traditional Japanese fermented soy food), and fermented drinks such as kefir and kombucha. Probiotics can also be found as dietary supplements, but the evidence is inconsistent as to whether supplementation with probiotics is helpful for preventing colds and flus (7)
Unless you have recently taken a course of oral antibiotics or have had about of food poisoning, it may be more effective to boost your immune function by nourishing the microbes already present within your gut, which can be achieved by increasing your consumption of prebiotic dietary fibres.
- Choose a wide variety of fruits and vegetables
- Include at least 6 serves of vegetables (3 cups cooked) and 3 serves of fruit (3 pieces/3 cups) every day
- Include legumes (such as chickpeas and lentils) every day
- Include whole grains such as dark rye bread and whole grain pasta every day
- Choose nuts such as cashews and almonds as a nutritious, prebiotic-rich snack
6. Get enough sleep
Several studies have shown that sleep deprivation can impair the function of the immune system, which increases susceptibility to infection (8).
If you are struggling to get enough sleep - see Lucy’s blog post Nutritional Strategies for Improving Your Quality of Sleep for more information on how to improve the quality of your sleep.
7. Get regular exercise
Along with a nutritious diet and adequate sleep, regular physical activity is a core component of a healthy lifestyle. Studies show that people who engage in regular physical activity (compared with those who are sedentary) have enhanced immune functioning (9).
However, it is important to note that the immune-boosting effect of exercise is credited to moderate physical activity (approximately 2.5-5 hours per for adults (10)), and that intense, prolonged physical activity (such as marathon running) may actually have a negative impact on immune system functioning (9).
Find a form of exercise you enjoy and aim to incorporate 30-60 minutes each day.
Finally – if you are looking for a simple, nourishing meal full of powerful immune-boosting phytonutrients, look no further than this delicious Spiced Carrot and Lentil Soup!
Spiced Carrot and Lentil Soup
- 1 medium brown onion, roughly chopped
- 2 garlic cloves, finely sliced
- 5 large carrots, peeled and roughly chopped
- 2 celery stalks, roughly chopped
- ½ cup dried red lentils
- 1 tablespoon fresh ginger, finely grated
- 1 tablespoon fresh turmeric, finely grated
- 2 bay leaves
- 1 litre vegetable stock, look for a low sodium variety
- To garnish: 1 large red chilli (thinly sliced), spring onions (thinly sliced), fresh coriander leaves (chopped)
- Heat a large pot over a medium heat, and add a splash of water (to prevent sticking), the onion, garlic, carrot, celery, bay leaf, turmeric and ginger. Cook for approximately 10 minutes until soft
- Add the red lentils and stock and bring to the boil. Reduce the heat to a simmer and cook for approximately 20 minutes until the carrots are tender
- Remove from the heat, discard the bay leaf, and allow to cool slightly before pureeing. You can either use a blender, a food processor or an immersion blender to puree. Blend until the soup is a smooth consistency
- Ladle the soup into a bowl, top with the garnishes as desired, season to taste with salt and cracked black pepper and serve with crusty whole grain sourdough bread
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3. Schäfer G, Kaschula CH. The Immunomodulation and Anti-Inflammatory Effects of Garlic Organosulfur Compounds in Cancer Chemoprevention. Anti-Cancer Agents in Medicinal Chemistry. 2014;14(2):233-240. doi:10.2174/18715206113136660370.
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5. Baeke F, Takiishi T, Korf H, Gysemans C, Mathieu C. Vitamin D: modulator of the immune system. Current opinion in pharmacology. 2010 Aug 31;10(4):482-96.
6. Rad AH, Akbarzadeh F, Mehrabany EV. Which are more important: Prebiotics or probiotics? Nutrition. 2012 Nov 1;28(11/12):1196.
7. Allan GM, Arroll B. Prevention and treatment of the common cold: making sense of the evidence. CMAJ. 2014;186:190–9.
8. Motivala SJ, Irwin MR. Sleep and immunity: Cytokine pathways linking sleep and health outcomes. Current Directions in Psychological Science. 2007 Feb;16(1):21-5.
9. Nielsen HG. Exercise and immunity. Current Issues in Sports and Exercise Medicine. 2013:121-40.
10. Australian Government Department of Health. Australia’s physical activity and sedentary behaviour guidelines [Internet]. 2012 [cited 12 June 2017]. Available from: http://www.health.gov.au/internet/main/publishing.nsf/content/health-pubhlth-strateg-phys-act-guidelines