Dietitians are often asked by people what should they be eating to keep themselves as healthy and as well as possible during the seasons. So, how do you keep your immune system running at its best, particularly during winter where you can feel run down and tired a lot of the time?
What is the immune system?
The immune system is a group of organs and cells that defend the body against infection, disease and foreign substances. It acts to protect us from infectious agents that exist in the environment (eg. bacteria, viruses, fungi, parasites). There are large variations in many immune functions amongst individuals. Genetics, age, gender, smoking habits, habitual levels of exercise, and history of infections and vaccinations all contribute to this variation and susceptibility to infection.
Does the way we eat affect the immune system?
Due to the complex nature of the immune system, it is very difficult to assess the effects of diet on immune function. However, research has shown that diet does not have a key role to play on immunity. There are several nutrients that have been demonstrated (in either animal or human studies) to be required for the immune system to function efficiently. Adequate intakes of these nutrients maintain an effective immune response, stimulating the activity of infecting fighting white blood cells and antibodies.
What are the particular key nutrients involved?
- Vitamins - A, B, B12, C, D, E, folic acid
- Minerals (trace elements) - Zinc, Selenium, Iron, Copper
- Omega-3 fatty acids
A deficiency in one or more of these nutrients have been shown to suppress the immune system.
Where are all these nutrients found?
Energy intake (ie kilojoules or calories) seems to have an important influence on immune activity. Undernourished people are at greater risk from infections. Hence poor nutritional intake impairs the immune system. Excessive energy intake and obesity may also compromise the immune system's ability to fight infection.
High carbohydrate foods are a great source of energy. Try some porridge or a wholegrain cereal for breakfast. Add some pasta or white or brown rice to a soup or stew.
If your appetite is lacking, try and eat small meals and snacks often. High energy and protein foods include milkshakes, low fat yoghurt cheese and biscuits, egg sandwich, tinned tuna, peanut butter on an English muffin.
Cook casseroles and soups during the winter and freeze portions. Then you will have a ready made meal handy when you are feeling tired but will ensure you do not skip meals
This vitamin is made in the body from beta carotene which is found in most yellow, orange and green fruits and vegetables.
Add chopped carrots or diced pumpkin to a casserole. Toss some sliced apricots or rockmelon in a salad.
Vitamin B6 (or pyridoxine) is found in a wide range of foods including organ meats (eg liver and kidney), muscle meats such as beef, chicken and pork, fish and eggs. Good sources of this water soluble vitamin also include fortified breakfast cereals, soybeans, peanuts, walnuts and unpolished rice. Adults require about 1.3-1. mg/day.
Choose cereals where vitamin B6 has been added. Many cereal provide up to 0.4 mg per 30 g serve which meets 25% recommended dietary intakes (RDI).
Vitamin B12 comes from foods of animal origin such as red meats, milk and dairy products, seafood and eggs. Hence, because plant food do not naturally contain B12, vegetarians are at risk of vitamin B12 deficiency. Despite the claims, mushrooms, tempeh, miso, seaweed and sauerkraut are not reliable sources of this vitamin. Lacking vitamin B12 can adversely affect neurological function including memory and concentration
Consume foods that have been fortified with vitamin b12. For example, some soymilks, cereals, soy burgers.
Since lean read meat is an excellent source of B12, make a casserole with diced beef.
This well known vitamin is naturally found in many fruits and vegetable including citrus fruits, berries, kiwi fruit, blackcurrants, tomatoes, red capsicum, broccoli, sprouts and cabbage. Adults need about 45 mg/day. One orange will provide 60 mg of vitamin C, one lemon 48 mg, half grapefruit 36 mg.
The major source of vitamin D for humans is exposure to sunlight, as this vitamin is made in the skin. Studies have shown that vitamin D deficiency is more common in the winter months. In Australia, fortified margarine are the major source of this vitamin together with types of of oily fish (eg salmon, herring, mackerel) and eggs (particularly the yolk).
The main source of this important antioxidant and immune booster is fats and vegetable oils. It is also found in seeds and nuts, some vegetables, and grains.
Use sunflower, safflower, soybean, corn, canola, cottonseed or olive oil in your cooking. Nibble on seeds and nuts if tolerated, as a snack.
Cereals, cereal products, vegetables (eg green leafy vegetables) and legumes are the major sources of folate in Australia according to the National Nutrition Survey undertaken in 1995. Many cereals are fortified with folate as are some orange juices.
Zinc is a mineral that is essential for a healthy immune system. The recommended dietary intake (RDI) for zinc is 8 mg/day for women and 14 mg/day for men. It is widely distributed in foods. The richest sources of dietary zinc are oysters, zinc fortified breakfast cereals, lean red meat (such as beef), dairy foods, fish (such as cod), poultry, wholegrain breads, legumes, pumpkin seeds, almonds, cashews, pecans.
Purchase cereals that have zinc listed in the Nutrition Information Panel. Some cereals contain 1.8 mg zinc per 30 g serve (15% RDI).
Selenium rich foods include seafood (eg tuna, red snapper, lobster, shrimp), chicken and egg yolks. Other sources of this trace element and antioxidant include wholegrains, vegetables (depending on the selenium content of the soil they are grown in), brown rice, cottage cheese, sunflower seeds, garlic, brazil nuts and lean red meat.
Sprinkle some sunflower seeds on a breakfast cereal or as a snack, nibble on a handful of brazil nuts. Nuts and seeds can even be thrown into a soup.
Iron is an essential mineral, vital for good health. There are two major types of iron in foods - haem and non haem iron. Haem iron is well absorbed by the body and s found in foods such as lean red meat, liver, kidney, seafood and poultry. Non haem iron is found in plant foods such as legumes, wholemeal breads and wholegrain cereals, green leafy vegetables, nuts and seeds. This type of iron is not as well absorbed by the body.
Maximise non-haem iron absorption from foods (by up to 2 to 3 times) by having a vitamin C source at the same meal. Top iron-fortified breakfast cereals with strawberries, or drink a small glass of orange juice with breakfast. Add tomato or red capsicum to lentil dishes, wholemeal pasta or rice dishes.
Copper is widely distributed is foods such as organ meats (eg liver), seafood (eg shellfish), nuts and seeds, legumes, wheatbran cereals and wholegrain products,. This mineral is mainly absorbed by the small intestine although some absorption may also occur in the stomach.
Omega-3 Fatty Acids
These polyunsaturated fats are important nutritional substrates which help improve immune function. Foods high in omega-3 fatty acids include salmon, sardines, mackerel, trout, halibut, herring, tuna and cod. Other sources are walnuts, flaxseed oil, canola oil, pumpkin seeds, lean red meat and omega-3 eggs (produced by hens that are fed flaxseed).
Aim to have some oily fish 2-3 times a week. Add a teaspoon of flaxseed oil to a fruit and yoghurt smoothie.
Other potential immune enhancing agents
There is increasing evidence that probiotic bacteria (ie "friendly bacteria" such as Acidophilus) can improve host immune function, as well as keep your digestive tract healthy. However, more research is needed in this area. Probiotics are found in dietary supplements or as a nutritional ingredient in fermented dairy products such as yoghurt.
Phytochemicals are natural protective substances found in plant foods that, like vitamins and minerals, help to boost the immune system. It is these substances that give fruit and vegetables their distinctive colours and smells. Generally, fruits and vegetables are classified into five colour groups according to the phytochemicals they contain. For exmaple, the phytochemical lycopene contributes to the red colouring of tomatoes, red capsicum, rhubarb, strawberries and radishes.
Add colour to your plate by choosing all different types of fruits and vegetables each day. That way you are maximising your phytochemical intake.
Add some green foods to your stews such as broccoli, green peas or spinach.
Add some white/brown foods to your soups such as garlic, cauliflower, mushrooms, onions and potatoes. Garlic is a well known antioxidant with immune boosting properties. Marinate meats or tofu with some crushed garlic or olive oil.
Include some purple/blue foods in your diet such as beetroot, eggplant, purple grapes, purple asparagus.
Orange/yellow foods can be easily added to your current intake such as mashed sweet potato and pumpkin, sliced squash or corn as a side dish. Oranges contain over 170 known phytochemicals!
Add herbs and spices to your cooking for added flavour and for their antioxidant power. Try fresh oregano, basil, thyme, rosemary or dill.
Though this article may seem basic, it does raise some good points about how general nutrition plays a big role in the prevention of colds, flu and most illnesses.
By adopting some simple and effective nutritional strategies, and using preventive natural medicine, you can easily make it through the seasons without so much as a sniffle.
Eating well, staying warm and keeping active are all very simple and easy ways to prevent the sniffles.
Using a natural supplement like Bioceuticals Armaforce will help to boost your immune system and fight the onset and symptoms of colds and flus. Echinacea is also a great immune booster - try Eagle Pharmaceuticals Echinacea Royale to give your body the best chance of fighting those nasty bugs.