Top 10 snacks to supercharge your immunity

riding in the rain

According to the Common Cold Research Centre in Cardiff, the average adult will suffer around two to five colds a year.

Apart from the sheer misery of a bunged-up nose and stuffy head, catching a cold can result in an untimely break in your training. In around 25 per cent of cases, symptoms can last for up to two weeks.

While it's possible to catch a cold at any time of year, rates of cold and flu leap upwards during the winter months, and can spread quickly. Although it's not fully understood why colds have a seasonal pattern, a lowered resistance to infection and the freezing air are thought to contribute.

Couple this with the temporary suppression in immunity after strenuous exercise, and you're at increased risk of developing a cold. If you do become infected (and few of us are likely to escape), your body's ability to fight off the virus will determine whether or not you go on to develop symptoms. This ability comes down to your immune response.

The immune system broadly consists of three parts, which work together to prevent you becoming unwell. Physical barriers such as the skin prevent the passage of microbes into the body, while specific immune cells (such as lymphocytes and white blood cells) work to locate, attack and eliminate foreign bodies that manage to find their way in.

Last but not least, antibodies recognise and neutralise foreign bacteria and viruses. Antibodies ‘remember' specific bacteria, which prevents us from becoming infected with the same virus. However, as there are over 200 types of cold virus, it's possible that you can become infected with a different type each time.

One organ that often goes unrecognised for its role in immune function is the digestive tract - around 70 per cent of immune cells are located within the lining of the digestive system (which includes your mouth, oesophagus, stomach and both large and small intestine), and these act as a physical barrier to prevent pathogens and bacteria from entering the body.

Red peppers and tomatoes are good immune boosting foods

Aside from the obvious precautions such as washing hands to prevent the spread of infection, getting plenty of sleep and avoiding overtraining, your diet also plays a key role in determining your body's immune function and ability to fight off a virus. Deficiencies in certain vitamins and minerals are linked with an increased risk of infection, while inadequate levels of protein can suppress the production of certain immune cells.

As well as specific nutrients such as vitamin D, selenium and zinc, there are certain foods and ingredients which have been linked with improvements in immune function. For example, garlic boasts potent antibacterial properties, and has been shown to stimulate the production of white blood cells which destroy harmful bacteria.

Bolstering your natural defences with more of the foods which will support your immune function is therefore a smart idea. Topping up your diet with immune-boosting snacks could help you sail through the winter months cold-free.

Top 10 Immune-boosting snacks

1. Greek yoghurt

Greek yoghurt has surged in popularity over the last couple of years thanks to its high protein and low sugar content, but it has another plus point in the form of good bacteria or ‘probiotics'. The naturally occurring bacteria in yoghurt support immune function by boosting existing levels of good bacteria in the gut, strengthening the natural barrier and creating a more effective barricade to bugs.

In one 2006 study, a daily serving of yoghurt (100-200g per day) was shown to stimulate innate immune response in a group of healthy young women over a four-week period.

Probiotics have also been shown to reduce the incidence of upper-respiratory tract infections in athletes during winter months, and may also reduce gastrointestinal distress often associated with longer bouts of training.

Although probiotics are available in capsule form, ingesting them from yoghurt is a cheaper alternative, plus you benefit from additional nutrients such as protein, which plays an important role in muscle recovery and weight control.

2. Tea

Good news for tea addicts - that afternoon cuppa does more than provide you with a much-needed break, it can also help to fight infection thanks to the high levels of antioxidants.

The best type of tea for bolstering immune function is up for debate, although black, camomile and green tea have all been shown to stimulate positive effects on the immune system. In research from Oregon State University, researchers found that a compound in green tea was responsible for boosted levels of infection-fighting blood cells in mice.

Whatever tea you enjoy, resist taking to the sugar bowl as this will put the brakes on the benefits.

3. Salsa and red pepper sticks

Tomatoes are rich in the antioxidant lycopene, a type of plant pigment which has been shown to enhance immune function by protecting virus fighting cells from damage. In a study led by researchers from the Federal Research Centre for Nutrition in Germany, male subjects supplementing their diet with a daily glass of tomato juice a day showed positive modulations in markers of immune function.

Cooked tomatoes contain more lycopene than raw, so opt for a salsa which is based on cooked rather than fresh tomatoes or make your own by cooking tomatoes, chilli and garlic and a small drizzle of olive oil - the fat boosts absorption of lycopene.

4. Pumpkin seeds

The mineral zinc is a major player in immune function, with deficiencies leading to impairments in the way immune cells function. It also helps to keep skin and mucosal cells healthy, which keeps physical barriers to viruses strong.

Next to seafood and meat, pumpkin seeds are one of the richest sources of zinc and are a convenient source of this important mineral.

As well as essential fats, pumpkin seeds also boast high levels of magnesium, which is a muscle relaxant. Try a handful with a cup of tea, or use to top salads, yoghurt, winter soups and stews. A handful contains around 170 calories.

5. Kiwi fruit

Despite a long-held belief that vitamin C can prevent a cold, an extensive Cochrane review in 2010 concluded that there's not sufficient evidence to support the theory in ordinary populations.

However, they did find evidence that vitamin C lowered the risk in subjects exposed to extreme physical stress, such as marathon runners, skiers, and those involved in winter exercise - in some cases by up to half.

In addition, there's some evidence to show that if you do catch a cold, upping your intake of vitamin C may shorten the duration and severity of symptoms, meaning you get back on your feet more quickly.

Kiwi fruits are one of the richest sources of vitamin C, containing around 70-100 mg per fruit, over 100 per cent of the recommended daily intake. Studies show that adding kiwi fruit to the diet is an effective way to boost plasma levels of vitamin C to optimal levels.

In one 2012 study of older adults experiencing symptoms of respiratory tract infections, those randomised to eat four kiwi fruit per day experienced fewer symptoms of head congestion and sore throat than those randomised to eat two bananas a day. The kiwi fruit group also had higher levels of plasma vitamin C and better antioxidant status.

6. Whey protein

If you've shied away from protein shakes in the past, it could be time to reconsider. Not only is whey protein an effective and convenient recovery aid (a single scoop contains the recommended 20-25g of protein needed to maximise muscle repair) it has also been shown to boost the body's ability to respond to infection.

In particular whey protein is rich in cysteine, an amino acid which the body needs to make glutathione, the ‘master' antioxidant of immune function. Whey protein contains four times as much cysteine as other proteins, making it a superior choice for boosting glutathione.

Two main components within whey protein known as beta-lactoglobulin and alpha-lactalbumin are known to stimulate production of neutrophils, a type of white blood cell involved in fighting off infection.

Both human and animal studies support the assertion that whey proteins can stimulate immunity. In animal studies where rodents are exposed to viruses, supplementation with whey protein results in higher levels of white blood cells, better antibody response and improved resistance to infection.

In a 2010 study evaluating the impact of whey versus soy protein supplement in the immune response of older adults, subjects receiving the whey protein demonstrated a better immune response to 12 of 14 types of bacteria, including the four most virulent strains.

Keep a tub of whey protein in your office drawer and use it to replace a mid-afternoon trip to the vending machine, or add to porridge oats or milk for a protein rich breakfast boost.

7. Pret Salmon and Quinoa Protein Pot

The essential omega 3 fats in oily fish have been associated with numerous benefits, from suppressing inflammatory conditions to heart health and a reduced risk of depression, but new evidence from Michigan State University confirms that they also work to support the immune system.

Although previously believed this was due to a reduction in inflammation, researchers now believe the benefits are down to enhanced activity of B-cells, a type of white blood cell which secretes antibodies.

Oily fish is also one of the few dietary sources of vitamin D, which white blood cells need to mobilise. Low levels of vitamin D have been linked with an increased susceptibility to colds and infection, so getting as much as possible through your diet is important, particularly when sunlight is limited during the winter months.

Pret's Salmon and Quinoa Protein Pot provides a dose of oily fish in a portable pack together with vitamin C-rich peas, lemon and tomato. The combination of protein and slow-release carbohydrate in this snack pot should also stave off hunger, and all for less than 150 calories.

8. Oatcakes

Porridge fans take note - oats are a good source of beta glucan, a type of soluble fibre which has been shown to strengthen mucosal immunity. In a recent study involving beta glucan supplementation in cyclists training in a heat-stress lab, those receiving the beta glucan had a 32 per cent increase in salivary immunoglobulin A (a marker of immune function) in the two hour post-exercise period.

It might not be practical to keep a bowl of porridge on the go during work hours, but oatcakes are a good portable alternative, and thanks to the high fibre content they are a source of slow release energy. Add a spread of peanut butter to keep you fuller for longer.

9. Almonds

In 2010 scientists from the Institute of Food Research in Norwich investigated the effects of almonds on immune function in a simulated human gut, and found that the skins had antiviral activity against the Herpes Simplex Virus.

Interestingly, when the almonds were tested without skins, they had little to no effect, leading researchers to conclude the benefits are down to a compound found in the fibrous outer shell. This fibre has also been associated with benefits in body composition when weight loss diets are supplemented with almonds.

A handful of 25 almonds provides around 180 calories, six grams of protein and around one third of the recommended intake of fibre for the day. Keep them unsalted and skin on in order to benefit.

10. Blueberries & red grapes

Getting plenty of richly coloured fruit and vegetables in your diet is a must as far as immune function is concerned. In a 2013 study from Oregon State University, scientists found that the pigments in red grapes and blueberries increased expression of the CAMP gene, which helps to regulate the immune system.

The pigments (such as stilbenoids) worked in synergy with vitamin D, adding more weight to the idea that the sunshine vitamin is crucial for a healthy immune system.

Team grapes with cheese, add blueberries to porridge, or eat them with a scoop of whey protein to get a double hit of immune-boosting nutrients.

This article was first published in the November 21 issue of Cycling Weekly. Read Cycling Weekly magazine on the day of release where ever you are in the world International digital edition, UK digital edition. And if you like us, rate us!

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Founded in 1891, Cycling Weekly and its team of expert journalists brings cyclists in-depth reviews, extensive coverage of both professional and domestic racing, as well as fitness advice and 'brew a cuppa and put your feet up' features. Cycling Weekly serves its audience across a range of platforms, from good old-fashioned print to online journalism, and video.