Many studies show that an unhealthy gut can have a direct, negative effect on the immune system. 

This ranges from general lethargy and frequent colds to developing autoimmune disorders.

An autoimmune response is where the immune system sees the own body’s cells as a risk and attacks them or creates an excessive immune response.

An underactive response means that it isn’t working at full speed. Either way, it can be difficult to pinpoint the causes.

Simon Bandy, general manager of the nutritional supplements brand Health Plus, which has been family run for more than 25 years, said "Staying active and eating a balanced diet can help to keep your body in tip top shape. 

"But something as simple as a tummy bug that goes untreated at the source can increase risk to your immune system.”

Here, Simon talks about the simple steps you can take to restore and maintain a healthy gut.

Bad bacteria, fungi, yeasts and parasites can get into our body and many are encountered in ways we don’t often realise. Here are some of the most common:

- Tap water

- Parasites from the environment or our food

- Food poisoning

- Fish from polluted waters

- Birth control pills

The best way to regain good gut flora balance and to establish a healthy digestive system (and therefore improved immune system) is simply to consume more good bacteria than bad.

There are plenty of things that you can include and remove from your diet to help aid a healthy gut and immune system.

Avoid foods that are high in yeast and refined sugar as these will encourage the bad bacteria to multiply.

Fermented foods are becoming increasingly popular in the UK and are incredibly rich in beneficial probiotic bacteria, so try to include a few fermented vegetables in your weekly meal plan.

Options include sauerkraut (finely cut fermented cabbage, widely available on the high street), kimchi (the Korean spicy version of sauerkraut which is also high in fibre), kefir (a fermented milk drink) and more easily found in the supermarket is live or cultured yoghurt.

Remember to also feed these good bacteria with prebiotics which can be found naturally in fruits and vegetables like artichokes, bananas and onions.

Simon added: "As research is showing us, the link between poor gut health and overall health is very strong.

"Too much bad bacteria can seemingly have an affect not only on our physical health, but also on our emotional wellbeing too.

"Links have been made to poor mood swings and even autism. Including fermented foods or a good probiotic in your daily life could make a huge change to your overall health and is a simple change to make.”