Eating for your gut microbiome

Throughout the past decade or two, more and more research has been done into the gut microbiome and its effects on our health. In fact, the more research is done on this, the more we realise just how much our microbiome affects us. Since the launch of the Gut Microbiome project in 2007 (NIH Human Microbiome Project, 2007), we have seen evidence that our microbiome can affect everything from our mood and our weight to our risk for developing certain diseases.

Our body is absolutely covered in bacteria; with estimates of between 10-100 trillion microbes living on us (LK. Ursell, 2012), the majority of these are found within our gut. Our gut microbiome is broadly colonised with two specific families of bacteria, known as Bacteriodetes and Firmicutes. Both of these families have hundreds of species within them, and it is these species that take up the majority of the 400-500 species of bacteria in our gut (Ramakrishna, 2005).

When we talk about our gut microbiome, we are usually referring to the microbiome found within our large intestine, colon and rectum. These are found at the end of our digestive tract and contain the large majority of our gastrointestinal bacteria. Other parts of the digestive tract do also have a microbiome; our mouth is a great example of this. However, it is unclear whether this microbiome vastly affects our health as much as our lower intestine microbiome, and as such the microbiome I am here on referring to are the bacteria in our lower intestines.

Our gut microbiome is very diverse and is unique to each person. The fascinating fact is that everything that happened to us during childhood, from the way we were birthed to the amount of time we played in the mud as a child, will influence this microbiome. For example, children who were born vaginally will have a very different microbiome than those who were born by c-section, due to the differences in sterility of a c section vs. vaginal birth. Equally, breast-fed vs. formula feeding, timing of introduction of solid food, and whether there are pets in the house, among other things, will all influence our microbiome. Emerging evidence is even suggesting that what our mothers eat and drink during gestation (the time we are in our mothers’ womb) will shape our gut microbiome and can influence how it develops (F.Bäckhed, 2015). By the time we are about 3 years old, our gut microbiome will have fully developed to a state that is similar to our gut microbiome in adulthood.

This isn’t to say that our gut microbiome can’t change, however. Our microbiome is a constantly evolving and ever-changing thing, and various things can influence the microbiome we have at that point in our life. For example, prolonged antibiotic use, for recurring infections, will often deplete the microbiome completely and can lead to an over-colonisation of bacteria that is “bad”. Equally, stress and chronic illness can also deplete the “good” bacteria and lead to over-colonisation of the “bad” kind.

The people and animals that you live with will also alter your microbiome, to the point that people who live together often share similar microbiome characteristics (N. Hasan, 2019).

This is not a one-sided relationship, however; although the things we do can influence our gut bacteria, our gut bacteria can influence us and our health.

This is an incredibly complex field of study, and even now, we don’t know the full picture. There are a few health benefits that are very strongly linked to our gut microbiome, however:

a) Our ability to absorb specific nutrients in our diet– studies have shown that children from different areas, who have very different diets, have very different microbiomes to help them get as much nutrition from their food as possible. For example, children who grow up on a very high number of starchy foods (such as places in Sub-Saharan Africa) will have gut bacteria that are very efficient at breaking down plant carbohydrates such as cellulose, making them available for the child to absorb. Other children, who have a diet that is full of less starchy foods will have a lower percentage of these bacteria, as they aren’t needed. Equally, if we change our diet from a meat heavy one to a vegetarian or vegan diet, our gut microbiome will change to cope with this; you would end up with a higher diversity of microbes on the plant-based diet, and a higher proportion of these would be able to digest the higher fibre plant matter (R. Krajmalnik-Brown, 2012).

b) Our ability to synthesise certain vitamins– our microbiome produces some vitamin K, and if we get little of this from our diet it is theorised that our microbiome population will change to accommodate this. Our gut microbiota also produces B12, B6, niacin, and folate. It must be noted, however, that they do not produce enough of these for us to live on, and thus we also need to supplement these in our diet (Hill, 1997).

c) Our likelihood of developing metabolic or autoimmune diseases– our good gut bacteria produce something called short-chain fatty acids, or SCFA’s, when fed with the right foods. These SCFA’s play a key role in reducing overall inflammation in our body, and as such reduce our risk for metabolic conditions such as diabetes, autoimmune diseases such as psoriasis, and can locally reduce the risk of colon cancers (K. Yeon Hur, 2015).

d) Our metabolic efficiency and our weight– Our good friends SCFA’s can help us utilise our brown adipose tissue far more effectively than usual. Brown adipose is one way our body burns off excess calories, and thus can keep us slimmer. This works in combination with the positive effects that SCFA’s have on controlling our appetite by regulating our hunger hormones (H. Xiao, 2020).

e) Our cognitive function: SCFA’s likely play a key role in our neurodevelopment when we are children and may also be linked to neurodegenerative disorders if deficient (YP. Silva, 2020).

As you can see, a wide range of benefits are caused by our gut bacteria producing something called short-chain fatty acids, or SCFA’s. These magical compounds are anti-inflammatory, and highly useful within our metabolism. Some bacterial groups, such as the Firmicutes family, will produce more SCFA’s than others. This is not to say that the others do not produce this, but just that Firmicutes produce more.

A proposed way to help us all get into better health is to try to increase the amount of SCFA’s that our microbiome produces. We can do this in two different ways; by eating enough of the foods that these bacteria like (pre-biotics) or by re-colonising our gut microbiome with live strains of the good bacteria (pro-biotics).

So how can we feed our existing microbiome?

Firstly, it is important that we are eating enough resistant starch. Resistant starch is a type of fibre, and is so called because it resists digestion and therefore can make it down into our lower gut intact, for our microbes to feast on (P. DeMartino, 2020). This type of starch is found naturally occurring in oats, wheat bran (found in bran flakes and all bran), cellulose and inulin (found in fruits and vegetables). We can also increase the amount of resistant starch in other starchy foods, by cooking them and leaving them to cool before either reheating them or eating them cold. This means foods like potato or pasta salads will often contain a good amount of resistant starch.

The general population across the Western world currently eats far too little fibre, with the average in the UK being just 18g a day (University of Cambridge, 2021). Increasing our fibre intake, specifically our resistant starch intake, has a huge range of health benefits, and not just on our microbiome. Fibre can help keep our bowel movements regular and smooth, making us more comfortable, but it also plays a role in reducing the risks of colon cancer as well as reducing the amount of cholesterol you absorb from food. Fibre is a wonder-food, and I would highly recommend you increase it in your diet if you can. However, it is important that you increase this slowly; if you aren’t used to large amounts of fibre in your diet, increasing suddenly can give you very unpleasant side effects, including painful indigestion and constipation.

Please note:

If you have any functional/medical bowel disorders (such as IBD, coeliac or diverticular disease), please talk to your dietitian before increasing your fibre intake.

A great way you can increase your fibre intake is by adding flaxseeds (otherwise known as linseeds) into your diet. These wonderful little seeds are a great source of omega-3 fats, but also contain a high amount of soluble fibre. This can help your bowel movements be more regular and can also ease both constipation and diarrhoea in those struggling with IBS. Starting with half a teaspoon and building up from there is a good place to start; sprinkle these on your porridge or on salads, or even mix them into yoghurt as a snack.

Trying seeded, wholemeal breads or porridge in the morning can also be a great way to boost your fibre intake. If you aren’t keen on brown breads, there are many great 50:50 options which can still help you increase your fibre.

Another great way to increase our fibre is by increasing the amounts of fruit and vegetables we eat per day. The vast majority of the UK do not meet there 5 a day, with the average being just over 2 portions a day (University of Cambridge, 2021). Increasing your fruit and veg intake, even by one per day, can be a great start. Make sure you are eating produce you really enjoy and find different and more flavourful ways to cook it.

Replacing white versions of pasta and rice, or leaving the skins on potatoes will also up your fibre intake easily, without big changes in taste. These may need a little longer cooking, so make sure you read the packet instructions.

You may also take pre-biotic supplements, such as chicory root extract, to help feed your microbiome. Ensure that you read the labels for these, as some fibre supplements (such as psyllium husk) can cause intestinal blockages if too much is eaten.

Some people may also choose to take a probiotic, either in the form of a fermented food or a probiotic supplement.

Probiotics are live cultures of bacteria that you take to replenish your “good” bacteria levels. Yoghurt based probiotic drinks are the first things that likely spring to mind when we discuss probiotics; think things like Yakult. These drinks are clinically proven to deliver a recommended dose of live bacteria to your gut, where they can help restore the balance of the good bacteria.

Foods such as yoghurt, kimchi and sauerkraut contain natural probiotics, because they are fermented. You may want to include these foods to give you a dose of these good bacteria.

But do probiotics actually work?

There is clinical evidence that they show some benefit in preventing diarrhoea when taken alongside antibiotics, and some individuals find that taking a daily probiotic will help with any symptoms of IBS. But in terms of treating other conditions, such as eczema or metabolic disorders, there is little evidence to show their efficacy (The Lancet, 2019). This being said, they are likely to not do any harm (unless you have an immune deficiency disorder), so you may still wish to take them if you like.

Overall, it appears that looking after our gut flora is a very beneficial thing for us to do, and we should be taking steps to facilitate the healthy form and function of our gut bacteria. Our gut bacteria can influence everything from our mood to our weight, and making sure we are feeding these with resistant starches and fibres may really help us in becoming healthier.

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