Leafy Greens and Gut Health: Nourishing your Microbiome

Introduction

Looking after your gut microbiome is one of the most important aspects of living a healthy lifestyle. The health of the community of trillions of microbes living in your gut can heavily affect your immune system, your metabolism, and even your mental health. 

As with the rest of your body, a healthy diet and eating habits go a long way to supporting your gut microbiome.  Leafy greens are one dietary component that is very important for the health of your gut microbiome. 

Here, we will cover which particular vegetables are most beneficial for your gut microbiome, how they support your gut bacteria, and how to include them in your diet in a way that maximises their beneficial properties.

Understanding the gut microbiome

Your gut microbiome is a community of over 100 trillion microorganisms that live in your digestive system - also known as the gastrointestinal tract. In healthy people, these microbes include an enormous diversity of bacteria, fungi, viruses, and protists, with estimates of between 300 - 500 different species of bacteria alone. Most of these microorganisms mainly inhabit your small and large intestine.

They form a complex ecosystem – your gut microbiome – which helps your body to break down and digest food, creates vital nutrients your body can’t produce itself, and prevents harmful bacteria from multiplying, spreading and causing illness. 

Having a balanced and diverse gut microbiome not only helps your body process food but also prevents disease. Healthy microbiomes are also associated strongly with healthier appetite regulation and mental health. One of the best ways to ensure your microbiome of microorganisms is healthy is to provide it with all the nutrients these microbes require through a healthy diet.

On the other hand, having a less diverse and unbalanced microbiome has been linked to obesity, type 1 and 2 diabetes, constipation, increased risk of gastrointestinal infections, inflammatory bowel disease, Crohn’s disease, eczema, and a host of other health complaints.¹

An imbalance in the gut microbiome is known as ‘dysbiosis’. Some of the main contributory factors to dysbiosis include poor diet, smoking, excessive alcohol consumption, stress, poor sleep, and inappropriate use of antibiotics.² It is also important to note that reduced diversity in the gut microbiome usually occurs to some extent as a part of ageing.³

However, in addition to avoiding these negative factors, you can positively promote a diverse and balanced microbiome by eating a balanced diet that contains plenty of leafy greens as an essential component.

The benefits of leafy greens for the microbiome

Leafy greens are by definition the leaves of any plant that is eaten as a vegetable, whether cooked or raw. Edible plant leaves are rich in essential nutrients like fibre, vitamins, and minerals.⁴

These nutrients are crucial for overall health and particularly for nourishing the gut microbiome. This is because a good number of these nutrients are prebiotics - particularly indigestible fibres and a group of chemicals produced by plants called polyphenols.

Prebiotics are nutrients that specifically feed our gut microbiome - it can be helpful to think of them as fertilisers for the garden of microbes growing in your body. By consuming plenty of prebiotics in your diet, you can help these microbes grow, creating a stable, thriving and benign microbial community.⁵

Leafy green prebiotics, ‘short-chain fatty acids’ (SCFAs), and your gut bacteria

There are many prebiotic substances that are abundant in leafy greens. Some of the main ones found in these leafy green vegetables include inulin, pectin, and various oligosaccharides.

Your gut bacteria break down these prebiotics into chemicals known collectively as ‘Short-Chain Fatty Acids’ or ‘SCFAs’. The most common SCFAs produced are acetate, propionate, and butyrate.⁶ Many types of microbe ferment prebiotics and produce these SCFAs. However,  more specifically, some of the most abundant beneficial types of bacteria producing SCFAs include Bifidobacteria,⁷ Bacteroides, Firmicutes,⁸ Lactobacilli,⁹ and Akkermansia muciniphia.¹⁰

SCFAs play many important roles in your gut. They help the cells lining your colon (‘colonocytes’) stay healthy by providing them with an energy source. They also maintain a low pH level in the gut, keeping it at the right range of acidity to keep in check bacteria that might otherwise potentially reach harmful levels.

Some SCFAs also help reduce the sort of inflammation that compromises the integrity of the gut barrier and is associated with conditions such as IBS, Crohn’s disease,¹¹ or leaky gut.¹²

Diversity in leafy greens for a diverse microbiome

Whilst many leafy greens contain this important prebiotics, different vegetables can have differing nutrient profiles, thereby providing different benefits. 

For example, whilst both kale and spinach contain high levels of prebiotic fibres, they have different levels of vitamins such as vitamin K, B9, and iron.⁴ This is one reason why it’s important to include a mixture of leafy greens in your diet.

Fortunately, there are many choices of leafy greens available, including:

• Rocket/arugula
• Bok choy
• Green cabbage
• Collard greens
• Iceberg or romaine lettuce
• Mustard greens
• Watercress
• Broccoli
• Brussel sprouts

How to include leafy greens in your diet

Are leafy greens best eaten raw or cooked?

There are a few things to consider when adding leafy greens to your meal plans. One choice to be made is whether to eat them raw or cooked because cooking can sometimes reduce the levels of some beneficial prebiotics such as polyphenols.¹³ However, cooking can also reduce the level of less desirable chemicals, such as oxalates, which people at risk of kidney stones should avoid.¹⁴ Therefore, researching in greater detail the benefits and disadvantages of eating various leafy greens, when raw or cooked, can help you make the right choice.

Prebiotic and probiotic combinations

Another way to maximise the prebiotic benefits of leafy greens is to combine them with probiotic-rich foods. 

Probiotics are live bacteria and yeasts that are naturally present in certain foods or can be taken as supplements. Enriching your gut microbiome with beneficial bacteria such as lactobacilli at the same time as feeding them with prebiotics has been shown to improve the growth and activity of beneficial bacteria.

Some examples of probiotic foods you can add to meals that include leafy vegetables are fermented foods or drinks like yoghurt, kefir, miso, tempeh, and kombucha.

Other foods like kimchi and sauerkraut directly combine leafy greens (cabbage) with probiotics by using them as the food source for fermentation.¹⁵

Leafy greens and food safety

It’s important to remember to safely prepare leafy greens before eating, particularly if raw. Always wash salad vegetables before eating them and consume them within the expiration date, as this avoids ingesting harmful bacteria such as E. coli or Salmonella that may cause ‘food poisoning’. 

Store leafy green vegetables in the fridge separately from products such as meat. If any of the vegetable leaves have visibly spoiled, avoid eating these as they are more likely to contain harmful bacteria.

Additionally, if the vegetables are not organically sourced, they are likely to have been treated with pesticides. This is another reason why washing the leaves thoroughly is an important step in preparing leafy greens.

Potential side effects

Whilst leafy greens have many health benefits, some individuals should consider which vegetables they choose to eat in moderation.

Some of the nutrients included in leafy vegetables are known as FODMAP (standing for ‘fermentable oligosaccharides, disaccharides, monosaccharides, and polyols’). Whilst not normally harmful, they can cause digestive distress in some individuals, such as people with Crohn’s disease or other gastrointestinal conditions.¹⁶

Those who have been recommended to follow a low-FODMAP diet by a healthcare professional should check whether the leafy greens are classed as low-FODMAP. Fortunately, many choices, such as spinach, endive, Swiss chard, and lettuce, fall under this category.

Summary

Prioritising your gut health through a balanced diet is vital for your well-being. Leafy greens are a cornerstone of any healthy diet, nurturing a thriving microbiome by providing an abundance of nutrients and prebiotic fibres. Leafy greens act as fertilisers for the diverse community of beneficial gut bacteria that are vital for colon health, efficient digestion, and a balanced gut environment.

Including a variety of leafy greens chosen and prepared to suit your dietary requirements, each offering unique nutrient and prebiotic profiles is a practical and effective approach to boosting the health of your microbiome. By taking a holistic approach and combining them with probiotic-rich foods, you can get the full spectrum of benefits offered by these vegetables, supporting not just your gut but also promoting all the other health benefits produced by the actions and impacts of a healthy microbiome.