The Foundations of Gut Health

The prevalence of people suffering from gut-related disorders is higher than ever before. This rise is occurring in tandem with the obesity epidemic and the production of ultra-processed foods (UPFs).

Modern supermarket shelves are dominated by foods that have been intensely processed to improve texture, taste, and shelf life using emulsifiers, additives, and preservatives. While convenient, these ingredients are foreign to our biology. Increased consumption of UPFs, along with modern-day stress (where we are scared of boredom and stress is chronic), is causing our gut to suffer. 

Understanding how to improve gut health through food is becoming increasingly important, as the benefits of gut health extend to our overall physical and mental well-being.

Your gut is home to over 100 trillion microorganisms, including bacteria, viruses, fungi, and archaea. Collectively, this ecosystem is known as the microbiome.

Think of your microbiome as a garden. When the soil is nutrient-rich and the plants are diverse, the ecosystem thrives. When the soil is stripped of nutrients (low fibre) and flooded with chemicals (UPFs), weeds take over.

The benefits of a healthy gut and diverse microbiome are systemic: 

Gut health is directly linked to how your body handles energy. When you consume fibre your gut bacteria ferment it to produce Short Chain Fatty Acids (SCFAs). These powerful compounds stimulate the release of gut hormones like GLP-1 (Zeng et al, 2023).

You can read more about metabolism here.

Roughly 70% of your immune system resides in your gut. A healthy microbiome is important for regulating inflammation and reducing the colonisation of proinflammatory bacteria, highlighting why gut health foods are essential for immune resilience.

Learn how to improve your immune function here.

A healthy microbiome ensures food is broken down efficiently, nutrients are absorbed, and waste is eliminated regularly without discomfort.

Your gut and brain are intimately connected via the vagus nerve, also known as the ‘gut-brain axis’. 

Gut to Brain: Neurotransmitters like serotonin (the ‘happiness hormone’) are largely produced in the gut. A healthy gut environment supported by gut health foods stablalises moods.

Brain to Gut: In an age of chronic stress, high cortisol levels can physically alter digestion, leading to bloating or changes in bowel habits. We often stress our bodies with UPFs and our minds with constant social stimulation, creating a cycle of dysfunction. This makes it more likely that the sympathetic branch of our nervous system is active. The ‘fight or flight’ branch. This reduces blood flow to our stomach, slowing digestion.

If the microbiome is the garden, fibre is the fertiliser. Fibre is the portion of plant foods that bypasses digestion in the small intestine and arrives in the large intestine to feed your bacteria.

However, not all fibre is the same. To improve gut health and build resilience, we need variety:

The key is to ensure we eat a diverse range of plant-based fibre. The more diverse the plants you eat, the more diverse the species in your gut. Aim for 30 different plant foods per week for optimal health. This includes fruits, vegetables, wholegrains, spices, nuts, seeds and herbs (McDonald et al., 2018).

A simple way to increase fibre intake here is to add a herb or nut garnish to your dishes.

The best foods for gut health include fermented foods. Alongside feeding our gut microbiome, they introduce already manufactured SCFAs and new healthy species to our ecosystem. 

Recent studies comparing high-fibre diets to high-fermented-food diets found something fascinating (Wastyk et al., 2021) :

How do they work? The bacteria in fermented foods (like kimchi, sauerkraut, kefir, and kombucha) may only survive in your gut for a few days, but they are powerful transients. They interact with your immune system cells, and even the receptors on their dead cells can help regulate inflammation.

The microbial species have already partially digested the food during fermentation (creating that complex, sour flavour profile), and they deliver a complex array of ‘post-biotics’ (beneficial chemicals) that the body uses immediately to promote health.

Recommendation: For general gut health aim for 3 servings of fermented foods per day (Newman and Kim, 2025).

To keep it simple, here are four tips that will improve your gut health

Everything you just read outlines the path to a healthy gut for the general population.

However, some people struggle with a condition called Irritable Bowel Syndrome (IBS). This is a functional disorder characterised by reduced microbial diversity and visceral hypersensitivity.

For an IBS sufferer, the ‘healthy’ recommendations above, lots of fibre and fermented foods, can actually make symptoms significantly worse.

A balanced diet meal plan is paramount for good health and feeling your best. Download the Calo App; our meal prep service offers delicious meal plans, delivered right to your door. We carefully design fibre-rich meals to nourish your gut microbiome without you having to think about it!

The best foods for gut health include fibre-rich plant foods, fermented foods, and minimally processed whole foods that support microbial diversity.

You can improve gut health by eating diverse plant-based foods, reducing ultra-processed foods, managing stress, and consuming fermented foods regularly.

A microbiome test analyses the composition of bacteria in your gut. While informative, most people can improve gut health without testing by focusing on diet and lifestyle first.

A microbiome diet focuses on eating foods for gut health and particularly fibre-rich plants and fermented foods, to support a diverse and resilient gut ecosystem.

Remember when we eat, we are eating for two; ourselves and our gut microbes. Gut health is integral to our overall health. Read more about the 80/20 rule and winter foods here, and more topics related to health on the Calo blog.

1- Zeng, Y., Wu, Y., Zhang, Q. & Xiao, X. (2023) ‘Crosstalk between glucagon‑like peptide 1 and gut microbiota in metabolic diseases’, mBio, 15(1), e02032‑23.

2- McDonald, D., Hyde, E., Debelius, J.W., Morton, J.T., Gonzalez, A., Ackermann, G., Aksenov, A.A., Behsaz, B., Brennan, C., Chen, Y., DeRight Goldasich, L., Dorrestein, P.C., Dunn, R.R., Fahimipour, A.K., Gaffney, J., Gilbert, J.A., Hugenholtz, P., Humphrey, G., Huttenhower, C., Jackson, M.A., Janssen, S., Jeste, D.V., Jiang, L., Kelley, S.T., Knights, D., Kosciolek, T., Ladau, J., Leach, J., Marotz, C., Meleshko, D., Melnik, A.V., Metcalf, J.L., Mohimani, H., Montassier, E., Navas‑Molina, J., Nguyen, T.T., Peddada, S., Pevzner, P., Pollard, K.S., Rahnavard, G., Robbins‑Pianka, A., Sangwan, N., Shorenstein, J., Smarr, L., Song, S.J., Spector, T., Swafford, A.D., Thackray, V.G., Thompson, L.R., Tripathi, A., Vázquez‑Baeza, Y., Vrbanac, A., Wischmeyer, P., Wolfe, E. & Knight, R. (2018) American Gut: an open platform for citizen science microbiome research, mSystems, 3(3), e00031‑18. doi: 10.1128/mSystems.00031‑18

Newman, T. & Kim, C. (2025) ZOE study: Fermented food improves mood, energy, and hunger. ZOE. Available at: https://zoe.com/learn/zoe-study-fermented-food?srsltid=AfmBOoph0xRNt844d3uMgbNn5nzMt7N_dG2sGuUJsjOrJtEt1MLy2pRh (Accessed: 6 January 2026).
Wastyk, H.C., Fragiadakis, G.K., Perelman, D., Dahan, D., Merrill, B.D., Yu, F.B., Topf, M., Gonzalez, C.G., Van Treuren, W., Han, S., Robinson, J.L., Elias, J.E., Sonnenburg, E.D., Gardner, C.D. & Sonnenburg, J.L. (2021) Gut‑microbiota‑targeted diets modulate human immune status. Cell, 184(16), pp.4137–4153.e14. doi: 10.1016/j.cell.2021.06.019.