WHY CONSUME A DIVERSE DIET - WORLD DIGESTIVE HEALTH DAY
We all know that there is no one food that can provide all the nutrients necessary for optimal health. Eating a diverse range of foods within and between food groups is essential to obtain adequate amounts of macro- and micronutrients from our diet. This is detailed in the Eatwell Guide, encouraging the general population to choose from across food groups, but predominantly fruits, vegetables, and wholegrains (1).
Dietary diversity, particularly diversity of plant foods, introduces many essential nutrients, fibre, and prebiotics into the diet. Prebiotics are defined as “substrates that are selectively utilised by host microorganisms conferring a health benefit” (2). Providing diverse prebiotic substrates to our gut bacteria helps to promote a diverse, stable, and resilient gut microbiota (3). These characteristics have been associated with healthy long-living people and the absence of certain gut-microbiota diseases.
Fermentable prebiotic fibres
Prebiotics are mainly fibres, but also include some non-fibre nutrients. There are many different types of naturally occurring prebiotics in food, but those added to food products or supplements are not often explicitly labelled. When looking for prebiotics added to foods or supplements, the specific name of the prebiotic (e.g., fructo-oligosaccharides) should be looked for rather than the general term ‘prebiotic’. There is currently no dietary recommendation for prebiotics in the UK, however the International Scientific Association for Probiotics and Prebiotics (ISAPP) recommends consuming at least 5g of prebiotics a day (4).
Galacto-oligosaccharides (GOS) include α-GOS (found in beans and pulses) and β-GOS (commercially produced and found in supplements or processed foods). GOS, particularly β-GOS, has been found to increase Bifidobacteria by selective fermentation. The bifidogenic effect of GOS leads to increased short-chain fatty acid production, thereby decreasing the pH of the colonic environment, and may also support calcium absorption (5).
Fructo-oligosaccharides (FOS) are highly concentrated in onion, garlic, asparagus, and Jerusalem artichoke. FOS have been researched in human trials exploring the possible benefits related to satiety, improved absorption of calcium and other minerals, and immunomodulatory effects (i.e., allergies and vaccine efficacy)(2).
Inulin, like FOS, is a type of fructan and found in similar food sources. Chicory inulin is currently the only prebiotic that has an approved health claim; ‘chicory inulin contributes to normal bowel function by increasing stool frequency’ (6).
Resistant starch is a portion of starch that cannot be digested by amylases in the small intestine and passes to the colon to be fermented by microbiota (7). Key food sources of resistant starch include whole grains or coarsely ground grains that are physically inaccessible to digestion, yellow-green bananas, and cooked then cooled starchy foods (i.e., cold potatoes or pasta). Resistant starches are classified into sub-types and appear to have different effects on different species of gastrointestinal bacteria, thus produce different metabolic by-products with varying health-promoting effects (8).
Some early research has shown that non-fibre nutrients including polyphenols, poly-unsaturated fatty acids (PUFAs) and lactulose may also exert prebiotic effects(2).
Non-prebiotic and low fermentability dietary fibre
Other fibres, such as psyllium, pectin, cellulose and xylans, do not promote the growth of specific, beneficial bacteria and/or have low fermentability, but may still promote the growth of a variety of gut microorganisms and have other health-promoting activities. For example, psyllium is a viscous and poorly fermented fibre, possessing a high-water holding and gel-forming capacity throughout the gastrointestinal tract, which helps to relieve constipation symptoms (9). Cellulose is another example of a poorly fermented fibre with stool bulking properties.
Higher consumption of dietary fibre is related to better cardiovascular health, colorectal health, reduced incidence for type 2 diabetes and intestinal transit time (10). Despite the benefits of increased fibre consumption, and national guidelines advising that adults consume at least 25g (Ireland (11)) and 30g (UK (12)) of fibre per day, the average intake is in fact only around 19g/day(13).
Dietary microbes are dead or live microbes introduced to our gastrointestinal system by ingesting foods (such as fermented or probiotic foods) or supplements (probiotics).
Fermented foods are made through desired microbial growth and enzymatic conversions of food components (14). An example of a fermented food is yoghurt, made from lactic-acid bacteria fermenting sugar and other nutrients in milk. Foods and drinks that have been fermented include most cheeses, kimchi or other fermented vegetables, tempeh, miso, kefir, natto and most kombucha. These foods retain live fermentation microbes.
Probiotics are live microorganisms, that when administered in adequate amounts confer a health benefit. Some probiotic products can be foods, but the genus, species and strain name need to be known, as well as the colony forming units (CFU) per serving (15).
How to increase diversity
Research has shown that people who eat more than 30 different unique plant species a week have a more diverse gut microbiome (16). This may sound like a lot for patients or clients, but it should be emphasised that increasing total plant intake across a whole week is beneficial for health. The good news is many foods regularly consumed may already fit into the different groups of plants to include for more diversity in the diet. Recommend including foods from the following groups: fruits, vegetables, nuts and seeds, legumes and pulses, whole grains, herbs and spices.
• Try a new fruit or vegetable each week – when visiting the supermarket, look for something new so that you are not always reaching for the same 6 fruits and vegetables.
• Add seeds or nuts as porridge or salad toppers
• Include a variety of whole grains in meals. Think porridge oats one day, wheat biscuits the next, mixed grain quinoa and rice with curry or rye bread instead of the usual toast.
• Mix up protein sources and opt for beans, pulses, tofu or tempeh to bulk out a Bolognese, chilli or curry.
• Swap your iceberg lettuce for a mixture of salad leaves
• Sprinkle some aromatic herbs and spices - this is a great way to add more plants to the diet and make food taste great too!
For inspiration we have worked on some new recipes that will be a great place to start for plant diversity:
1. The Eatwell Guide (2016). Available from [https://www.gov.uk/government/publications/the-eatwell-guide]
2. Gibson et al. (2017) Nat Rev Gastroenterol Hepatol 14:491–502.
3. McBurney et al. (2019) J Nutr 11(149): 1882-1895
4. ISAPP (2017) Prebiotics. Available at: http://4cau4jsaler1zglkq3wnmje1-wpengine.netdna-ssl.com/wp-content/uploads/2019/04/Prebiotics_Infographic_rev1029.pdf (Accessed: April 2022).
5. Whisner et al. (2013) Br J Nutr 110(7):1292-1303.
6. EFSA NDA Panel (EFSA Panel on Dietetic Products, Nutrition and Allergies). Scientific Opinion on the substantiation of a health claim related to “native chicory inulin” and maintenance of normal defecation by increasing stool frequency pursuant to Article 13.5 of Regulation (EC) No 1924/2006. EFSA https://www.efsa.europa.eu/en/efsajournal/pub/3951 (2015).
7. Englyst HN & Cummings JH. (1985) Am J Clin Nutr.42:778–87
8. Diane F et al. (2013) Advanc Nutr. 4(6): 587–601
9. Gill et al. (2020) Nat Rev Gastroenterol & Hepatol. 18: 101–116
10. SACN Carbohydrates and Health Report (2015). Available from [https://www.gov.uk/government/publications/sacn-carbohydrates-and-health-report]
11. FSAI: Scientific Recommendations for Healthy Eating Guidelines in Ireland (2011). Available from [https://www.fsai.ie/WorkArea/DownloadAsset.aspx?id=16765]
12. PHE: Government Dietary Recommendations (2016). Available from [https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/618167/government_dietary_recommendations.pdf]
13. The Institute of Grocery Distribution (2018). Available from [https://www.igd.com/Portals/0/Downloads/Charitable%20Impact/IGD-Consumer-research-into-fibre.pdf]
14. Marco ML et al. (2021). Nat Rev Gastroenterol & Hepatol. 18(3):196-208.
15. Hill C et al. (2014). Nat Rev Gastroenterol & Hepatol. 11(8):506-14.
16. McDonald D et al. (2018) mSystems. 15;3(3):e00031-18.