WIDLIMS ep #14 – Legumes… forgotten superfoods?

In today's episode, host and final year medical student Linda (she/her) discusses all you ever wanted and needed to know about legumes, pulses, whatever you want to call them (beans, peas, lentils, etc.). Listen to find out...

• what legumes are
• their health benefits
• common concerns being addressed and myths busted
• things to keep in mind when preparing legumes

Mentioned in the episode

• General summaries of benefits of legumes that are short and accessible can be found here and here
• Study on longevity and legumes – read it here
• Episode 12 – Carbohydrates and insulin – click here
• Episode 13 – Anti-diet approaches to PCOS – click here
• Second meal effect – read more here
• Short chain fatty acids’ role in metabolism – read paper here
• Lectins and other anti-nutrients – read article here
• Gut dysbiosis and elimination – read more by Dr B here (or check out his book, Fiber Fueled)
• Fart health article – read it here
• Some of my recipes such as a 10-minute lentil bolognese, Shepherd’s pie or smokey black beans on toast

Bean basics and legume lovin’

What are legumes?

Legumes are essentially a family group of plant foods that includes beans, lentils, peas, chickpeas, soybeans and peanuts (1). They are seeds that grow in pods, and also deemed to be one of the four major food groups according to the PCRM (Physicians’ Committee for Responsible Medicine) Power Plate; these are vegetables, fruits, whole grains and legumes (2). Legumes, or pulses if you would rather call them that, are also recommended by the American Heart Association, the NHS and Diabetes UK (3,4,5). So why are legumes so important that they are deemed to be an entire food group of their own as part of a balanced diet?

All legumes will contain different proportions of carbohydrates, proteins and fats. They will also contain different types and proportions of essential minerals and vitamins such as iron, zinc, potassium and folate (6). Eating a variety of beans is great as they are a source of plant protein very low in saturated fat, high in gut-healthy fibre, containing good types of carbohydrates that are low GI, keeps a person full managing their weight without restriction, and are also very versatile and delicious!

Known benefits of legumes

General mortality and cancer prevention

In general, looking at the bigger picture, we know that legumes play a role in cancer prevention, such as colon cancer and especially soybean products in hormone-related prostate and breast cancers (more on that in the show notes for episode 8 of WIDLIMS – Dairy: ditch or don’t as well as episode 13 on PCOS) (7).

Increased bean consumption was also found to be a predictor for longer lifespan in a study examining mortality in older people in several countries. For every 20g of beans consumed daily (and that is not a lot!), there was a 7-8% reduction in mortality hazard ratio observed (8).

Metabolic syndrome, cardiac disease and diabetes

Legumes are also incredible for regulating cardiometabolic risk factors. They can lower LDL cholesterol, increase good HDL cholesterol, reduce triglycerides, lower blood pressure in hypertensive people, and improve insulin resistance as they are low GI and high in good fibre and carbohydrates (9-12). So that is why they are recommended by heart health and diabetes charities, as well as for people with insulin resistance such as those with PCOS (again mentioned in episode 13).

There is something quite remarkable about most legumes, in that they are very low GI. That means they cause a low spike in blood glucose/blood sugar levels after a meal, despite having a good going carbohydrate content. They contain good complex carbohydrates, and are therefore great in insulin resistance. But it would appear that eating beans, for example, does not only blunt the general blood sugar spike after that one meal: it also has an effect on the next meal! So say you had a bean burrito for dinner, and then a smoothie at breakfast the next day. Your blood glucose spike would be lower than for someone who did not have beans at dinner, but the same smoothie the next day! This has been called the lentil effect, or the second meal effect, and is pretty fascinating (13-15). Read more about it in the references for sure!

Gut health

Legumes are also great for gut health, as they are an excellent source of fibre which in turns feeds our ‘good’ gut bacteria, making up our gut microbiome. Feeding them results in the synthesis of short-chain fatty acids (SCFAs), which in turn have important roles in our metabolism, being able to for example lower cholesterol and influence glucose metabolism (16). Pulses are therefore great for contributing to a flourishing gut microbiome, in turn predicting health with positive outcomes for other conditions such as cardiovascular and brain health, as well as for example digestion (17,18).

Do keep in mind that the biggest predictor for gut health is plant diversity, though, so make sure to eat a wide range of different legumes, and not just zoning in on for example chickpeas, for maximum benefit (19). That way, you will also be getting a wide range of different micronutrients, as mentioned above.

Common worries: dispelling myths

Okay, so there really is no reason to not eat beans (unless you have a genuine food allergic reaction to them – but there are many different beans to try!) and many many reasons for including beans in your diet. In fact, eating no beans may increase mortality (20).

However, some people may be reluctant to eat them.

Lectins and other anti-nutrients

You may have heard of lectins, or phytic acid, or other so-called anti-nutrients, which ‘trap’ nutrients or are toxic. They can impair the absorption of nutrients such as iron, calcium and zinc, and irritate the cells lining your gut (21). BUT the thing is, these anti-nutrients are largely or completely eliminated by the time the legumes are prepared and edible. They are high in raw kidney beans for example, but who would eat raw kidney beans?? You certainly should not, as it first of all would not be pleasant and second of all, certainly not as beneficial as a properly prepared one.

It is worth noting that there are studies on some anti-nutrients such as lectin, showing they may be beneficial in small amounts in cancer prevention situations due to their antioxidant potential (22) – either way, there is no study showing increased mortality from consuming legumes (quite the opposite, as you will know have you read this far), so there is no argument against it in this department, really.

Flatulence, gas… and sensitive tummies!

This is probably the biggest one – farts! People are terrified of getting gassy and smelly if eating more beans. And of course, nobody wants to be terribly smelly or bloated due to what they eat, if it can be avoided. However, research has shown that consuming pulses does not significantly increase reported flatulence, as much as people may believe (23).

Please also remember that it is normal to have some gas and bloating and to fart – it is part of being human. There is a lovely little article on fart health by Dr B I recommend checking out, if you are seriously concerned about the way your farts are smelling for example (24).

Some people may genuinely struggle with eating certain foods, and not just legumes. If that is the case, though, it is important not to eliminate them completely without guidance from a professional. Generally speaking, eliminating an entire food is not beneficial to our health – remember gut microbiome diversity? As Dr B says, we need to think of our gut as a muscle: use it or lose it! If we avoid eating beans, all the gut microbes that would normally digest those beans and thrive, will die off and other less beneficial bacteria may over-grow instead. Be sure to eat smaller amounts but still of a diverse range of foods – long-term elimination diets such as a low FODMAP diet, are usually not a good idea for long-term health (25,26).

Some tips for consumption

Remember that you are doing yourself a huge favour in terms of your health, and often also your wallet, as well as the planet by eating more beans (especially if it means you eat less meat) (27)!

The cheapest way to eat beans would be to buy them dry in bulk, then soak and cook them. This also reduces/gets rid of the aforementioned anti-nutrients. But that can be a bit of a hassle if you do not have the time (although soaking overnight is pretty easy), or if you do not have a handy pressure cooker. I personally consume a lot of canned beans and lentils. Some more tips about that in my veganuary guide! Remember to not buy canned pulses with lots of added sugar or salt – I try to buy them canned in water, then drain and rinse them. Nutrition-wise, they are pretty much equivalent to beans cooked from scratch (28).

Ways to eat: hummus, daal, chickpea curry, tofu recipes, Shepherd’s pie, lentil bolognese, as part of desserts, burritos, tacos, beans on toast, burgers and falafel… Check out some of my linked recipes or just have a google!

REFERENCES

1) What are legumes? https://www.healthline.com/nutrition/legumes-good-or-bad#what-they-are

2) PCRM Power Plate Brochure. https://p.widencdn.net/ktho8u/Power-Plate-Brochure

3) https://www.heart.org/en/healthy-living/healthy-eating/eat-smart/nutrition-basics/the-benefits-of-beans-and-legumes

4) https://www.nhs.uk/live-well/eat-well/beans-and-pulses-nutrition/

5) https://www.diabetes.org.uk/guide-to-diabetes/enjoy-food/eating-with-diabetes/food-groups/pulses-and-diabetes

6) NutritionFacts.org. Health benefits of beans. https://nutritionfacts.org/topics/beans/

7) NutritionFacts.org. Health benefits of legumes. https://nutritionfacts.org/topics/legumes/

8) Darmadi-Blackberry I, Wahlqvist ML, Kouris-Blazos A, Steen B, Lukito W, Horie Y, Horie K. Legumes: the most important dietary predictor of survival in older people of different ethnicities. Asia Pac J Clin Nutr. 2004;13(2):217-20. PMID: 15228991. http://apjcn.nhri.org.tw/server/APJCN/13/2/217.pdf

9) Mattei J, Hu FB, Campos H. A higher ratio of beans to white rice is associated with lower cardiometabolic risk factors in Costa Rican adults. Am J Clin Nutr. 2011;94(3):869-876. doi:10.3945/ajcn.111.013219 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3155926/

10) Lowers LDL cholesterol https://www.jlr.org/content/38/6/1120.long Duane WC. Effects of legume consumption on serum cholesterol, biliary lipids, and sterol metabolism in humans. J Lipid Res. 1997 Jun;38(6):1120-8. PMID: 9215540.

11) Abeysekara S, Chilibeck PD, Vatanparast H, Zello GA. A pulse-based diet is effective for reducing total and LDL-cholesterol in older adults. Br J Nutr. 2012 Aug;108 Suppl 1:S103-10. doi: 10.1017/S0007114512000748. PMID: 22916805. https://pubmed.ncbi.nlm.nih.gov/22916805/

12) Reduced risk for metabolic syndrome: http://www.ams.ac.ir/AIM/NEWPUB/12/15/9/005.pdf Hosseinpour-Niazi S, Mirmiran P, Amiri Z, Hosseini-Esfahani F, Shakeri N, Azizi F. Legume intake is inversely associated with metabolic syndrome in adults. Arch Iran Med. 2012 Sep;15(9):538-44. PMID: 22924370.

13) Jenkins DJ, Wolever TM, Taylor RH, Barker HM, Fielden H. Exceptionally low blood glucose response to dried beans: comparison with other carbohydrate foods. Br Med J. 1980;281(6240):578-580. doi:10.1136/bmj.281.6240.578 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1713902/?page=2

14) NutritionFacts.org. Why you should eat more beans. https://nutritionfacts.org/2014/03/11/why-you-should-eat-more-beans/

15) NutritionFacts.org. Beans and the ‘second meal effect’ https://nutritionfacts.org/video/beans-and-the-second-meal-effect/

16) den Besten G, van Eunen K, Groen AK, Venema K, Reijngoud DJ, Bakker BM. The role of short-chain fatty acids in the interplay between diet, gut microbiota, and host energy metabolism. J Lipid Res. 2013;54(9):2325-2340. doi:10.1194/jlr.R036012 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3735932/

17) PCRM. Healthy gut: prebiotics and probiotics. https://pcrm.widen.net/view/pdf/vbwxkjsbel/Healthy-Gut-Prebiotics-and-Probiotics?t.download=true&x.share=true&x.portal_shortcode_generated=gr0kpkol&x.app=portals

18) PCRM. Fiber is the key to good health. https://pcrm.widencollective.com/portals/gr0kpkol/factsheets

19) Plant diversity = predictor of gut health. American Gut Project. DOI: 10.1128/mSystems.00031-18 https://msystems.asm.org/content/3/3/e00031-18.short

20) Chang WC, Wahlqvist ML, Chang HY, Hsu CC, Lee MS, Wang WS, Hsiung CA. A bean-free diet increases the risk of all-cause mortality among Taiwanese women: the role of the metabolic syndrome. Public Health Nutr. 2012 Apr;15(4):663-72. doi: 10.1017/S1368980011002151. Epub 2011 Sep 7. PMID: 21899787. https://pubmed.ncbi.nlm.nih.gov/21899787/

21) Healthline. Legumes: good or bad? https://www.healthline.com/nutrition/legumes-good-or-bad#antinutrients

22) Dispelling myths about lectins. https://www.hsph.harvard.edu/nutritionsource/anti-nutrients/lectins/

23) Winham DM, Hutchins AM. Perceptions of flatulence from bean consumption among adults in 3 feeding studies. Nutr J. 2011;10:128. Published 2011 Nov 21. doi:10.1186/1475-2891-10-128 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3228670/

24) Bulsiewicz, W. https://theplantfedgut.com/fart-health/

25) Bulsiewicz, W. https://www.mindbodygreen.com/articles/biggest-gut-health-mistake-we-need-to-fix-in-2020

26) https://nutritionfacts.org/video/gut-dysbiosis-starving-microbial-self/

27) https://www.hsph.harvard.edu/nutritionsource/legumes-pulses/

28) https://nutritionfacts.org/video/canned-beans-or-cooked-beans/