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Legumes Are The Rock Stars of the Nutrition World

Ask anyone born before 1945 and they would absolutely know what a legume is and probably have eaten a few dishes containing them. My grandmother in England often cooked a lentil soup while my husband's grandmother in Hawaii made Portuguese Bean Soup. Fast forward to 2019 and fewer and fewer people recognize a legume let alone have cooked with one. How have these rock stars of the nutrition world fallen out of favour so fast?

Most likely this is due to meat playing a more prominent role in the food supply as it has become more economical and more widely available.

But from a nutrition standpoint, legumes should play a role in anyone's diet whether they are omnivore or vegan. This is due to the powerful nutrients found in legumes that can improve health in multiple ways.

But first, lets define legumes. Legumes include all forms of beans and peas from the Fabaceae (or Leguminosae) botanical family. There are thousands of different species of legumes but the ones you most likely have heard of are chickpeas, peas, black beans, pinto beans, kidney beans, navy beans, split peas, lentils, soybeans, and peanuts.

So what makes legumes so special? Probably the most important thing about legumes is their unique fibre. They contain prebiotic fibre and resistant starch that "resist" digestion meaning they travel to the colon instead of being absorbed higher up in the digestive tract. This means the starchy carbohydrates in legumes are not all absorbed making them low GI. In fact, you can even mash up legumes and they still resist digestion. This cannot be said for whole grains because as soon as you pulverize them into flour, they are more easily digested and have a higher GI.

Once the fibre and resistant starch reach the colon they get fermented (or broken down) by the gut bacteria living there. Through the process of fermentation the gut bacteria generate byproducts or metabolites that are called short chain fatty acids. Three important short chain fatty acids generated from the consumption of legumes are acetate, proprionate and butyrate.

Cell. 2016 Jun 2;165(6):1332-1345. doi: 10.1016/j.cell.2016.05.041 (To read the full study see here)

As this figure shows, acetate, propionate and butyrate travel through the blood stream and bind to organs all over the body helping them work better. Some bind to the brain signalling to it that we feel full which increases satiety. Others travel to the lungs helping reduce inflammation and asthma. Some message fat cells and tell them to reduce fat accumulation helping us with weight loss. Some travel to the liver and pancreas helping our insulin work better so that we can maintain healthier blood sugar levels. Still some travel to the kidney blocking the enzyme renin which helps lower blood pressure. And some go to the liver and tell it to make less cholesterol. And finally some stay right in the colon feeding the colonic cells and if those cells have turned cancerous, they enter the cell and inhibit an enzyme necessary for the cancerous cells to multiply, making them strong anti-tumour agents.

In addition to the above health effects, legumes are also a great source of protein, are low in saturated fat and are rich in vitamins and minerals. They contain numerous B-group vitamins (especially folate), iron, zinc, calcium and magnesium. They are also rich in phytonutrients, plant based chemical compounds, that reduce the risk of certain diseases, such as cardiovascular disease and some cancers.

And just in case you are concerned about legumes containing anti-nutrients (phytates that bind to minerals preventing them from getting absorbed - you know that Paleo myth that just won't die?) relax. Our gut bacteria in our colon produce a special enzyme called bacterial phytase that breaks down the phytate, allowing the minerals to be released and absorbed by the body.

So you see, legumes are nutritional powerhouses. Perhaps that is why they are a staple food of every single Blue Zone culture. Blue Zones are longevity hotspots where people live longer lives with less chronic disease.

You don't have to give up meat to enjoy legumes, they are not mutually exclusive. Why not try replacing half the mince in your next batch of bolognaise with lentils. Your family probably won't even notice and you will all benefit from the awesome health effects of this humble rock star.

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