Why We Should Eat More Beans

Why You Should Eat More Beans

We’ve known for decades that beans have an exceptionally low glycemic index. You give someone cooked beans, peas, or lentils and they don’t even get half the blood sugar spike that they would get with the same amount of carbs in the form of bread, pasta, or potatoes. So if you’re going to eat some high glycemic food like white rice, consider having some beans with it, and the more beans the better. If you check out my 3-min video Beans and the Second Meal Effect, you can see that as the subjects’ bean to rice ratio increases, cardiometabolic risk factors continually improve. Substituting one serving of beans for one serving of white rice was associated with a 35 percent lower risk of metabolic syndrome (pre-diabetes).

Why do beans have such a low glycemic index? Maybe it’s because they’ve got so much fiber that absorption is just slower or something? It was this study that blew everyone’s minds.

It started about as expected. Give people bread for breakfast, and they get big spikes in blood sugar and insulin levels, but give the same amount of carbs in lentil form and you blunt the effect. (Lentils for breakfast? Well, the Brits like baked beans on their toast, but I’ve started using a handful of sprouted lentils in my breakfast smoothie. See A Better Breakfast and Antioxidants Sprouting Up). What they did different, though, was follow through to lunch.

For lunch both groups got the same meal; they both got bread. Those that had lentils for breakfast, though, had less of a glycemic reaction to the bread. At the time they called it the “lentil effect,” but subsequent studies found chickpeas appear to work just as well. It has since been dubbed the “second meal effect.” Eat lentils for dinner, and then for breakfast, even if forced to drink sugar water, we have better glycemic control. Beans moderate your blood sugar not just at the meal we eat them, but even hours later or the next day.

How is that even possible? The mystery has since been solved. Remember what our gazillions of gut bacteria do with fiber? They produce compounds like propionate with it (see Fawning Over Flora and Boosting Good Bacteria in the Colon Without Probiotics) that get absorbed into our system and slow down gastric emptying—the rate at which food leaves our stomach—so we don’t get as much of a sugar rush. It’s like symbiosis. We feed our good bacteria and they feed us back. So, we have a bean burrito for supper and by the next morning it’s time for our gut bacteria to eat that same burrito and the by-products they create may affect how our breakfast is digested.

Researchers figured this out by giving people rectal infusions of the amount of propionate your good bacteria might make from a good burrito, and the stomach relaxes within minutes. I guess if you forgot to eat any kind of beans for supper and need to blunt the effect of your breakfast doughnut, it’s theoretically not too late—but in general I encourage people to administer their food orally.

What about the gas? Check out my blog post Beans and Gas: Clearing the Air.

Which beans are most antioxidant packed? See The Best Bean and The Healthiest Lentil (hint: skip the jelly variety). Which lower cholesterol the most? See Soy Worth a Hill of Beans?

What other superpowers do beans posses? They are packed with potassium (Preventing Strokes with Diet), mad with magnesium (Mineral of the Year—Magnesium), and a preferred source of protein (Plant Protein Preferable). They improve breast cancer survival (Breast Cancer Survival and Soy), reduce hot flashes (Soy Foods & Menopause), delay premature puberty (The Effect of Soy on Precocious Puberty), and they’re a great bargain to boot (Eating Healthy on a Budget).

-Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my videos for free by clicking here and watch my full 2012 – 2015 presentations Uprooting the Leading Causes of Death, More than an Apple a Day, From Table to Able, and Food as Medicine.

Image credit: Renee Suen 孫詩敏 / Flickr

  • PaulB

    They are also an excellent source of resistant starch with the fiber and promote satiety. I like bean milks made with just whole beans soaked and cooked 1/2 soy and 1/2 either black, adzuki, kidney… pick your bean and filtered through a nut milk bag. Add the pulp or fiber to soups or smoothies as a thickener. The bean milks are wonderful. Getting a soymilk maker is about $100.

  • Ignatius Turchi

    How about bean sprouts?

  • Absolutely, beans are great, but people who have cancer should watch the amounts they eat due to high copper (also in certain nuts and seeds and dried vegetables) and low zinc. Copper drives angiogenesis. Leafy greens will help bind copper, and as Dr. G points out, onions and garlic will help you absorb zinc. http://eatandbeatcancer.wordpress.com/2014/03/01/anti-cancer-diets-and-the-pitfalls-of-plants-part-1-copper-and-zinc/#more-2822

  • pm

    The only downside to beans is the phytic acid content, which can block mineral absorption. Just make sure that the beans are properly soaked or better still, sprouted to reduce the phytic acid.

    • Our thoughts about phytic acid are actually changing. See for example my video Phytates for the Prevention of Osteoporosis.

      • I saw that video and I’m still wondering: Doesn’t phytic acid interfere with absorption of amino acids? To what degree are bean proteins bioavailable?

        Eating more beans is not the solution–don’t need the extra calories or extra copper.

  • My problem with vegan diets is that of absorption of iron from beans and other vegetables such as spinach. I’ve suffered from iron deficiency anemia most of my life and the only solution is to consume heme iron from any available source. I’m very sure that my condition is not rare; anemia affects about 25% of the population over 65 years.
    I eat plenty of beans and spinach, but I need heme iron for survival. The problem is that I must eat the required amount of heme iron without elevating cholesterol and copper levels in my blood.

    • neale_blackwood

      Are you also consuming enough vitamin C which helps the body absorb the iron?

    • b00mer

      The link below is a fairly comprehensive review of the literature on iron deficiency anemia in vegetarians and vegans by Jack Norris, RD. You may have read this already but if not you may find it helpful:


      I found this excerpt particularly noteworthy:

      “If your iron stores are too low, your doctor might suggest eating meat or taking an iron supplement. Anemia in meat-eaters is normally treated with large doses of supplemental iron, not with eating more meat. Similarly, vegetarians with anemia do not need to start eating meat but can also be treated with supplemental iron and vitamin C. If your doctor insists that you eat meat, you might want to show him or her this article.”

      As a personal anecdote, my Hbg levels increased from about 11.8 g/dL (borderline anemic for premenopausal female) to 13.7 g/dL after adopting a vegan diet. My daily iron intake is nearly always 18 mg or higher. It may be important to note that my vitamin C intake is also typically 300-500% of my rda. However, from the way you describe it, it sounds like you have some other underlying chronic disease state affecting your iron levels? Do you believe it is the absorption rate on a vegan diet that is the problem, or do you find it difficult to consume enough?

      • b00mer
        I also found the excerpt particularly notable. Thank you, but the only solution for my anemia is the consumption of calf, beef, chicken and pork liver. This is based on my medical history and a mostly plant-based diet. I’ve been referred to a hematologist twice, and had three colonoscopies and two upper endoscopies because of abnormally low levels of Hemoglobin. My next colonoscopy is scheduled for 20017, but until then I’ll continue get my iron from Heme sources and to follow NutritionFacts.org, which I do religiously.

  • Tracy Minton

    Lentils for breakfast? I say absolutely. We eat lentils for breakfast frequently. We often blend local oranges w/ greens & flax first, then have lentil soup or lentils cooked w/ more veggies after as our first meal. It has made a huge difference for me in staying satiated, maintaining blood sugar, and healthy elimination. Beans rule!

  • Michael

    Does soy milk count as “beans?”

    • Mike Quinoa

      I’m guessing no, Michael. There’s not a lot of fibre in soy milk.

  • Em Crone

    I LOVE BEANS!!!!! :) yay

  • Susan M. Risk

    I used 1/3 cup of chickpea flour in a recipe for pizza bread. The recipe was 2 c flour, so I subbed for one third of a cup. The result was not only really tasty and with an excellent texture, but highly digestible compared to unbleached white flour. So a person can have their cake and eat it too!!!!

  • Sergio

    Dr. Greger,
    Does donating blood lower blood sugar levels like it does with iron?

  • 1704212

    If you have a partner be sure that both of you eat them together.

  • Jenna

    How much lentils/beans/peas must one consume to experience the second meal effect. Is there a threshold value/amount?