Transcript: Beans & the Second Meal Effect
Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.
We’ve known for decades that beans have an exceptionally low glycemic index. You give someone cooked beans, peas, or lentils, and you don’t even get half the blood sugar spike you 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.
Check it out, as your bean-to-rice ratio increases from left to right, from more rice-with-some-beans, to more like beans-with-some-rice, you can see these trends towards improving cardiometabolic risk factors. “Substituting one serving of beans for one serving of white rice was associated with a 35%…lower risk of…metabolic syndrome [or 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. But, it was this next study that blew people’s minds.
Started out same as before. Give someone some bread for breakfast, and get a big spike in blood sugar and insulin levels, but give the same amount of carbs in lentil form, and you blunt the effect. Okay, but now, let’s follow through to lunch.
At breakfast, same as before, big spike with the bread; small spike with lentils. But then, for lunch, both groups got the same meal. Both got bread, and those that had lentils four hours earlier with breakfast had less of a glycemic reaction to the bread. At the time they called it the “lentil effect,” but chickpeas appear to work just as well, so it has since been dubbed the “second meal effect.” Eat lentils for dinner, and then for breakfast, even if forced to drink sugar water, you have better glycemic control. Beans moderating your blood sugar, not just at the meal you eat them, but hours later; even 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, which gets absorbed into our system and slows down gastric emptying—slows 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; they feed us back. So, you have a bean burrito for supper, and by the next morning, it’s time for your gut bacteria to eat that same burrito, and the by-products they create with it may affect how our breakfast the next morning is digested.
They figured this out by giving people rectal infusions of the amount of propionate your good bacteria might make from a good burrito. And, you can see the stomach relax within minutes of the rectal infusion. So, I guess if you forgot to eat any kind of beans, peas, or lentils 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.
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