Beans, the musical fruit: the two studies behind the video
Everything I said in this morning's video, and where each number came from: two studies, one federal diet survey, and the USDA's food tables.
The tablespoon
“This is how many beans the average American eats in a day. A single tablespoon.”
Twenty years of federal diet surveys (1999 to 2018) put the average at 12 grams of cooked beans, lentils, chickpeas and dried peas per person per day. A cup of cooked black beans weighs 172 grams, so a level tablespoon works out to about 11 grams. The average is that low because on a given day only 17.2% of people reported eating any. In 2017 and 2018, about 1 in 5 reached the 1.5 cups a week that the Dietary Guidelines called for at the time.
“The more you eat, the more you toot”
“They fed people half a cup of beans a day. In the first week, about half of them noticed more gas. By week three, nearly everyone was back to normal.”
Three feeding trials gave adults half a cup of beans a day for 8 to 12 weeks and asked them every week whether they had more gas than usual. In the first week, 50% of people eating pinto beans and 47% eating baked beans said yes. With black-eyed peas it was 19%. In the trial that compared pinto beans with black-eyed peas, only one or two people still reported it from week three on.
Two limits. The trials were small (17, 29 and 80 people), and the gas was self-reported. Between 3% and 11% of people reported more gas while eating the comparison foods, which had no beans in them.
Why beans do this.
Beans carry sugars called raffinose and stachyose. Human digestive enzymes cannot break them down, so bacteria in the colon ferment them, and most intestinal gas comes from that fermentation. The same paper notes that many people avoid beans because they expect the gas.
“The more you toot, the better you feel”
“A cancer center in Texas gave patients a cup of beans a day. The helpful bacteria in their gut went up, and the harmful ones went down.”
This is the BE GONE trial at MD Anderson Cancer Center in Houston. It followed 48 adults over 30 with obesity and a history of bowel lesions. Three in four had had colorectal cancer, and the rest had high-risk precancerous polyps. They added canned navy beans to their usual diet, working up over two weeks to one cup a day, for eight weeks in all. Their gut bacteria became more diverse. Faecalibacterium, Eubacterium and Bifidobacterium went up, and bacteria the researchers classed as opportunistic went down. The changes faded once people stopped eating the beans.
What it did not show: the trial measured gut bacteria in stool and markers in blood. It did not measure whether people felt better. These were also patients at high risk, so the size of the effect may differ in other people.
Zhang and colleagues, eBioMedicine, 2023MD Anderson: summary of the trial
“The gas is those bacteria getting fed.”
That sentence is my summary, and it joins the two studies. Neither one measured gas and bacteria in the same people. The first explains where the gas comes from: colon bacteria fermenting the sugars in beans. The second shows that a daily cup of beans shifted those bacteria in a favorable direction.
What is in a cup
“One cup of black beans has about as much fiber as the average American eats all day, and about a third of your vitamin B1.”
USDA's food tables list black beans cooked from dry at 8.7 grams of fiber and 0.244 milligrams of thiamin (vitamin B1) per 100 grams. A cup weighs 172 grams, so that is 15 grams of fiber and 0.42 milligrams of B1. The average American eats 16 grams of fiber a day. The daily value for B1 is 1.2 milligrams, so a cup of home-cooked black beans covers 35%.
Canned black beans have less B1: 0.14 milligrams per 100 grams, which comes to about a fifth to a quarter of the daily value per cup, depending on how much of the liquid you keep. The fiber holds up in the can at 6.9 grams per 100 grams.
USDA FoodData Central: black beans, cookedUSDA FoodData Central: black beans, cannedUSDA: fiber intake of the U.S. population (PDF)
If you want to start
- Half a cup a day is the amount used in the gas studies.
- Black-eyed peas were the gentlest in those trials: 19% noticed more gas in week one, against about half with pinto or baked beans.
- If you have IBS or a sensitive gut, go slower. Beans are high in the fermentable sugars that can set off symptoms. Monash University, which developed the low-FODMAP diet (an eating plan that limits those sugars), says canned beans that are drained and rinsed are lower in them because some leach into the canning water. Its example serving is a quarter cup of canned chickpeas.
Monash University: including legumes on a low-FODMAP diet
For clinicians
- Winham and Hutchins measured perceived flatulence on a weekly questionnaire, with no objective measure of flatus. The authors conclude that concern about excessive flatulence from beans may be exaggerated and that response varies by person and by bean type.
- BE GONE was a randomized crossover trial with 8-week periods. The shifts in the microbiome and its metabolites regressed when participants returned to their usual diet. Of 55 patients randomized, 48 completed it. The paper lists the American Cancer Society as funder and discloses that the study beans were bought with an award from the Dry Bean Health Research Program, which was created by the Northarvest Bean Growers Association.
- The consumption analysis was funded by the USDA Agricultural Research Service's Pulse Crop Health Initiative.
Not medical advice for your situation. If you have a digestive condition, check with your own doctor before changing your diet.
Know someone this is for? Send them this page.
Every number on this page links to where it came from. If I got one wrong, tell me and I'll correct it here.
Rick Pescatore, DO
I'm an emergency physician, the editor-in-chief of Emergency Medicine News, and a former chief physician for Delaware's Division of Public Health. I founded BellyMD to work on the gut-brain problems medicine tends to wave off.
The formulas I make
MGB+ is the daily gut-brain line I formulated at BellyMD. Three formulas, each built for one pattern.
Every first order carries the 12-week money-back guarantee. Feel the difference or it's free, and you keep the bottles.