Ban on beans ignores their benefits, including “resistant” starch
Given the benefits of high-protein/low-carb diets — like the Paleo and keto plans — it seems odd to make a case for starch.
We know that the refined starch in processed foods presents big health problems when eaten to excess, as in the typical American diet.
Starch — especially the stuff in potatoes and foods made with cornstarch or white flour — raises blood sugar levels without contributing vitamins, minerals, or antioxidants.
But one kind — called “resistant” starch — is something that people should get more of, because it improves blood sugar control, digestive health, and weight management.
Many leading advocates of Paleo diets ban beans from their recommended eating plans. But as we'll explain at the end of this article, their reasons for that ban don’t make sense.
What is resistant starch?
The term "resistant starch" refers to starchy fibers that resist digestion in the small intestine and then get fermented (digested) by beneficial bacteria, typically in the large intestine.
Resistant starch (RS) abounds in beans, lentils, peas, and whole grains, and small amounts form when you cook and then chill potatoes, rice, or pasta.
Manufacturers are also making synthetic RS and selling it to food companies for use as an additive or flour-replacer to blunt the blood-sugar impacts of processed foods.
Resistant starch falls into four categories:
- Type 1: Found in the cell walls of grains, seeds, and beans or other legumes.
- Type 2: Found in uncooked potatoes, unripe bananas, and plantains. Cooking these foods converts their resistant starch into digestible starch.
- Type 3: Also called retrograde RS, this type forms in plant foods that are first cooked and then chilled. Retrograde RS occurs in parboiled rice and in cooked/chilled potatoes or pasta. The resulting RS changes back into digestible starch when cooked at temperatures above 130 degrees F.
- Type 4: This category encompasses synthetic RS derived from corn, green bananas, potatoes, tapioca, and wheat. Some corn-derived synthetic RS (e.g., Hi-Maize 260) is Non-GMO Project verified.
What are the benefits of resistant starch?
Resistant starch has been tested in more than 200 human clinical trials.
The clinical studies published to date have probed the impacts of RS on colon health, appetite, weight, and the body’s insulin/blood-sugar response.
And America’s current epidemic of diabetes and pre-diabetes explained why the ability of resistant starch (RS) to improve blood sugar control has received the most attention.
These are some of its clinically documented benefits:
- Improved blood sugar control: Increased insulin sensitivity, reduced insulin levels, reduced glycemic and insulin response of foods.
- Improved weight control via increased satiety, reduced hunger, higher metabolic (calorie-burning) rates, and other beneficial changes.
- Improved digestion, reduced constipation, improved regularity, and diminishment of diarrhea.
One typical clinical study found that when overweight and obese men consumed 15 or 30 grams of resistant starch daily, they showed improvements in insulin sensitivity comparable to those seen when men lose about 10% of their body weight (Maki KC et al. 2012).
Resistant starch even exerts beneficial effects on a meal eaten several hours later, such as healthier blood-sugar responses to breakfast following a dinner rich in resistant starch (Brighenti F et al. 2006; Nilsson AC et al. 2008).
Recent research in rodents also suggests that RS may benefit immune health, and improve so-called “leaky gut” syndrome, which is linked to immune-related disorders (Zegarra-Ruiz DF et al. 2019).
And research is beginning to reveal other potential benefits of diets rich in RS, including better kidney health, reduced inflammation, lower blood pressure, and better eye health.
To learn more about its effects on blood sugar and weight control, see Beany Starch Curbed Men's Diabetes Risk, Can Beans (and Fish) Match Meats for Appetite Control?, and Beans Aid Weight and Blood Sugar Control, which provides links to other relevant articles.
How does resistant starch produce its benefits?
The answer to this question lies mostly in the microbiome of the human gut, whose composition is critical to human health.
Because only beneficial bacteria feed on it, consumption of RS helps shift the composition of gut microbiome in a healthy direction.
When beneficial bacteria feed on (ferment) RS they generate short chain fatty acids (SFAs) that exert beneficial effects on colon and overall health: acetate, propionate, and butyrate.
Of the three SFAs generated when bacteria ferment RS, butyrate may be the most important, for three reasons:
- Butyrate raises your metabolic (calorie-burning) rates.
- Butyrate dampens inflammation and boosts resistance to stress.
- Butyrate is the preferred energy source of the cells lining your colon.
Some of the apparent benefits of RS may be linked to other effects, such as beneficial changes in gene expression — the same “nutrigenomic” mechanism by which foodborne antioxidants bring their benefits (Vidrine K et al. 2014).
Best sources of resistant starch (RS)
These foods are the richest natural sources of resistance starch:
- Beans/Lentils — white beans have the most RS, followed by lentils, chickpeas, kidney beans, pinto beans, black/brown beans, and mung beans
- Cornflakes (whole grain)
- Corn tortillas (whole grain)
- Puffed wheat (whole grain)
- Pumpernickel bread (whole grain)
- Rye bread (whole grain)
Although some processed grain foods — rice square cereal, breadsticks, toasted Italian bread, baked pizza dough, and fried potatoes — have substantial amounts of RS, they lack the essential nutritional attributes of whole-grain products (Murphy MM et al. 2008).
How much RS do we get and need?
Americans used to average about 40 grams (1.4 ounces) of resistant starch a day, but most of us now get only get about 5 grams (one-fifth of an ounce) daily.
The historically higher level of RS consumption occurred when Americans ate more whole foods, consumed far less processed food, and enjoyed lower rates of diabetes and other chronic metabolic disorders.
Fibers are usually classified as soluble or insoluble, but those terms don’t relate to their effects on the body, so some experts propose three new classifications:
- Fermentable fibers such as resistant starch, inulin, and oligosaccharides serve as “prebiotics” that feed beneficial bacteria and trigger beneficial health effects.
- Bulking fibers such as wheat bran — sometimes called “roughage” — are only minimally fermented by gut bacteria, absorb a good deal of water, and promote regularity.
- Viscous fibers such as the beta-glucan in oats, mushrooms, and barley reduce absorption of dietary cholesterol and sugar, and lower blood cholesterol levels.
Paleo-advocates’ reasons for banning beans don’t add up
Many leading Paleo-diet advocates advise people to avoid beans, but their reasons don’t make much sense.
First, they cite the fact that beans contain lectin-type proteins, oxalates, and phytic acid, which allegedly exert bad health effects.
But that objection doesn’t square with the facts:
- Oxalates are acids that bind to and reduce the absorption of dietary calcium. But they occur in many plant foods, and beans are not especially high in oxalates. Dark leafy greens like spinach containing levels 10-15 times higher than in beans, while almonds and cashews contain 5-8 times more oxalates than beans. And it’s worth noting that only 20-40% of the oxalates in our blood comes from foods, with the rest being produced internally.
- While the phytic acid in any plant food impairs absorption of its iron, the extent of that effect varies, and any negative health consequences appear very minor, at most.
- Lectin-family proteins can be toxic, but they get neutralized by thorough cooking. While legumes are high in lectins compared with most other plant foods, other relatively high-lectin foods include tomatoes, whole grains, eggplant, peppers, potatoes, onions, mushrooms, and winter squash. Importantly, it only makes sense to avoid lectins if you have an autoimmune or other disorder that’s clearly aggravated by lectins. (Weirdly, the chief accusations against lectins in Stephen Gundry, M.D.’s best-selling book “The Plant Paradox” aren’t backed by good evidence, and the studies he cites to support his claims do not actually support them.)
- Ironically, compared with legumes, many “Paleo-approved” foods — such as nuts, leafy greens, and many common vegetables — contain as much or more lectins, oxalates, and/or phytic acid.
- There's no good evidence that people suffer ill health effects when they consume properly cooked legumes.
Second, Paleo-diet advocates claim that humans didn’t eat legumes until quite recently, and either assert or imply that the human body is therefore not well-adapted to legumes, making them unhealthful.
However, a recent analysis of Neanderthal tooth plaque revealed that they ate wild legumes. Other Paleolithic humans are believed to have eaten a more diverse diet than Neanderthals did, so it seems likely they ate legumes too, when available (Henry AG et al. 2011).
And modern hunter-gatherers who apparently eat diets of ancient origin — such as Africa's Kung San (bushmen) people — eat a very wide range of wild foods, including legumes.
More importantly, large proportions of the Earth’s population have been eating beans and other legumes for centuries or millennia without any apparent ill effects, which strongly suggests that humans are well adapted to legumes.
Fortunately, some followers and advocates of keto in Paleo diets have realized the RS-related benefits of legumes, and that avoiding legumes and other “heretical” sources of RS (like whole grains) can degrade the gut microbiome.
- Brighenti F, Benini L, Del Rio D, Casiraghi C, Pellegrini N, Scazzina F, Jenkins DJ, Vantini I. Colonic fermentation of indigestible carbohydrates contributes to the second-meal effect. Am J Clin Nutr. 2006 Apr;83(4):817-22.
- Maki KC, Pelkman CL, Finocchiaro ET, Kelley KM, Lawless AL, Schild AL, Rains TM. Resistant starch from high-amylose maize increases insulin sensitivity in overweight and obese men. J Nutr. 2012 Apr;142(4):717-23. doi: 10.3945/jn.111.152975. Epub 2012 Feb 22.
- Maziarz MP, Preisendanz S, Juma S, Imrhan V, Prasad C, Vijayagopal P. Resistant starch lowers postprandial glucose and leptin in overweight adults consuming a moderate-to-high-fat diet: a randomized-controlled trial. Nutr J. 2017 Feb 21;16(1):14. doi: 10.1186/s12937-017-0235-8.
- Murphy MM, Douglass JS, Birkett A. Resistant starch intakes in the United States. J Am Diet Assoc. 2008 Jan;108(1):67-78. Erratum in: J Am Diet Assoc. 2008 May;108(5):890.
- Nilsson AC, Ostman EM, Holst JJ, Björck IM. Including indigestible carbohydrates in the evening meal of healthy subjects improves glucose tolerance, lowers inflammatory markers, and increases satiety after a subsequent standardized breakfast. J Nutr. 2008 Apr;138(4):732-9.
- Vidrine K et al. Resistant starch from high amylose maize (HAM-RS2) and dietary butyrate reduce abdominal fat by a different apparent mechanism. Obesity (Silver Spring). 2014 Feb;22(2):344-8. doi: 10.1002/oby.20501. Epub 2013 Oct 15.
- Zegarra-Ruiz DF et al. A Diet-Sensitive Commensal Lactobacillus Strain Mediates TLR7-Dependent Systemic Autoimmunity. Cell Host Microbe. 2019 Jan 9;25(1):113-127.e6. doi: 10.1016/j.chom.2018.11.009. Epub 2018 Dec 20.