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:
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:
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:
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:
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:
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:
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.