The Best Source of Resistant Starch

Resistant starch wasn’t discovered until 1982. Before that, we thought all starch could be digested by the digestive enzymes in our small intestine. Subsequent studies confirmed that there are indeed starches that resist digestion and end up in our large intestine, where they can feed our good bacteria, just like fiber does. Resistant starch is found naturally in many common foods, including grains, vegetables, beans, seeds, and some nuts, but in small quantities, just a few percent of the total. As I discuss in my video Getting Starch to Take the Path of Most Resistance, there are a few ways, though, to get some of the rest of the starch to join the resistance.

When regular starches are cooked and then cooled, some of the starch recrystallizes into resistant starch. For this reason, pasta salad can be healthier than hot pasta and potato salad can be healthier than a baked potato, but the effect isn’t huge. The resistant starch goes from about 3 percent up to 4 percent. The best source of resistant starch is not from eating cold starches, but from eating beans, which start at 4 or 5 percent and go up from there.

If you mix cooked black beans with a “fresh fecal” sample, there’s so much fiber and resistant starch in the beans that the pH drops as good bacteria churn out beneficial short-chain fatty acids, which are associated both directly and indirectly with lower colon cancer risk. (See Stool pH and Colon Cancer.) The more of this poopy black bean mixture you smear on human colon cancer, the fewer cancer cells survive.

Better yet, we can eat berries with our meals that act as starch blockers. Raspberries, for example, completely inhibit the enzyme that we use to digest starch, leaving more for our friendly flora. So, putting raspberry jam on your toast, strawberries on your corn flakes, or making blueberry pancakes may allow your good bacteria to share in some of the breakfast bounty.

Another way to feed our good bacteria is to eat intact grains, beans, nuts, and seeds. In one study, researchers split people into two groups and had them eat the same food, but in one group, the seeds, grains, beans, and chickpeas were eaten more or less in a whole form, while they were ground up for the other group. For example, for breakfast, the whole-grain group got muesli, and the ground-grain group had the same muesli, but it was blended into a porridge. Similarly, beans were added to salads for the whole-grain group, whereas they were blended into hummus for the ground-grain group. Note that both groups were eating whole grains—not refined—that is, they were eating whole foods. In the ground-grain group, though, those whole grains, beans, and seeds were made into flour or blended up.

What happened? Those on the intact whole-grain diet “resulted in a doubling of the amount excreted compared to the usual diet and produced an additional and statistically significant increase in stool mass” compared with those on the ground whole-grain diet, even though they were eating the same food and the same amount of food. Why? On the whole-grain diet, there was so much more for our good bacteria to eat that they grew so well and appeared to bulk up the stool. Even though people chewed their food, “[l]arge amounts of apparently whole seeds were recovered from stools,” but on closer inspection, they weren’t whole at all. Our bacteria were having a smorgasbord. The little bits and pieces left after chewing transport all this wonderful starch straight down to our good bacteria. As a result, stool pH dropped as our bacteria were able to churn out so many of those short-chain fatty acids. Whole grains are great, but intact whole grains may be even better, allowing us to feed our good gut bacteria with the leftovers.

Once in our colon, resistant starches have been found to have the same benefits as fiber: softening and bulking stools, reducing colon cancer risk by decreasing pH, increasing short-chain fatty acid production, reducing products of protein fermentation (also known as products of putrefaction), and decreasing secondary bile products.

Well, if resistant starch is so great, why not just take resistant starch pills? It should come as no surprise that commercial preparations of resistant starch are now available and “food scientists have developed a number of RS-enriched products.” After all, some find it “difficult to recommend a high-fiber diet to the general public.” Wouldn’t be easier to just enrich some junk food? And, indeed, you now can buy pop tarts bragging they contain “resistant corn starch.”

Just taking resistant starch supplements does not work, however. There have been two trials so far trying to prevent cancer in people with genetic disorders that put them at extremely high risk, with virtually a 100-percent chance of getting cancer, and resistant starch supplements didn’t help. A similar result was found in another study. So, we’re either barking up the wrong tree, the development of hereditary colon cancer is somehow different than regular colon cancer, or you simply can’t emulate the effects of naturally occurring dietary fiber in plant-rich diets just by giving people some resistant starch supplements.

For resistant starch to work, it has to get all the way to the end of the colon, which is where most tumors form. But, if the bacteria higher up eat it all, then resistant starch may not be protective. So, we also may have to eat fiber to push it along. Thus, we either eat huge amounts of resistant starch—up near the level consumed in Africa, which is twice as much as were tried in the two cancer trials—or we consume foods rich in both resistant starch and fiber. In other words, “[f]rom a public health perspective, eating more of a variety of food rich in dietary fibre including wholegrains, vegetables, fruits, and pulses [such as chickpeas and lentils] is a preferable strategy for reducing cancer risk.”


What’s so great about resistant starch? See my video Resistant Starch and Colon Cancer.

I first broached the subject of intact grains in Are Green Smoothies Bad for You?.

Why should we care about what our gut flora eats? See Gut Dysbiosis: Starving Our Microbial Self.

Did I say putrefaction? See Putrefying Protein and “Toxifying” Enzymes.

Berries don’t just help block starch digestion, but sugar digestion as well. See If Fructose Is Bad, What About Fruit?.

The whole attitude that we can just stuff the effects into a pill is a perfect example of reductionism at work. See Reductionism and the Deficiency Mentality and Why is Nutrition So Commercialized? for more on this.

In health,
Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live, year-in-review presentations:

The Best Dried Fruit for Osteoporosis

“We are in an epidemic of osteoporosis. There can be no doubt about that.” Ten million Americans have it, and one in three older women will get it. “We urgently need public health strategies to maintain bone health throughout the life cycle and to prevent osteoporosis in later life.” Might fruits and vegetables be the unexpected natural answer to the question of osteoporosis prevention? My video Prunes for Osteoporosis sought to find out.

Evidence from a variety of studies “strongly points to a positive link between fruit and vegetable consumption and indexes of bone health,” such as bone mineral density, and the “size of the effect in the older women [is] impressive: doubling the fruit intake” is associated with a 5 percent higher spine mineralization. The same relationship exists with young women, too. And, eating lots of fruit in childhood may protect bones throughout life—something that was not found for milk intake, as I’ve explored before in my video Is Milk Good For Our Bones?

Bone health isn’t just about calcium. There are several key nutrients found in vegetables, fruits, and beans that are associated with better bone mineral density, but does that translate into lower hip fracture risk? The Singapore Chinese Health Study found that a “diet rich in plant-based foods, namely vegetables, fruit, and legumes such as soy, may reduce the risk of hip fracture.” But, why?

“The underlying mechanism in postmenopausal osteoporosis (PO) is an imbalance between bone resorption [disappearance] and formation,” and oxidative stress may play a role in this balance.

There are two types of bone cells: “the bone-forming osteoblasts and the bone-dismantling osteoclasts.” Osteoblasts are continually laying down new bone, while osteoclasts chisel away old bone, using free radicals as the molecular chisel to chip away our bone. Too many free radicals in our system, though, may lead to excessive bone breakdown. Antioxidant defenses appear “markedly decreased in osteoporotic women,” and “elderly osteoporotic women had consistently lower levels of all natural antioxidants tested than controls.”

“Because excessive [free radicals] may contribute to bone loss, it is important to elucidate the potential role antioxidant-rich fruits play in mitigating bone loss that leads to the development of osteoporosis.” The thought is that fruits up-regulate the bone building cells, and down-regulate the bone-eating cells, tipping the balance towards greater bone mass. So, let’s put a fruit to the test. Which one do we pick? Dried plums were chosen because they have among the highest antioxidant ranking among commonly consumed fruits and vegetables—and because the researchers received a grant from the California Dried Plum Board!

When you think of prunes, you think of bowels, not bones, but, over a decade ago, researchers at Oklahoma State tried giving a dozen prunes a day to a group of postmenopausal women, using a dozen dried apple rings as a control. After three months, only the subjects who consumed the prunes had significant elevations in an enzyme marker of bone formation, although prunes didn’t seem to affect markers of bone breakdown. So, prunes may help more with building bones than preventing bone loss. However, the reverse was found with almonds, so maybe a little prune-and-almond trail mix is in order. 

With this bump in bone formation indices, one might expect that if they did a longer study, we would actually see an impact on bone mineral density. And nine years later, just such a study was done: 12 months on dried plums versus apples. Both dried fruit regimens appeared to have “bone-protective effects,” though the prunes seemed to work better in the arm bone and spine.

So, the dried plum marketing board wants everyone to know that dried plums are “the most effective fruit in both preventing and reversing bone loss,” but only two fruits have ever been tested: plums and apples. If this pans out for other plants, though, “a ‘fruit and vegetables’ approach may provide a very sensible (and natural) alternative therapy for osteoporosis treatment, one that is likely to have numerous additional health-related benefits.” All we have to do is convince people to actually do it.


For more on bone health, see:

What else can prunes do for us? Check out Prunes vs. Metamucil vs. Vegan Diet.

Apple rings have their own benefits. See Dried Apples vs. Cholesterol.

In health,
Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live, year-in-review presentations:

Eating the Way Nature Intended

The Paleolithic period, also known as the Stone Age, only goes back about two million years. Humans and other great apes have been evolving for the last 20 million years, starting back in the Miocene era. We hear a lot about the paleolithic diet, but that only represents the last 10 percent of hominoid evolution. What about the first 90 percent?

During the Miocene era, the diet “is generally agreed to have been a high-fiber plant-based diet…” For the vast majority of our family’s evolution, we ate what the rest of our great ape cousins eat—leaves, stems, and shoots (in other words, vegetables), as well as fruits, seeds, and nuts. I explore this in my video Lose Two Pounds in One Sitting: Taking the Mioscenic Route.

“Anatomically, the digestive tracts of humans and great apes are very similar.” In fact, our DNA is very similar. So, what do our fellow great apes eat? Largely vegetarian diets with high greens and fruit consumption. Just largely vegetarian? It’s true that chimpanzees have been known to hunt, kill, and eat prey, but chimpanzees’ “intake of food of animal origin is still at a very low level…with only 1.7% of chimpanzee feces providing evidence of animal food consumption.” This is based on eight years of work collecting nearly 2,000 fecal samples. So, even the most carnivorous of great apes appears to eat about a 98 percent plant-based diet. In fact, we may be closest to the diet of bonobos, one of the less known great apes, who eat nearly exclusively plant-based diets, as well.

Even our Paleolithic hunter-gatherer ancestors must have done an awful lot of gathering to get the upwards of 100 grams of fiber a day they may have consumed. What would happen if researchers put people on an actual Paleolithic diet? Not a supermarket-checkout-aisle-magazine paleo diet or some caveman blogger diet, but an actual 100-grams-of-daily-fiber diet or, even better, a mioscenic diet, taking into account the last 20 million years of evolution since we split with our common great ape ancestors.

Dr. David Jenkins and colleagues gave it a try and “tested the effects of feeding a diet very high in fiber.” How high? We’re talking 150 grams of daily fiber, far higher than the recommended 20 to 30 grams a day. However, 150 grams is similar to what populations in rural Africa used to eat—populations almost entirely free from many of our chronic killer diseases, such as colon cancer and heart disease.

The high-fiber diet didn’t mess around. Lunch, for example, could include Brussels sprouts, okra, green peas, mushrooms, filberts, and a plum. And dinner? How about asparagus, broccoli, eggplant, carrots, and honeydew melon? Surely, simply eating a lot of fruits, veggies, and nuts can’t be very satisfying, right? Actually, it got the maximum satiety rating from every one of the ten subjects, unlike the starch-based and low-fat diets which scored lower. Why? “All of the diets were designed to be weight-maintaining,” meaning the researchers didn’t want weight loss to confound the data. So, to get a full day’s calories of whole plant foods, the subjects had to eat about 11 pounds of food a day! Not surprisingly, this resulted in some of the largest bowel movements ever recorded in the medical literature, with men on the high-fiber vegetable-based diet exceeding a kilogram of fecal weight per day. You know how some people on weight loss diets lose two pounds a week? Well, in this study, the subjects dropped two pounds in one sitting.

That wasn’t the only record-breaking drop: A 33 percent drop in LDL cholesterol within just two weeks was seen. Even without any weight loss, bad cholesterol levels dropped by one-third within two weeks. That’s one of the biggest drops I’ve ever seen in any dietary intervention—better than achieved on a starch-based vegetarian diet or  a low saturated fat American Heart Association-type vegetarian diet. This was a “cholesterol reduction equivalent to a therapeutic dose of a statin” drug. So, we need to take a drug to get our cholesterol levels down to where they would be normally were we to eat a more natural diet.

We’ve been eating 100 grams of fiber every day for millions of years. This diet is similar to what’s eaten by populations who don’t suffer from many of our chronic diseases. Maybe this shouldn’t be called a “very high fiber” diet. Maybe what we eat today should be considered a very low, extremely fiber-deficient diet.

Maybe it’s normal to eat 100 grams of fiber a day. Maybe it’s normal to be free of heart disease. Maybe it’s normal to be free of constipation, hemorrhoids, diverticulitis, appendicitis, colon cancer, obesity, type 2 diabetes, and all other the diseases of Western civilization.


How do we know our ancient ancestors ate more than 100 grams of fiber a day? We can examine their fossilized fecal matter, as I discuss in my video Paleopoo: What We Can Learn from Fossilized Feces.

For more evidence on what our natural diet is, see my What’s the Natural Human Diet? video.

Other popular paleo videos include:

Excited to share what you’ve learned about diet? Well, it turns out you can share more than my videos. Check out How to Become a Fecal Transplant Super Donor.

In health,
Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live, year-in-review presentations: