We’ve all heard the warning: Beware of excess carbs. But we’ve also learned that not all carbohydrates are created equal. And now we’re finding out there are certain carbs we may not be getting enough of.
Just as we discern between “good fats” and “bad fats,” it’s important to remember that carbohydrates are a macronutrient, and many forms contain important health-promoting properties. Resistant starch — a little-known but powerful glucose chain contained within certain carbohydrates — is a good example.
It’s well accepted that simple carbs such as refined sugar spike glucose levels and can lead to insulin resistance, contributing to obesity and type 2 diabetes. Some health experts now argue that even complex carbs — particularly those found in grains — can contribute to chronic systemic inflammation and conditions like irritable bowel syndrome (IBS), colon cancer, and even dementia.
But that’s not the whole story, explains John Bagnulo, MPH, PhD, a nutritionist and educator based in Yellow Springs, Ohio. “When people talk about carbs as the culprit for all these diseases, that’s an oversimplification. The truth is more nuanced.”
Most starches are formed by two types of glucose molecules: amylopectin and amylose. Amylo-pectin easily breaks down in the small intestine, releasing glucose into the bloodstream. Amylose, on the other hand, has a tighter molecular structure that’s harder to crack.
Resistant starch — found in foods such as beans, whole grains, rice, and potatoes — is high in amylose. It stays intact as it passes through the stomach and small intestine, and doesn’t enter the bloodstream (hence the “resistant” part of its name).
“What we think is detrimental about easily digestible carbohydrates and simple sugars — that they drive up our glucose levels — doesn’t apply to resistant starch,” says Jens Walter, University of Alberta associate professor and Campus Alberta Innovates Program chair of nutrition, microbes, and gastrointestinal-tract health. Research into the nutritional benefits of resistant starch is relatively new, but results so far indicate that this form of carbohydrate delivers all sorts of health benefits, including improved gut health, weight control, and potentially even cancer protection.
Feed Your Microbes
Recent science has established that the health of our microbiome — especially the organisms that live in our intestines — is directly tied to our broader well-being. To bolster our gut ecosystems, many of us consume probiotics: living bacteria found in supplements or fermented edibles like yogurt and sauerkraut (for more on this, see “Probiotics at Work“).
Yet downing probiotics and -fermented foods is not enough to keep our guts healthy.
“Even if I give you the very best probiotics — and large amounts of them — those bacteria live less than an hour, then they’re gone,” says Robynne Chutkan, MD, author of The Microbiome Solution.
We have to feed those bacteria so they can survive and thrive. That’s where prebiotics come in.
Prebiotics — including resistant starch and specific types of fiber — are indigestible nutrients that ferment in the large intestine, providing nourishment for the gut’s healthy bacteria. Unfortunately, the standard American diet, high in processed ingredients, doesn’t provide enough prebiotic foods.
“With the Western diet, the colon has become malnourished,” says Stephen O’Keefe, MD, professor of medicine at the University of Pittsburgh.
When intestinal bacteria don’t get enough prebiotic food, they start to feed off the colon’s mucosal lining. Lacking appropriate nutrition, beneficial microorganisms grow frail and become unable to ferment prebiotics. This causes the colon to become more alkaline, which creates an environment for acid-sensitive bacteria — like strains of E. coli and salmonella, as well as other potent pathogens — to bloom.
The proliferation of harmful bacteria can set off a microbial imbalance, known as dysbiosis, and lead to problems such as leaky gut. This in turn can trigger autoimmune disease and metabolic disorders. (For more on this, see “How to Heal a Leaky Gut“.)
Sluggish prebiotic fermentation also creates a self-reinforcing pattern that further restricts the creation of food for our friendly microorganisms.
Build Up Butyrate
While resistant starch behaves like fiber in many ways, it has distinct qualities, most notably its ability to rapidly churn out a colon-critical substance called butyrate.
Butyrate is a short-chain fatty acid that is a vital nutrient for the colon — and the primary energy source for the cells of the large intestines. “Where other organs around the body use glucose, the colonic cells are unique in needing butyrate,” explains O’Keefe.
As the direct supply of nourishment to the cells along the intestinal lining, butyrate helps keep this membrane strong. A healthy colon wall prevents leaky gut, IBS, constipation, ulcerative colitis, and diverticulitis (an inflammation or infection in the digestive tract).
Butyrate also inhibits inflammation-signaling molecules called cytokines. In doing so, it mediates the colon’s inflammatory response — a trigger that can weaken the intestinal lining and set off a cycle of bodywide swelling that’s tough to tame.
Butyrate also appears to make the colon an inhospitable place for cancer. In the lab, butyrate has been shown to inhibit the growth of tumor-cell lines and has induced the death of colorectal cancer cells. It also seems to prevent angiogenesis — the forming of new blood vessels from existing ones, a fundamental step in the transition of tumors from benign to malignant.
More research is needed, but as studies unveil more about the key role of resistant starch in supporting gut health — and by extension, overall health — consensus is growing on the value of this carbohydrate.
One of the most potent results O’Keefe and his colleagues discovered is how quickly the gut microflora respond to resistant starch.
“This is very good news,” O’Keefe explains, “because it suggests you don’t have the excuse ‘I’ve been eating junk food all my life so it’s too late to help my colon.’ It’s never too late.”
Get More Resistant Starch in Your Diet
People in developing nations, where whole-plant foods are more common and where diseases like type 2 diabetes and colon cancer are rare, consume 30 to 40 grams of resistant starch per day. In the United States and Europe, people typically eat about 3 to 8 grams of resistant starch daily. So unless you already focus on eating foods high in resistant starch, it’s safe to assume you’re not getting enough.
While there is no recommended daily allowance — that research is under way — Stephen O’Keefe, MD, of the University of Pittsburgh School of Medicine, says doubling your intake of resistant starch is a good place to start. If you have bloating, gas, and discomfort from the fermentation (a possible side effect of getting too much resistant starch at once, especially if you suffer from a digestive disorder like IBS), scale your portions back and increase them slowly over a few weeks.
Though resistant-starch supplements — such as raw potato starch — are available, real foods are the healthiest sources. The whole foods shown here are rich in resistant starch (note that cooking sometimes affects the amount in food). Experiment with working them into your eating plan, and see if you notice an improvement in your digestive health.
The Weight-Loss Connection
In contrast to carbs made up of easily digested starches, those with more resistant starch can support your efforts to lose or manage weight in these ways:
Help you feel full longer, on less. Your body’s slow metabolizing of resistant starch leads to greater bulk in the digestive tract, which makes you feel full longer. Also, because the glucose molecules in resistant-starch foods are hard to access, your body extracts only two calories of energy per gram — about half the amount extracted from starches with higher amylopectin content. So you stay sated on fewer calories.
Regulate your hunger hormones. The short-chain fatty acids, including butyrate, that resistant starch produces in the colon trigger the release of leptin, peptide YY, and glucagon-like peptide-1 — all hormones that diminish -appetite.
Burn stored fat. Another short-chain fatty acid produced by fermentation in the colon, propionate, can inhibit the breakdown of carbs in the liver. This may encourage your body to extract energy from tucked-away fat.
Stabilize your blood-sugar levels and insulin response. The carb’s indigestibility means the amount of nutrients released into the bloodstream from the small intestine is low, which aids in blood-sugar stabilization. And since resistant starch doesn’t turn into glucose, your pancreas releases less insulin, so cell receptors aren’t routinely bombarded with the chemical.