Dear Doctor: I keep reading about something called “resistant starch.” People are saying I should get it into my diet. Why is it so important? How much do I need?
Dear Reader: As with so many areas of diet and medicine these days, the answer leads directly to the gut microbiome. That’s the vast and complex community of bacteria, fungi, yeasts and viruses that live in our intestines. They number in the trillions, can account for 2 to 5 pounds of our weight and, as we’re learning every day, play complex and crucial roles in our physical and even mental health. In fact, because these microscopic creatures are necessary to survival, the gut microbiome is increasingly regarded as an organ in its own right.
One of the keys to a healthy and diverse gut microbiome is keeping our microscopic residents well-fed. This involves prebiotics, a type of dietary fiber that stimulates the growth and activity of the good-guy bacteria in the gut. For fellow science nerds, prebiotic foods contain high levels of a starchy substance known as inulin and certain types of sugars, including fructo-oligosaccharides and galacto-oligosaccharides. Although apples, oats, lentils, leeks, Jerusalem artichokes, garlic, asparagus and bananas are cited as good sources of prebiotics, the fact is that a wide range of fruits, vegetables, grains and legumes contain prebiotics in varying amounts.
Another potential source of prebiotics is the subject of your question -- resistant starch. As the name suggests, these are starches, or carbohydrates, that resist digestion. That means they survive the journey through the digestive tract and make it all the way to the colon, where they become available to gut microbes. Resistant starches fall into four general categories. They may be protected by fibrous cell walls, as with grains, seeds and legumes. They are available in certain raw foods, such as raw potatoes or raw plantains. And they can be manufactured via a chemical process. What’s of particular interest is the final category. This is a range of carbohydrates that, when cooked and then cooled, develop into resistant starch. These include rice, potatoes, yams, pasta and whole grains such as oats and barley.
One benefit is that, instead of being broken down into glucose and raising blood sugar levels, these types of carbohydrates pass into the colon. This improves glycemic control, an important factor in good health. Once in the colon, resistant starches feed the beneficial bacteria that live there. Through the process of fermentation, bacteria turn resistant starch into compounds known as short-chain fatty acids. These include butyrate, which is linked to lower rates of colorectal cancers, and propionate, which has been shown to lower inflammation and improve immune support.
How much resistant starch do we need? There’s no set amount. Instead, think in terms of daily goals for dietary fiber in general. Most Americans get less than half the recommended 25 grams per day for women and 38 grams per day for men. We recommend eating from a diverse range of fresh fruit, vegetables, whole grains, legumes and nuts. If they’re new to your diet, add them slowly to avoid gas and bloating. And with every bite, know you’re making your gut microbiome very happy.
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