Resistant starches join the gut microbiome chat

Cooking and then cooling certain high-carb foods, such as rice, transforms those carbs into resistant starch.
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Q: I’ve been learning about the gut microbiome, and the terminology keeps changing. I understand probiotics. Then came prebiotics and postbiotics, which I think I finally get. But now people are talking about resistant starch. What is it, and why is it important?

A: It’s fascinating how quickly academic research into the gut microbiome moves into the public domain. In the last decade, we have gone from rarely hearing the word “probiotics” to seeing it every day, and seemingly everywhere.

Probiotics are in countless dietary supplements, as well as personal products such as shampoo and conditioner, makeup, lotions, soaps and deodorants. They are even infused into clothing. And, as you point out, our gut-related vocabulary is constantly expanding as well. The theory that the body contains beneficial microbes reaches back centuries.

The idea of “probiotics,” introduced by a German scientist in 1953, is far more recent. Today, the word refers to the live bacteria and other microbes that support health and bodily functions. It is also commonly used to indicate products and supplements that contain those microbes.

In the last decade, the terms prebiotics and postbiotics have come into the conversation, too. Prebiotics refers to compounds that serve as a food source for the microbes in our guts, and which foster their growth and well-being. Postbiotics are certain substances produced by the microbes, which also benefit human health.

And this brings us to resistant starch. We have discussed it here before, but it’s so interesting, we’re happy to address it again. Resistant starch is a carbohydrate that resists digestion. Instead of being broken down and absorbed by the small intestine, resistant starch moves on, largely unchanged, to the large intestine. There, it is fermented and consumed by the trillions of microbes in the gut. Skipping the small intestine means resistant starch doesn’t contribute to blood glucose levels. Research has linked it to improved intestinal and colonic health.

Studies have found diets that include resistant starch help with blood sugar control, yield more healthful blood lipid levels and improve feelings of satiety after eating. They have also been linked to lower risk for colon cancer. As bacteria in the gut ferment resistant starch, they create compounds known as short-chain fatty acids. These include butyrate and propionate. The former is associated with lower rates of colorectal cancers. Propionate has been shown to lower inflammation in the body and also improve immune support.

Foods that are high in resistant starch include nuts, seeds, beans, legumes, whole grains, unripe bananas and plantains. It has also been found that cooking and then cooling certain high-carb foods transforms those carbs into resistant starch. These include rice, potatoes, yams, whole grains such as oats and barley, and pasta. Someone looking to increase their consumption of resistant starch should consider allowing those foods to cool completely before consuming them.

Research shows that for the first four days after cooking, each chill day increases the percentage of resistant starch. A caveat: If foods high in resistant starch are new to your diet, add them gradually in order to avoid gas and bloating.

A case against GPS?

Q: My wife and I have a running argument with our kids about GPS. We enjoy maps and use them to plan our routes. Our kids call us old-fashioned and always use GPS. I just read that can erode your spatial skills. Is that true? If so, maybe it will persuade them to use a map.

A: There’s no denying the ease of plugging an address into a GPS device and getting turn-by-turn guidance to your location. This typically includes an arrival time that gets updated based on your progress; alerts about accidents, road conditions and other delays; and offers of alternative routes as needed. But recent studies suggest that ceding the planning and execution of daily travel to global positioning systems can exact a cognitive price. That is, when GPS use becomes habitual, it’s not just the skills associated with reading a map that get rusty. A growing body of research suggests that a specific area of the brain associated with navigation and spatial location may suffer as well.

Worries that new information-related technologies can harm the brain date back centuries. In the 1700s, novels soared in popularity. This raised alarms over their potential to damage mental acuity and mental health. The advent of broadcast radio at the start of the 20th century, soon followed by television, led to similar worries.

A study from Johns Hopkins University in Baltimore suggests worries about too much TV may have merit. Researchers tracked the viewing habits of 599 volunteers. After 11 years, those who had logged the most hours had the greatest reduction in volume of the entorhinal cortex. That’s an area of the brain associated with memory, navigation and the perception of time.

And that brings us back to reliance on GPS. At issue is the hippocampus, an ancient structure located deep in the brain, behind the ear and near the base of the skull. It oversees spatial orientation and memory, is key to planning and decision-making and appears to play a role in our ability to imagine the future. A reduction in the size of the hippocampus is seen in Alzheimer’s disease and other types of cognitive impairment. Aging, depression and chronic stress can also cause the hippocampus to atrophy. Now, recent research suggests that we stop exercising that important part of the brain when we rely on GPS.

A study in the journal Nature Communications found that people responding to spoken directions while driving had measurably less activity in the hippocampus than did those doing their own navigation. Researchers in Canada saw marked declines in spatial memory in chronic GPS users. Coming at the question from a different direction, neuroscientists in England found that the hippocampi of newly hired London cab drivers grew significantly larger year by year, as their knowledge of the city’s streets increased.

The takeaway is that engaging in navigation can improve the health of your brain. In fact, neurologists recommend upping the ante by adding physical activity into the mix. Activities such as orienteering, a sport in which participants use a map and a compass to navigate unknown terrain, can help maintain, and even boost, brain plasticity.

• Dr. Eve Glazier is an internist and associate professor of medicine at UCLA Health. Dr. Elizabeth Ko is an internist and assistant professor of medicine at UCLA Health. Send your questions to askthedoctors@mednet.ucla.edu.

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