Are all calories the same? Your gut microbes don’t think so.

 Are all calories the same?  Your gut microbes don't think so.

For years scientists have believed that when it comes to weight gain, all calories are equal.

But an intriguing new study, published in the journal Nature Communications, suggests that’s not true. The body appears to react differently to calories ingested from fiber-rich whole foods versus ultra-processed junk foods.

The reason? Inexpensive processed foods are absorbed more quickly in the upper gastrointestinal tract, which means more calories for your body and fewer for your gut microbiome, which sits near the end of your digestive tract. But when we eat high-fiber foods, they’re not absorbed so easily, so they make the entire journey up the digestive tract to the large intestine, where the trillions of bacteria that make up the gut microbiome are waiting.

By eating a high-fiber diet, you’re not only feeding yourself, but also your gut microbes, which, new research shows, effectively reduce your calorie intake.

The study reveals that inside all of us, our gut microbes are in a tug of war with our bodies for calories, said Karen D. Corbin, a researcher at the AdventHealth Translational Research Institute of Metabolism and Diabetes in Orlando and lead author of study. study.

With a Western diet that doesn’t feed the microbes much, almost all of the energy goes to us and very little goes to the microbes, Corbin said. We don’t give microbes any chance to use up the calories we’ve eaten because we use them all up. We pull the string to one end.

Keep your gut microbes happy

Corbin and his colleagues wanted to understand how the gut microbiome might be involved in regulating weight and metabolic health, so they designed a small but rigorous clinical study.

They recruited 17 healthy men and women and compared what happened when they were fed a high-fiber diet versus a diet of highly processed foods. The researchers provided the participants with all of their meals and had them follow each diet for 22 days.

For half of their time on each diet, the participants lived in a metabolic ward, where researchers tracked every calorie they ate and controlled their physical activity levels. They also spent six days during each phase of the diet in a small, airtight room called a metabolic chamber. This allowed the scientists to determine exactly how many calories the participants burned. The researchers collected bowel movements and used special techniques to analyze things like the amount of energy and bacteria in their stool.

The two diets were polar opposites. One, called the Western diet, contained many highly processed foods typical of what the average American eats foods such as puffed rice crispy cereal, white bread, American cheese, ground beef, cheese puffs, vanilla wafers, deli meats, and other processed meats and sugar snacks and fruit juices.

The other diet was called the microbiome enhancer diet and was designed so that as much of the nutritious food as possible reached the gut microbiota. When we eat fiber, our gut microbes thrive on it and break it down through a process called fermentation. This produces many healthy byproducts, such as short-chain fatty acids, which are good for our metabolic health.

In the study, the microbiome enhancer’s diet contained many foods that have a special type of fiber called resistant starch, which is found in things like oats, beans, lentils, chickpeas, brown rice, quinoa and other whole grains. The diet also includes plenty of nuts, fruits and vegetables.

To prevent food from being absorbed too quickly and to maximize the amount of food that would reach the microbes in the large intestine, the researchers avoided processed, ground or refined foods. Participants received whole nuts, for example, instead of nut butter, and ate chunks of steak instead of ground beef. The meals were designed to minimize highly processed foods.

The two diets provided each participant with the same amount of calories and similar amounts of protein, fat and carbohydrates.

They had the same calories, but one went down into the colon and fed the microbes, and the other was completely digested and given to us, said Steven R. Smith, study co-senior author and chief scientist. at AdventHealth. The Microbiome Enhancer Diet was truly designed to make your gut microbiota happy.

Find the calories lost in poop

The scientists found that the participants absorbed significantly fewer calories on the high-fiber diet than on the processed diet. On average, they lost 217 calories a day on the high-fiber diet, about 116 more calories than they lost on the processed foods diet.

But there was a wide range: Some participants lost nearly 400 calories a day on the high-fiber diet. These lost calories showed up in their stool in a number of ways. For example, participants had more undigested food in their stool. But they also had significantly more bacterial biomass and short-chain fatty acids in their stool, a sign that their gut microbes were busy multiplying and fermenting.

It takes energy to make bacteria, Corbin said. So instead of the energy going to us, it’s going to expand this community, and we know that because in their poop, the biomass has increased about eight and a half times.

This has created many benefits for the participants. On the high-fiber diet, they had higher circulating levels of short-chain fatty acids and increased levels of hormones such as GLP-1, which promotes satiety. (Popular new diabetes and weight-loss drugs, Ozempic and Wegovy, work by mimicking the action of GLP-1.)

Participants lost slightly more weight and body fat on the high-fiber diet. Yet despite absorbing fewer calories per day, they showed no signs of increased hunger.

Daniel Drucker, an endocrinologist and professor of medicine at the University of Toronto, called the study very rigorous, careful and well done. He said the finding that a high-fiber diet is good for you wasn’t surprising, but that the study sheds light on some of the mechanisms that explain why.

He called the research an interesting proof of concept, but said more research is needed to see if the findings could apply not only to healthy young adults, but also older adults and people with metabolic diseases.

These were healthy people studied in a controlled setting, he said. Would we see the same quantitative and favorable changes in a real-world population of people with obesity, heart disease, and diabetes? This is a difficult study to do.

Cut down on processed foods

Many studies have suggested that the gut microbiome plays a role in our weight and body composition. Scientists have found that people with obesity, for example, have lower bacterial diversity in their guts and other differences in their microbiomes than thin people.

Sean Gibbons, a microbiome specialist and assistant professor at the Institute for Systems Biology in Seattle, said the new study is surprising because it indicates people could lose weight and body fat simply by switching to a diet that targets their microbiome. bowel, even without exercising. more or reducing calories.

Gibbons, who was not involved in the new study, said it confirms what he saw in his research: that a diet that increases the growth and activity of gut microbes is markedly good for being metabolically healthy and losing weight.

Globally, many people are increasingly switching to processed foods, he said. It’s not great for our microbiomes or our metabolic health.

Have a question about healthy eating? E-mail EatingLab@washpost.com and we may answer your question in a future column.

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