Find out just how much of this healthy carb you need to benefit your immune system in this unique way.
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When you peek at a nutrition label or a recipe's nutrition information (if you do, that is), what's the first number you seek out? Perhaps protein content? Carbs? Calories? The length of the ingredient list?

All of these details are valid to keep in mind, but regardless of the eating pattern you lean into, there's one very important detail that you might want to prioritize: fiber. Previously, we've shared 10 major health benefits of fiber—including lower risk for heart disease, certain cancers and type 2 diabetes as well as stronger bones and even increased longevity. Not to mention that fiber is essential as part of our overall gut health, and we're learning that our microbiomes are linked to everything from our mental health to our immune systems and so much more.

Now that we know how vital fiber is for so many facets of our well-being, researchers are diving into the "hows" (why it's so impactful) and the "how much-es" (how much of each kind of fiber is best to promote health).

As an overall recommendation, the latest U.S. Dietary Guidelines for Americans recommends a fiber intake based on your daily calorie consumption: 14 grams of fiber per 1,000 calories. With that in mind, they set a daily goal of 25 grams of fiber or more for women and 38 grams or more for men.

granola and fruit and pills on a designed surface
Credit: Getty Images / Francesco Carta fotografo (bowl) and Getty Images / DBenitostock (pills)

There's not just one type of dietary fiber, either. There are three:

  • Soluble fiber: Think of this like a sponge within the digestive tract that "soaks up" fat and cholesterol so they're not absorbed as easily within the body. Sources include barley, oats, beans, lentils, peas, seeds, nuts and some produce (including carrots, berries, artichokes, broccoli and winter squash).
  • Insoluble fiber: Similar to a broom, this aids in cleaning out the intestines and helps escort food and waste through the digestive system and out of the body through the stool. Get your dose via whole-wheat flour, wheat bran, nuts, beans, cauliflower, green beans and potatoes.
  • Functional fiber: This is extracted from natural sources or made synthetically, then added back into foods, drinks or supplements. (Those powdered drink mixes are an example of this. Functional fiber, BTW, is the type of fiber least recommended by dietitians since it doesn't come in a whole-food package that also offers vitamins and minerals.)

New research from the USDA suggests that a specific amount of one of these types of fiber might be especially beneficial for one reason in particular. Healthy adults who consume a diverse diet that includes at least 8 to 10 grams of soluble fiber per day have fewer antibiotic-resistant microbes in their guts, according to a study published June 10 in the journal mBio.

What This Fiber Study Found

To reach this conclusion, the researchers studied 24-hour dietary recalls as well as the microbiome composition for 290 adults enrolled in the USDA Nutritional Phenotyping Study. After crunching the numbers, the scientists found that a high-fiber diet with lower levels of protein, especially from beef and pork, was correlated with lower levels of antimicrobial-resistance genes (ARG) among their gut microbes.

Animal protein consumption was not the strongest independent predictor of lower levels of ARG, however. That award goes to high soluble fiber consumption, and you'll score bonus points if said fiber comes from a wide array of sources, according to Danielle Lemay, Ph.D., a research molecular biologist with the Western Human Nutrition Research Center and the study's lead author.

"Modifying the diet has the potential to be a new weapon in the fight against antimicrobial resistance. And we're not talking about eating some exotic diet either, but a diverse diet, adequate in fiber, that some Americans already eat," Lemay tells the USDA Agricultural Research Service News. "Surprisingly, the most important predictor of low levels of ARG, even more than fiber, was the diversity of the diet. This suggests that we may want to eat from diverse sources of foods that tend to be higher in soluble fiber for maximum benefit."

So what are antimicrobial-resistance genes and why are they so important?

Antimicrobial resistance occurs when fungi, viruses and bacteria grow strong and smart enough to evade the drugs that were originally designed to kill them, per the Centers for Disease Control and Prevention. The germs stay alive and multiply as they continue to pose problems for our immune systems.

More than 2.8 million antibiotic-resistant infections (one of several forms of antimicrobial resistance) occur in the U.S. each year, according to CDC's 2019 Antibiotic Resistance Threats Report.

This is only becoming more deadly and more common, the researchers explain: "Antimicrobial resistance—the term that refers to bacteria, viruses and fungi that are resistant to antibiotics—is likely to worsen throughout the coming decades."

They suggest that this is due to the fact that more antibiotics are being incorporated into farming practices. At the same time, they tend to be over-prescribed by doctors for minor conditions like a sore throat. Plus we, as patients, don't always take these medicines according to prescription instructions. The study authors say that antibiotic resistance is growing so quickly as a health issue that it will likely rise to become a major cause of death worldwide by 2050.

In humans, antimicrobial resistance is controlled by what's happening in our gut microbiome, where the microbes carry genetically encoded details that help them survive contact with the drugs made to kill them. Study participants with the lowest levels of ARG in their guts had the greatest quantity of healthy, inflammation-taming bacterial species. Those with the highest levels of ARG had less diverse gut bacteria.

"Our diets provide food for gut microbes. This all suggests that what we eat might be a solution to reduce antimicrobial resistance by modifying the gut microbiome," Lemay adds.

The Bottom Line

Since this was a small, observational study rather than a long-term diet-prescribed one, the researchers hope to use this as a launchpad for future related research.

"In the end, dietary interventions may be useful in lessening the burden of antimicrobial resistance and might ultimately motivate dietary guidelines that will consider how nutrition could reduce the risk of antibiotic-resistant infections," Lemay says.

Until we learn more, eating a rainbow-hued, varied diet full of high-fiber foods will only benefit your body, your gut bacteria and your potential ability to steer clear of any antimicrobial-resistant infections. Try our 30-day high-fiber dinner plan for a jump-start, and add these 12 fiber-rich foods to help with good gut bacteria to your next shopping list.