Why people on protein-heavy diets need to eat more fiber

Americans can’t seem to get enough protein.

Typically the go-to fuel of bodybuilders and athletes, protein has become the wellness world’s ultimate nutrient for weight loss, energy and muscle maintenance.

Nutritionists and gastroenterologists warn that the more we load up on protein, another vital nutrient is being left behind: fiber.

“A lot of times when people are on a high-protein diet they’re eliminating other sources of food,” said Christina Fasulo, a nutritionist in the department of digestive diseases at UCLA Health. “Most people need to have a set amount of fiber in their diet, and a lot of that is getting displaced by a high-protein diet.”

Dietary guidelines recommend 25 grams of fiber per day for women and 38 grams for men. Yet the average American consumes just 15 grams daily.

Only 5% of men and 9% of women meet the recommended intake, according to recent estimates.

And for protein diets that consist mostly of meat, it’s even more important to balance with fiber to keep things moving.

Why fiber is a crucial nutrient

Fiber is a type of carbohydrate that the body can’t digest. It’s commonly broken down into two categories, soluble and insoluble fiber. It’s considered necessary for maintaining healthy bowel habits. It also helps control blood sugar by slowing the rate at which sugar gets absorbed from our food into the bloodstream.

“It prevents some of those spikes in our blood sugars that you see from our more simple sugars, which are digested much more quickly,” Fasulo said.

Fiber is crucial for maintaining a healthy gut microbiome and may lower rates of chronic diseases such as diabetes. A diet high in fiber has been linked to lower rates of colon cancer which might be because of an ability to bind to potential carcinogens, or cancer-causing agents, in our intestines and eliminate them, Fasulo said.

Fiber’s real power is connected to the gut microbiome, which needs the carbohydrate to flourish.

The gut microbiome is the diverse community of trillions of microorganisms such as bacteria that live in the digestive tract, playing a vital role in digestion and immune function. When the microbiome is out of balance, called dysbiosis, it can include a lack of diversity of bacteria, too little beneficial bacteria or an overgrowth of harmful bacteria. Changes to the microbiome have been linked to a variety of chronic diseases including obesity and diabetes.

In fact, recent research suggests that a toxin produced by certain harmful gut bacteria may be behind the rising incidence of colon cancer.

Gut bacteria can ferment fiber, producing a molecule known as butyrate, a short-chain fatty acid that is believed to have anti-cancer properties, including inhibiting tumorous cell growth and promoting death in cancerous cells, Fasulo said.

“If you don’t have enough fiber in your diet, it’s as if you’re starving your microbiome,” said Dr. Rabia de Latour, a gastroenterologist at NYU Langone Health. “When you get a really nice, fiber-healthy meal, it’s like you’re giving them their Thanksgiving dinner,” she said.

In other words, if gut bacteria doesn’t have enough fiber to eat, it can create chronic problems in the microbiome.

Fiber is also linked to lower rates of heart disease, possibly reducing the amount of cholesterol that is absorbed from our diets into our bloodstream. Experts say more research is needed, however.

Types of fiber

There are two types of fiber. Soluble fiber is found in foods such as seeds, beans and lentils. It attracts water and forms a gel in the digestive system.

“Soluble fiber is kind of like a sponge, where it’s really slowing things down that are passing in our digestive tract,” said Fasulo.

Insoluble fiber, found in vegetables and whole grains, doesn’t dissolve in water and helps food move through the digestive system. Fasulo compares it to a street sweeper passing through our intestinal tract to help aid with constipation.

“Insoluble fibers in particular kind of mechanically stimulate the gut,” said Dr. Olufemi Kassim, a gastroenterologist at Northwestern Medicine in Chicago.

It’s important to get a mixture of both types of fiber, she added, as they each provide their own set of benefits to digestion. However, some may want to consume more insoluble fiber depending on their symptoms.

“If you’re someone who’s more prone to having loose stools, you probably want to avoid the insoluble fibers,” which can aggravate symptoms, she said. “Soluble fibers will be easier to tolerate.”

At least one fiber-rich food every meal

Legumes, seeds and nuts are excellent sources of both fiber and protein. Fruits and vegetables are high in fiber.

“If you can hit 20 to 30 grams of fiber from food, that’s ideal,” said Kassim. “You’re not just getting the benefit from fiber from eating an apple a day, but you’re also getting all of the great micronutrients like vitamins.”

Kassim includes at least one fiber-rich food in every meal.

Some of her favorite sources of fiber are apples and spinach, both of which have 4 grams of fiber per serving, as well as popcorn, which has about 6 grams of fiber.

In her own diet, de Latour places a strong emphasis on lentils. Lentils contain about 15 grams of protein and fiber each.

Experts prefer getting the daily recommended fiber through food alone. But if that’s a struggle, over-the-counter fiber supplements that include psyllium husk, inulin and methylcellulose can help.

Methylcellulose is a soluble fiber that’s not fermented so it doesn’t cause as much gas and bloating as some other fiber supplements. Inulin is a type of soluble fiber that is naturally found in various plants like chicory root.

Kassim, who treats patients with irritable bowel syndrome, often recommends methylcellulose as a supplement over the popular psyllium husk because people will be more likely to stick with it.

‘Slow, steady and hydrate’

Going beyond the recommended daily amount isn’t seriously harmful but can lead to discomfort. Kassim said it’s about listening to how your body reacts to more fiber. Don’t increase fiber intake too quickly or you may get some unwanted side effects like bloating or excess gas.

“If you start to notice that you’re feeling a little bit more gassy or you’re going to the bathroom a little bit too much, then you can back off a little bit,” she said.

Fasulo recommends a gradual increase of 3 to 5 grams per day until reaching the recommended daily amount.

“Slow, steady and hydrate,” she said.

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