It’s understandable that you might be hesitant to up your fibre intake—regardless of whether you’re experienced or new to the sport. After all, fibre is notorious for, and we’re not going to mince words, making you poop. And the last thing you want to deal with while out running is having to duck behind a bush.

That said, fibre, which is a type of carbohydrate, is an incredibly important nutrient of which most people do not get enough. And that’s a problem.

A 2019 meta-analysis published in the The Lancet found that people with the highest fibre intakes had a 30 percent lower risk of death from heart disease, a 22 percent lower rate of stroke, and a 16 percent lower rate of type 2 diabetes and colorectal cancer compared to people who ate the least amount of fibre.

While the recommended daily intake for fibre is 25 grams per day for adults assigned female at birth and 38 grams per day for adults assigned male at birth, most people get less than 20 grams per day, Andrew Reynolds, Ph.D., one of the study’s coauthors, previously told Runner’s World.

“That’s mostly because we eat a Western processed diet of fast food, fried food, processed grains, and sugary sodas,” says Natalie Rizzo, M.S., R.D.

Without enough fibre, you can run the risk of constipation, irregular bowel movements, increased cholesterol and blood glucose levels, and even an increased risk of colorectal cancer, Rizzo says. For example, a study published in the American Journal of Clinical Nutrition found people who consume high amounts of fibre have a decreased risk of colorectal and colon cancers.

While there isn’t a blood test to measure your fibre levels, like there is for vitamin D, these are signs that indicate you might not be getting enough, and how you can change that.

1. You’re constipated or bloated

Constipation looks a little different on everyone. According to the U.S. National Library of Medicine, you might have three or fewer bowel movements per week. Rizzo points out that even if you don’t go every day, your schedule, so to speak, should be regular.

If you’re constipated, it will also be very difficult to poop, and that poop may be physically hard and dry.

Not consuming enough fibre (or in some cases, eating too much fibre) might also lead to bloating, says sports dietitian Lindsey Cortes, M.S., R.D., C.S.S.D. She emphasises the importance of addressing fibre intake before testing for food sensitivities if you experience these symptoms.

2. You have haemorrhoids

Related to constipation is the development of haemorrhoids, or swollen veins in your anus and lower rectum. They can be a sign of a low-fibre diet and can occur as a result of straining or pushing while trying to poop, explains Cara Harbstreet, M.S., R.D.

A diet high in fibre helps soften poop and reduces the time it spends in the colon, which helps it pass more easily.

3. You’re always hungry

Fibre, like protein, is incredibly important to keeping you feeling full, according to Rizzo.“It promotes satiety after a meal,” she says.

That’s because it moves slowly through the digestive tract, Harbstreet explains.

4. Your cholesterol or blood glucose levels are elevated

While you can’t test for a fibre deficiency or inadequacy, Rizzo explains, there are other red flags that may point to a problem. Because fibre, particularly beta-glucan (a type of fibre), plays such a key role in decreasing cholesterol levels—which can affect heart health—if your numbers are elevated, it’s worth discussing your diet with your healthcare professional, Rizzo says.

A 2019 review published in Nutrients points out that more than a few studies have found that dietary fibre has a “protective effect” when it comes to heart health.

Fibre also regulates our blood glucose levels, or our blood sugar.

“White bread spikes blood sugar more than whole wheat bread because whole wheat has more fibre” Rizzo says. “If you have a low-fibre diet over the long term you can develop insulin resistance, and that’s the first step to type 2 diabetes.”

How to get more fibre in your diet

Fibre is found in a wide variety of foods, most notably fruits and vegetables, Rizzo says.

“Any fruit or vegetable you want to eat will have a good serving of fibre in it,” she says, noting that if you peel the skin from an apple or a potato, for example, you’ll lose most of the nutrient.

“Most people don’t get enough fibre because they don’t eat enough fruits and vegetables,” Rizzo says.

Other foods that are high in fibre include whole grains—brown rice and pasta, for example—oats, farro, legumes, beans, soy, tofu, tempeh, and nuts and seeds.

Here’s the fibre content breakdown of five common foods:

• 1 medium-size apple, skin on: about 4 grams of fibre
• 1 cup of cooked brown rice: about 3.5 grams of fibre
• 1 cup of cooked oatmeal: 4 grams of fibre
• 1 avocado: 14 grams of fibre
• 1 cup of beans or lentils: anywhere from 2-16 grams of fibre

How to balance fiber intake and running

So yes, fibre’s number-one job is to, well, help you go number two. And understandably, that can scare runners who need to move for hours at a time. But, Rizzo says, you can get enough fibre without running to the bathroom mid-workout. It’s all about timing—and trial and error.

“Everyone is a little different,” Rizzo says. “Some people can eat a huge bowl of oatmeal before a race and they’re fine. Other people might get an upset stomach from that oatmeal.”

She recommends practicing prerun fueling to determine what your body can tolerate. If you know that a fibre-rich meal before a run can cause stomach troubles, Rizzo says, limit that fibre and eat those fruits and veggies after your workout.

“Try a slice of white bread instead of whole wheat an hour or two before a run, or avoid having a salad for lunch if you’re an afternoon runner,” she says.

Your best bet is to plan out your meals and snacks to make sure you’re getting the fibre you need without upsetting your stomach.

For an afternoon workout, one way to do that, Harbstreet says, is to prioritise a high-fibre breakfast, a piece of fruit with the skin for a snack, a low-fibre lunch and pre-workout snack, and a high-fibre dinner. This, she says, takes into account that it takes about two to four hours for digestion.

The short answer is probably not, Rizzo says. There are easy dietary changes you can make to up that fibre intake before turning to a supplement like Metamucil. (Plus, eating whole foods helps you consume other important nutrients, including iron, calcium, and potassium.

“If there’s a reason why you’re potentially not getting enough fibre or are more prone to constipation due to certain medications, a fibre supplement might help you stay regular,” Rizzo says.

In general, Harbstreet recommends that athletes first assess their diet before adding any sort of supplement.

“While a target supplement like Metamucil is perfectly safe to use as directed, it may not be necessary if there are opportunities to introduce more fibre-rich foods,” she says. “As training intensifies and energy needs go up, your increased food intake is another opportunity to meet the recommended fibre intake without resorting to a supplement.”

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