10 dangers of a low-fibre diet, from constipation to colon cancer

Cheese pizza is not a good source of fibre. Shannon O’Hara/Getty Images
  • Most Americans don’t get nearly enough fibre, and diets lacking whole grains and fruits, like the keto diet, can also make fibre difficult to consume.
  • A lack of fibre can mean an unhealthy digestive system, which can lead to both short and long-term health complications.
  • Low-fibre diets have been linked to dangers like colon cancer, unhealthy cholesterol levels, and diverticulosis.
  • Focus on fruits, vegetables, whole grains, and legumes to up your fibre intake gradually, and make sure you increase your water consumption, too.

Fibre promotes regularity and satiety, but it does a lot more for your health than that. For instance, consuming the right amount of fibre regularly also helps slow down blood sugar response and manage cholesterol levels.

Problem is, most Americans only get about half the recommended dose of fibre, which is 25 to 30 grams per day from food (not supplements), according to UCSF Health. To make things worse, popular diets like keto make it extra hard to get enough fibre, which is mostly found in fruits, vegetables, legumes and whole grains – foods the diet limits or forbids.

So before you dive into more processed foods and fewer fruits, consider these risks of a low-fibre diet.

Too little fibre can cause constipation

“Fibre is good to help regulate the digestive system and to help move the food along the gastrointestinal tract,” Emily Tills, a registered dietitian in New York state told INSIDER. When we don’t have enough fibre in our diet, she said, we can experience severe constipation, which can cause pain, bloating, and sometimes even hospitalisation and surgery.

Read more: 6 ways the Mediterranean diet can affect your digestion

A low-fibre diet can cause diverticulosis

“Without adequate fibre, the digestive tract can lose its muscle tone,” said Seattle-based registered dietitian Liz Wyosnick. That can lead to diverticulosis, an incurable condition in which small pouches develop in the wall of the digestive tract. Diverticulosis is uncommon in parts of the world where people eat plenty of grains, fruits, and vegetables, the American Society for Gastrointestinal Endoscopy reports.

Low-fibre intake can cause loose stools

“Our gut microbiome feeds off short-chain fatty acids, which are synthesized from resistant starches from plant-based foods high in soluble fibre like grains, fruits, and vegetables,” said New York City-based registered dietitian Rachel Fine.

Since these acids help to absorb water in the colon, inadequate production from low fibre intake can result in the passing of excess water, which leads to loose stools.

Low-fibre intake can mess up your blood sugar levels

Research shows that eating fibre-rich foods can help slow your blood sugar response after a meal, which is especially beneficial to people with diabetes,” said San Diego-based registered dietitian Elizabeth Ann Shaw. A low-fibre diet can do just the opposite, causing that meal to have an immediate effect on your blood sugar. Over time, constant blood sugar spikes can lead to complications, including diabetes.

Low-fibre diets may raise the risk of colon cancer

Over the years, hard stools and irregular bathroom patterns – which a low-fibre diet can induce – “can add up to conditions that are right for cancerous polyps to grow,” said registered dietitian Laura Yautz, who’s based in Pittsburgh. On the flip side, research has linked diets high in fibre from cereals and fruit with a reduced risk of colon cancers. While some colon cancers are genetic, Yautz said, the majority are related to poor lifestyle habits.

Without enough fibre, it’s hard to fight inflammation

Chronic inflammation in the body will eventually end up as a disease, so it’s vital to make sure you eat foods that fight inflammation – or those with antioxidant properties – frequently, Yautz said. The foods with the most antioxidant properties are plants (fruits, vegetables, and whole grains), since they contain naturally occurring fibre.

A low-fibre diet can disrupt the microbiome, leading to chronic health issues

“Fibre is the main food source for the good bacteria in our gut,” Yautz said. Without it, they die, she explained, and your gut can become overrun with more harmful bacteria that can cause myriad health problems. Some research suggests, for instance, that unbalanced gut bacteria can lead to inflammatory bowel disease, obesity, and cancer. It’s best to eat fibre from different types of foods to keep the good guys fighting in your corner, Yautz said.

A low-fiber diet isn’t helping your PMS symptoms

Some PMS symptoms seem to be related to hormonal changes, like an increase in estrogen. A low-fibre diet doesn’t help: “Excess estrogen is more aptly eliminated with the help of fibre, and a moving digestive system,” said Wyosnick, who makes sure to discuss fibre intake with patients who experience significant PMS.

Eating plenty of fibre can help control your weight. Rostislav_Sedlacek/iStock

Not enough fiber may make it harder to control your weight

“Fibre is absolutely imperative because it provides a volume within meals for little-to-no calories, fat, or sodium,” Wyosnick explained. In other words, adding a giant salad, two cups of roasted broccoli, or shredded cabbage to your curry dish can provide more volume within your meal, help to distend the stomach, and signal to your brain that you have been adequately fed, she said.

A low-fiber diet can negatively affect your cholesterol levels

Fibre can also help lower your cholesterol levels, Tills said. A diet high in soluble fibre, or the type found in oatmeal, for instance, can help pull out cholesterol from the liver and excrete it, she said. Skimping on the nutrient, on the other hand, is associated with lower levels of HDL (good) cholesterol.

Ready to load up on fibre? Be sure you add both soluble fibre (whole grains, oats, beans) and insoluble fibre (skins of fruit and non-starchy vegetables) to your everyday diet, Wyosnick said. You can think of soluble fibre as the bulking agent that helps to exercise the gastrointestinal tract, she said, and insoluble fibre as the pipe cleaner that sweeps the surface to move things along.

Drink plenty of water, too. “The important things to keep in mind if you want to increase your fibre intake is to increase gradually, and drink plenty of water,” Wyosnick said.