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5 Major Side Effects Of Not Getting Enough Fiber, Says Science

Fiber is your friend.
FACT CHECKED BY Cheyenne Buckingham

It's no secret that fiber is an essential component of a healthy diet—and researchers have found yet another reason to bulk up your plate with roughage. A recent study published in the American Society for Microbiology found that boosting dietary intake for a short period of time can have a major impact on the digestive system.

Graduate students at the University of California, Irvine (UCI) were instructed to consume ten high-fiber, unprocessed meals each week—for a total of 25 grams of fiber per day, on average—for two consecutive weeks, along with collecting their own stool samples in order to track their gut microbial composition. At the conclusion of the 14-day experiment, the professors discovered that the students' gut flora had been "significantly altered," which included an increase in a group of beneficial bacteria Bifidobacterium.

"At this time during a pandemic, when we need our immune health and healthy vaccine responses, we encourage everyone to think about the plant diversity of their diets and add some beans, berries, and avocados where they can," said Katrine Whiteson, an associate professor of molecular biology and biochemistry at the UCI Microbiome Initiative, in a press release.

The study authors noted that the average North American consumes approximately less than 50% of the recommended fiber levels while the 2020-2025 Dietary Guidelines for Americans labeled fiber as one of the "dietary components of public health concern for the general U.S. population." (Related: The 7 Healthiest Foods to Eat Right Now).

"Lacking in fiber means that the gut microbiome is not optimized and research is starting to understand all of the myriad health consequences associated with the gut microbiome, including your immune system," says Julie Upton, MS, RD, founding partner of the nutrition marketing and communications firm AFH Consulting.

How much fiber should you eat daily?

The Academy of Nutrition and Dietetics advises women to consume about 25 grams of fiber per day and men to take in around 38 grams (or 14 grams per every 1,000 calories) on a daily basis. Since dietary fiber is found in plant foods, Upton adds that the reason why most Americans have a limited fiber intake is due to high consumption of processed meals and low consumption of fruits and vegetables. She also points out a possible pitfall that may occur if you're a fan of a low-carb lifestyle.

"People who follow low-carb diets can often load up on protein and fats and forget that the foundation of the healthiest low-carb plans, like an Atkins 100 plan, is based on vegetables—not loads of meat and other animal proteins," she says.

The Academy of Nutrition and Dietetics suggests making high-fiber food swaps, such as opting for steel-cut oats over a bowl of sugary cereal and choosing whole-wheat pasta in lieu of white pasta. In addition, the academy recommends adding more fiber-rich fruits, including raspberries and pears, and vegetables such as peas and broccoli to your plate.

"Skimping out on fiber can have long-term, serious health consequences," Upton adds. Here, we offer five reasons why you may want to make fiber your friend, and then don't miss 9 Warning Signs You're Not Eating Enough Fiber.

If your diet lacks fiber, you may experience…

Weight gain.

Yunmai/ Unsplash

When your fiber intake goes up, the scale will likely go down. One study published in the Journal of Nutrition examined the effects fiber had on shedding unwanted pounds among participants who followed a calorie-restricted eating plan for six months. Even when compared to other macronutrients, including "good" fats (such as polyunsaturated and monounsaturated fatty acids), dietary fiber helped promote weight loss, along with assisting the overweight and obesity volunteers in sticking to their healthier lifestyle.

"It's simple—fiber keeps you fuller longer and reduces cravings for carbs," Upton says.

Increased risk of depression.


Yes, your gut health may be associated with your emotional state. Medical researchers from the North American Menopause Society (NAMS) looked into any possible links between dietary fiber and women of various ages and life stages. The study, which involved more than 5,800 females and was published in the journal Menopause, discovered that premenopausal women's risk of depression could be affected by their fiber consumption.

While further research is necessary, the investigators believe that fiber promotes a diverse gut microbiome, which in turn can produce neurotransmitters. As for why postmenopausal women didn't benefit from this gut-brain interaction, the authors believe the answer lies in estrogen depletion since estrogen is a factor in balancing gut microbiota.

"Nonetheless, it has never been more true that 'you are what you eat,' given that what we eat has a profound effect on the gut microbiome which appears to play a key role in health and disease," says Dr. Stephanie Faubion, NAMS medical director, in a press release.

Elevated blood sugar levels.


In a meta-analysis that examined the results of 18 studies, authors from Cambridge University noticed that the volunteers who consumed the highest amount of fiber—mostly from cereal and vegetables—each day (an average of 26 grams) reduced their risk of developing type 2 diabetes by 18% compared to those who took in a small amount of fiber (19 grams or less). However, when the researchers added body mass index (BMI) to the equation, fiber no longer made a difference, leading experts to believe that fiber may be associated with maintaining a healthy body weight, which plays a key role in staving off diabetes.

"Fiber slows the release of blood sugar into the bloodstream, helping to keep your energy levels more stable over time," Upton adds.

Heart-related conditions.

doctor patient

Researchers from Europe analyzed an impressive amount of data—185 observational studies and 58 clinical trials that spanned a period of 40 years—that involved healthy adults. They honed in on premature deaths caused by multiple conditions, including cardiovascular disease such as coronary heart disease, as well as cardiovascular events like stroke, and calculated that per every 8 grams of daily fiber increase can result in a 5-27% decreased chance of suffering from (or dying from) coronary heart disease, among other possibly fatal illnesses.

"Fiber helps trap and excrete unhealthy cholesterol, so it's one of the reasons why people on high fiber diets tend to have a lower risk for coronary heart disease," Upton states.

A shorter lifespan.


While eating more high-fiber foods means making more trips to the bathroom, it could also be a sign of more birthday cakes in your future. In an article published in The Journals of Gerontology that used data from more than 1,600 adults over the age of 50, medical researchers from Australia found that fiber intake had the strongest effect on successful aging—a term that describes not being diagnosed with functional disability, depressive symptoms, cognitive impairment, respiratory symptoms, and chronic diseases (including cancer).

"Essentially, we found that those who had the highest intake of fiber or total fiber actually had an almost 80% greater likelihood of living a long and healthy life over a ten-year follow-up," said Bamini Gopinath, PhD, lead study author, in a press release.

And be sure to check out One Surprising Side Effect of Eating More Fiber, According to Science.

Amy Capetta
Amy Capetta has been writing articles on healthy living for more than two decades. Read more about Amy
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