Recommended fiber intakes are more complex than at first blush, and they vary worldwide and by age. Overall, 25 g–30 g or more of daily fiber is recommended for adults. Originally, these levels were based on providing for normal bowel movements and heart health, but emerging evidence shows that adequate fiber levels also benefit gut microbiota. 

In the US, Canada, and Europe, grain-based foods make up most of the dietary fiber consumed, followed by vegetables, fruits, and potatoes. Legumes, nuts, and seeds contribute little, according to researchers writing in the BMJ.

McKeown NM, Fahey GC Jr, Slavin J, et al. Fibre intake for optimal health: how can healthcare professionals support people to reach dietary recommendations? BMJ. 2022 Jul 20;378:e054370.

 

 

 

Worldwide deficiencies

 

Globally, most people fall short in terms of fiber intake. The dietary guidelines in most countries stress food vs nutrients, with most people not eating enough fruits, vegetables, legumes, or whole grains.

“People are unlikely to understand the type or quantity of individual foods or food combinations needed to achieve recommended dietary fibre intakes,” wrote the BMJ authors. “Coupled with this, some consumers do not recognise the contribution of whole grains to fibre intake, and others do not know how to identify whole grain, compared with refined grain products.” The authors also note that those who adopt a low-carb diet, typically for weight-loss reasons, are also likely to fall short of meeting fiber recommendations. 

 

Benefits of fiber

 

All physicians are aware of the two types of fiber: soluble and insoluble. Soluble fibers mix with water and slow digestion, and they are linked to a lower risk of heart disease, improved glycemic control, and lower cholesterol levels. They are found in some grains, legumes, seeds, and certain vegetables. Insoluble fibers add bulk to the stool and are found in whole grains, beans, and root vegetables. Interactions with the gut microbiome also mediate the benefits of different dietary fiber.

Gearhart-Serna L. Health benefits of dietary fibers vary. NIH Research Matters. May 24, 2022.

 

 

 

Risks of fiber overconsumption

 

Despite the health benefits of fiber, the Nutrients authors explain that there are necessary limits to its intake. Excess consumption of natural dietary fiber can result in bloating, flatulence, diarrhea, and intestinal obstruction in people who don’t chase fiber intake with adequate fluids.

Fiber intake must be limited in patients with Crohn’s disease or intestinal obstruction, with such consumption monitored by a medical professional. Additionally, patients who experience malabsorption should approach the consumption of fiber with care. Patients who have undergone bowel surgery should also be wary of fiber intake. In all patient populations, increased fiber intake should be paired with higher fluid intake to minimize the chance of dehydration. 

In patients with a predisposition to phytobezoars, improper chewing can exacerbate the problem. Aging can play a role and result in the loss of intestinal elasticity, with constipation further promoting the formation of phytobezoars.

Fiber content can lower intestinal transit times, thus decreasing the bioavailability of drugs and decrease their pharmacodynamic effects. As well, excessive fiber intake can hinder the absorption of essential minerals from foods, such as calcium, iron, or zinc.