High fiber, high protein diet leads to bloating: Study

People who eat high fiber diets are more likely to experience bloating if their high fiber diet is also protein-rich, as compared to carbohydrate-rich.

More protein, more problems 

The new study, published in the journal Clinical and Translational Gastroenterology​, researchers at Johns Hopkins Bloomberg School of Public Health combed through a dietary clinical trial that was conducted in 2003 and 2005 at the Johns Hopkins ProHealth Clinical Research Unit. Known as the Optimal Macronutrient Intake Trial to Prevent Heart Disease (OmniHeart), it included 164 participants who had above-normal blood pressure. They were assigned to three different diets over six-week periods separated by two-week "washout" intervals during which participants returned to regular eating habits.

The primary results of the OmniHeart trial, published in 2005, found that the plant-protein-rich and fat-rich diets were the most effective in reducing blood pressure and improving measures of blood cholesterol. 

For the new analysis, researchers examined secondary data from the trial on the participants' reports of bloating, which found that those who ate high fiber diets rich in fiber and carbohydrates were less likely to feel bloated.

The researchers examined the diets of the 164 participants. They determined that when the trial participants ate versions of a heart-healthy, high-fiber diet that was relatively rich in plant protein, they were about 40% more likely to report bloating symptoms than when eating a carbohydrate-rich version of the same high fiber diet.

Implications on diet

The research brings fresh insight to macronutrients substitution and could help make some diets more tolerable.

In the clinical trial, participants were all on what is considered high-fiber, low-sodium "DASH" diets. They all consumed  the same number of calories, but macronutrients varied. The high carbohydrate version was  58% carbohydrate, 15% protein, and 27% fat; The plant-protein-rich version was 48% carbs, 25% protein, 27% fat; While the high-rich version was 48% carbohydrate, 15% protein, and 37% fat.

The study suggests that people who want to eat a high fiber diet would be less likely to experience bloating if the diet were relatively had more carbs and less protein. Substituting healthier carb calories, such as whole grain, for protein calories might reduce bloating for those on high fiber diets.

The gut bacteria shuffle 

The findings also imply macronutrients such as carbs and proteins play a role in modifying bacteria in the gut. According to the research, high-fiber diets are believed to cause bloating by boosting certain populations of healthful fiber-digesting gut bacteria species, which produce gas as a byproduct. 

"It's possible that in this study, the protein-rich version of the diet caused more bloating because it caused more of a healthy shift in the composition of the microbiome,"​ said study co-senior author Noel Mueller, Ph.D., an assistant professor in the Department of Epidemiology at the Bloomberg School. "Notably, the protein in these diets was mostly from vegetable sources such as beans, legumes, and nuts."​

Several studies have pointed to diet as a key player in shaping the microbiome, with experiments showing that dietary alterations can induce large, temporary microbial shifts within 24 hours​. These shifts in the gut microbiome result in greater microbial production of beneficial metabolites. Mueller believes that the plant-protein-rich diet caused more bloating because it caused a robust shift in the microbiome.

Still, high fiber diets may be healthier overall

"Bloating may be just a consequence of a healthy shift in the microbiome, so that if somebody is able to put up with the bloating caused by a high-protein, high-fiber diet, they may ultimately benefit more in other health measures,"​ Mueller said. 

Mueller and the research team are working on a follow-on study of the effects of similar dietary patterns on the gut microbiome.

Source:​  Clinical and Translational Gastroenterology​

Jan 15 2020; DOI: 10.14309/ctg.0000000000000122​

“Effects of High-Fiber Diets and Macronutrient Substitution on Bloating”​

Authors: M.  Zhang, et al