Effects of High-Fiber Diets and Macronutrient Substitution on Bloating: Findings From the OmniHeart Trial.

To examine the effects of high-fiber, isocaloric, macronutrient substitutions on bloating. The OmniHeart study is a randomized 3-period crossover feeding trial conducted from April 2003 to June 2005. Participants were provided 3 isocaloric versions of high-fiber (∼30 g per 2,100 kcal) diet, each different in carbohydrate, protein, and unsaturated fat composition. Each feeding period lasted for 6 weeks with a 2- to 4-week washout period between diets. Participants reported the presence and severity of bloating at baseline (participants were eating their own diet) and at the end of each feeding period. One hundred sixty-four participants were included in the analysis (mean age: 53.1 years; 45% women; 55% black). The prevalence of bloating at baseline and at the end of the carbohydrate-rich, protein-rich, and unsaturated fat-rich diet period was 18%, 24%, 33%, and 30%, respectively. Compared with baseline, the relative risk of bloating for the carbohydrate-rich, protein-rich, and unsaturated fat-rich high-fiber diet was 1.34 (95% confidence interval [CI]: 0.93, 1.92), 1.78 (95% CI: 1.32, 2.40), and 1.63 (95% CI: 1.17, 2.26), respectively. The protein-rich diet increased the risk of bloating more than the carbohydrate-rich diet (relative risk = 1.40; 95% CI: 1.03, 1.88). Bloating did not significantly vary between protein-rich vs unsaturated fat-rich or unsaturated fat-rich vs carbohydrate-rich diets. Black participants compared with non-black participants had a higher risk of bloating after all 3 versions of the high-fiber OmniHeart diet (P-value for interaction = 0.012). Substitution of protein with carbohydrate may be an effective strategy to decrease bloating among individuals experiencing gastrointestinal bloating from a high-fiber diet.