Evidence for impaired assimilation and increased colonic fermentation of protein, related to gastric acid suppression therapy

Aliment Pharmacol Ther. 1998 Oct;12(10):1011-9. doi: 10.1046/j.1365-2036.1998.00377.x.


Background: Although the role of gastric digestion (by acid-dependent pepsins) in overall protein assimilation has never thoroughly been studied, it is generally considered to be limited. Protein that escapes assimilation in the small intestine is intensely fermented by the colonic flora. Phenol and p-cresol are specific bacterial metabolites of tyrosine.

Aim: To elucidate the role of gastric digestion of protein by evaluating the influence of acid suppression therapy on overall protein assimilation and fermentation.

Methods: Protein assimilation was studied in 16 healthy subjects under basal conditions and after omeprazole treatment using the combined 14C-octanoic acid/13C-egg white breath test. The degree of protein fermentation was estimated by measuring the urinary output of phenol and p-cresol in 41 healthy volunteers and in 17 patients treated for more than 1 month with omeprazole because of peptic disease.

Results: Protein assimilation was significantly impaired after omeprazole treatment. Gastric emptying, conversely, was not affected. The urinary output of phenol and p-cresol was increased in patients treated with omeprazole as compared to untreated controls.

Conclusion: Gastric acid suppression therapy hampers protein assimilation and may promote protein malabsorption. Gastric digestion is likely to play a substantial role in overall protein assimilation.

Publication types

  • Clinical Trial
  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Anti-Ulcer Agents / pharmacology*
  • Breath Tests
  • Carbon Dioxide / metabolism
  • Cresols / urine
  • Dietary Proteins / metabolism*
  • Enzyme Inhibitors / pharmacology
  • Female
  • Gastric Acid / metabolism*
  • Humans
  • Male
  • Omeprazole / pharmacology
  • Phenol / urine


  • Anti-Ulcer Agents
  • Cresols
  • Dietary Proteins
  • Enzyme Inhibitors
  • Carbon Dioxide
  • 4-cresol
  • Phenol
  • Omeprazole