DOI: https://doi.org/10.36347/sjams.2026.v14i05.001

Pages: 638-652

Bloating, visual abdominal distension, irritable bowel syndrome (IBS), functional dyspepsia (FD) and small intestinal bacterial overgrowth (SIBO) are some of the symptoms that have been associated with the volume of intestinal gas produced. A reduced intake of fermentable carbohydrates as oligosaccharides, disaccharides, monosaccharides and polyols (FODMAP) has been suggested may reduce intestinal gas related symptoms. In this report formulas to quantify the maximum theoretical gas volumes (VTG) that could be produced from fermentable carbohydrates if completely fermented, although not expected to be reached due to substrate depletion on forming new biomass, would allow the possible scale of gas production to be considered. Only the main gases from fermentation as hydrogen (H2), carbon dioxide (CO2) and methane (CH4) were considered. To calculate VTG it was assumed the mass (m) of carbohydrate underwent complete hydrolysis /fermentation to produce hexose (C6H12O6) which was then further fermented with water to form a maximum possible 12 mole H2 and 6 mole CO2 per mole hexose according to the equation C6H12O6 + 6H2O → 12H2 + 6CO2. With these assumptions and the use of the ideal gas equation at 25oC and 1 atmosphere pressure, it was calculated the volume of H2 and CO2 was VTG(H2 + CO2) ≈ m x 2.5 litres (L) or ≈ 2.5 L per gram of fermentable carbohydrate of which 2/3 the volume is H2 and 1/3 the volume is CO2. If all the H2 and CO2 were reacted to form methane (CH4) leaving some residual CO2, the new volume becomes VTG (CH4 + CO2) = m x 0.82 L or ≈ 0.82 L per gram of fermentable carbohydrate of which 1/2 the volume is CH4 and 1/2 the volume is CO2 according to the equation 12H2 + 6CO2 → 3CH4 + 3CO2 + 6H2O. For FODMAP carbohydrates consumed at an average 19(16-22) g/day, gas volumes can be calculated as VTG(H2 + CO2) ≈ 19 x 2.5 ≈ 47 L/day with VTG(H2) ≈ 47 x 2/3 ≈ 31 L/day and the VTG (CO2) ≈ 47 x 1/3 ≈ 16 L/day. If lactose, with consumption ≈12(7.7-16) g/day was exclud