Naked Science Forum

Life Sciences => Physiology & Medicine => Topic started by: chris on 17/05/2017 07:29:35

Title: How much flatulant gas in a cup of milk?
Post by: chris on 17/05/2017 07:29:35

Donald has been in touch to ask:

The average cup of milk has 9 grams of lactose. How much flatus in litres could this produce if converted to CO₂ in the large colon by Lactobacilli? How much CO₂ is in one cup of carbonated soda? If I did not burp, would any of this CO₂ make it to my large colon?

Title: Re: How much flatulant gas in a cup of milk?
Post by: evan_au on 17/05/2017 11:15:35

Looking up some basic information on lactose (https://en.wikipedia.org/wiki/Lactose):
- Chemical formula: C₁₂H₂₂O₁₁
- mass: 342g/mol

If your body is totally deficient in lactase enzyme production, then the lactose will continue through your gut without being absorbed.

There is an assumption here that bacteria would convert lactose entirely into CO₂. However, they are more likely to convert it into other substances that they can absorb and metabolize - especially in the oxygen-deprived environment of the lower gut. It is more likely to be converted into bacterial bodies, which are then excreted.
Lactobacillus (https://en.wikipedia.org/wiki/Lactobacillus) convert lactose into lactic acid or alcohols.

However, let's persist with that assumption:
- 9g of lactose represents 9/342 = 0.026 mole of lactose
- 1 mole of lactose would be converted to 12 moles of CO₂ if there were ample oxygen, and this were the only reaction product
- 9g of lactose would produce .026 x 9 = .23 moles of CO₂
- 1 mole of any gas at room temperature occupies 22.4litres volume.
- 9g of lactose would produce .23 x 22.4 = 5.2 litres of CO₂

This sound quite uncomfortable - if I were lactose intolerant, I would stay away from milk!