Methanol is of interest to nutritional scientists because it is metabolised in the body to formate, high plasma concentrations of which can lead to metabolic acidosis and blindness. While methanol is a metabolic toxin, it is present naturally in a number of commonly consumed foods and drinks. Methanol intake in humans comes mainly from fruit and vegetables. The methanol content of fruit juices has been estimates to be as high as 140 mg per litre. Methanol is also present as 10 % of the aspartame molecule. The methanol concentration is estimated to be 55 mg per litre in aspartame flavoured drinks. Another route of methanol intake is the colonic microfloral degradation of the fruit fibre pectin. Pectin is found in high concentrations in the cells walls of limes, lemons, grapefruits and oranges.
To understand the fate of pectin in humans, researchers used faecal bacterial colonies to assess the degradation of pectin to methanol1. The results showed that over a 3 day period, the human gut bacteria were able to breakdown the pectin fibre and produce methanol. However, the researchers were unsure as to the fate of this methanol and suggested that it might undergo further metabolic conversion to methane, or alternatively be used as a carbon source by some bacteria. The researchers did conclude that the levels of methanol produced were far lower than the toxic dose for methanol and that colonic degradation of pectin fibre is very unlikely to cause any form of ill health from formate toxicity. This study was not performed in vivo and so care must be taken when interpreting the data.
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