As many of our followers are already aware, the Monash FODMAP team is committed to ensuring that the science behind the low FODMAP diet remains up to date. As part of this commitment, we regularly re-test foods that were analysed for FODMAP content in the past, particularly those that were tested more than 10 years ago. This is because we know that the composition of foods can change over time for various reasons, which we have explored in a previous blog. We also recognise that testing techniques have improved and been refined over time.
Avocado is one of the early foods to have been tested when the low FODMAP diet was first being developed over 15 years ago. At that time, avocado was found to be a particularly rich source of sorbitol - one of the key sugar polyols that is limited as part of a low FODMAP diet.
As such, avocado has featured heavily in many low FODMAP diet resources throughout the years, often labelled as one of the key foods to ‘avoid’ when following the first step of the diet.
So you can imagine our surprise when we recently re-tested avocado for FODMAPs, and did not find that it was high in sorbitol! Instead, our scientists noticed a peculiar looking ‘peak’ on the read out from our high performance liquid chromatography (HPLC) equipment that was quite close to where our sorbitol ‘standard’ peak was detected, however, it did not exactly match…
This was quite puzzling to our team, so we began diving into the research to see if we could identify another sugar that may be present in avocado and explain this mystery peak in our analysis.
What we found was lots of avocado research in the field of ‘botany’ and not our usual ‘medical/nutrition science’ genre. As it turns out, avocados are rather a unique fruit in terms of their composition. Unlike other fruits, which tend to accumulate carbohydrates (or sugars) as they grow and ripen, avocados accumulate oils (fats) and have a very unique carbohydrate (sugar) profile.
One of these unique carbohydrates found in avocados is a sugar polyol called ‘perseitol’.
To test our theory and confirm that the mystery peak we were seeing in our data was indeed perseitol and not sorbitol, our team sourced a pure perseitol standard and ran it concurrently with the avocado sample on the HPLC. This test revealed that our mystery peak and the perseitol standard were a match! Interestingly, we also tested both ripe and unripe samples of avocado and found that unripe avocado actually had more perseitol than ripe avocado. This was consistent with what we had read in the avocado research, which noted that the perseitol content of avocados decreases during the ripening process.
So what do we know about perseitol and how it behaves in the gut? Actually, not a whole lot as it is a very unique sugar polyol specific to avocados. However, this is what we do know about how other sugar polyols behave in the gut:
The combination of these actions in the gut, paired with increased gut sensitivity, is why sugar polyols can trigger symptoms in some people with IBS.
As perseitol is larger in size than sorbitol, we can speculate that it might fall under point 3 above and potentially have more significant effects in the gut than sorbitol. As such, perseitol could be considered to fall under the ‘FODMAP’ definition as a polyol that is unique to avocados.
So does this mean avocado is back on the menu?
Based on this discovery, we have contemplated as a team what to do with these new results. Although it has been established that what was thought to be sorbitol detected in avocados is actually perseitol, we are hesitant to change the FODMAP rating of avocados in our app from high (red) to low (green) in a standard serve. This is because, as outlined above, perseitol is likely to have similar effects in the gut to sorbitol and mannitol, so may be a symptom trigger for those with IBS who are sensitive to polyols. Avocados also have a very high fat content, and fat is another potential symptom trigger for some individuals with IBS.
As a compromise, we have decided to update the overall serving size information and traffic light ratings for avocado according to the new results for perseitol. For the purposes of the app, ratings for perseitol will appear where sorbitol would, however we have included an asterisk referencing a special statement outlining the presence of perseitol as an important sugar polyol unique to avocados.
What about reintroduction?
Whilst we have now identified that avocado is probably not the most representative food to use for the reintroduction of sorbitol, avocado remains a very popular and often sorely missed food for people with IBS. For this reason, we would still encourage completing a separate food challenge with avocado to test your own tolerance. You can find more information about this process on our blog here.
In conclusion…
We are excited to share these results with you, as this again highlights how the science of FODMAPs and IBS is evolving over time and the ongoing importance of our food testing program. This case was a great reminder to us that food and nutrition science is undoubtedly complex, that there is still so much we don’t know and new discoveries to be made!
