What is fructose?

Fructose is a small sugar naturally found in a wide range of foods like apples, mangoes and honey. However, it is also found in a wide range of processed foods (e.g. soft drinks) in the form of “high fructose corn syrup”. This is sometimes listed as HFCS – keep an eye out for this on food labels.

What is dietary fructose intolerance?

Over 30% of patients with IBS have fructose intolerance. Our body absorbs fructose through a number of sugar transporters found in the small intestine.

Unabsorbed fructose may draw water into the small intestine. Our body does this to rebalance the environment and reduce the high concentration of fructose. In some people, this excess water may result in diarrhea, but it can also force the undigested food into the colon. Our gut microbes may break down this undigested food, releasing gas. This excess gas can result in symptoms, including abdominal pain, bloating and diarrhea.

What can doing the Fructose Challenge with my FoodMarble AIRE tell me?

Every person will respond differently to fructose. Their own response might also change depending on a number of lifestyle factors like diet, stress, sleep and exercise. It’s important to get an understanding of your own personal tolerance level, and the Fructose Challenge can help with that.

We wanted to share some of the different results that we have seen from our users, and give you an overview of what the results mean. We have chosen a number of results from users who experienced different responses to one another.

Each user consumed 25g of fructose – this is approximately the amount of fructose in a small mango (3/4 of a regular sized mango).

If you have already done a Fructose Challenge and recorded high fermentation and symptoms, you could consider trying a Custom Challenge but using a much lower dose of fructose.

Finding the foods that are absorbed well and don’t cause symptoms for you is important, so that you can avoid unnecessary eliminating foods.

PLEASE NOTE: FODMAP Challenges are tested in a fasting state, which reduces the chance of experiencing uncomfortable symptoms. However, if you were to eat or drink something containing fructose after a meal containing a large amount of fermentable foods, that could result in symptoms, as the combination could result in an excessive amount of gas production. Since the effect of what you eat and drink is cumulative, it’s important to log your meals and take multiple breath readings over the day to see the combined effect of your meals.

Fructose Challenge Result: Low Fermentation Score

Screenshot of low fermentation result in Fructose Challenge

The final result for this challenge is 1.8/ 10. The level of hydrogen produced during the challenge was low overall. The user did not experience any uncomfortable digestive symptoms.

The lack of hydrogen production indicates that the fructose was well absorbed in the small intestine and is well tolerated.

This user said they usually experienced digestive symptoms after eating certain fruits like apples and pears. Interestingly, these fruits contain fructose and sorbitol in large amounts. Our recommendation to them was to try a Sorbitol FODMAP Challenge next.

Fructose Challenge Result: High Fermentation Score returning to low baseline

Screenshot of high fermentation score returning to baseline during Fructose Challenge

The final result for this challenge was 8.8/ 10. There was quite an early hydrogen peak, starting at 60 minutes.

Fructose is a small sugar and can travel quickly through the digestive tract. The user did not fully absorb the 25g of fructose, indicated by the increased levels of breath hydrogen. They also experienced some abdominal bloating, but no pain or diarrhea.

The level of hydrogen production returned to the baseline (starting point) which indicates that the sugar passed through their digestive system quite quickly. This user is unable to fully absorb large amounts of fructose, resulting in some bloating and excess gas. Our recommendation would be to take this into consideration when planning meals and avoid large amounts of fructose in one go.

There are lots of fruits and vegetables that are lower in fructose. For guidance, we recommend using our food database on the app as it allows users to filter based on each FODMAP.

Fructose Challenge Result: High Fermentation Score sustained throughout the challenge

Screenshot of high fermentation score sustained through the Fructose Challenge

The final result for this challenge was 7.5/ 10. This user saw a significant increase in breath hydrogen, which suggests that the portion of fructose was malabsorbed.

The user experienced a looser stool than usual but this returned to normal by their next toilet visit. They also felt uncomfortably bloated during the testing period and for a few hours after. The level of hydrogen production was quite prolonged and peaked towards the end of the challenge. When this occurs, we suggest that users continue to take a few breath tests the challenge has ended and log symptoms when they occur.

This result indicates that the user is unable to absorb this amount of fructose. We would recommend they perform a Custom Challenge using a lower amount of fructose. For example, a medium sized apple contains approximately 8g of fructose. Identifying your tolerance level is key so you can avoid eliminating foods entirely.

Fructose Challenge Result: Medium/ High Fermentation Score

Screenshot of medium fermentation score during Fructose Challenge

The final result for this challenge was 6.7/ 10. The user experienced an initial hydrogen peak starting at 60 minutes, but the level of gas decreased after. They experienced some mild bloating, which was resolved before the end of the challenge.

This result indicates the user did not fully absorb the fructose, however, they appear to be well equipped to release the excess gas, some via breath and the rest is likely to be released as flatulence (farts).

Excess flatulence is undesirable for many, so reducing the amount of fructose that is eaten in one sitting is a good way to keep the excess gas at bay. Again, we suggest checking the food database for foods containing lower levels of fructose.

Before you go…

Check out my blogs on the Lactose, Sorbitol and Inulin Challenges. If you complete a challenge and would like to discuss your result, please feel free to contact us! You can email hello@foodmarble.com or contact us on any of our social media channels!

FoodMarble AIRE is the world’s first personal hydrogen breath tester. It is a pocket-sized breath analysis device. It helps people with chronic digestive issues determine the foods that work best with their digestive system. To learn more about FoodMarble, visit foodmarble.com or follow us on