Fructose Part 3:   Gut Integrity and Exercise

Fructose Part 3: Gut Integrity and Exercise

 In this Part 3 of our series on Fructose we'll round out the story by looking at the progressive research relating to gut health and fructose.  With recreational endurance athletes training 15 hours a week, and in many cases over 20 hours per week,  the daily consistent impact to the gut is worth acknowledging and thinking about how to support it better. 

There are really three areas of the gut under fire here, 1) the membranous tissue of the small intestine, the mucous membrane, and the bacterial flora of the small and large intestines.   For the endurance athlete, it's a perfect storm of factors impacting gut integrity, 

1) the shunt of the circulation away from the gut to the working muscles,
2) varied degrees of dehydration and heat in the core,
3) dietary food-fluid intake risks - which we'll cover below, and, 
4) mechanical stressors to the gut.   

So, why does this matter?

Well first, there's the direct short-term implication for the athlete, looking to minimize Gut-GI distress during training racing, and second, there's the longer-term concern on the more systemic implications from gut-integrity issues and general health.

In the 1970s, terms like 'gut permeability', and 'leaky gut' were becoming mainstream - although orthodox medical circles looked at it with a healthy dose of skepticism. It's true, that much of the research was animal-based, however, human studies began to also highlight the association of fructose and the breakdown of gut integrity, either the mucous membrane, the membrane itself and/or the microbiome.

In a comprehensive research paper published in 2020, researchers (1) shared animal gut membrane microscopic images that were on control or higher-fructose diets. The images showed the detrimental effects Fructose was having on mucous membrane thickness and gut microbial populations. It was this impact on gut integrity, that researchers highlighted as being at least partially, responsible for the exacerbated inflammatory condition of the gut (colitis).

A subsequent study (2), highlighted that fructose was associated with gut membrane junction proteins becoming more permeable, and allowing the flow of bacterial endotoxins from gut membrane to the liver. The paper highlighted the decrease in the membrane junction integrity between cells in the gut membrane, of animals exposed to high fructose diet.

Now we should point out, that the ratio of fructose in these animal studies was high - and raises the question of how/if this applies to human modeling. However, in the case of animal studies, the study duration was mostly in the range of 'weeks', whereas comparatively, humans could easily be over-consuming fructose for years.

So it was back in 2008 (3), when researchers published the findings from human studies. It was here, that similar to animal studies, Fructose was highly associated with gut membrane breakdown, bacterial endotoxins in the liver, and subsequent non-alcoholic fatty liver disease.

So, in Part 2 we highlighted the role of Fructose over-consumption blunting an athlete's aerobic development, and here in Part 3, the role of Fructose in affecting gut integrity.

Considering there are other carbohydrate (and fat) sources that athletes can use as fuel for competition, it only stands to reason these should be considered.

The studies highlighted through this series, informed SFuels to consider other carbohydrate options, beyond Fructose. We felt we should embrace every opportunity to explore alternate carbohydrate ingredients (for our Racing product portfolio) in seeking to mitigate both 'in-race' Gut-GI distress risks, as well as longer-term complications of over-consumption of fructose.

So, not to be ashamed of being repetitive, we list below the major Fructose food-drink watch list - and some better options to replace them with. Hopefully you find this useful on your phone.



1) Montrose et al. Dietary Fructose Alters the Composition, Localization, and Metabolism of Gut Microbiota in Association With Worsening Colitis. Cellular and Molecular Gastroenterology and Hepatology. 2020 Sep.

2) Young-Eun Cho et al. Fructose Promotes Leaky Gut, Endotoxemia, and Liver Fibrosis Through Ethanol-Inducible Cytochrome P450-2E1-Mediated Oxidative and Nitrative Stress. Hepatology. 2021 Jun.

3) Thuy S et al. Nonalcoholic fatty liver disease in humans is associated with increased plasma endotoxin and plasminogen activator inhibitor 1 concentrations and with fructose intake. The Journal of Nutrition. 2008 Aug.

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