Fructose: How to combine optimally & what to do in case of fructose intolerance?
General information about fructose
Like glucose (= dextrose), fructose (= fruit sugar) belongs to the monosaccharides (= simple sugars). They consist of many individual sugar molecules.
Pure fructose has a high degree of sweetness; it is twice as sweet as pure glucose. Among all sugars, fructose has the highest sweetening power. Fructose is contained in almost all fruits and vegetables in varying concentrations, and honey also contains a high amount of fructose. Fructose intensifies the taste in food and is excellently soluble in water.
Pure fructose is produced from inulin, a so-called reserve carbohydrate. This is found, for example, in artichokes, dandelion roots or Jerusalem artichokes. With the help of enzymes or acids, inulin is broken down and decomposed to fructose.
Fructose intolerance vs. fructose malabsorption
Very often you hear about people with fructose intolerance. However, the term that would most often apply is fructose malabsorption. This means that the body can only absorb a limited amount of fructose, as the intestine can only absorb certain amounts at a time.
There are transport proteins in the mucosa of the small intestine. Among other things, fructose is transported into the body via some of these transporters. Unfortunately, not unlimited amounts of fructose can be transported via these transporters. This capacity limit is not the same for everyone, it varies greatly.
If only a very small amount of fructose is transported into the blood via the transporters, the fructose reaches the large intestine. Bacteria are found in the large intestine, which rapidly break down this fructose and use it as a source of energy. In the process, gases and fatty acids are formed, which trigger the typical symptoms of fructose malabsorption.
Probably the most common symptoms are bloating and diarrhea, but abdominal pain and nausea are also among the symptoms of fructose malabsorption.
Some of the gases are absorbed into the blood and exhaled through the lungs. For this reason, a diagnosis can be made with the help of a breath test. The increase in concentration of the gas in the breath is detected by the test and used for diagnosis.
What to do as an athlete with fructose intolerance or fructose malabsorption?
It is estimated that up to 50% of the population will experience symptoms when 25g or more of pure fructose is ingested at one time. However, this figure should not cause panic, such high amounts of pure fructose are supplied rather rarely.
It is important to understand that fructose malabsorption does not mean absolutely no fructose intake. Each person affected must find out for him/herself how much fructose is tolerated.
In a “test phase” you can find out step by step how much fructose from which source is tolerated. This means that athletes suffering from fructose malabsorption can still use products with fructose content. Fructose has several advantages for athletes.
Advantages of fructose for athletes
Compared to glucose, fructose is absorbed rather slowly in the intestine. Fructose has a very low glycemic index, which means that blood sugar levels rise only slightly when fructose is consumed.
The absorption or metabolism of fructose is insulin-independent. In the liver, fructose is converted to glucose, glycogen and fatty acids.
Studies have investigated the effects of fructose in combination with other sugars in solutions in athletes/cyclists and have shown the following results:
- The combination of fructose and glucose appear superior in terms of stimulating intestinal fluid absorption compared to the individual substrates (1)
- Carbohydrate oxidation rate (= total carbohydrate burned in the body) and thus improved exercise performance can increase by up to 50% or more with a mixture of fructose and glucose or maltodextrin (compared to glucose alone), for the same total amount of calories ingested (2,3)
In all likelihood, the increase occurs because fructose and glucose or maltrodextrin are carried in the body by two different transport molecules. Thus, the combination may allow a higher intake of total carbohydrate in the same period.
That is why our professional carbohydrate drinks FAST CARB and POWER CARB created on the basis of fructose and maltrodextrin. Due to the special mixture of different carbohydrate sources and pineapple fruit powder, POWER CARB can even absorb up to 76 g of carbohydrates per hour during exercise.
Our RACE CARB X with its special mixture of different carbohydrate sources (fructose, tapioca starch and rice syrup) even allows an intake of up to 120 g of carbohydrates per hour (at 150 ml). We created the carbohydrate concentrate together with world-class triathlete Laura Philipp especially for long-term endurance competitions.
And all this in a way that is particularly gentle on the stomach – which is especially important for athletes with fructose malabsorption. Top athletes, for whom optimal tolerability is the be-all and end-all due to high ingested amounts, confirm the exceptional digestibility.
Important: We recommend to test such high dosages in advance of a competition (“train the well”), so that the tolerance is given in any case!
1 Shi X, Summers RW, Schedl HP, et al. Effects of carbohydrate type and concentration and solution osmolality on water absorption. Med. Sci. Sports Exerc. 1995; 27:1607-15.
2nd Jentjens RL, Moseley L, Waring RH, Harding LK, Jeukendrup AE. Oxidation of combined ingestion of glucose and fructose during exercise. J. Appl. Physiol. 2004; 96:1277-84.
3 Rowlands DS, Thorburn MS, Thorp, RM, Boradbent S, Shi X. Effect of graded fructose coingestion with maltodextrin on exogenous 14C-fructose and 13C-glucose oxidation efficiency and high-intensity cycling performance. J. Appl. Physiol. 2008; 104:1709-19.