What is Fructose?
Fructose is a carbohydrate, specifically a monosaccharides meaning that it exists as a single molecule. This is different to disaccharides, such as sucrose, which is composed of two carbohydrate molecules (glucose and fructose). Fructose is also known as a fruit sugar. Fructose shares the same molecular formula as glucose, C6H12O6. The difference between glucose and fructose include: 1) fructose has a five structure ring, while glucose is a six structure ring; 2) fructose has a keto group at the number two carbon while glucose has an aldehyde group at the number one carbon.
Fructose was originally discovered in 1847 by the French chemist Augustin-Pierre Dubrunfaut. However, the name fructose was not used until 1857 where the English chemist William Allen Miller coined the term.
Sources and Manufacturing
Fructose can be found naturally occurring in honey, fruits, and vegetables. It can also be found bound to glucose in the form of sucrose. Fructose can also be derived in a commercial setting through the processing of sugar beet, cane sugar, and corn. Over 200,000 tons of fructose is commercially produced each year. Despite its name, high fructose corn syrup (HFCS) is composed of glucose and fructose and comes in different variation such as HFCS-42 (42% fructose, 53% glucose), HFCS-55 (55% fructose, 41% glucose), HFCS-90 (90% fructose, 5% glucose), etc. The use of sucrose as the preferred sweetening agent has decreased over time with HFCS being the preferred agent due to its cost favorability.
Qualities
Of the carbohydrates, fructose has the highest sweetness profile. Due to the sweetness profile of fructose imparting a “fruity” flavor, fructose is often added to juices and foods to improve the palatability and flavor profile. Fructose is 1.2-1.8x more sweet than sucrose although the perceived sweetness is roughly the same as sucrose between 5 to 50 degrees celsius. Fructose can also be added to baked goods to enhance appearance and flavor.
Fructose has the same energy content as other carbohydrates (glucose, maltodextrin, etc.) containing ~4kcal per one gram.
Although fructose shares the same chemical formula as glucose, due to its different molecular structure fructose is absorbed via a different transporter (GLUT5/SLC2A5) compared to glucose (SGLT1). This is why fructose is often leveraged in sports nutrition products to allow for greater gut absorption of carbohydrates.
Once absorbed by cells lining the gut, fructose is transported through the hepatic blood supply where it is primarily absorbed into the liver where it is enzymatically processed through a process known as fructolysis. Some fructose metabolism has been noted to occur in the kidney, but the kidney’s contributions are minor if there is fructose in the blood supply, which are typically in very low concentrations or absent. Subsequently, fructose can be converted into glycogen, glucose, lactate, and other glycolytic intermediates. Some of these products can then be converted into fatty acids and triglycerides. During exercise, the ingested fructose is metabolized in the liver where the glucose and lactate products are released into the blood and can be utilized by the muscle for energy.
Because of the processing that occurs in the liver, the glycemic index of fructose is lower than that of glucose (in the form of dextrose, maltodextrin, etc.). Additionally, fructose is a less energetically efficient energy source compared to glucose due to the aforementioned required metabolic processes.
In some individuals, excessive fructose consumption can lead to gastrointestinal distress and increased flatulence. This is thought to be caused by the malabsorption of fructose where unabsorbed fructose can be metabolized by the gut bacteria leading to the production of undesired gas and organic acids.
Other Uses
In some foods, fructose can be added to increase the viscosity of a carbohydrate solution as it reduces the point at which a starch begins to gelatinize.
Fructose has value in recovery products as it has been shown to improve liver glycogen resynthesis rates after exercise over using glucose alone.
Fructose in Carbs Fuel Products
Fructose is purposely used in all Carbs Fuel products to maximize carbohydrate absorption and oxidation rates. Due to the limitation of glucose uptake in the gut, fructose is used as an alternative carbohydrate source so that more carbohydrates can be absorbed by the gut per minute, thus increasing the amount of total exogenous carbohydrate that can be delivered to and used by the muscle.
