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What is galactose?
Name origin: From the Greek gala = milk, and -ose, which denotes sugar.
Picture 1. Galactose vs glucose structure
Nutrition Facts for Galactose
- Calories per gram = 4.1
- Glycemic index (GI) = ?
- Sweetness relative to sucrose = 30%
- Net carbohydrates = 100%
Is galactose an essential nutrient?
Galactose is not an essential nutrient, which means you do not need to get it from food to be healthy; galactose can be synthesized in the human body from glucose.
Galactose Functions in the Human Body
- In the human body, most of the ingested galactose is converted to glucose, which can provide 4.1 kilocalories per gram of energy, which is about the same as sucrose .
- Galactose can bind to glucose to make lactose (in breast milk), to lipids to make glycolipids (for example, molecules that constitute blood groups A, B and AB), or to proteins to make glycoproteins (for example, in cell membranes).
- The main dietary source of galactose is lactose from milk and yogurt, which is digested to galactose and glucose [2,3].
- Foods containing small amounts of free galactose include low-lactose or lactose-free milk, certain yogurts, cheeses, creams, ice creams and other foods artificially sweetened with galactose . Plain natural foods (fruits, vegetables, nuts, grains, fresh meats, eggs, milk) usually contain less than 0.3 g galactose per serving .
- Certain medications may contain galactose as a filler.
Galactose is absorbed in the small intestine by the same mechanism as glucose, that is by the help of SGLT-1 and GLUT-2 transport proteins in the small intestinal lining .
In the rare genetic disorder glucose-galactose malabsorption, the absorption of galactose and glucose is reduced .
Most of the absorbed galactose enters the liver, where it is mainly converted to glucose, which is then either incorporated into glycogen or used for energy .
The Effect of Dietary Galactose on Blood Glucose Levels
- Galactose ingestion results in lower blood glucose and insulin levels than glucose ingestion [5,9].
- In one study, 75 grams of glucose ingested 30 minutes before exercise was mainly metabolized during the first hour of exercise and the same amount of galactose (at another occasion), during the third hour of exercise; this means that consumption of both glucose and galactose in the meal before exercise could provide better distribution of energy than either nutrient alone .
Galactose and Tooth Decay
Galactose and lactose, which is composed of glucose and galactose, can promote dental caries .
Galactosemia or “galactose diabetes,” is a rare genetic disease, in which the lack one of the enzymes needed to convert galactose to glucose results in the buildup of galactose in the blood and a subsequent damage of the liver, brain, kidneys and eyes . When infants with galactosemia are fed with breast milk or formula containing galactose or lactose, they may develop lethargy, enlarged liver, hypoglycemia, convulsions or jaundice in the first days of their lives . Galactosemia cannot be treated, but symptoms may be prevented by a strict life-long galactose-free and lactose-free diet.
Other genetic disorders of galactose metabolism include glycogen storage disease type 1 with enlarged liver and impaired growth  and galactokinase deficiency, a benign disorder with cataract present at birth .
Other Nutrients That Contain Galactose
- Lactose is a disaccharide that contains galactose and glucose.
- Galactans are oligosaccharides that contain different monosaccharides, from which at least one is galactose.
Galactose and Cooking
- Galactose is commercially available as a white crystalline powder with no odor, about 30% as sweet as sucrose [15,16].
- Galactose is not hygroscopic – it does not readily attracts moisture (info from a producer).
- Galactose solubility in water at 25 °C is 215 g/100 mL . Galactose is slightly soluble in ethanol .
- Galactose melting point is 325-336° F (163-169 °C) .
- Galactose is a reducing sugar , which readily undergoes the Maillard browning reaction in the presence of amino acids .
- Caramelization of galactose starts at 320 °F (160 °C) .