Galactose is a simple sugar, a type of carbohydrate classified as a monosaccharide, meaning it is a single sugar unit. It acts as a fundamental building block for more complex carbohydrates. Its chemical formula, C₆H₁₂O₆, is identical to that of glucose, but a minor structural difference gives it distinct properties. While it can be found on its own, it is most often bonded with other sugar molecules to form larger structures.
Galactose in the Diet
The most common dietary source of galactose is dairy products. It joins with glucose to form lactose, the sugar found in milk and milk-derived foods like cheese, yogurt, and ice cream. When consumed, your body breaks down lactose into its two components: glucose and galactose.
Galactose is not exclusively found in dairy. It is also present in smaller amounts in a variety of other foods, including certain fruits, vegetables, and legumes. Examples include tomatoes, bell peppers, persimmons, some melons, chickpeas, and lentils. Some organ meats also contribute minor amounts of galactose to the diet.
These non-dairy sources are relevant for individuals who must manage their galactose intake for health reasons, as the quantities can still be a factor in strict dietary plans. The sugar is also sometimes used as an additive in processed foods and certain medications, requiring careful label reading for those on restricted diets.
How the Body Uses Galactose
Once consumed, galactose is absorbed through the small intestine into the bloodstream and transported to the liver, the primary site for its processing. The liver contains specialized enzymes that convert galactose into a more readily usable substance for the body.
This metabolic pathway, known as the Leloir pathway, converts galactose into glucose-1-phosphate. This molecule is then changed into glucose-6-phosphate, an intermediate product in the body’s energy-producing cycle. The converted galactose can then follow the same path as glucose from other carbohydrates.
The resulting glucose can be released into the bloodstream to supply immediate energy to cells throughout the body, including the brain and muscles. If energy needs are already met, the glucose can be stored in the liver and muscles as glycogen, a readily available energy reserve.
Galactosemia and Metabolic Issues
Galactosemia is a rare, inherited genetic disorder that impairs the body’s ability to metabolize galactose. The condition is caused by a deficiency in one of the enzymes needed for the Leloir pathway. The most common form, Classic Galactosemia, results from a lack of the enzyme galactose-1-phosphate uridyltransferase (GALT).
This accumulation can lead to severe health consequences, particularly in newborns who rely on milk for nutrition. If left untreated, the condition can cause liver dysfunction, jaundice, feeding difficulties, and lethargy within weeks. Over time, more serious complications like irreversible liver damage, cataracts, and brain damage can occur.
Due to the severity of these outcomes, newborn screening for galactosemia is standard practice in many countries. A small blood sample from the baby’s heel can detect the enzyme deficiency, allowing for immediate intervention. The treatment for galactosemia is a lifelong, strict dietary regimen that eliminates all sources of lactose and galactose.
It is important to distinguish galactosemia from lactose intolerance. Galactosemia is a serious metabolic disorder stemming from an inability to process galactose itself, which can be life-threatening if not managed. Lactose intolerance, conversely, is a digestive issue caused by a shortage of the lactase enzyme. While it can cause discomfort, lactose intolerance does not lead to the toxic buildup and organ damage associated with galactosemia.