Galactose
A simple sugar (monosaccharide) that, combined with glucose, forms the lactose in milk, is processed by the liver and is involved in some brain functions.
Galactose is a monosaccharide that, bonded to glucose, makes up lactose (milk sugar). During lactose digestion, lactase releases it, and the liver then converts it into glucose.
A fresh angle (beyond milk, a structural role): galactose is not merely a “by-product” of lactose. It plays important structural roles:
- It makes up the galactolipids and glycoproteins of the brain and nerve membranes (notably myelin)
- It takes part in cell signalling (protein glycosylation)
This is why breast milk, rich in lactose (and so galactose), supports the infant’s rapid brain development.
Galactosaemia, a rare but serious disease: some babies are born with an enzyme deficiency (galactosaemia) that prevents them from metabolising galactose. Without a galactose-free diet from birth, it causes serious damage (liver, brain, cataracts). It is one of the conditions screened for at birth (heel prick test).
Scientific debate on ageing: a curiosity, at very high experimental doses, galactose is used in the laboratory to induce accelerated ageing in animals (a research model), through oxidative stress and glycation. This has fuelled speculation about milk and ageing, but the experimental doses are nowhere near normal dietary intake, so no alarmist conclusion about milk should be drawn.
Sources: milk and dairy products (via lactose), beetroot, certain fruit and vegetables in trace amounts.