Lactose is the natural sugar found in milk and dairy products. It is only mildly sweet — far less than table sugar — and is rarely used as a sweetener on its own. It is best known as the sugar that people with lactose intolerance cannot fully digest.
Lactose is a sugar — a disaccharide — made of two simple sugars, glucose and galactose, joined together. It occurs naturally in the milk of mammals, including cow's milk and human breast milk, and is therefore present in dairy products such as milk, yogurt, soft cheeses and cream.
Lactose is only about a fifth as sweet as table sugar, so it is not used as a sweetener in the way sucrose is. Where lactose appears as an ingredient — for example in some baked goods, processed foods or as a carrier in medicines and supplements — it is usually there for texture, bulk or browning rather than for sweetness.
To absorb lactose, the body must first split it into glucose and galactose, using an enzyme called lactase produced in the small intestine. When lactase is present in sufficient amounts, lactose is digested normally; it contributes about 4 calories per gram and has a relatively low glycemic index.
Many people produce less lactase after early childhood — the basis of lactose intolerance, discussed below. The prevalence of this varies widely between populations.
The single most-asked question about lactose concerns digestion, not sweetness.
Lactose intolerance is reduced ability to digest lactose, due to having less of the enzyme lactase.
When there is not enough lactase to break down the lactose that has been eaten, the undigested lactose passes into the large intestine, where it is fermented by gut bacteria. This can cause bloating, gas, cramps and diarrhea. Lactose intolerance is common, and the degree varies — many people who are lactose intolerant can still handle small amounts, or tolerate dairy such as hard cheeses and yogurt, which are lower in lactose.
Lactose intolerance is a digestive condition, not an allergy, and it is not a safety problem with milk itself — it is a difference in how individuals digest a normal food component. It is also distinct from a milk allergy, which is an immune response to milk proteins, not to lactose. Lactose-free milk products, in which the lactose has been pre-split with added lactase, are widely available for people who prefer to avoid lactose.
The lactose naturally present in milk is not an added sugar; lactose added to other foods is.
The 2025–2030 Dietary Guidelines for Americans note that the naturally occurring sugars in plain milk are not counted as added sugars. The same Guidelines do list lactose among the names added sugars can appear under on ingredient labels — meaning that when lactose is added to a manufactured food, it counts as an added sugar, even though the lactose in a glass of plain milk does not.
| Property | Lactose | Allulose |
|---|---|---|
| Type of ingredient | Sugar (disaccharide) | Rare sugar (monosaccharide) |
| Calories per gram | ~4 | ~0.4 |
| Glycemic index | Low (~46) | Zero |
| Sweetness vs sugar | ~20% | ~70% |
| Digestive note | Affects people with lactose intolerance | Generally well tolerated in normal use |
| Typical role | Milk sugar; texture/bulk ingredient | Sugar substitute / sweetener |
Lactose and allulose are rarely direct alternatives — lactose is the mildly sweet sugar inherent to milk, not a chosen sweetener, while allulose is used specifically to sweeten. Allulose is far sweeter, far lower in calories, and not connected to lactose intolerance.
Lactose is the natural sugar in milk, a disaccharide made of glucose and galactose. It is only mildly sweet and is found in milk and dairy products.
Lactose intolerance is a reduced ability to digest lactose because the body produces less of the enzyme lactase. Undigested lactose is fermented in the large intestine, causing bloating, gas, cramps and diarrhea. It is common and varies in degree.
No. Lactose intolerance is a digestive difficulty with the sugar lactose. A milk allergy is an immune response to milk proteins. They are different conditions.
No — the lactose naturally present in plain milk is not counted as an added sugar. However, lactose added to a manufactured food does count as an added sugar on the label.
See how lactose and the other sweeteners line up on calories, glycemic impact and sweetness — all 21 side by side.
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