Lactose

Studies in people

• Open question

  Milk digestion⁵

  Many adults worldwide cannot digest lactose well, but some can still drink a glass of milk with a meal.

• Benefit

  Milk symptom relief⁸

  In people with lactose intolerance, lactose-free milk caused far fewer symptoms than regular milk did.

• Benefit

  Gut bacteria in allergic infants⁹

  In infants with cow's milk allergy, adding lactose to their formula raised helpful gut bacteria and lowered others.

• Open question

  Digesting milk sugar¹¹

  Lactose intolerance symptoms are often not measured or reported well in studies.

• Concern

  Diarrhoea during cancer treatment¹⁴

  In people having chemotherapy for colorectal cancer, eating lots of lactose-rich foods went with more diarrhoea.

• Benefit

  Gut symptoms from milk¹⁵

  In people with lactose intolerance, lactose-free milk greatly cut belly pain, gas and diarrhea compared with regular milk.

Study type not stated

• Concern

  Gut bacteria and inflammation¹⁸

  In mice, lactose fed a gut bacterium that worsened inflammation, and people who absorb lactose poorly cleared it less well.

• Open question

  Milk sugar and digestion¹⁹

  People who cannot digest lactose may avoid milk, and labels do not clearly say how much lactose is in foods.

Allergies and intolerances

These are about people with an allergy, an intolerance or coeliac disease. The signal is about the ingredient itself, and these are about the person eating it, so the signal does not count them.

• Digestive discomfort from milk sugar²

  People who cannot digest lactose get belly pain, gas and diarrhea, and may have higher risk of other diseases.

• Milk sugar digestion³

  Lactose is the sugar in milk; some people lack the enzyme to digest it, causing gas, bloating and diarrhea.

• Tummy symptoms after dairy⁴

  Lactose can cause bloating, wind and loose stools in people who cannot digest it well.

• Gut symptoms from dairy⁷

  Lactose intolerance is when lactose in dairy foods causes stomach symptoms, but it is often confused with other gut problems.

• Dairy sensitivity overlap¹²

  In adults with lactose intolerance that persists on a lactose-free diet, many also test positive to cow's milk proteins.

• Milk digestion in adults¹³

  Many adults who test poorly on lactose get gas or cramps from a glass of milk.

• Milk sugar in babies¹⁶

  Lactose showed up in the urine of some babies who could not tolerate it.

How it’s made and used

• Milk reactions in babies⁶

  Lactose intolerance and cow's milk allergy look alike, so babies may get the wrong formula.

• Tummy trouble from dairy¹⁰

  In children, lactose intolerance can be assessed by eliminating lactose from the diet or by testing.

• Fuel use during exercise¹⁷

  In people cycling, lactose gave similar energy from the drink as sucrose but burned more fat.

• Infant formula nutrition²⁰

  Lactose-free infant formulas had more added sugar, protein and higher glycemic index than lactose-based ones.

The signal at the top counts the findings in people and in animal and lab studies. A concern in studies of people outranks animal and lab studies, and “No concerns” needs at least one finding in people. When most findings in people point one way, the page leans that way (“Mostly”), and every finding is still shown. Findings whose study type is not stated are shown but not counted. This page is a reference, not medical advice. It describes what regulators and published research say. Talk to a doctor or dietitian about your own diet.