Is whey protein isolate lactose free?
Whey protein isolate is not guaranteed lactose free, but it is very low in lactose. A typical isolate scoop holds well under a gram of lactose, compared with several grams in a glass of milk, which is why most people who avoid dairy tolerate it comfortably.
Why isolate has so little lactose
Whey starts as a liquid by-product of cheese making. To turn it into concentrate it is filtered once; to turn it into isolate it is filtered further, until the powder is roughly 90% protein by weight.
Lactose is a sugar, not a protein, so each extra filtering pass carries more of it away. That is the whole difference between a concentrate and an isolate in practical terms: less sugar, less fat, more protein per scoop.
Who should still be careful
People with a diagnosed milk allergy should avoid whey entirely — the allergy is to the milk proteins, and those are exactly what is left in an isolate.
People with lactose intolerance are usually fine, because tolerance is dose dependent and the remaining amount is small. If you react to even trace dairy, a plant protein is the safer choice.
What to check on the label
Look for the word isolate as the first protein source, not 'whey protein blend'. Blends are usually mostly concentrate.
Check the sugar line on the nutrition panel. In an unflavoured isolate it should be around a gram or less per serving.