The buying guide
Whey isolate and low-FODMAP claims: what to check
Whey isolate and whey concentrate are not interchangeable labels, but neither name alone verifies the FODMAP status of a finished flavored powder.
Separate the base ingredient from the formula
Monash notes that whey concentrates generally contain more lactose than isolates. That is background about processing; it does not quantify the lactose or FODMAP content of the particular tub in your cart.
Read the rest of the ingredient panel as well as the protein source. A finished product can add sweeteners, fibers, or other ingredients. Check exact-product evidence and its serving rather than turning the word isolate into a suitability badge.
Ask a precise product question
A useful manufacturer question includes the product name, flavor, market, and proposed serving: what testing or certification supports the low-FODMAP claim for this version? Request a link you can keep with your notes.
If you also need information about milk allergy, that is a different question from lactose or FODMAPs. Do not treat a lactose-related statement as allergen clearance. Bring the exact label to the professional helping you manage your dietary requirements.