Does “denaturing” nutrients in milk by boiling it make them less useful, or actually more useful, as they undergo “denaturation” anyway during digestion? I've read online that boiling milk "denatures" nutrients such as protein, calcium and others contained in milk, rendering the milk less nutritious. At the same time, I've also read that because the nutrients in milk (and other foods) undergo "denaturation" in our body during digestion anyway, boiling it will not make milk less nutritionally valuable, and will actually help the body to more readily absord the nutrients in it into the bloodstream right after ingestion. What is the truth in this matter? Thanks for any knowledgeable answers! I put the word "denature" in quotes because it's a technical term and I'm not really sure in which ways it can correctly be used.
In short: Cooking milk has probably only a minor effect on its nutritional value.
According to USDA Table of Nutrient Retention Factors (p. 5), in milk heated for 10 minutes, the vitamin loses are: vitamin B1, B6 and choline: 10% ; vitamin C and folate: 15% ; vitamin B12: 20%. Other vitamins and minerals are not affected.
From the mentioned vitamins, milk is high only in vitamin B12, so it seems that destruction of 20% of vitamin B12 is the only meaningful negative effect of cooking milk on micronutrients.
Milk cooking appears to have no significant effect on the bioavailability (absorption and utilization) of calcium (ScienceDirect, 2013).
Proteins are denaturated by cooking and stomach acid (Elmhurst.edu). Denaturation affects only "the shape" of the protein molecule but not its composition or nutritional value. Proteins are digested (broken down) into amino acids before absorption and cooking makes them more digestible (concluding from cooked/raw egg protein digestibility study).
Lactose, the major carbohydrate in milk, is not affected by cooking and decomposes to glucose and galactose only at 203.5 °C (PubChem, section 5.3).
Fats should also not be affected by milk cooking (concluding from the smoke point - the temperature at which fatty acids start to break down - of most oils, which are all well above 100 °C).