Does boiling pasta made from veggie flours like kale and spinach (or lentils) decrease the nutrients from these sources significantly? Like on the package, it says 40% Thiamine but when you cook the pasta, is that actually what you’re getting?
thiamine is water soluble so when cooking in water a part will be transferred to water, the percentage is a little more complicated as there is a solubility coefficient for each chemical substance (although some condemn me for using the word chemical when talking about healthy food) for each temperature.
That being said, it is or should be common knowledge that any type of modification to food, whether heating (boiling, soaking, roasting, grilling, etc.) or even drying or acidifying (add vinegar or lemon) will alter the characteristics of the food as it causes chemical reactions, in the case of pasta in particular they acquire a palatable texture and an improvement in flavor but when cooking some of the nutrients will go into the water, if you drain this water it will throw the nutrients that went into it, the reverse is also true if cooked in broth, a part of the nutrients of the broth will go to the dough, coating it and sometimes seeping into the interior (I recommend using cooking water to make soups and base broths such as vegetable broths for this very reason).
with that said, I have technical training in chemistry and food technique (although this one is more focused on preservation and industry, I still learn a lot about nutrition).