I’ve googled calories of many protein sources . For eg it says that 100 g of beans has 350 cal but 100 gm of boiled beans has 165 cal. How is that possible? Also on boiling lentils, eggs or beans does the protein content decrease ? And by how much ?
Boiling the beans increases moisture content adding weight, reducing the nutrients per gram.
50g of pure protein has 1g of protein per gram of weight. If I add 50g of water, the new mixture has 0.5g of protein per gram of weight.
For the beans, it is relevant for calorie tracking if you’re weighing before or after cooking.
they absorb 2-4 times of their dry weight in water. also when cooking beans you only bring the water to a boil very briefly and then simmer.
high temperatures denaturate protein, but that just means rendering its 3d shape no longer functional (which happens during digestion anyway). Uncooked they would either be not digestible or at least harder to, so cooking actually enables you to get more protein out of most food sources. So even if they lose some protwin from cooking, it‘s not like we have a choice to eat them raw instead.
protein in meat and eggs don‘t change significantly either before and after cooking
Other nutrients can be significantly reduced from cooking eg vitamins that dissolve in water. That‘s why it‘s good to mix up prep methods and opt for „gentler“ methods like steaming: https://www.ars.usda.gov/ARSUserFiles/80400525/Data/retn/retn06.pdf