Some vegans choose to follow a raw food diet. I don't know much about this topic, but I've heard that food can be considered raw if it's not processed at more than 42 degrees Celsius (about 108 Fahrenheit). Why? What happens after this threshold?
From Raw Food Diet FAQ, heating above that point allegedly:
Kills enzymes. Enzymes help you digest your food. Your body can create enzymes but that process takes a lot of energy. This process makes you feel tired and heavy after a cooked food meal. Further, the enzymes your body makes are not as efficient and effective as the ones that were destroyed in your food.
Consequently, your food is not be broken down as well and thus harder to digest. This also results in food starts rotting in your intestines, that parasites have more chance to survive
It is further believed that your body has a limited amount of enzymes that it can produce. If the supply is finished, body organs will function less and less. It will accelerate aging.
Changes the pH of the food and makes food acidic. We like to eat alkaline foods. Eating acidifying food makes your body a welcome feeding ground for disease.
Converts easy to absorb minerals into inorganic - hard to absorb - minerals. INorganic minerals such as calcium are hard to absorb and might cause calcium stones, whereas organic ones are easier to digest, make you alkaline, help you get rid of too many acids
Destroys most vitamins
Destroys the life force. Eating cooked food is eating dead food. This will make you feel heavy and tired. Live food has live energy. It will give you energy. Simply put. A raw seed will grow, a cooked seed won't. When you pick (raw) unripe fruit it continues to ripen for weeks. Cooked fruit starts to decay within days.
I find these claims to be fairly extraordinary and extreme, and there were no citations provided in the FAQ. But, that's the reasoning behind the temperature threshold.
Around this temperature, enzymes (which are complex protein structures) begin to denature, and this is usually cited as the reason for setting a temperature threshold here. See
- Raw foodism on wikipedia
- article on The Spruce, typical of those I surveyed and agrees with what I've read elsewhere
As the wikipedia article points out, enzymes are broken down by digestion anyway (or they could not be absorbed in the gut, as they are too large to pass through the gut wall) so it is unclear what benefit they can have when consumed. Presumably if they are to assist the body's own digestive enzymes, they must somehow be activated by the environment inside the body (higher temperature?)
It's also worth noting that vitamin C starts to break down at around 45 degrees Celsius and that some other vitamins, such as E, and some fatty acids, also can't withstand high temperatures without chemical changes.