There is no animal species in the world that eats food that is deliberately heated or cooled (the reason being of course that they have no method to cook or refrigerate.) It used to be that humans didn’t eat heated or cooled food either.
So since eating cooked food is technically “unnatural,” does having hot or cold food enter the digestive tract have any effect on the system (i.e., affect the esophageal lining or stomach lining?) Obviously, we’ve been eating hot/cold food for millennia, but since it’s unnatural, is it bad?
I’ve read that cooking meat denatures the proteins and makes it easier for the enzymes to break it down and digest. I don’t really have a deeper understanding of that statement though, if it’s easier to digest, is it more efficient allowing for more leisure time or brain growth or something. I know I’ve also heard stuff about how the cooking habits of humans may have driven our own evolution and brain development in some ways.
Point of fact: man has known and used fire to prepare food not just for thousands of years, but for many tens of thousands of years. Homo sapiens evolved alongside their ability to control fire, to the point that I dare say it is perfectly natural for our breed of great ape to consume and digest cooked foods.
See Wikipedia entry. See subsection “Impact on human evolution” and “The cooking hypothesis.”
For clarification, I’m not asking about ease of digesting denatured protein or things like that, but the actual thermal effect that hot and cold food have on the stomach/esophageal linings, or any other such temperature impact.
There are plenty of animals in cold climates that eat food very close to the freezing temp (and drink ice-cold water as well).
Any thermal effect is going to be very temporary, as heat from the rest of your body will soon migrate in to warm up the contents of the stomach.
A similar concept applies to hot food. The stomach is just the first stage in a day(s)-long digestion process; by the time food has been shuffled off into the small intestine, it’s been warmed/cooled to match body temp.
Simply chewing (er, masticating) your food for a few seconds does a pretty good job of getting the food to body temperature. (NOTE: Does not apply to people who swallow their ice cream in big gulps because they enjoy ice cream headaches.)
Animals who eat meat usually eat it heated, as the animal they attacked is still warm.
I have noticed that my stomach feels upset if I drink something too cold or eat something too hot.
The wet food I feed my feral and wild cat colony is heated in a microwave. The heat simulates a fresh kill. I’ve also notice the cats are much healthier (especially during winter) because they eat all of the wet food in the course of about an hour or so, rather that come back later and attempt to eat cold, even now frozen wet food. They have dry food available all day long so they never go without.
The short and simplified version is that humans evolved from tree-dwelling creatures who used to come down from the trees to scavenge nearby large kills left by bigger predators - so we evolved to eat “well-aged” meat. (Also evolved bipedal walking because it left two hands free to carry a load back to the safety of the trees) When humans discovered fire, they found cooking - not quite burning food, maybe boiling it - had the same effect as letting it age for a few days at room temperature; it was easier to digest. So controlling fire helped humans exploit a new concentrated source of protein (and fat). One study I read said that apes spend a lot of their waking life chewing the plants they forage - humans eating large chunks of softened protein instead freed up a lot more time for other exploits.
But - as several people pointed out - hot or cold food very quickly becomes the same temperature as the body; the only downside would be if you consumed too much, too hot, and burned your mouth and/or esophagus. I’ve burned my mouth and tongue a few times, but I think instinct pretty much prevents anyone from trying to swallow excessively hot mouthfuls. You can swallow ice cubes, it will probably not be pleasant, but the short term effects will be limited to that discomfort. I have not heard of any longer term issues. I would imagine burning your palate or tongue too many times might deaden the sense of taste.
We could almost start a new thread for this. IANAB(iologist), but I’ve been led to believe that the factors that led to development of bipedalism in humans is still a matter of debate. Possible explanations I’ve heard are:
As you say, it was nice to be able to carry things in the hands.
(Keeping in mind that all ape species now extant are capable of some degree of bipedalism) As climate change led to deforestation in parts of Africa where human ancestors evolved, it was advantageous to walk upright at least periodically in order to a) spot predators at a greater distance and b) minimize surface area exposed to the hot sun (greater endurance, less susceptibility to heat injury). Those ancestors who could walk upright for longer due to perhaps having a “misshapen” or “mutated” (to their peers) hip/shoulders/spine (or what have you) that aided balance while walking upright might have actually faired better in such endeavors, and so selection pressure favored them through greater odds of survival in the endeavor of crossing open savanna. Also c) once you had a sufficiently warped back and hips, you could actually walk across open spaces much more efficiently (less energy expenditure over a given distance traversed) than your “non-mutant” peers clamoring along on all fours.
Perhaps related to 2 above and the problem of climate change, as trees grew sparser, it became advantageous to stand upright in trees so that, rather than crawling along a single narrow branch on all fours to get the fruit at the end, our tree-dwelling ancestors could stand with our feet down/wrapped around (when our ancestors still had the more dexterous feet) one branch, while they stood erect and gripped a branch above to distribute weight and go out farther and on narrower branches and thus get fruit that they might not otherwise have been able to get. The more adept at this, the greater the odds of getting scarce food and therefore surviving. Selection pressure follows. Similar behavior (bipedal movement in trees by gripping branches above) has been observed in Orangutans, our most distantly-related great ape cousin still in existence.
Our ancestors tended to walk upright on the ground prior to Chimps and possibly other extant lineages branching off, and it’s those damn dirty apes (that is, all great apes except us) that are wrong for NOT routinely walking on two legs when down on the ground. Our most distantly related of all extant ape relatives (Gibbons—lesser apes) have been observed walking upright as a matter of routine when on the ground, so maybe humans didn’t develop bipedalism at all, but rather the other great ape species and humans together evolved from a now-extinct ape species that was fairly adept at bipedalism, but that somewhere along the line(s) our extant great ape cousins’ ancestors (Gorillas, Chimps, Bonobos, Orangutans) found their niche in heavily forested areas, areas which remained so for long enough that they became optimized to tree-dwelling in ways that our more immediate ancestors did not, and they (the other great apes and their lineages) lost the ability to walk upright on two-legs with ease. Though, as noted above, they can still do it, just not quite as effortlessly.
That’s an interesting source; an earlier paragraph than the one quoted says that “Ayurveda advises against the practice of drinking chilled water”. It also claims later that hot water increases “detoxification”. So, I don’t think this is a good source for the latest in peer-reviewed scientific research.
But let’s not just pooh-pooh a claim, let’s show why it’s ridiculous. Let’s look at how much energy it takes to heat up a full liter of ice water to body temperature. Which probably will cause some minor short-term discomfort but let’s look at the energy cost of regulating that temperature. We’ll round up body temperature to 40 C for simplicity, so we’re raising the liter of water by 40degrees C. It takes one small calorie (1/1000 of a dietary Calories) to raise 1 gram of water by 1degree C, so one full dietary Calorie to raise 1 liter of water by 1 degree C, or 40 Calories for the whole liter to body temperature.
I don’t think there’s anyone reading the Dope right now who will miss 40 Calories. And that’s if it’s cold out and your body isn’t trying to cool off;if it is hot, your body has just gotten rid of 40 Calories of heat that it would otherwise have to sweat away.
That’s an excellent heat balance. However based on my chemical engineering understanding it’s a miracle how the body does it. Also I don’t understand fully how the body does it:
So let’s take your example of the body heating 1 liter of water from 0 to 40C. Now the body only has about 4 liters of blood and it may (?) only use a portion of it to heat up the digestive system because you don’t want to overheat the rest of the body. So maybe the body increases the temperature of the blood (don’t know by how many degrees) and maybe also the flow rate (again don’t know by how much) to the digestive system. Now the blood returning will be colder, so maybe that needs heating up too. And all of this requires precise temperature measurement and control.
Duplicating the above system with precision and repeatability at the industrial (or laboratory) scale is not trivial especially when you consider that only 4 liters of blood is available and all the heat that can be added is by triggering chemical reactions.
4 liters of blood, sure, but 50 to 100+ kilograms of body mass (which the blood is cycling through and so introducing convective heat flow). A liter of water is nothing compared to that.