When I was studying the feeding behavior of wild chimpanzees in the early 1970s, I tried surviving on chimpanzee foods for a day at a time... Having eaten nothing but chimpanzee foods all day, I fell upon regular cooked food in the evenings with relief and delight.
About 25 years later, it occurred to me that my experience in Gombe of being unable to thrive on wild foods likely reflected a general problem for humans that was somehow overcome at some point, possibly through the development of cooking... In 1999, I published a paper [pdf] with colleagues that argued that the advent of cooking would have marked a turning point in how much energy our ancestors were able to reap from food.
To my surprise, some of the peer commentaries were dismissive of the idea that cooked food provides more energy than raw. The amazing fact is that no experiments had been published directly testing the effects of cooking on net energy gained... thanks particularly to the work of Rachel Carmody, a grad student in my lab, we now have a series of experiments that provide a solid base of evidence showing that the skeptics were wrong.
Whether we are talking about plants or meat, eating cooked food provides more calories than eating the same food raw. And that means that the calorie counts we???ve grown so used to consulting are routinely wrong.
Part of the reason this had never been addressed before was that several areas of research had been overlooked, even by nutritionists. Especially fascinating were the physiological studies on people who subsist only on raw foods. I was impressed to learn that raw-foodists are thin compared to those eating cooked diets, given that in most cases they are eating domesticated foods with lots of nutrients, are processing them in machines like electric blenders, and of course, living as most do in the developed world, never suffering through seasonal food shortage. Yet despite all these advantages over anyone who might try eating wild foods raw, the average woman on a 100% raw diet did not have a functioning menstrual cycle. About 50% of women entirely stopped menstruating! When a raw-foodist???s reproductive system does not allow her to have a baby even when her diet is composed of processed, high-quality, agricultural foods, the obvious explanation is that she is not getting enough calories....
Rachel Carmody led a study in which mice were given regular mouse pellets for six days at a time, interrupted by four days of eating sweet potatoes or beef. Half the time the sweet potato or meat was presented raw, and half the time cooked; half the time it was also pounded and half the time unpounded. She and Gil Weintraub carefully measured the exact amount of food eaten by the mice, and then calculated the animals??? gain or loss of weight over four days as a function of the weight of food eaten, using both wet weights and dry weights of food to check the results. For both meat and sweet potato, Rachel found that when the food was cooked the mice gained more weight (or lost less weight) than when it was raw. Pounding had very little effect.
We suspect that there are two major reasons for cooked beef providing more calories than raw beef. In cooked beef, the muscle proteins, like the sugars in cooked starch, have opened up and allowed digestive enzymes to attack their amino acid chains. Cooking also does this for collagen, a protein that makes meat difficult to chew because it forms the connective tissue wrapped around muscle fibers. However, we do not know the exact mechanisms. What we do know, though, is that the mice had a spontaneous preference for eating cooked meat over raw meat, and their choice made sense, given that they fared better on it.
Mechanism aside, though, what the experiments indicated was some serious discrepancies in how calorie counts are measured. The USA uses the Atwater Convention for assessing calories in food, a century-old system that treats food as being composed of a certain number of components, each of which has a fixed calorie value???such as 4 kcals for a gram of protein, 4 kcals for a gram of sugars, 9 kcals for fats [ed: kcals are popularly called "calories"]. ..
But the Atwater Convention has two big flaws. First, it pays no attention to the extent to which food has been processed. For example, it treats grain as the same calorie value whether it is eaten whole or as highly milled flour. But smaller particles are less work to digest, and therefore provide more net energy. Second, it treats foods as equally digestible (meaning, having the same proportion digested) regardless of processing. But cooked foods, as we???ve seen, are more digestible than raw foods.
..So people can be deluded into thinking that feeding their children on 100% raw foods is a healthy practice, whereas I believe it would be dangerous for them...
The more highly processed our foods, the more calories we get out of them...
The next wave of research will decide how profound the effects of cooking are. My best guess, based on studies of the increased digestibility of starch or eggs eaten cooked compared to raw, is that the increase in net calorie gain from cooking will prove to be in the region of 25???????50%. That is only a guess, but I am confident it will be much higher than 10%. It is going to be exciting to find out.
When I was a raw food vegan I weighed 145 at 6'3" and I definitely ate 2-3k calories per day and met minimum protein and fat recommendations. So if raw food is so undigestible then should we all be cooking the sh*t out of our veggies and meats or what? What are your thoughts on this in general? Would knowing this change any of your practices?
asked byStephen_4 (10989)
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on June 14, 2013
at 03:38 AM
While the end question it raises is valid enough, I do have to chuckle at the almost Keanu Reaves style "whooooa" that seems to be projected during the setup. It's been a popular hypothesis, for as long as I personally can remember, that cooking lead to easier digestibility which meant not having to spend so many calories to extract calories. This, in turn, supposedly, freed up a lot of time that would have been spent foraging for more calories, thus allowing for the finer arts, sciences and other interactions to evolve.
So, yes, cooking does a bit of the "digesting" for us. This saves us some of the energy otherwise lost exerting the extra effort it takes to digest raw food. I'd definitely say it is one reasons I tend to cook everything, even my leafy greens (rather than just a cold salad). It has the potential to save on the grocery bill over an extended period of time.
As for the objective caloric value of a food it would be foolhardy to believe that they are truly representative of what we are extracting. We are not walking bomb-calorimeters. That said, if you're comparing the calories we biologically extract versus the measurement of a bomb-calorimeter then we are almost definitely eating FEWER calories than we are measuring. I would find it difficult to believe that our systems are more efficient than simply burning the food to heat water. But this is just semantics. An egg is no more slimming after this revelation than before. As long as the ratio of bio-available calories remains constant then it remains a useful measurement for day to day purposes. That ratio, however, can be effected by cooking. Full circle. You could measure again after cooking, but cooking may have made no difference to the fire whereas it makes a large difference to us. In such a case a new method would have to be devised (in fact, I believe there is one as I am told that bomb calorimetry is rather outdated).
All THAT said there is obviously going to be a point of diminishing, or even negative, returns when it comes to cooking. A medium rare steak may net you more calories than a rare one but I doubt you would get much if you went so far as to turn it into charcoal.
on June 14, 2013
at 09:28 AM
Interesting, I always feel more full after a cooked meal, I used to put this down to it being more difficult to digest rather than easier, or due to their being more calories. It makes sense that if you roast vegetables and they caramelize, the sugars could boost the calorie content.
Recently I tend to do half cooked half raw, like when I eat a steak i'll eat half of it raw (the lean part) then cook the other half (the fattier part) later, same with broccoli or leafy greens. I also eat about 3 raw eggs per day and about 3 cooked eggs. I'll make liver pate, but while making it down some raw liver.
It feels quite natural to graze/snack on raw things during the day then settle down & have some cooked food at night
on June 14, 2013
at 03:02 AM
This brings to mind something Matt Lalonde said in a podcast. He advises cooking vegetables slightly, not eating them raw and not cooking them too much. He said something along the lines of cooking them too much leaches too many of the nutrients from them, and eating them raw leaves our bodies unable to absorb enough nutrients. I tend to eat mostly cooked vegetables, with the occasional raw pepper. My completely unresearched guess is that there would be some benefit to consuming vegetables cooked a various variety of ways (shamelessly stealing that line from Gregg Everett). My idea is that you would absorb a broader spectrum of nutrients by doing so. This should be something to send over to the 30BaD crowd. Over here I don't think many people are in danger of going infertile due to a lack of calories if they are eating enough meat/fat.