If they were obese it's because they had a caloric surplus (I doubt it).
The laws of thermodynamics applied then, as they do now.
The laws of thermodynamics applied then, as they do now.
The general argument about carbs or any food with high glycemic response is that these foods are like adding "wet sticks" to the fire. There's considerable science and anicdote to support this.
If you're interested (And not simply not throwing around pithy sound bytes about physics) check out: Why we get fat (And what to do about it) By Gary Taubes (http://garytaubes.com/)
For some very compelling anicdotal evidence (That also supports some concepts of Paleo) check out http://www.reddit.com/r/keto
Now, of course for the people sitting around the fire, some of the heat that would be warming them up or used for cooking is instead used to force a phase change in the water, so it won't be as much "useful" heat, but that meaning of utility - which I believe is the one you want - is outside of thermodynamics.
For what it's worth, "for some very compelling anecdotal evidence" of the thermodynamic approach, see The Hacker's Diet at http://www.fourmilab.ch/hackdiet/ , which uses the "Rubber Bag" model. Unlike the garytaubes.com web site, the entire book and supporting materials are available for free download. The basic premise is the thermodynamic "if you eat more calories than you burn, you gain weight; if you eat fewer calories than you burn, you lose weight." (See also 'Food and fact' where "The rubber bag view of the body and considering only the calorie content of food is obviously oversimplified." and some of the complications are mentioned.)
I believe you are making a different argument, which is that you can't always measure the caloric impact of foods. Under the Hacker Diet, that makes little difference. It uses a feedback system based on weight trends rather than specific calorie counting. There's no need to know that oak combustion produces about 15MJ/kg and boiling water from room temperature takes about 3MJ/kg, because it only looks at 'is there enough heat'?
As for my metaphor - actually I think it holds very true to what you're saying. You pre-qualified that the fire be hot enough to overcome the dampness of the sticks. That's my exact point. Think of the water as insulin and the stick itself as the fat you want to burn. If you're consistently slamming yourself into insulin shock then you'll never burn fat, and you'll end up looking like most of America(Myself included). It takes very little insulin response to put our fire out.
No one is refuting thermodynamics here - simply stating that making the assumption that the body is a perfect machine (Or set at some guaranteed rate of efficiency) is a flawed outlook.
Taubes makes a great case for this in his examination of Native American Women and their children.
So, insulin shock is the specific heat of water and/or the heat of evaporation? Does fire "slam into" the water?
As a technical point, there's a distinction between heat and temperature. The fire does not need to be "hot", it just needs to have enough heat to evaporate some of the water on the new wood, and of course hot enough to catch the wood on fire. At that point the reaction becomes self-sustaining.
I don't know how to apply that heat/temperature distinction to the metaphor.
If the "fire is out" then what are we using to survive?
(These are rhetorical. I think I know the point you're trying to get across.)
Also, what does a "perfect machine" have to do with anything? Surely not from a thermodynamics viewpoints. I can't think of anyone who thinks of the human body as a perfect machine, and I have a hard time thinking of what that would even mean.
You make a valid point - lets pull heat and temperature out of it. I'll take the whole metaphor out. If I were to waterdown the through process of ketogenic diets (which are what I'm talking about and share some things with Paleo) I would explain them as such: Insulin prevents your body from breaking down it's natural stores of energy. When you eat anything with a high glycemic index (Which is most food in the American diet) you have an insulin reaction. While having an insulin reaction, you don't burn fat stores. If you can't burn your fat stores, you don't lose weight. If you can't burn your fat stores and you run out of immediately available energy your bodies 'fire' dims (You crash after that sugar rush)
Ketogenic diets are the only diets that make sense to me, because they so easily explain the different states of weight gain/loss and energy level. I'm interested in hearing other methods of weight management.. but I really feel the ketogenic concept explains the body best.
While I understand the hypothesis, we haven't even determined that a 'sugar rush' exists. Quoting from Wikipedia (Fount of All Knowledge), http://en.wikipedia.org/wiki/Sugar_high#Nutrition.2C_food.2C... :
> Sugar does not cause hyperactivity in children. Double-blind trials have shown no difference in behavior between children given sugar-full or sugar-free diets, even in studies specifically looking at children with attention-deficit/hyperactivity disorder or those considered sensitive to sugar.
From the citation, at http://www.bmj.com/content/337/bmj.a2769 :
> At least 12 double blind randomised controlled trials have examined how children react to diets containing different levels of sugar.2 None of these studies, not even studies looking specifically at children with attention-deficit/hyperactivity disorder, could detect any differences in behaviour between the children who had sugar and those who did not.3 This includes sugar from sweets, chocolate, and natural sources. Even in studies of those who were considered “sensitive” to sugar, children did not behave differently after eating sugar full or sugar-free diets.3
> Scientists have even studied how parents react to the sugar myth. When parents think their children have been given a drink containing sugar (even if it is really sugar-free), they rate their children’s behaviour as more hyperactive...
If a hypothesis depends on a mechanism we haven't observed, then I don't think it's likely to be real.
Compelling anecdotal evidence is an oxymoron, especially when the scientific evidence to the contrary is so strong.
Your phrase "Compelling anecdotal evidence is an oxymoron" seems strange. If 5 people told me they saw my wallet outside, I'd be compelled to check, by anecdote, if I'd dropped it on my way in.
Please show me your science.
But even people coming from the complete opposite end of the argument to the paleo crowd ("Eat more whole grains!") agree that the amount of heat produced by a substance when it's burnt in a calorimeter doesn't tell the full story about its potential for causing obesity.
You already made it clear that you more than doubt they they had that luxury, you definitively said they did not. Again, the question is why?
What I do know is that bodymass is lost and gained with deficits and surpluses of calories.
Transient spikes in insulin and stuff like that are irrelevant. This is well established in nutritional science.