- The most common meaning is that is it impossible for two isocaloric diets to lead to different weight loss. (Feinman 2004)
It is this latter point that Richard Wrangham exploits in his skillfully effected book "Catching Fire". This is about the effect that the cooking of foods has had on our very evolution. Like all great popular science books Wrangham threads his prose through several disciplines to produce a very readable tome that touches on quite diverse subjects such as biology, chemistry and behavioural science (such as the sexual division of labour - which I thought was a profound interpretation of the effect of our ability to cook).
Surely Raw Beats Cooked?
Wrangham opens with a broadside against raw-foodists drawing on the Giessen study. This piece of research from Germany found that unlike women (vegetarian or otherwise), on cooked diets who 'rarely fail to menstruate', female raw-foodists 'had a lower BMI and that this was associated with partial or total menorrhea'. What we are dealing with here is an 'energy deficiency'.
Wrangham notes that 'ovarian function predictably declines in women suffering from extreme energy depletion, such as marathon runners and anorexics'. Research has also identified a decline in sexual function amongst raw-foodist males. The prospect an infertile-state has a greater liklihood amongst traditional foragers (as evidenced by nutritional stress present in bones and teeth of HG remains), who would not have the quality of food available to those middle classes in the Giessen study.
This last point illustrates the poor survival chances of HG raw foodists; the point being that modern raw foodists enjoy superior foods in the modern age - and yet their reproductive capability in the majority of cases is largely compromised.
Another advantage of modern raw foodists is the variety of processing techniques available to sequester energy from their raw food. These include 'mild heating, blending, grinding, and sprouting) and the consumption of oils. Yet still their infertility suffers.
There is another side to this coin. The Giessen study had no indication of physical exercise. Anyone who has attempted to forage for food will be aware of how labour intensive it is. 'Less in' means atrophy and/or adjustment of expenditure. Finally, the vagaries of season and fortune would mandate periodic subsistence level existence - something that the subjects of Giessen would be able to avoid.
Given our sole purpose on earth (to allow our genes to survive), this relationship between available energy and the ability to procreate has quite profound implications. For foragers, Wrangham goes on to suggest that an infertility rate of greater than 50% would be devastating. We can see that despite many advantages over foragers, several of the Giessen subjects were suffering this fate.
Raw foodism would appear to be a poor choice of dietary approach.
Cooking; A means to maximise calorie extraction
Wrangham's argument in support of cooking as the great point of leverage in our evolution requires that we draw maximum nutrition from our food. We have to optimise the bioavailability of the energy and nutrients within our food.
Apes optimise this extraction by several 'digestive specialisations' denied to modern man. Wranghman lists some of these as:
- Small mouths "chimpanzees can open their mouths twice as far as humans",
- Small mouth-volume,
- Small and weak lips; "When eating juicy foods like fruits or meat, chimpanzees use their lips to hold a large wad of food in the outer part of their mouths and squeeze it hard against their teeth, which they may do repeatedly for many minutes before swallowing".
- Weaker jaws; "[Our] chewing muscles, the temporalis and masseter, are small. In non-human apes these muscles often reach all the way form the jaw to the top of the skull, where they sometimes attach to a ridge of bone called the sagittal crest, whose only function is to accommodate the jaw muscles....by contrast [human] jaw muscles barely reach half way up the side of our head".
- Human chewing teeth (molars) are "...the smallest of any primate species in relation to body size".
- Small stomachs - "the surface are of [a human] stomach is less than one-third the size expected for a typical mammal of our bodyweight, and smaller than in 97% of other primates".
- Smaller colon = "[the human colon] is less tha 60% of the mass that would be expected for a primate of our body weight....[which] means we cannot retain as much fiber as the great apes can and therefore cannot utilize plant fiber as effectively for food".
Reducing the Cost of Digestion
Wrangham refers to an interesting experiment that gives us a useful insight in to the cost of digestion using pythons. The pythons are kept in a box and analysis is made of the oxygen level before and after a meal,
- "...the physical structure of a python's diet influences its cost of digestion. If the snake eats an intact rat, its metabolic rate increases more than if a similar rat is ground up before the snake eats it.
So the obvious thing to do now is to look for something that joins the dots between the idea of an anatomical evolution to a change in food. This is exactly what Wrangham does, referring to a study of Galapogos Finches:
- "...during a year when finches experienced an intense food shortage caused by an extended drought. the birds that were best able to eat large and hard seeds, - those with the largest beaks - survived best. the selection pressure against small-beaked birds was so intense that only 15% of birds survived and the species as a whole developed measurably larger beaks within a year."
As for softer food - it enables humans to eat comparatively quickly. Several studies have shown that we chew around 4-13% of the day (8% average). What reduces chew-time? Soft foods. Cooked foods,
- "...humans devote between a fifth and a tenth as much time to chewing as do the great apes."
Another nice idea he puts forwards is our trade off of human hair for greater cooling. Losing body hair has meant we do not overheat quickly (as we lack insulation), and can cool quite effectively. This means unlike a chimpanzee who will pant heavily after a short run, we can run for extended periods and move during the hottest part of the day when other animals are more sedentary (think back to some of my posts on sleep for the implications of this).
Hair enables gorillas to sleep uncovered in the cooler mountainous regions. But the loss of hair would have been deadly to humans had we not found another means of keeping warm; fire. Here we see a tentative idea for a positive feedback mechanism which exploits a single utility.
The Atwater System
The final piece of Catching Fire I want to mention, ties in to the first. Wilbur Atwater was a chemistry professor who pioneered the estimation of energy values of foods. Wrangham notes two key problems of Atwater's system for assessing our own caloric consumption:
- The Atwater system does not recognize that digestion is a costly process. When we eat our metabolic rate rises, the maximum increase averaging 25%...and the cost of digestion can be reduced or raised depending on the food type.
- The Atwater system assume that the proportion of food digested is always the same, regardless of whether the food is in liquid or solid form, part of a high-fiber or low-fiber diet, or raw or cooked....digestibility of [food varies according] to its physical state...[and] the digestibility of the same item varies according to the food context in which it is consumed.
So there you go. I have tried hurriedly to pull references on several paleo bases that this book touches. With Xmas coming this would be a great read for any paleo enthusiast. Richard Wrangham serves up some sublime food for thought!