Two weeks ago I wrote about a book – Catching Fire by Richard Wrangham – which postulated that the discovery of cooking greatly improved the food success of the hominid species and led to the evolutionary change that produced us. Many side issues arise as a result of this premise. A very important one is that pairing of males and females may have been driven by a need to protect cooked food rather than primarily for sexual or reproductive reasons; another was that this led to the male domination of women.
The issue that seemed to raise the most interest was how this relates to the issue of obesity in the modern first world. Caro pointed out some scary statistics. Wrangham notes that at the start of the 21st century, 61% of Americans were “overweight enough to begin experiencing health problems as a direct result.” He notes that fifty years after the observation was first made, more people in the US die from too much food rather than too little. Diet conscious people wonder around the supermarket reading calorific values on food packages.
I don’t pretend to have any expertise whatsoever in this area, but Wrangham makes some points and observations that seem at least plausible. In his book's epilogue – titled The Well-Informed Cook – he discusses the way in which food value is measured, which, in broad brush-stroke terms, goes back to Atwater’s meticulous and pioneering work in the nineteenth century. Sparing you the details, he found that food could roughly be divided into three components – proteins, fats, and carbohydrates – and that within these components the available energy was fairly uniform. He also estimated how much of the food material was absorbed by the body. So a mass/energy balance tells you how much energy is available from each food group. Nice and simple and basically the way in which foods are labelled and treated to this day.
Wrangham points out two major flaws in this. Firstly, it doesn’t take into account how much energy it requires to digest the foods. Thus highly processed, soft, cooked foods are rapidly and easily broken down by the digestive enzymes and take little energy to absorb. Conversely, rough-milled and raw foods are much more difficult to digest, and while the body works hard at doing so, much more energy is used in the process. Thus the same amount of calories in different forms leads to a substantially different net gain. Protein costs more to digest than carbohydrates and fats have the lowest digestive cost of the three. A study in 1987 showed that people on a high fat diet achieved the same weight gain as people eating around five times that number of calories in carbohydrates. This suggests that the Atwood system is far too simple to be useful in the modern environment, yet it is still the basis for food labeling.
The second related issue with the system is that the state of the food – liquid, soft cooked solid, meat, raw food – makes a large difference to the cost of digestion. The latter items lead to a much higher excretion rate, which Atwood had assumed to be essentially constant at around 10%. Detailed data on this is hard to obtain for multiple forms of multiple foods and so it is expressed only in qualitative terms like “eat less processed foods,” “roughage is good for you,” “eat fresh salads.” None of this is really helpful, and certainly doesn’t appear in the nutritional food labels. What you see is what you get, but it isn’t very meaningful.
|Richard Wrangham with non-cooking friend|
This is how Richard Wrangham concludes his discussion:
“The human ancestral environment was full of uniform problems: how to get fuel, how to regulate feeding competition, how to organize society around fires. The big problem of diet was once how to get enough cooked food, just as it still is for millions of people around the world. But for those lucky enough to live with plenty, the challenge has changed. We must find ways to make our ancient dependence on cooked foods healthier.”
If Wrangham is right, we now need to avoid the very foods we have evolved to seek. The problem is that those are therefore exactly the ones we like.
Michael – Thursday.