Wednesday, March 16, 2011

Grass On Fire

I previously posted a link to a short version of a video of the author referenced below, and really enjoyed the "Grass" summary, which starts off with a thought experiment:
Consider two groups of animals:
    Group one - cattle, gorillas, and sheep
    Group two - humans, lions, and polar bear

Which of these two groups of mammals are “designed” to digest a low fat diet?

Neither!Digestion and ingestion are different processes. Clearly the first group of mammals ingest a low fat, high fiber diet. But mammalian enzymes cannot hydrolyze (digest) the cellulose and other complex carbohydrates that make up plant fiber. Microorganisms, however, produce enzymes that can. Herbivorous mammals live in a symbiotic relationship with these organisms. The host mammal possess digestive systems that permit fore-gut fermentation (the cattle and sheep, for example, via their reticulo-rumen), or hind-gut fermentation (the gorilla, for example, via it’s enlarged colon and cecum). In either case, the products of these fermentation processes are short-chain, volatile fatty acids (principally acetic, propionic, and butyric acids). Interestingly enough, 60 – 80 % of a ruminant’s (Pond, 2005) and 66 % of a gorilla’s (Popovich, et al., 1997) energy needs come from these fatty acids. These animals digest a high fat diet!
Another taste of Grass' post:
Mankind has been consuming animal products, especially fat, for a very long time. Several authors have argued that one of the two critical drivers for the development of our species, Homo sapiens, is the consumption of a diet consisting primarily of organ meats, animal fats, and muscle meats (Kaplan et al., 2000, Stanford and Bunn, 2001, Bramble and Lieberman, 2004). The other developmental driver was the practice of cooking (Wrangham, et al., 1999, Wrangham, 2006). Wrangham’s book, Catching Fire: How Cooking Made Us Human is a fascinating and very readable examination of this topic.

All living tissue requires energy for maintenance. Our basal metabolic rate, when adjusted for total body size, is the same as other primates (Leonard and Robertson, 1997). By eating a truly nutrient dense diet, one based upon animal products, our ancient ancestors no longer needed to maintain the large digestive tracts required by mammals living on high fiber diets. Our large intestine, or colon, is less than 60 percent of the mass that would be expected from our total body mass (Martin, et al., 1985). In fact, the volume of the entire human gut is only 60 percent of what would be expected from our total body mass (Aiello and Wheeler, 1995). This reduction in human gut size frees up at least 10 percent of the expected basal metabolic rate for our brain’s requirement (Aiello and Wheeler, 1995). In addition, the cholesterol (and other nutrients, including choline) provided by a diet based on animal products provided the vital “raw material” to build the brain (Leonard, et al., 2007). Plant-based diets lack these vital nutrients.

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