Most helpful critical review
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A bit dodgy on the research
on September 5, 2012
The Vegetarian Myth by Lierre Keith is well-written and appears to be well-researched, on the surface.
The book makes a lot of points about our food system, but the one that Keith most wants vegans to accept is that a decision to not consume animal products out of a desire not to kill anything is a dishonest one. Every means of feeding ourselves requires that organisms die. Monoculture, particularly as applied to the production of grain, relies on herbicides, pesticides, and chemical fertilizers. This results in the degradation of soil and the death of every living organism that lives in it or creates it. Vegans, according to Keith, rely on grains as a staple and therefore their lifestyle is just as damaging as a lifestyle that relies on animals for food.
That's an indictment of agriculture, and not of plant-based nutrition. I think people are increasingly aware that monoculture is degrading to the earth. Plants consume more than just nitrogen (N), phosphorous (P), and potassium (K). Feeding plants with commercial NPK fertilizers starves the plants as well as the soil. People are also increasingly aware that the grain we eat in North America is overly refined, hybridized and genetically modified, to the extent that it's not a healthy food. In terms of solutions, it would be more reasonable to look at sustainable and natural methods of growing plants (and of raising livestock).
When Keith writes that all food choices mean that something must die, her argument against veganism loses momentum because vegetarianism or no, something must always die. In that regard, it doesn't matter what you eat.
Keith then goes on to assess the human digestive system and its bearing on our ability to eat plants.
There is a table in Keith's book that shows the physical characteristics to support her argument that we are not meant to eat plants. It's taken from Walter Voegtlin's book The Stone Age Diet. Many of the data points in the table are simply incorrect.
- The table shows that the human jaw is capable only of vertical (crushing) motion and not rotary (grinding) motion. Our jaws move in both a vertical and a rotary fashion. We close our jaws vertically until the teeth make contact, then we rotate slightly to grind the food.
- The table shows that mastication is unimportant to human digestion. On the contrary, mastication is the first step in human digestion; it breaks the food into smaller particles and mixes it with salivary amylase which converts starch to sugar. Humans who do not properly chew their food have a myriad of digestive ailments.
- The table shows that gastric acidity in human stomach is strong yet the digestive activity in the stomach is weak. That's like saying the acid has no purpose.
- The table shows that food absorption in the human stomach is non-existant and that's true but irrelevant because we absorb through our small intestines. However the table skips the small intestine completely, which is necessary if you want it to support a claim that we are not meant to ingest plants.
- The table shows that humans can survive without a stomach, colon, cecum, microorganisms, and plants but not without animal protein. That claim is absurd and easy to ignore in light of the lack of data to support it.
- The table says the ratio of body length to digestive tract in humans is 1:5 and less than that of a dog. Keith has been badly mislead by Voegtlin's 'data'. Body length for purposes of comparing digestive systems refers to the distance from mouth to anus. A human's body is between 2 feet and 3 feet long, and our digestive system is about 27 feet long (with 23 of them taken up by the small intestines), which gives us a ratio that ranges from 1:13 to 1:9. The fact that most of the digestive tract is devoted to the small intestine, which Keith ignores in her data, very clearly shows that food is intended to take a long time to get through the system. This clearly supports the inclusion of plant matter in our diet.
Keith claims that 'vegan guru' David Wolfe writes books about diet without knowing a thing about how humans actually digest. Wolfe argues that you can get protein from plants as shown by the capability of gorillas, hippos, zebras, giraffes, rhinos and elephants to build muscle from plants. Keith argues that the gorilla can build muscles from plant protein only because of microorganisms in its gut that can digest cellulose. Keith argues that humans are not physically designed to eat grains (or even plants) because we cannot digest cellulose.
Keith's argument fails in several ways:
First, very little of the plant's protein is found in its cellular membranes (cellulose): most of the protein in plants is in the form of enzymes. Enzymes contribute to all chemical reactions in the plant, and after being consumed by animals, those enzymes contribute to the digestion, absorption, and utilization of the plant's nutrients inside the body.
Second, cellulose, or undigested fibre, promotes the movement of food through the human digestive system. Without it, we suffer from the effects of constipation. Without regular elimination of body wastes, toxins remain in the body longer and cause more damage.
Third, cellulose is found only in the outer membrane of the plant's cell walls. We can break the membrane in our consumption of the food, by chewing, and in our preparation of the food, by chopping, cooking, or fermenting. After the membrane has been broken, the macro- and micronutrients are easily accessed.
It appears that Keith has a poor understanding of both plant physiology and human digestion.
Keith's arguments also tend to be weighted heavily towards protein. Plants provide far more than just protein. There is a growing body of evidence to show that we need the vitamins, minerals, and phytonutrients in plants to stay healthy. More evidence is produced daily to show the effects of plant-based nutrients in the prevention of lifestyle-related conditions such as heart disease and cancer.
I don't advise people to avoid reading Keith's book. It is important to understand the arguments that people make against plant-based nutrition. After reading Keith's book, I deduced that agricultural practices are the issue here, and not plants as a food source. It might not be as easy for everyone to disregard the 'data' that Keith uses in support of her argument against eating plants. To that end, I suggest that you research digestion and nutrition yourself or consult with a qualified holistic nutritionist.