Great ideas, observations and questions. My own personal theory is that the current horrible dietary habits around the world are driven by overpopulation. The human evolutionary line broke off from fruit and plant eating apes 2.5 million years ago. Since then our ancestor hominids have been eating ever more and more meat until the human step about 100,000 years ago when we became "top chain" predators and survived for millennia on pretty much meat alone, only eating plants during times of shortage and starvation. There is good paleontological evidence for this. One of my favorites is this lecture by Dr. Barry Groves, a colleague of Dr. Yudkin who first sounded the warning on sugar but was silenced by Ancel Keyes.
. The movie "The Perfect Human Diet" actually has interviews with the paleontologists and laboratory scientists who have given us this data. It can be streamed here.
. What I believe happened is that humans overpopulated many areas starting about 10,000 years ago. In some of these like the Fertile Crescent, the Indus Valley and in China about the same time this is what I believe occurred. The meat available was over hunted creating a famine and some clever humans discovered the farming of crops and also domestication of meat animals which were synergistic. Using this combination 10 times as many or more humans could occupy a given area of land. The problem however was that the diet high in plant based foods was not nearly as nutritious as the preceding meat based diet and the fossil record shows us that after they made this transition there was a significant decline in the general health of the population. Average height dropped 6 inches. Average brain volume dropped 20%. The jaws did not form fully and people developed impacted wisdom teeth because the jaws were no longer big enough for them. The nasal passages for air shrunk bringing us sinus problems. Infectious diseases like tuberculosis started to be seen in the bones and tooth and gum disease which was unknown in meat eater became common. Vitamin and mineral deficiencies like iron deficiency and rickets became common. The larger populations of the plant eaters were able to free up lots of people to develop advanced weapons, build fortified cities and standing armies which they used to invade the territories of the remaining hunter-gatherers, subjugating them and turning them into farming societies. The only hunter-gather societies that survived till today were in harsh climates or very isolated locations like the Inuit Eskimos, the Siberian Meat People the Nemetz, the Amazon Basin Tribes and the Masai on the dry plains of Africa. All of which are unsuitable for agriculture.
You asked about how I thought the addiction problem fit in regarding plants. I think that sweet tasting foods are the most addictive because anytime the sweet taste buds in our mouths are stimulated by anything including calorie and carb free sweeteners, signals are sent to our brains which trigger the same reward pathways as cocaine, heroin and nicotine and are thus in my opinion equally addicting. Here’s a scholarly article that reviewed the available literature in this subject and came to this conclusion: “Food is not ordinarily like a substance of abuse, but intermittent bingeing and deprivation changes that. Based on the observed behavioral and neurochemical similarities between the effects of intermittent sugar access and drugs of abuse, we suggest that sugar, as common as it is, nonetheless meets the criteria for a substance of abuse and may be “addictive” for some individuals when consumed in a “binge-like” manner.”
The sweet signals also cause the part of the brain called the satiety center which tells us we have had enough to eat to “turn off” leading to overeating. Here's an article about that.
I went low carb 4+ years ago I initially included many plant foods. I listened to a lot of lectures on the benefits of "low carb" berries like blueberries and raspberries. And how they were wonderful because of the anti-oxidants. I started eating them but found I frequently "lost control" and instead of having 1/2 cup a day at 10 carbs I would be sneaking a 2nd and 3rd 1/2 cup and my 1/2 cups were more like 3/4 cups. I got into trouble with spaghetti squash just 10 carbs a cup but I would find myself eating 3-4 or even more cups a day because it reminded me of spaghetti which I was addicted to since childhood. I truly believe that at least 90% of people who are fat, are fat because they are insulin resistant and have the Metabolic Syndrome which will eventually lead to diabetes. From the thousands of studies I have reviewed and numerous books I have read on the subject, I feel the preponderance of the evidence suggests that an insulin resistant individual needs to limit their carbohydrate intake to no more than 20 grams of carbohydrate a day and that many of the most severely affected need also to limit themselves to 1.5 grams of protein per kg ideal body weight per day or their disease of the metabolic syndrome is likely to progress much the detriment of their health. I think for someone that includes plant foods in their diet, even reportedly "healthy ones" runs a great risk of exceeding this 20 gram magic number. Eating only fatty meat, eggs, cheese and butter is in my opinion is the easiest way to meet the 2 goals I mentioned without hunger or loss of lean body mass. And I think the data shows us that for most people total abstinence is the only way to truly beat and addiction not eating plant foods is the easiest and most nutritious way to totally avoid sweets in my opinion.
Yes you can probably treat the metabolic syndrome/diabetes successfully using plants if you stick to kale and spinach and lettuce but then you run into what I consider the 2nd major danger of plants and that is Autoimmune diseases caused by damage to the gut lining by direct trauma of the plant fiber and plant toxins that loosen the tight junctions between the gut cells that shield the immune system from plant antigens. This process is called "Leaky Gut Syndrome" The plant antigens that reach the immune system cells can trigger auto-immune diseases like Type 1 diabetes (strong link to wheat consumption see Dr. Davis wonderful book "Wheat Belly"), Rheumatoid Arthritis, Lupus, Psoriasis (strong like to carb containing foods see this lecture by Dr. Richard Bernstein)
I personally believe we will someday learn that the leaky gut syndrome is the driver behind many more autoimmune diseases. Here's a description of the process that I've written: "One of the main reason I don't eat fruit or vegetables of any kind is because those non-soluble plant fibers are like tiny razors cutting and damaging the cells that line the gut causing them to become inflamed and loosening the "tight junctions” between them. This allows foreign proteins in the gut to present themselves directly to our immune systems leading to antibody formation and subsequent allergy problems. In the worst case, some of the plant proteins are so similar to human proteins that the antibodies we produce to them can attack our own cells. This is called an “auto-immune disease”. Examples are Type 1 diabetes, Lupus, Rheumatoid Arthritis, Crohn's disease and thousands of other autoimmune diseases. Here's a nice article that talks about how fiber damages our intestines. Here's a link to a scientific description of the "leaky Gut Syndome". The zonulins found in many vegetables especially wheat also cause the tight junctions in our gut that normally protect our immune systems against this exposure to foreign plant antigens to loosen triggering exposure and the potential for many autoimmune diseases. Here’s a scholarly link about that.
Once you have antibodies against a plant protein whether it produces common allergies or an autoimmune condition every time you damage your gut with fiber or the zonulins found in all grains that also loosen the tight junctions between gut cells you risk reexposure to the plant protein that caused the initial antibodies to form. You have "memory" white blood cells for every antibody you are able to produce including the bad ones that attack your own body. When the memory cells are re-exposed to the antigen they are programmed for they cause the antibody producing cells to go into high gear producing antibodies against that protein. If it's an allergy, you get allergy symptoms, if it's an autoimmune disease, you get a flair of your condition for example an outbreak of a scaling rash in psoriasis. Too much fiber is also associated with hemorrhoid formation, something I can do without. Let the animals take the risk of eating the plants!"
As for plant toxins and anti-nutrients, they are numerous. And I am not aware of a single plant food that doesn’t contain at least one. Here's a nice summary article that describes many of them. If you prefer a lecture then this is probably the best I've found. It's from the Harvard trained and employed physician Dr. Georgia Ede
My own personal opinion is that a meat only diet is the most nutritious way of eating and indeed after 510 days of doing so I have never felt or looked better in my life.