Lately, things have been clicking like crazy. All the confusion and contradictory information from Ray Peat, Paleo, and 80-10-10 is finally congealing into a framework that I think makes a lot of sense and which resolves itself into a diet which is essentially the reverse Perfect Health Diet by which I mean that fat and carbohydrate ratios are reversed and the preferred carbohydrate source is fruit/simple sugars. Let me explain further.
The main tenets of what I have read in relation to Ray Peat seem to resolve into reducing absolute PUFA levels as much as possible, maintaining a high calcium/phosphorus ratio, preference of sugar to starch as a fuel source, the importance of salt, and balancing your amino acids by limiting more common (and more inflammatory) amino acids such as tryptophan and preferring less common (anti-inflammatory) amino acids such as gelatin. These lead to several base recommendations of his such as high dairy consumption (especially milk), avoiding muscle meats, and eating a lot of fruit. I believe these explain a lot of the successes and difficulties of those following an 80-10-10 protocol as well as some of the problems of a Paleo diet as usually done.
As you already no doubt know, Paleo is about getting rid of beans and grains and eating meat, vegetables, and fruit. The first iteration of Paleo was low carb while the second iteration was at least moderate carb. In both cases, the preferred fuel source has been saturated fat and the preferred carbohydrate source has been starch. Sugar has always been demonized within Paleo even in fruit which has generally led to very low sugar consumption among this demographic. I would like to suggest that the most common Paleo diet is really the diet that humans adapted to once we began moving to more northern climates and that this switch over was relatively easy due to the metabolic flexibility most humans have. However, I would also like to suggest that perhaps lingering issues on a Paleo diet are due to the fact that your main fuel sources (saturated fat and starch) are later adaptations that are more difficult for you to process due to metabolic damage sustained through multiple generations. I will get into this more in a second but first.
So how does Ray Peat explain the success and failure of 80-10-10? The extremely low fat levels in 80-10-10 will produce extremely low levels of absolute PUFA in the diet, the high consumption of greens mandated by the diet (half by volume) will produce a very good calcium/phosphorus ratio, and the very low protein consumption coupled by the lack of animal protein means pro-inflammatory proteins are basically eliminated. The dental problems (and probably also the skin problems) encountered on 80-10-10 are due to a lack of fat soluble vitamins and could be solved by adding eggs, butter, and liver to the diet. Low body temperature can be explained by the fact that the thyroid is likely being suppressed by any raw cruciferous vegetables being consumed and the fact that low protein (as Matt Stone has pointed out) depresses thyroid. Simply by eating more protein and not being vegan, this diet becomes a lot better and I think may potentially represent a truer picture of the Paleo diet.
A Hypothesis on the Evolution of the Human Diet
If we look at bonobos then we see that before our evolution into humans, we were likely frugivores with a small consumption of meat and vegetables. Higher consumption of meat is likely what forced our digestive tracts to change (shrink the colon, increase the size of the large intestine, etc) and with this came the capability of relying on more calorie dense foods. If we consider cooking to be an adaptation that comes some amount of time after eating meat then we see that humans likely ate very little starch until the advent of cooking at which point the caloric density of root vegetables became available. I am thus proposing that there is a hierarchy of foods we are best adapted to and that this hierarchy is as follows: fruit, meat, greens, starch. Considering that humans evolved in equatorial Africa, it makes perfect sense that the diet would be as such since there would be no need to suddenly stop eating fruit in a place where fruit is abundant year-round. I believe the move to starch as a main energy substrate for diet is likely the result of the fact that roots grow and store well in northern climates thus making them suitable for humans there and the fact that because roots are so much more calorie dense, they may be seen as a more efficient energy source than fruit. This is why I think most modern foragers rely on starch or fat for bulk calories rather than fruit. The first authentically human diet appears from this to be either high sugar with some meat and greens or high fat with some fruit and greens. However, seeing as we began as frugivores, there is no reason why we would suddenly switch to eating so much meat.
Because humans are built to be flexible and adaptive, the northern diet should present no challenges to the normal human and, indeed, this is why you see such a huge variance in diets among human cultures. You see the Inuit, the Masai, the Kitavans, and so on. Each group eats highly different ratios of food yet all are lean and healthy on their traditional diet.
Matt Stone has also pointed out that people coming from traditional cultures can often withstand much more stress than your average person including the stress of subpar and denatured foods while those from the industrial cultures suffer allergies and bad digestion rampantly. If we can suppose that most people in the industrial nations suffer many of their ills as a result of reduced ability to withstand stress from the buildup of multi-generational malnutrition and lifestyle then perhaps the metabolic flexibility that allowed humans to moved from a high sugar, meat, and greens diet to a high fat, starch, meat, and greens diet has been impaired also. These people, in particular, I believe may benefit from the tropical (or southern) paleo diet which may be viewed as a more relaxed, omnivorous 80-10-10 or a sugar fueled reverse Perfect Health Diet.