1. Very little peer-reviewed research published to support these types of diets
2. Imprecise data from the Paleolithic times; indirect procedures must be used to reconstruct the traditional diet of pre-agricultural humans.
3. The view of the authors of these books has been challenged on several grounds by other eminent scientists and researchers, such as assuming that contemporary hunter-gatherers are representative of historical hunter-gatherers.
4. There is no evidence that genetic adaptations favoring the consumption of animal-based foods could have occurred to convert early humans into true carnivores.
5. Humans cannot synthesize vitamin C, which is only made in plants. Other mammals that require vitamin C are all plant eaters, so why would humans be any different?
6. For most of the early human history, people did not have the speed or strength [or methods] to catch and slaughter large animals for food, making the possibility of diets high in animal protein rather slim.
7. Human anatomy compares well with that of our nearest non-human primate relatives, like chimpanzees, who have always relied on a primarily plant-based diet. Humans and chimpanzees share a similar intestinal anatomy, and the diets of the non-human primates consist of only 4 to 6 percent animal-based food, mostly from termites and ants.
8. The highly questionable nature of animal versus plant food dietary estimates taken from archaeological studies, due to the fact that plant foods leave little to no trace in fossilized remains is suspect. Additionally, we don’t know much about the lifespans of prehistoric humans; if they didn’t live long enough to develop food-related diseases, then fossil remains can’t be used as evidence about long-term health consequences of a particular diet.
9. There are no peer-reviewed studies showing an association of lower rates of diet-related diseases and low-carb/Paleo diets.
10. A whole-foods plant-based diet has been repeatedly shown to provide substantial health-related benefits that are fairly rapid and relatively free of side effects. There is a substantial body of evidence to support a vegetarian, vegan and even raw foods diet as being much healthier for most humans, than a low-carb or “Paleo” diet has shown. Stick with a roughly 80% carbohydrate, 10% protein and 10% [or less] fat and most people will do much better in maintaining their health.
You can read more about the contrasts of a whole-foods, plant-based diet to low-carbohydrate, high protein/high fat diets in the following books:
The Low-Carb Fraud by Campbell and Jacobson
The China Study by Campbell and Campbell
Dr. Dean Ornish’s Program for Reversing Heart Disease by Dean Ornish
Prevent and Reverse Heart Disease by C.J. Esselstyn
The Starch Solution by John McDougall and Mary McDougall
21-Day Weight Loss Kickstart: Boost Metabolism, Lower Cholesterol, and Dramatically Improve Your Health by Neal Barnard
Eat to Live: The Revolutionary Formula for Fast and Sustained Weight Loss by Joel Furhman
The 80/10/10 Diet: Balancing Your Health, Your Weight, and Your Life, One Luscious Bite at a Time by Dr. Douglas N. Graham