At PerfectHealthDiet.com we’re advocates of protein restriction. We recommend:
- Avoiding all protein-containing plants, as plant proteins tend to be toxic;
- Striving to eat fatty, not lean, meats and fish, in order to keep protein intake down and fat intake up.
Protein restriction helps protect against viral and bacterial infections by promoting autophagy, the process of intracellular protein scavenging, digestion, and recycling. During autophagy, bacteria and viruses, as well as junk human proteins and damaged organelles, are digested. Autophagy has been strongly linked to longevity  and is protective against many diseases.
Our advocacy of low protein intake separates us from many other Paleo bloggers. Loren Cordain, the dean of the Paleo movement, has long advocated consumption of lean meats. Although he has moderated his stance somewhat, the front page of his site still places lean meats first among his favored foods:
Learn how a diet based on lean meats …
The Paleo Diet is a way of eating in the modern age that best mimics diets of our hunter-gatherer ancestors – combinations of lean meats …
(The other major difference we have with Dr. Cordain is his exclusion of starchy foods from a “Paleo” diet, even though starchy tubers have been part of the ancestral human diet for 4 million years. But that is a story for another day.)
Those who have read the pre-publication draft of our book know that we place high store on human breast milk as an indicator of the optimal composition of the human diet. Human breast milk provides only 7% of calories in the form of protein. (Carbs are about 38% and fats about 55%.) One can debate whether 7% is the right level of protein for adults; but, if the principle of natural selection is sound, it must be that infants need a low-protein diet.
Science bears this out. As our book notes, diets containing 20% of calories as protein are highly toxic to infants. Pre-term infants fed 20% protein diets had more fever, lethargy, and poor feeding than infants fed 10% protein diets, and lower IQs at ages 3 and 6 years.  Even a slight increase in the protein content of formula, from 7% to 9%, significantly increased the likelihood that babies would be overweight by age 2. 
Given our skepticism toward high-protein diets, especially for babies, we were pleased to see Dr. Cordain in his most recent newsletter [The Paleo Diet Update v6, #20 – Protein Intake for Pregnant Women] acknowledge the dangers of high protein intake by pregnant mothers. Dr. Cordain advises a pregnant mother:
[Y]ou probably should increase your fat and carbohydrate consumption, and limit protein to about 20-25% of energy, as higher protein intakes than this may prove to be deleterious to mother and fetus for a variety of physiological reasons….
“Protein intakes above this [25% of total calories] threshold may affect pregnancy outcome through decreased mass at birth and increased perinatal morbidity and mortality.” 
The physiological basis for this aversion stems from a reduced rate of urea synthesis during pregnancy that is evident in early gestation  as well as increases in the stress hormone cortisol . Hence, pregnant women should include more carbohydrate and fat (i.e. fattier meats) in their diets and limit dietary protein to no more than 20-25% of their total caloric intake.
What are the long-term effects of a high-protein diet during pregnancy on the offspring? In long-term follow-up studies of the adult children of mothers who ate high protein diets while pregnant between 1948 and 1954, it was found that by age 40 offspring commonly had high levels of the stress hormone cortisol  and high blood pressure [7,8]. The effects of faulty maternal diets can be long-lasting.
At PerfectHealthDiet.com, we think 20% is still likely to be a bit more protein than is desirable. We would advise pregnant mothers to restrict protein to about 15% of calories and to strive to obtain 30% of calories as carbohydrates. As long as adequate carbs are obtained, there is only a modest need for protein and as little as 10% of calories as protein may be sufficient.
Note that this advice is very close to the ratios of 30% carb, 15% protein, and 55% fat that we recommend to adults and children generally. Pregnant women may benefit from slightly more starch and slightly less protein than others; but on the Perfect Health Diet, pregnancy should not require a significant change in eating habits.
 Jia K, Levine B. Autophagy is required for dietary restriction-mediated life span extension in C. elegans. Autophagy. 2007 Nov-Dec;3(6):597-9. http://pmid.us/17912023.
 Goldman HI et al. Clinical effects of two different levels of protein intake on low-birth-weight infants. J Pediatr. 1969 Jun;74(6):881-9. http://pmid.us/5781798. Goldman HI et al. Effects of early dietary protein intake on low-birth-weight infants: evaluation at 3 years of age. J Pediatr. 1971 Jan;78(1):126-9. http://pmid.us/5539071. Goldman HI et al. Late effects of early dietary protein intake on low-birth-weight infants. J Pediatr. 1974 Dec;85(6):764-9. http://pmid.us/4472449.
 Koletzko B et al; European Childhood Obesity Trial Study Group. Lower protein in infant formula is associated with lower weight up to age 2 y: a randomized clinical trial. Am J Clin Nutr. 2009 Jun;89(6):1836-45. http://pmid.us/19386747.
 Speth JD. Protein selection and avoidance strategies of contemporary and ancestral foragers: unresolved issues. Philos Trans R Soc Lond B Biol Sci. 1991 Nov 29;334(1270):265-9; discussion 269-70. http://pmid.us/1685584.
 Kalhan SC. Protein metabolism in pregnancy. Am J Clin Nutr. 2000 May;71(5 Suppl):1249S-55S. http://pmid.us/10799398.
 Herrick K et al. Maternal consumption of a high-meat, low-carbohydrate diet in late pregnancy: relation to adult cortisol concentrations in the offspring. J Clin Endocrinol Metab. 2003 Aug;88(8):3554-60. http://pmid.us/12915635.
 Campbell DM et al. Diet in pregnancy and the offspring’s blood pressure 40 years later. Br J Obstet Gynaecol. 1996 Mar;103(3):273-80. http://pmid.us/8630314.
 Shiell AW et al. High-meat, low-carbohydrate diet in pregnancy: relation to adult blood pressure in the offspring. Hypertension. 2001 Dec 1;38(6):1282-8. http://pmid.us/11751704.