Background
In several of his articles, Ray Peat suggests that cancer can't occur on PUFA-free diets. As proof, he repeatedly cites an old German publication by Bernstein and Elias from 1927 (source)."Cancer can't occur, unless there are unsaturated oils in the diet." - Ray Peat in "Unsaturated Vegetable Oils: Toxic"
"In 1927, it was observed that a diet lacking fats prevented the development of spontaneous tumors." - Ray Peat in "Oils in Context"
"When I was studying the age pigment, lipofuscin, and its formation from polyunsaturated fatty acids, I saw the 1927 study in which a fat free diet practically eliminated the development of spontaneous cancers in rats (Bernstein and Elias)." - Ray Peat in "Unsaturated fatty acids: Nutritionally essential, or toxic?"
"In 1927, Bernstein and Elias found that rats eating a fat free diet had almost no spontaneous cancer [...]" - Ray Peat in"Cancer: Disorder and Energy"
Review of Bernstein and Elias study
I went through this study and found that it doesn't show what Peat cites it to show:- The study was done in mice, not in rats. There were several experiments with mice (2 per box) that got either a normal diet or a specially prepared lipidfree diet. Some mice got a lipidfree diet supplemented with cholesterol or lecithin.
- It didn't study the effect of diet on spontaneous cancer but on cancer that has been injected into the mice.
- In experiment B, tumors were found in 9/9 mice with the normal diet (mean tumor weight 0.96g) and in 5/7 mice with the lipidfree diet (mean tumor weight 0.4g). In percentage, tumor weight was roughly 60% smaller and tumor incidence was 30% less on the lipidfree compared to the normal diet. Mice on the lipidfree diet lost 18% of weight and gained 1% of weight on the normal diet.
- In experiment R, tumors were found in 9/9 mice on the normal diet (mean tumor weight 0.18g) and in 7/9 mice in the lipidfree diet (mean tumor weight 0.1g). In percentage, tumor weight was roughly 60% lower and tumor incidence was 25% lower on the lipidfree diet. Mice on the lipidfree diet lost 19% of body weight compared to a 2.3% loss on the normal diet.
- Interestingly, in experiment R mice that got a lipid-free diet supplemented with cholesterol had a higher tumor weight than both normal and lipid-free eaters (5/5 mice with tumors, mean tumor weight 0.74g). In experiment B, the cancer-increasing effect of cholesterol was less pronounced (10/15 mice with tumors, 0.6g mean weight). Any conclusions from that are limited as the level of cholesterol in the mice diet was very high (approx. 10%).
- In the summary of all experiments (205 mice total), mean tumor weight on the normal diet was 6.1g and on the lipidfree diet it was 2g (~65% reduction). Unfortunately, they didnt report absolute tumor numbers in this summary. On average mice lost 13% body weight on the lipidfree diet and gained 1.3% on the normal diet.
- At last, mice on the lipid-free diet (even without getting injected with cancer) had a increased mortality and died already after around 3 weeks. On the next morning, those mice were found without brains, as it was eaten by their "lipidhungry comrade".
