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Senin, 20 April 2009
Cordain on Saturated Fat
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I recently signed up for Dr. Loren Cordain's Paleo Diet newsletter, and I just received my first update. For those of you who aren't familiar with him, Dr. Cordain is a researcher at Colorado State University who studies the effects of hunter-gatherer and modern diets on health. He's made a number of important contributions to our understanding of nutrition and health. He's in my "Nutrition Hall of Fame" on the right sidebar.
His update was about saturated fat. In the past, I've disagreed with Dr. Cordain on this issue, because I thought he felt that saturated fat contributes to the risk of heart attack (although he never described it as a dominant factor). He has recommended trimming the fat off meats and using canola oil rather than just eating the fat. I don't know if I had misunderstood his stance, or if he's had a change of heart, but his current position seems quite reasonable to me. Here are a few brief quotes:
The effect of a food on an animal's health has everything to do with what that animal is adapted to eating. Feeding a rabbit cholesterol gives it high blood cholesterol and atherosclerosis, but you can't give a dog high cholesterol or atherosclerosis by feeding it cholesterol, unless you kill its thyroid first. Feeding studies in Masai men showed that replacing their fatty, cholesterol-rich milk and blood diet with a cholesterol-free refined diet low in saturated fat caused their total cholesterol and body weight to increase rapidly. Adding purified cholesterol to the cholesterol-free diet did not affect their blood cholesterol concentration. Feeding cholesterol-rich eggs also has a negligible effect on blood cholesterol in most people.
I do still have a slight difference of opinion with Cordain on the saturated fat issue. While I think his numbers for pre-agricultural saturated fat intake are reasonable, his range is probably too narrow. Non-agricultural diets are so variable, I would expect the range to be more like 5 to 30% saturated fat. 5% would represent diets low in fat such as certain Australian Aboriginal diets, and 30% would represent the intake of Northern hunter-gatherers relying heavily on ruminants in fall and winter. During this time, ruminants store most of their fat subcutaneously, and their subcutaneous fat is roughly half saturated. Given that such a wide range of saturated fat intakes are part of our species' ecological niche, it follows that saturated fat is unlikely to be an important determinant of health in the context of an otherwise healthy lifestyle.
His update was about saturated fat. In the past, I've disagreed with Dr. Cordain on this issue, because I thought he felt that saturated fat contributes to the risk of heart attack (although he never described it as a dominant factor). He has recommended trimming the fat off meats and using canola oil rather than just eating the fat. I don't know if I had misunderstood his stance, or if he's had a change of heart, but his current position seems quite reasonable to me. Here are a few brief quotes:
By examining the amounts of saturated fats in pre-agricultural hominin diets, an evolutionary baseline can be established for the normal range and limits of saturated fats that would have conditioned the human genome. While these diets varied due to geography, climate, etc., there is evidence that all hominin species were omnivorous. Thus, dietary saturated fats would have always been present in hominin diets.And the conclusion:
There is also evidence that the hominin species that eventually led to Homo began to include more animal food in their diet approximately 2.6 million years ago. Clear evidence shows tool usage to butcher and disarticulate carcasses...
This data suggests that the normal dietary intake of saturated fatty acids that conditioned our species genome likely fell between 10 to 15% of total energy, and that values lower than 10% or higher than 15% would have been the exception.
Consequently, population-wide recommendations to lower dietary saturated fats below 10% to reduce the risk of CAD have little or no evolutionary foundation in pre-agricultural Homo sapiens... So we do not need to restrict ourselves to only tuna and turkey breast, avoiding every last gram of saturated fat.AMEN, brother. I'd like to point out that the average American eats about 11% of his calories as saturated fat (down from 13% in the 1970s), on the low side of what Cordain considers normal for Homo sapiens. This is from the NHANES nutrition surveys.
The effect of a food on an animal's health has everything to do with what that animal is adapted to eating. Feeding a rabbit cholesterol gives it high blood cholesterol and atherosclerosis, but you can't give a dog high cholesterol or atherosclerosis by feeding it cholesterol, unless you kill its thyroid first. Feeding studies in Masai men showed that replacing their fatty, cholesterol-rich milk and blood diet with a cholesterol-free refined diet low in saturated fat caused their total cholesterol and body weight to increase rapidly. Adding purified cholesterol to the cholesterol-free diet did not affect their blood cholesterol concentration. Feeding cholesterol-rich eggs also has a negligible effect on blood cholesterol in most people.
I do still have a slight difference of opinion with Cordain on the saturated fat issue. While I think his numbers for pre-agricultural saturated fat intake are reasonable, his range is probably too narrow. Non-agricultural diets are so variable, I would expect the range to be more like 5 to 30% saturated fat. 5% would represent diets low in fat such as certain Australian Aboriginal diets, and 30% would represent the intake of Northern hunter-gatherers relying heavily on ruminants in fall and winter. During this time, ruminants store most of their fat subcutaneously, and their subcutaneous fat is roughly half saturated. Given that such a wide range of saturated fat intakes are part of our species' ecological niche, it follows that saturated fat is unlikely to be an important determinant of health in the context of an otherwise healthy lifestyle.
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