Hi Dr. Cordain,
I read your book “The Paleo Diet” several years ago and on page 122 you mention that “Canning also increases the level of oxidized cholesterol in fish, specifically increasing a molecule called 25 hydroxycholesterol that is extremely destructive to the linings of arterial blood vessels. This is so destructive, in fact, that oxidized cholesterol is routinely fed to laboratory animals to accelerate the artery-clogging atherosclerotic process in order to test theories of heart disease. In animal models of atherosclerosis and heart disease, only 0.3 % of the total ingested cholesterol needs to be in the form of oxidized cholesterol to cause premature damage to arterial linings.
Many health-conscious people eat canned fish for the supposed health benefits and are not aware of the book’s claims. Also noticed you only mention canned tuna but no other species of fish.
Is consuming canned fish really a serious danger to people’s arterial blood vessels and should we avoid eating these products? Appreciate if you could refer me to research studies that confirm the above and if you aware of any recent studies?
Your thoughts are appreciated and I look forward to your reply.
Dr. Cordain’s Response:
Good to hear from you and good question. The bottom line is that we should steer clear from oxidized cholesterol derived from any and all foods in our diet (see references 1-9). Clearly it is an impossible task to completely remove oxidized cholesterol from our diets, given that we are no longer hunter gatherers and that we enjoy cooked meats and fish in 21st century contemporary “Paleo Diets”. In references (10-21) you can see how the canning, smoking and preservation process of fish dilutes its nutritional characteristics and increases the production of oxidized cholesterol which is frequently referred to as oxysterols.
So, I recommend to reduce oxidized cholesterol in your diet. Try to eat meat, fish, poultry and eggs that have been slowly cooked under low heat like steaming, slow cooking crock pots, low heat baking, poaching, and other low temperature cooking techniques, including microwave. Try to avoid foods that have been cooked under high temperatures like frying, broiling, high temperature barbecuing, and searing. Additionally, canned meats and fish are almost always cooked at high heats to prevent botulism, which increases their oxidized cholesterol content. Clearly, canned tuna contains many healthful elements (high protein, high omega 3 long chain fatty acids) and should be part of contemporary Paleo Diets, but fresh tuna and fish is a better option if it is available and you can afford it.
Loren Cordain, Ph.D., Professor
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