Monday, 4 March 2013

How little vitamin A is enough?

There have been many discussions between me and the zero carb community as to how much vitamin A is needed to avoid deficiency, they maintain that fatty muscle meat has enough to prevent deficiency and that extra source such as egg yolks, dairy fat, or the dreaded liver aren't needed. I could not find data showing the amount of vitamin A in beef, most nutritional databases have is zero. But as promised I continued my search into why many do not seem to be becoming deficient in this nutrient...

In human tissue, there is some retinol (vitamin A) present in the fatty tissue, muscle, and heart: fatty tissue contains on average 1.46ug/gm, muscle 0.35ug/gm, and heart 1.08ug/gm [source, table 1 page 253]. Assuming beef is about the same (not condoning cannibalism here :P ), a diet of 500g lean muscle meat and 200g fat (for 100g protein and 200g fat, ~2000 calories ~80% from fat) would give us ~467ug of retinol (~1556.5IU).

The USDA RDA for vitamin A is 900ug or 3000IU, which is about double our calculations; assuming increased absorption from plenty of fat and lack of anti-nutrients, this may well be enough to prevent deficiency. The paper also investigates blood plasma retinol levels and concludes that 1,200ug retinol is needed to maintain a healthy blood level, and under 600ug a day is when eye changes start to occur [page 273-274]. Again assuming increased absorption on a carnivore diet, fatty muscle meat way well be enough to prevent deficiency, but may not be enough to maintain a more desirable blood level.

For comparison, the amount of vitamin A in our calculations above can be found in 55g of cheese or 20g of butter or two eggs. So adding any of these to your diet would mean you reach the USDA RDA. To get the 1,200ug retinol that the article recommends you need to eat ~5,100 calories of meat, or just 2,000 calories of meat plus 15g of beef liver a day (or 10g lamb liver).

A whole cow will generally give 442lbs of bonless meat, 27lbs shanks/oxtail, 6lbs liver, 2lbs heart, and 2lbs tongue. This means that eating the whole animal you'd eat a pound of liver every 40 days if eating 2lbs. This is roughly similar to the Bear eating liver once a month. The cheese in his diet would have also provided some vitamin A/retinol. As I don't have the exact make up of his diet (other than him mentioning eating liver about once a month) I can't work out exactly how much vitamin A he was getting over the years but he was roughly eating liver in proportion to meat as found in a whole cow which is a very good strategy. A pound of beef liver every 40 days (~11g per day) gives us on average ~561ug retinol (~1876IU) a day, making the total in addition to the meat above 1,028ug (3,432.5IU) a day, above the USDA RDA and almost to the article's recommended 1,200ug retinol; so with some cheese we can easily reach this target.

A diet of meat, daily cheese, and liver every 40 days would quite likely be enough to even maintain optimal blood retinol levels, while a diet of just fatty muscle may be enough to just avoid deficiency.

So while fatty muscle meat may be enough to prevent deficiency, I still maintain that there is a difference between outright deficiency and optimum nutrition and will be sticking with the WAPF's recommendation for vitamin A in my carnivore RDA project, which is 10,000IU. This means including egg yolks, dairy fats, and of course occasionally the dreaded liver.