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You only need about 4% of calories as fat to have adequate absorption of carotenes according to Bullock and Rosenthal's Pathophysiology text book.

I used to think that that AJCN study showed that 45% of people don't convert carotenes to vitamin A. However, when I read it more carefully, I noticed that 7 of 11 subjects had been taking retinol supplements before onset of the study, an average of 9300 IU daily, i.e. intake adequate to maintain high stores in individuals with low requirements. Also, the authors state:

"Starting on day 10 and throughout the remainder of the study, each subject received a vitamin A supplement of 1250 IU (375 RE, or 1.31 µmol as retinyl palmitate in cod liver oil) every other day at breakfast."

Giving people with previously adequate or even excessive intakes of vitamin A a regular dose of vitamin A virtually ensures that some will NOT respond to B-carotene by converting it to vitamin A since the body does the conversion on demand. For some people, 1250 IU preformed vitamin A every other day might be a sufficient intake to suppress conversion of B-carotene to retinol.

To test conversion of B-carotenes to A you should use people with history of very low to no intake of preformed vitamin A, and run the study with 0 intake of preformed vitamin A for the duration (to maximize the demand for carotene conversion), neither of which applies to this study. In other words, this study was almost by design destined to produce the outcome reported. It was poorly designed.

Again, I have been unable to find any medical report of even one case of a person eating a low fat diet, with adequate B-carotene from whole foods, but no preformed vitamin A, resulting in vitamin A deficiency.

Here's an example of a study on Filipino kids with low fat diets and whole foods rich in carotenes. With mimimal fat, only 7 g (6% of energy) per day, a diet rich in carotenes doubled vitamin A stores over a 9 week period.

http://www.ajcn.org/content/85/4/1041.long

This study fulfills my criteria: no previous intake of vitamin A supplements or preformed vitamin A from foods, and only 12 mcg dietary retinol daily (less than 3% of requirements) during the 9 weeks of the study. So, under conditions of very low fat intake and very low retinol intake, humans successfully convert carotenes to retinol enough to enlarge stores, even during growth and development periods of high demand for vitamin A.

July 7, 2011 8:16 PM

Sorry, in last comment I made a mistake. During the Filipino study I cited, on 5 days per week the preformed vitamin A intake was 82 mcg per day 5 days per week, and 141 mcg on the other 2 days. So on most days the intake of preformed retinol was 14% of requirements, and twice weekly it was 23% of requirements. In any case, these children had a demand for vitamin A that was met by carotenes with a very low fat intake.

July 7, 2011 8:27 PM

We have plenty of evidence that isolated Inuit had severe and early onset osteoporosis [4, 5].  Similar to the Pueblos, largely vegetarian Bantu women eating grain-based diets have extremely low rates of osteoporosis despite very low (200-450 mg/d) intakes of calcium and a high number of pregnancies (~10 per woman) with prolonged breastfeeding [6 ]. 

Muistaakseni jossakin vaiheessa kyselin, löytyykö juttua, jossa Don kertoo mikä meni pieleen vegeilyssä. Nyt blogin kommentteihin on linkitetty tuollainen vanha teksti:

Don's Diet Experience: Why I (Finally) Gave Up On Vegetarian Diets

Varsin kiinnostavaa, kun ottaa huomioon Donin nykyisen linjan... Sanoisinko, että ristiriitaisuus on melkoista. No, odotellaan Donin omaa selitystä, jos sellaista yleensä on luvassa.

No kato kun tuolloin Donilla oli confirmation bias. Nyt Don näkee asiat selvästi. 

Veikkaan, että vegaanina ollessaan Don on myös osannut perustella aukottomasti miksi veganismi on the only way to go ja kertonut myös loistavasti hän itse voi ollessaan vegaani. Vähän tulee mieleen erinäiset superfoodgurut.