Following ill-informed nutritionists and textbooks, vegetarians commonly claim that people can get all the vitamins they need from plants. They say that humans can get all the vitamin A they need from vegetables and fruits high in beta-carotene.
In The Garden of Eating, I pointed to research that indicated that at least 45 percent of adult men and women do not efficiently convert carotenes to vitamin A (retinol), making dietary retinol, found only in animal products, an essential nutrient for these folks [1, 2].
A new study published in the Federation of American Societies for Experimental Biology Journal has confirmed this. Quoting the UPI report:
"Researchers at Newcastle University in England, led by Dr. Georg Lietz, found 47 percent of volunteer group of 62 women carried a genetic variation that prevented their bodies from effectively converting beta-carotene into vitamin A."
This clearly indicates again that at least 47 percent of women have bodies adapted to animal-derived nutrition. It means that their ancestors ingested animal-source retinol so frequently that the diet selected against preservation of the genetic equipment necessary for producing the enzymes that convert carotenes to vitamin A.
If you do a search on PubMed, you will find also that a growing body of research shows that even among people who do convert carotenes to retinol, the conversion occurs inefficiently and rarely suffices to meet vitamin A requirements.
Notes:
1. Lin Y, Dueker SR, Burri BJ, Neidlinger TR, Clifford AJ. Variability of the conversion of beta-carotene to vitamin A in women measured by using a double-tracer study design. Am J Clin Nutr 2000 June;71(6):1545-54.
2. Hickenbottom SJ, Follett JR, Lin Y, Dueker SR, Burri BJ, Neidlinger TR, Clifford AJ. Variability in conversion of beta-carotene to vitamin A in men as measured by using a double-tracer study design. Am J Clin Nutr 2002 May;75(5):900-7.
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