Updated: Oct 30, 2018
There was a recent claim by William Cole, a Functional Medicine Practitioner, stating that the vegan diet “ruined” his life due to having a deficiency in many vitamins including vitamin A. I’m curious to know exactly what his diet consisted of because a healthy vegan diet full of various vegetables, fruits, beans, nuts, seeds, spices, etc. along with supplementation of certain vitamins such as vitamin B12 shouldn’t cause all the problems he claims he had. Also, I’m pretty sure the purpose of his whole claim was to try and sell a new diet he created. Moving on…
Vitamin A is an essential nutrient to our health. It is important for vision, immune function, skin health, and normal growth and development. Vitamin A can be found in animal products as retinol or in plants, fungi, and algae as a carotenoid. There are over 50 different carotenoids that the body can convert to vitamin A in the small intestine (and possibly elsewhere too). The most common one is beta-carotene (known as provitamin A). Consuming too much vitamin A in the retinol form (again from animal products) can be harmful to the body. However, there is no risk for over consumption of vitamin A in the beta carotene form because the body will only metabolize the amount it needs (1).
Studies show that vegans actually have the highest intake of beta carotene and obtain adequate amounts through food by having a selective diet (1). Approximately 10-90% of beta carotene can be absorbed from foods. The ability to absorb beta carotene depends on a few factors such as the food source, the processing, if a source of fat or fiber is present, or if there are other carotenoids present as well (1).
Among rich, plant-based sources of beta carotene, algae (spirulina specifically) has a higher bioavailability than fruits or vegetables (2). Cooking vegetables can make the beta carotene more bioavailable (from 18% to a 6-fold increase!). Eating a source of fat along with fruits and vegetables enhances the body’s ability to absorb beta carotene since beta carotene is converted to vitamin A, which is a fat soluble vitamin. An example is pairing avocados (healthy fat) with red peppers (high in beta carotene). The carotenoids lutein and canthaxanthin have been shown to reduce the bioavailability of beta carotene when simultaneously consumed together (3). Dietary fiber such as cellulose or wheat bran has been shown in some studies to increase the absorption of beta carotene. Another factor that could contribute to the body’s ability to absorb beta carotene is genetics. However, more research needs to be done to get the specifics (1).
Plant-based foods high in beta carotene:
All in all, the vegan diet provides enough vitamin A if the right foods are eaten and if other measurements are taken such as consuming healthy fats and cooking the vegetables to enhance the absorption of beta carotene. If you think you may be deficient in vitamin A or any other type of vitamin, or are interested in learning more about the vegan diet, you can set up an appointment to talk to Nichole Dandrea, a Registered Dietitian who specializes in it all!
1. Grune T, Lietz G, Palou A, et al. β-Carotene Is an Important Vitamin A Source for Humans. The Journal of Nutrition. 2010;140(12):2268S-2285S. doi:10.3945/jn.109.119024.
2. Wang J1, Wang Y, Wang Z, Li L, Qin J, Lai W, Fu Y, Suter PM, Russell RM, Grusak MA, Tang G, Yin S. Vitamin A equivalence of spirulina beta-carotene in Chinese adults as assessed by using a stable-isotope reference method. Am J Clin Nutr. 2008 Jun;87(6):1730-7.
3. Karin H. van het Hof, Clive E. West, Jan A. Weststrate, Joseph G.A.J. Hautvast; Dietary Factors That Affect the Bioavailability of Carotenoids, The Journal of Nutrition, Volume 130, Issue 3, 1 March 2000, Pages 503–506, https://doi.org/10.1093/jn/130.3.503
Casie Cuneio is currently in the Master of Science- Coordinated Program in Nutrition at Georgia State University. Casie is passionate about all things related to nutrition and cannot wait to obtain her registered dietitian's license to help others feel and look their best. Outside of studying nutrition, Casie enjoys exercising and hanging out with her pups!