The old meat vs. no meat debate. One of the biggest topics of controversy in nutrition today. While some claim a plant based diet healed them from disease, others have to go against cultural or ethical views by reintroducing animal products, as they feel they can’t function as a normal human without them. I have seen this enormous variance in clinic a lot. For many this can be absolutely mind boggling. How can one person bounce off the walls when omitting animal products, however when you try, you’re a walking corpse?!
Luckily for us all, science is starting to uncover the injustice of it all, and it appears that our genes are responsible.
It is no secret that omega 3 fatty acids are great for health. However, their origin can be quite important. Plant sources of omega 3’s are enriched in ALA (think flaxseeds and walnuts). In order for this form to be used by the body it must be converted to DHA and EPA. This is in contrast to omega 3 fatty acids from fish and other animal sources which come enriched in EPA and DHA and therefore do not have to undergo the complex conversion steps.
Science is now uncovering that the ability of the body to convert plant based omega 3’s to DHA or EPA could depend on your genetics. It is thought that individuals who have descended from populations that consumed a lot of fish may not be as efficient at converting the plant based version (as they haven’t needed to) as individuals who didn’t (1). Thereby if you are one who doesn’t convert ALA to DHA and EPA very well you may be at risk of not getting enough Omega 3 fatty acids from plant sources alone.
Vitamin A is an incredible important vitamin. It supports normal growth and development, reproductive function, vision and the immune system(2), just to name a few. Now the funny thing about this crucial vitamin is that plant foods don’t contain the active form of vitamin A (retinol) whilst animal sources do. Plant-based foods contain Vitamin A precursor (beta-carotene) which needs to be converted by BCMO1 in the liver and intestine in order to be used by the body.
Now several gene mutations can inhibit this enzyme and therefore make the individual unable to get vitamin A from plant based sources. An example is two polymorphisms in the BCMO1 gene that can reduce beta-carotene conversion by 69%(3). It has been estimated that a staggering 45% of the population could have low plant based beta-carotene conversion due to their genetic makeup(4).
Amylase and starch tolerance
I have touched on individual carbohydrate tolerance in a previous blog post so I will keep this brief.
However in a nutshell, scientists have discovered that there may be some variation in whether someone can thrive on a high carbohydrate diet whilst overs cannot (we are looking at your annoying friend who downs French fries and pizza like there’s no tomorrow and looks like a Victoria’s secret model).. This could be due to a variation in their AMY1 gene. The AMY1 gene is responsible for salivary amylase, an enzyme that breaks down starch in the mouth. For those with the low amylase producing gene, an increased starch intake could mean poor sugar regulation and weight gain(5), not ideal!
Why does this relate to vegans or vegetarians you ask? Because with the small exception, plant-based diets tend to be higher in carbohydrates than omnivorous ones(6). This is due to these individuals often having to rely on high carbohydrate foods such as chickpeas and lentils in order to get their protein. This is absolutely fine if you have a lot of amylase in your saliva, but for those who don’t, it can have large consequences.
Choline is an essential nutrient for metabolism, the brain and methylation just to name a few (7). Most sources of choline are animal products such as egg yolks and liver with smaller amounts available from plant sources.
Now the good news is, our body can actually produce choline through phosphatidylethanolamine-N-methyltransferase (PEMT). In most people the small amounts of choline in plant foods, coupled with the body’s own mechanism to produce it, is more than enough to reach requirement(7).
But (and there’s always a but!) genetics plays a role in how much choline our body actually requires, and this varies greatly between individuals. Another factor is that oestrogen upregulates PEMT meaning post-menopausal women could have reduced choline production(8). Other mutations and polymorphisms can either increase choline requirements or downregulate production(9). Therefore, it can be concluded that variations in PEMT activity and individual choline requirements can determine whether someone is able to get sufficient choline from a vegan diet.
So what should you do?
The point of this post is not to put anyone off a plant based lifestyle, but more to highlight the fact that we are all different. What works for one, may not work for others. It also raises some important points so that if you do choose to omit animal products from your diet, there are certain things you may need to watch out for. Unfortunately there is not yet a reliable and affordable way to test our genetic make-up and know exactly what we should be eating, so in the meantime, listen to your body and it will most likely tell you everything you need to know!
1. Davis BC, Kris-Etherton PM. Achieving optimal essential fatty acid status in vegetarians: current knowledge and practical implications. Am J Clin Nutr. 2003;78(3 Suppl):640s-6s.
2. D’Ambrosio DN, Clugston RD, Blaner WS. Vitamin A Metabolism: An Update. Nutrients. 2011;3(1):63-103.
3. Leung WC, Hessel S, Meplan C, Flint J, Oberhauser V, Tourniaire F, et al. Two common single nucleotide polymorphisms in the gene encoding beta-carotene 15,15'-monoxygenase alter beta-carotene metabolism in female volunteers. FASEB journal : official publication of the Federation of American Societies for Experimental Biology. 2009;23(4):1041-53.
4. Lietz G, Oxley A, Leung W, Hesketh J. Single nucleotide polymorphisms upstream from the beta-carotene 15,15'-monoxygenase gene influence provitamin A conversion efficiency in female volunteers. The Journal of nutrition. 2012;142(1):161s-5s.
5. Falchi M, El-Sayed Moustafa JS, Takousis P, Pesce F, Bonnefond A, Andersson-Assarsson JC, et al. Low copy number of the salivary amylase gene predisposes to obesity. Nature genetics. 2014;46(5):492-7.
6. Janelle KC, Barr SI. Nutrient intakes and eating behavior scores of vegetarian and nonvegetarian women. Journal of the American Dietetic Association. 1995;95(2):180-6, 9, quiz 7-8.
7. Sanders LM, Zeisel SH. Choline: Dietary Requirements and Role in Brain Development. Nutrition today. 2007;42(4):181-6.
8. Fischer LM, da Costa K-A, Kwock L, Galanko J, Zeisel SH. Dietary choline requirements of women: effects of estrogen and genetic variation. The American Journal of Clinical Nutrition. 2010;92(5):1113-9.
9. da Costa K-A, Kozyreva OG, Song J, Galanko JA, Fischer LM, Zeisel SH. Common genetic polymorphisms affect the human requirement for the nutrient choline. The FASEB journal : official publication of the Federation of American Societies for Experimental Biology. 2006;20(9):1336-44.