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Fatty acids in humans and great apes

  1. Aug 29, 2016 #1
    I've been researching several nutritional questions after changing to a plant-based diet and while I've been able to more or less nail down much of my uncertainty, there are a few things that I haven't been able to easily find out. One of these is the matter of Omega-3 fatty acids (FA) in the diet.

    From what I've read there is some ambivalence about the relative benefits of alpha-linolenic acid (ALA) whereas there is more robust evidence for the beneficial/protective roles of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in regard to chronic diseases such as cancer, insulin resistance and cardiovascular disease.

    For most people, the main Omega-3 FA obtained from diet is ALA. ALA can be converted to EPA and DHA however in humans the conversion rates seem pretty low, perhaps as low as 5%. This means that even people on a typical diet may be deficient in these longer chain FAs. People can effectively "supplement" their diet through consumption of oily fish which are high in DHA and EPA (which the fish source directly from sea plants). As far as I can tell, DHA and EPA are only available directly from sea plants and not from land plants and thus only ALA is obtained from plant sources in human diets.

    My question is not about these facts, it is more about the biology at work. As humans are members of the family Hominidae, I assume that at the broad level the nutritional requirements of humans and great apes are very similar. This raises the obvious question of how great apes derive their Omega-3 FAs. Presumably, they simply get ALA from diet and synthesise EPA and DHA from that (few apes go fishing as far as I know).

    What I am curious about is the conversion rates for great apes. Are they as low as for humans, or are they greater? More exactly, is there any research about nutritional efficiencies of great apes in terms of fatty acids and the comparative health effects?

    I suppose what I am getting at is that biologically and evolutionarily speaking, why should I be worried about chasing EPA and DHA supplementation on a plant-based diet when it seems that other members of Hominidae seem to be getting along just fine consuming foods that offer ALA only? After all, early humans wouldn't have been fishing cold water fish, and in fact a large percentage of the modern population wouldn't be eating these fish if we hadn't invented fishing trawlers and international supply chains...

    I have no particular view on this, it's just an obvious question that springs to mind that I haven't quickly found an answer to. Can anyone point me in the direction of research/info that might shed some light on this for me?
     
  2. jcsd
  3. Aug 29, 2016 #2

    jim mcnamara

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    Other folks have similar questions - http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3257695/ provides a little insight.

    Note that wild game and seafood ( as you noted) are cited as sources of omega-3 FA's. Since early man ate wild animals and fish there was no issue. Our development of agriculture has caused problems.

    This Uppsala Univ article answer your question, I think.
    http://www.uu.se/en/news/news-document/?id=1777&area=2,4,8,10,16&typ=artikel&lang=en

    The idea here is that early humans (the genetic line that became modern human) had mutations that allowed conversion of of plant-based oils to the FA required for supporting our large brains in times of Omega-3 FA scarcity, which other lineages (they claim Denisovans and Neanderthals) lacked.
     
  4. Aug 30, 2016 #3
    Thanks Jim, that NCBI reference is particularly valid. However, taken together those two linked references do add to my confusion somewhat.

    The Uppsala University article makes a case for a genetic adaptation in humans that enables enhanced synthesis of Omega-3 and -6 FAs from vegetable sources and they claim this as a key factor in human brain development. However they aren't citing just which Omega-3s. Given ALA is generally obtained from plant sources and it is EPA and DHA that we can synthesise from that, and DHA in particular that is implicated in brain development, I could assume that this is what they mean (ie an adaptation to facilitate "increased production" of DHA and EPA from plant sourced ALA).

    Yet other sources argue against the efficacy of that exact process in humans. For example in the NCBI reference, it states that "endogenous synthesis of DHA from ALA in humans is much lower and more limited than previously assumed". This is also reflected in this reference
    http://lipidworld.biomedcentral.com/articles/10.1186/1476-511X-8-33
    where it states that "The International Society for the Study of Fatty Acids and Lipids (ISSFAL) recently... concluded that the conversion of ALA to DHA is on the order of 1% in infants, and considerably lower in adults".

    From what sources I have uncovered, it seems agreed that EPA and DHA synthesis from ALA is extremely limited and in the order of 5-15% (or even lower as that ISSFAL statement suggests).

    So, what is Uppsala saying? That the adaptation improves our ability to obtain ALA from plant food, or that the adaptation improves our ability to obtain EPA and DHA from the ALA that we obtain from plant food?

    I note too that the NCBI reference talks about "modern humans (evolving) with a staple source of preformed docosahexaenoic acid (DHA) in the diet". This paper essentially argues that as synthesis of DHA in particular is very limited in humans, and yet the presence of sufficient DHA was critical to human brain development, it must have been consumption of preformed DHA that was a critical factor in our evolution. They posit that it was adoption of a diet richer in seafood around 200-300,000 years ago that made rapid brain development possible.

    So right there are two conflicting claims - on the one hand evolutionarily adaptive changes to enable improved derivation of N-3 PUFAs from vegetable sources thus supporting brain development, and on the other availability of preformed DHA from marine sources supporting brain development.

    I am inclined to take the Uppsala claims with a pinch of salt without a clearer idea of just what they are suggesting. Yet I am also left with a sense that the NCBI reference is aimed at advancing some kind of seafood diet hypothesis - that is, a diet rich in seafood was a critical factor in brain development in humans.

    So I seem to be left with the following:

    Human brain development (and modern metabolic demands for such large brains) requires greater availability of DHA for humans when compared to other apes.
    EPA and DHA synthesis from the ALA precursor is very poor in humans which suggests that a human would require substantially more plant-based foods to obtain sufficient EPA and DHA when compared to other apes.
    Sufficient direct dietary sources of DHA in particular seem to be largely limited to marine sources.

    That seems reasonable and answers my question regarding differences between us and other apes, but I am still left with the nagging uncertainty around marine sources of DHA. It's not obvious from my reading that significant levels of DHA are found in all sea animals. For example Wikipedia's entry for DHA states that "most of the DHA in fish and multi-cellular organisms with access to cold-water oceanic foods originates from photosynthetic and heterotrophic microalgae", which kind of implies that high DHA levels are more likely to be found in cold-water, oily fish. I'm not sure how that squares with the NCBI reference arguing for consumption of seashore and freshwater marine animals as being a primary source of DHA in the past. Perhaps there is enough DHA in the typical seafoods eaten by ancient peoples, which to my mind would be more likely to be shellfish etc...
     
  5. Aug 30, 2016 #4
    Just a quick update on that last comment of mine, I've just spent some time looking up 22:6 n-3 and 20:5 n3 presence in a range of sea animals including such things as oysters, crabs and trout and it looks like these are present in nutritionally sufficient quantities, so perhaps it is possible to get enough direct DHA simply through eating crabs, molluscs and fish even in relatively small quantities. I note that according to the nutritional database I used, DHA is not especially available in things like beef, pork and chicken...

    http://nutritiondata.self.com/foods-015000000000000000000-1.html?

    That said, the NCBI reference above notes that in a 2005 study "Dietary intake and status of n-3 polyunsaturated fatty acids in a population of fish-eating and non-fish-eating meat-eaters, vegetarians, and vegans and the product-precursor ratio [corrected] of α-linolenic acid to long-chain n-3 polyunsaturated fatty acids: results from the EPIC-Norfolk cohort.", it was found that conversion rates from ALA to DHA in vegans were increased over fish and meat eaters. "Thus the precursor/product ratio in vegans was twice that of fish-eaters. This finding suggests basal conversions from ALA to DHA that may be up-regulated by the absence of-and down-regulated by the presence of-dietary preformed DHA."

    Interesting.

    As an aside and of interest to me, if we consider that this may lead to conversion rates for ALA to DHA in the order of 3-5% for vegans, a single tablespoon of flaxseed oil delivers around 7000mg of ALA and thus could produce an acceptable daily intake of DHA.
     
  6. Aug 30, 2016 #5

    jim mcnamara

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    There is an oops in your reasoning. Wild game, for example, has DHA, so does grass-fed beef. So focusing on marine FA sources is too limiting, IMO.

    Grass fed beef:
    https://nutritionj.biomedcentral.com/articles/10.1186/1475-2891-9-10

    Wild venison has low fat by modern standards for meat grading:
    https://ndb.nal.usda.gov/ndb/foods/...&qlookup=&offset=&format=Full&new=&measureby=
    Note 2.6% lipids by weight.

    Abstract only:
    http://www.sciencedirect.com/science/article/pii/S0309174097001447

    For comparison
    Commercial chicken white meat has ~4% lipids, which is considered low and is recommended for people with cardiovascular disease.

    Detrimental fat profiles, like you mention in beef, develop during finishing. The idea in finishing beef is to have the livestock gain substantial weight over a period of say 6 weeks. High calorie, grain based feeds give the best results in terms of weight gain.

    Do a google scholar search for 'DHA in wild game' if you want. Use google scholar or you will be unindated with garbage. In fact this is true for most nutrition related searches. I get pill pusher websites when I forget or am too lazy.

    The assumption that the only good DHA and EPA source is marine may not be good. Unless of course you do not eat beef, lamb, or mutton. So it is not clear to me how we got here in the first place. I always have thought that vegetarians generally did not eat fish, oysters, etc. There is a broad range in how people define themselves as vegetarian, vegan, and so on. And of course it is up to them, not me. But, nonetheless, I'm confused. Help me out here.
     
  7. Aug 30, 2016 #6

    jim mcnamara

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    One other point - AFAIK there is no exact consensus about what a recommended daily allowance of the FA's in question should be. The amount is not mind boggling, BTW, circa 1g per day.

    One site has a sort of "average":
    This is not overly scientific, as I've seen values published by Australia that are more than double.
     
  8. Aug 30, 2016 #7
    Thanks for the further comments Jim. I gather you are asking exactly what my interest is and in what context? As I mentioned, I have recently chosen to pursue a plant-based diet. I suppose if I were to label that, I would say I am an ethical vegan. Naturally given that in Western countries the food industry is geared around meat and dairy, it is apparently harder to get adequate nutrition on a diet that excludes these foods.

    I think with vegetarians there are a few different kinds, for example those that don't eat meat but will eat eggs etc. Vegans are stricter in that they tend not to eat anything derived from animal origins. In my view, veganism is only an option in societies which can actually exercise that option - for example hunter/gatherer societies and those in some nations are limited in what choices they can make. In my case, I can exercise that choice and it's on an ethical basis.

    However in doing this I've found there are a few questions around getting the right nutrition and fatty acids is one of them - in my reading I've found it hard to get a clear sense of what the best strategy is. I have no great knowledge of the science of nutrition so I've been trying to get to the bottom of the whole Omega-3 and 6 thing. Various websites argue different things so I wanted to better understand just what is being said. That is, get a better handle on what the actual science says from a biological/nutritional perspective rather than the often vague or inconsistent statements on websites.

    Of course I am sure that at a deep technical level it is all far more complex than my superficial take on it here, but I think for my purposes a sound understanding of the basics is sufficient. On a plant-based diet, it seems pretty clear that one can get plenty of the ALA precursor to EPA and DHA. But there are always these warnings about EPA and DHA and conflicting views about that. In trying to get a better handle on it, the obvious question for me was how on earth are all the other mammals, especially apes, getting adequate nutritional FAs if they aren't out there catching fish or using supplements.

    Thanks to your references I gather that our greater need for DHA in particular is due to our larger and more energy intensive brain (though I'd love to see the evidence for that, I think I'll do some more digging). But what I am also noting is that it is DHA that is the real issue. And as far as I can tell from those sources I've found, the only way to get enough preformed DHA in the diet is via marine animals or supplements (or from certain marine plants), unless one eats a lot of plants high enough in ALA to convert down to the RDA of EPA and DHA.

    I'm not sure about the idea that beef and wild game etc are good enough sources of DHA. But I have no idea how I'd be certain about that. And because I am just skimming over a lot of science without the actual technical understanding, I'm not even sure I am not completely misunderstanding it all.

    Take venison as an example. According to this data, the actual FAs in 100g of roast venison is 27mg of n-3 and 76mg of n-6. The n-3 breaks down to 28mg of ALA and no DHA or EPA at all.

    http://nutritiondata.self.com/facts/lamb-veal-and-game-products/4816/2

    Or take a decent sirloin steak at 300g. This offers up 920mg of n-3, but again it's all ALA with no EPA or DHA at all, if I am reading things properly.

    http://nutritiondata.self.com/facts/beef-products/3796/2

    So if the larger proportion of n-3 FAs in animal muscle meat is really ALA, we are back with the same problem of low conversion to DHA that characterises plant-based foods. That Science Direct abstract you link to doesn't really shed any more light on things as it seems to be suggesting that grain fed animals deliver high n-6 FAs. I didn't get a sense from this abstract that the authors are suggesting any significant levels of EPA/DHA in any case. But this is where my understanding is limited and it's not clear to me why these articles seem to slip between being specific, and more general.

    Or take the Nutrition Journal link. In their Table 1 they offer the FA profile of various grain/grass fed cattle and again it's not obvious to me there is any direct EPA or DHA in those profiles. Do I assume that regardless of food source for the animals, we are still in the situation that we have to convert some other FA to EPA and DHA?

    What I am getting at is that as far as my naive take goes, it looks to me like we can only get nutritionally significant direct EPA and DHA from marine sources. Otherwise, regardless of whether we eat land plants or animals, we are getting ALA and then have to convert to EPA and DHA and that the conversion rate to DHA in particular is extremely poor.
     
    Last edited: Aug 31, 2016
  9. Sep 1, 2016 #8
    Jim, thanks so much for you help on this one. Your references were excellent and I've tracked down the original paper from the Uppsala Uni team, which adds yet more dimension to the question. I think I am much happier with my overall understanding now. I'll have to see if I can find out how well their proposal has been accepted.

    http://www.cell.com/ajhg/fulltext/S0002-9297(12)00158-9
     
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