Dry Eye and Fish Consumption

Let’s say that dry eye is caused by lack of omega-3. If you eat enough omega-3, you’ll never get it. Here is a recently-discovered association with tuna consumption:

Tuna consumption [1 serving was 113 g (4 oz)] was inversely associated with DES [Dry Eye Syndrome] (OR: 0.81; 95% CI: 0.66, 0.99 for 2–4 servings/wk; OR: 0.32; 95% CI: 0.13, 0.79 for 5–6 servings/wk versus =< 1/wk P for trend = 0.005).

If tuna were a good source of omega-3, eating 5-6 servings per week would completely prevent dry eye. But it doesn’t. Which supports what I have come to believe for other reasons: oily fish, in the quantities most people eat it, is a mediocre source of omega-3. Even if you eat tuna almost once/day, you don’t get enough. To get enough omega-3, look elsewhere.

Thanks to Brent Pottenger.

17 Replies to “Dry Eye and Fish Consumption”

  1. Omega-3 and Omega-6 compete for the same receptors in the body and thus displace each other. So your Omega-3 needs are related to how much Omega-6 you need to offset, a rather confounding variable.

  2. It might be more meaningful to compare the fish that is always recommended; salmon. There’s a reason it’s so popular; a 154g serving of chinook has 3301 mg of omega-3 to only 433 mg for an equivalent serving of tuna. So a person eating one serving of salmon would be getting more omega-3 from fish than the highest six servings of tuna a week.

  3. If this is an evolved human dietary need we’re talking about and not a cross-species universal elixir of life, what the hell way of life did cavemen have where they could eat all this salmon every week? Are humans actually river-fishing/shellfish-harvesting specialists rather than the generalists we’re usually assumed to be?

    I do usually keep a tub of cod liver oil around, but I still have doubts. I mean, cows live on grass – they are large complex mammals like us. There was a guy in the UK, Dave Nunley, who had an extreme food-phobia and could only eat mild cheddar cheese. That was all he ate until the age of 29. He led an active life and seemed healthy.

    I’ve heard tantalising study results about this and that food-item over the years, but from the wide-angle view it doesn’t make sense to me that we have such finnicky, specific needs. Hunter-gatherers eat special items once in a blue moon, ‘medicinally’; they don’t on a weekly basis consume kilos of what we now think of as ‘superfoods’. I’m generalising but you get my drift.

  4. Hal, my point about cows eating nothing but grass was more general than the question of how much omega-3 they get. Dogs live on low-grade meat and here we are saying that tuna doesn’t have enough omega-3 for our purposes. Why do we need so much? I am suggesting that maybe we are making insignificant tweaks to a system that is normally broadly robust.

    I suppose I would like to believe that I would live an extra ten or twenty years in good health by eating berries and salmon more than normal, but I’m not sure it’s an efficient cause. I don’t believe or disbelieve.

    I feel like an absurd picture builds up once someone delves further and further into a narrow interest – they come to think their specialism is all-important – the people who think ascorbate is the Elixir of Life say we should eat oranges every day and the omega-3 people worry about where their yellowfin tuna comes from and whether their beef is grass-fed. It seems like fussy mircomanagment in a broadly uncertain world, to me.

    Either humans have evolved with this crazy dietary requirement (that, by the way, if you’re at all concerned, is not ecologically sustainable at current population-levels) or omega-3 really is some kind of cross-species universal elixir.

  5. Flax oil is the best source of omega three. Unfortunately, like fish, it deteriorates rapidly. All sources of omega three deteriorate rapidly, and the better they are, the faster they deteriorate. So fish oil tablets are not necessarily doing you any good. So the solution is to take flax seeds, since seeds will preserve their oil as long as the seed remains alive – but does anyone have any satisfactory method of preparing flax seeds into something edible and digestible?

  6. If this is an evolved human dietary need we’re talking about and not a cross-species universal elixir of life, what the hell way of life did cavemen have where they could eat all this salmon every week?

    Cavemen lived largely on deer and suchlike – which have a lot more omega three than cows and suchlike.

  7. G, as I understand the theory, if you eat animals that graze on grass (as humans did in the past), you get a rough balance of omega-3 and 6. However corn is almost all omega-6 (as far as poly fats). I’m not sure if this is specific to corn or if it’s because corn is all seeds. Anyway, our diet today is very much biased towards omega-6, we eat 10 or even 20 times as much 6 as 3. Now omega-6 is pro-inflammatory and omega-3 is anti. Many of the modern diseases are associated with excess inflammation, such as atherosclerosis. Again the theory is that this may be linked to excess consumption of pro-inflammatory omega-6 and not enough omega-3.

    It’s not that omega-3 is an elixir, it’s that we evolved with a certain balance in our diet, and with factory farming, this balance has changed very drastically. Theoretically, if you switched your diet to eat 10 times as much omega-3 as omega-6, that would be just as unhealthy, because you’d have too little inflammatory response and might be vulnerable to infection or other failures of the body to repair itself.

    The point of omega-3 supplementation (and reducing omega-6 consumption) is to get back to the historical balance and hopefully help the body achieve a healthy level of inflammatory response. However I doubt you would extend lifespan by 20 years because most of these diseases hit late in life, and we have medical treatments for them anyway. Still I’d think you could hope for a few years more of health.

  8. So Hal, how definitive is the proof for this? I haven’t a clue. It just sounds too simple and elegant – the whole 3/6 fat-balance balance thing. Maybe it is!

  9. Last time I went to the supermarket I compared the Omega 3 content of a can of tuna and sardines. I was surprised to see tuna contains much less than sardines (in % to weight). I bought sardines.

  10. Although flawed (as in imperfect, not unacceptable), read The Queen of Fats for a rather well-researched account of the discovery of n-3 fats (by Susan Allport). If someone knows of a better account (in one place, not in scattered articles), please post it.

    I wonder if one issue with self-experimentation is when people don’t try enough. I have greatly reduced my allergies through high probiotic/bacteria intake (yogurt, kimchi, doenjang), but one of my friends who wanted to try it balked at eating 2c of yogurt/day and making these changes. Adding one dollop of yogurt likely would not be enough to see changes. Likewise, eating small amounts of fish and thinking you have changed your n-3 consumption (or the overall n-3/n-6 balance) may not be enough, but may be all some people are willing to try.

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