Home / G. Health and nutrition / Part IND
"Only fish provides omega-3."
fish produce little long-chain omega-3 (EPA and DHA): most of it comes from the algae at the base of the marine food chain, which fish eat directly or indirectly. Algal oil supplements provide the same DHA at the source, without the fish. And short-chain omega-3 (ALA) is found in flaxseed, chia and walnuts.
Short answer
Fish make little omega-3: most of it comes from algae, directly or indirectly. Algal oil supplements provide the same DHA, straight from the source. Flaxseed, chia and walnuts provide ALA, another type of omega-3. Fish are middlemen, and they bring risks such as mercury and other contaminants with them. The need is for omega-3, not for fish.
For children
Omega-3 is a fat that's good for the brain. Fish have omega-3 because they eat algae, tiny sea plants that make this fat. We can get omega-3 straight from algae, without needing the fish. And there's omega-3 in flaxseed, chia and walnuts too.
"If the omega-3 in fish comes from algae, why not go straight to the source?"
Como pode aparecer
"You have to eat fish twice a week."
"Flaxseed doesn't give you DHA."
"Only fish provides omega-3."
"Vegans will have brain problems without fish."
"Conversion of ALA to DHA is inefficient."
"Sustainable fishing and aquaculture solve it." (which is H10)
The strongest version
"You have to eat fish twice a week. Flaxseed doesn't give you DHA."
Strongest version (steelman):
- P1Long-chain omega-3 (EPA and DHA) is important for the heart, brain and eyes.
- P2Common plants provide only ALA, which the body converts to EPA and DHA in small proportions.
- P3Oily fish are the main dietary source of EPA and DHA.
- CSo you have to eat fish to get adequate omega-3.
P1, P2 and P3 are true. The problem lies in the conclusion: the EPA and DHA in fish come from algae, which can be consumed directly as a supplement.
The argument is valid. Its soundness fails because it ignores the original source of omega-3.
Full answer
- a
Reconstruction and diagnosis
The argument ignores where omega-3 comes from:
Type of omega-3 Who produces it Where to find it ALA (short chain) Plants Flaxseed, chia, walnuts, canola oil EPA and DHA (long chain) Marine algae Algae, algal oil supplements; fish, who accumulate them - b
Where the argument breaks
1. Algae are the source.
The EPA and DHA in fish come from the microalgae at the base of the marine food chain. Farmed fish are often given fish oil or algal oil in their feed.
2. Algal oil provides DHA directly.
Algal oil supplements are a vegan source of EPA and DHA, recognized by the US National Institutes of Health.
3. ALA is in common plants.
Flaxseed, chia and walnuts provide ALA. Conversion to DHA is limited, which is why many dietitians recommend an algal supplement on vegan diets.
4. Fish carry contaminants.
Fish can accumulate mercury and other pollutants. Microalgae grown in tanks for supplements are kept away from that contamination.
5. The recommendation is for omega-3, not fish.
Advice to eat fish exists because it's a common source, not because it's the only one.
- c
Data and sources
Source What it says Note NIH, omega-3, fact sheet for health professionals EPA and DHA come from fish and algal oil; ALA comes from flaxseed, chia, walnuts and plant oils Official fact sheet of the US National Institutes of Health Academy of Nutrition and Dietetics, 2016 Well-planned vegan diets are adequate; mentions microalgae as a source of DHA Official position - d
The strongest counter-reply: supplements aren't the same as food
The most serious version grants that algal oil provides DHA, but says eating fish also brings other nutrients, and that there are more studies on fish than on algal supplements.
- e
Why the counter-reply doesn't reach the conclusion
The other nutrients in fish are in other sources.
Protein, iodine and vitamin D can be obtained in vegan ways.
DHA is the same molecule.
The body doesn't distinguish its origin.
Fishing has enormous costs.
An estimated 0.8 to 2.3 trillion fish are caught each year, and fishing damages the oceans (H10).
Trials of supplements have mixed results.
That applies to fish oil as much as to algal oil; the argument doesn't favor fish.
- f
Back to the moral question
If omega-3 can be obtained straight from algae, the need to fish disappears. And fish, according to current science, are sentient beings (A6). The question becomes moral again: what justifies killing fish to obtain something algae provide directly?
Reasoning errors
Logical
Is the form valid?
Confusing nutrient and source
Epistemological
Does the evidence support it?
Not knowing the food chain
Moral
Is the criterion coherent?
Invented necessity
Biases
Extrapolations
The principle being tested is: "if an animal accumulates a nutrient, we need to eat that animal".
If it applied to…Vitamin B12Tap to see
We'd need meat, even though B12 comes from bacteria
This is the argument of G3
If it applied to…CalciumTap to see
We'd need milk, even though calcium comes from the soil
This is the argument of G5
If it applied to…Omega-3Tap to see
We'd need fish, even though it comes from algae
The pattern repeats
Contradictions
Many people take fish oil capsules, which are also supplements.
Most people who use the argument don't follow the recommendation.
And mercury is found precisely in fish.
What the argument gets right
What is true
Long-chain omega-3 is important, and it's true that conversion from common plant sources is limited. Vegans should consider a source of DHA, such as algal oil, and it's good to say so clearly.
But
But fish are middlemen. The source is algae, and it's available directly, without fishing and without contaminants.
Connections
Usually comes before
Usually comes after