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Comment by wackycat | Hacker News Reader

This is an interesting association and I am glad the authors took care to mention that more studies are needed to understand the cause of association. It feels like one where many people may want to infer causality - that the lack of meat causes depression but I would be curious as to the actual cause. My own guess as someone who doesn't eat meat is that if someone pays attention to things like animal rights or health or whatever is motivating their decision to avoid meat, they are also likely paying attention to the other issues in our world which, quite frankly, can be depressing.

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As a fellow vegetarian, this was my first thought as well.

I don't think this paper can be taken as sufficient evidence to rule out nutritional deficiencies that could contribute to mental health issues (e.g., decreased B vitamins, iron, vitamin D, tryptophan, etc). I know that when I diligently take these kinds of supplements, I do have more energy and sleep better. However, the "humans are destroying the world" sad feelings that drove me to stop eating meat persist, making me wonder if this is quite confounded relationship.

This also took place in Brazil, which is a country famous for its meat-heavy common diet. It seems probable that there are less diverse and available vegetarian options there (just speculation though)

Have to find the papers, but I know there's a connection between creatine and depression. As creatine would only be found in red meat, wouldn't be surprised if that would be atleast one if the factors.

Creatine is also found in seafood and plant-based sources as well. I don't know the exact concentrations though. Iron is really the big one when it comes to a meatless diet. You can't easily get enough iron from other sources without a supplement.

I've been vegetarian for most of my adult life now and have no clue where this myth comes from. If you eat the same amount of calories on a vegetarian diet you will almost surely hit your iron requirements, even if you are physically active. Lentils, tofu, chickpeas, spinach, beans all have more iron than beef on a gram-for-gram basis.

You have to switch it up sometimes to get all of the amino acids humans can't synthesize, but it's not exactly hard. Rice and beans (a staple in huge parts of the world) contains all of the essential amino acids you need and is a "complete" protein. There are many such examples.

There's nothing special about cows or pigs or chickens. Our bodies are so similar that we mostly use bacteria to digest meat, which is why you lose the ability to stomach it if you stop regularly eating flesh. It's also why we're looking at pigs for organ transplants.

The main supplements for vegans/vegetarians are omega-3s and B12. Both are available from plant sources, and the latter is given as a supplement in feed since animals only synthesize it on a grass-fed diet.

I didn't experience that in practice, and it seems that the difference is between heme and non-heme iron. Spinach has non-heme iron which isn't absorbed very well, and absorption makes a huge difference.

I did a quick search and found:

"Iron from food comes in two forms: heme and non-heme. Heme is found only in animal flesh like meat, poultry, and seafood. Non-heme iron is found in plant foods like whole grains, nuts, seeds, legumes, and leafy greens. Non-heme iron is also found in animal flesh (as animals consume plant foods with non-heme iron) and fortified foods."

https://www.hsph.harvard.edu/nutritionsource/iron/

I would advise not taking anyone seriously who advocates for an ideologically driven vegan diet and makes statements like "There's nothing special about cows or pigs or chickens. Our bodies are so similar that we mostly use bacteria to digest meat, which is why you lose the ability to stomach it if you stop regularly eating flesh."

Let's start with the fact that the human stomach acid pH which you can feel free to Google. It's nothing like the other animals he's talking about. Our stomach acid is extremely acidic due to our early evolutionary history as carnivorous carrion eaters. He also parrots another myth which is that once you are vegan you lose the ability to digest meat. My father has been vegan for 20 years and I was vegan for 5 and was able to digest meat right away with no issues when I went back to meat. It's a myth repeated by vegan ideologues and is completely unfounded in science.

Do I think someone can be very healthy on a vegan diet? Yes. But the last people you should ever listen to are vegan ideologues. They already have an answer in mind and do nothing but cherry pick facts to support their chosen answer.

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