While making my bone broth, I was watching a video on Youtube (actually it was about how to make Water Kefir) by some gal who have made a few videos about water kefir and then decided to go raw vegan. I was curious and checked out a couple more of her videos.
So in one of her videos she was telling a horrifying story how her husband and herself went to her mom's for dinner. Both her husband and herself are raw vegans. However, her mother prepared fish (salmon) that night. Everybody ate it and was fine except for them. They ate it too, but the same night both her husband and her got so sick that they had to go to ER.
Her conclusion is that there are toxins in fish and her wonderful raw vegan diet helped them to get rid of all the toxins so now they feel sick every time they eat something with toxins.
I know, it is a very lame explanation. However, her story got me thinking. Both her husband and her stopped eating fish and now they are fish-intolerant (okay, I know it is a made-up word but still).
Many people who give up grains (like me) become grain intolerant.
Tons of people who give up dairy become dairy-intolerant.
One of the ways to explain it is that our bodies stop making some essential enzymes to break down the food we no longer eat. But that does not happen to all foods, only some foods.
Some people who quit smoking become nicotine (whatever) intolerant.
I see a pattern. However, I gave up all fruit for three months and I did not become fruit intolerant. On the contrary, my body was screaming with happiness when I finally caved in and had a banana. Or rather a whole bunch of bananas.
Anyway, my question is this: why does this happen? What are the mechanics of it and why is it so selective - some things you become intolerant to and some you don't.
I hope I am making sense.
I am a microbiologist, and I would say the main reason is because diet drastically influences the types and quantitites of bacteria in our guts. Bacteria and fungi are fabulous at breaking down plant matter...all other organisms (including humans) are not.
While humans are quite good at breaking down protein on our own (we produce protein degrading enzymes in our stomachs), we pretty much suck at breaking down plant matter. Actually all mammals do. Ruminants (cows, horses, deer, etc.) and rabbits have huge, unique digestive tracts designed specifically to cultivate gut bacteria...because it's their gut bacteria, not the ruminant itself, that breaks down the plant matter. Even insects like termites suck at breaking down plant matter...it's their gut bacteria that do it.
So again, keep in mind that bacteria are responsible for breaking down the VAST MAJORITY of plant matter. Scientists still struggle to find ways to break down cellulose without using bacteria and fungi.
So if you eat a lot of plant matter, studies show that not only are you healthier (less likely to be obese and have health problems), but that you have different types and quantities of gut bacteria than people who eat a lot of processed food (grains, dairy, salt, refined oils and sugars). Like the ruminant, you cultivate/select for bacteria designed to break down plant matter.
Thus, if you go back to processed food, when your gut bacteria is designed for plant matter, you will experience digestion problems. And vice-versa. I know sooo many people who eat all processed/refined foods and then get bloated if they eat plant matter...and it's because they haven't cultivated the right bacteria through proper, natural diet. Unprocessed meat, fruits, and veggies are the way to go.
As far as those vegan people...they are idiots. Humans are omnivores. My guess is that they starved themselves of important animal-derived nutrients by eating only plant matter. Then, when they ate a rich and healthy animal product, it was a shock to both their malnourished bodies and gut bacteria.
As far as intolerance to food goes, your body needs a constellation of enzymes (and other biological compounds) to process foods. Different foods require different enzymes, and your body regulates the amount you produce based on what food you eat. In some cases, when you stop eating a type of food for a long time, your body down-regulates the enzymes so much that you won't be able to process them. In this case, the vegetarians lacked the levels of enzymes necessary to break down the fish, leading to a host of digestive issues.
I don't know why this effect is more pronounced for some foods than others. I'm sure it's biological. (I'm good at tautologies.)
Regarding the argument that toxins in the fish are to blame, they probably are... but there are toxins in plants, too (cough gluten cough). Your body also regulates the process of toxin disposal, and there are toxins that are somewhat unique to seafood that they might not have been able to process.
That being said, their experience is no legitimate argument against the general consumption of seafood. It is, however, an argument for the existence of confirmation bias.
The body is an amazing thing. It finds ways to get to homeostasis no matter what you give it. Whether that is fuel or toxins or exercise, once it is sure it will have readily available source it will find a way to get back to homeostasis.
I switched from SAD to Primal style of eating I was sick for two weeks. My body was craving carbs and sugar. Then my body started to accept its new way of eating. And became healthier than before. If I were to go back I would likely go through a similar transition.
I have experienced weird food intolerances a few times in the past with dietary changes. I had gone gluten free a few times in the past when on a low carb diet, and when I would come back to SAD eventually (young and dumb!) I would get hives and other weird reactions when I started eating wheat again, and would get crazy sugar high rushes and crashes, but I would "eat my way through it" and eventually I could eat it with no problems, maybe it was my body getting used to it again? I think fish would be a pretty big jump from a raw vegan, especially if it was a full portion. That is a pretty severely limited diet. I have a friend who has been vegetarian since she was 10 (peanut butter and jelly sandwich junk food type vegetarian) and she claims to get sick every time she tries to eat meat. She has been able to add chicken and fish but is so afraid of beef and lamb. It is pretty crazy how adaptable the human body is and how it can adjust/not want to adjust to new changes.