Maybe just a quick recap what my rules are currently (knowing they will almost certainly change substantially again going forward):
*Avoid all animal products, maybe with the exception of occasional cheese
*Avoid all high-arsenic foods (esp. rice, but also apples, pears, grapes and in the US cremini/button/portobello mushrooms)
*Avoid foods high in oxalic acid (spinach, beet greens, rhubarb, chard, but also whole grains, quinoa, poppy seeds, sesame)
*Have a moderate intake of lysine (1.5-2.0 grams per day is probably ok)
*It's probably best to avoid all nightshades except a low amount of fresh or pureed tomatos occasionally
*Consume fruit in isolation, entire meal must be fruit only. Best fruit appear to be berries.
*Avoid all high-Omega 3 foods (hempseeds, linseeds, chia seeds, walnuts and their oils), but also moderately high foods like rapeseed oil. Limit low-omega 3 foods like olive oil and avocado. Use very low Omega 3 oils for cooking (high-oleic sunflower oil seems to be very good)
*Avoid all leafy greens
*Avoid allium (onions, spring onions, garlic) and brassica (cabbage family) foods.
*Let at least 5-6 hours elapse in between meals to avoid meal mixing in the stomach
*Limit carbs intake to 100g per meal (about 2 pounds of fruit, 150g of pasta, 200g of most legumes in one meal)
*Don't allow a prolonged calorie deficit, keep BMI around 22.
I also want to stress again that all these things are completely worthless if thyroxine replacement isn't managed to keep TSH in a narrow band of 0.4-0.9, which in my case is a daily dose of 162.5 micrograms in the morning on an empty stomach with a 1 hour delay to the first meal of the day. If TSH leaves this narrow band even minimally, no improvement can be made.
It's also important to note that getting one thing wrong makes any improvement impossible, so for instance, following all the rules, but consuming too much lysine will lead to no gains or even worsening.
It also appears that some foods appear to be harmful only when another of the rules isn't followed. For instance, while I was on a high-lysine diet this fall, fruit (isolated in the morning) definitely caused symptoms. Now that I have reduced lysine again, fruit in the morning at 9 o'clock (entire meal, no other foods until 3pm) appears to be unproblematic again.
This maybe illustrates how complicated all of this is. I am 100% convinced that what I have is a specific medical condition and while it is certainly very rate, I am sure that a large number of people have the same thing, but they never find out because selecting the right foods is so complicated.
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It took me 7 years from the first suspicion that foods maybe responsible to the insight that this is definitely the case.