https://www.researchgate.net/profile/Derrick-Lonsdale
Some links to get you started. B1 deficiency can be caused by things like alcoholism. He also thinks we don’t get enough of b1 in our diet and the current scale is not sufficient.
Symptoms can vary and can involve different nervous systems. Things like tingling, insomnia, fatigue.
A lot of people talk about getting paradoxical reaction or refeeeding syndrome, meaning once they start taking b1 they get massive flare up of symptoms.
Back in the day when we were all doing enough work (men, women, children) to need over twice our base-metabolic-rate number of calories per day, and eating whole foods, particularly red and white offal and leafy greens like collard and beet greens, steamed and roasted, we got enough of these mesonutrients and micronutrients.
Twice your BMR is about 5000 Cal/day for an adult male. You need to do eight hours' physical work (shoveling, threshing, chopping, sawing, lifting, doing the laundry by hand, etc.) to burn off the extra.
Now, the hypothesis says, we are deficient in many of these nutrients because we simply do not eat enough food, only 2500 Cal/day.
I have no investment in the hypothesis. Just reporting it.
e.g. tomatoes have lost most flavor and nutrition over past few decades, some efforts are underway to hybridize them with older variants to get the best of both worlds.
can't speak for nutrition (nor do you provide support for that claim) but as to flavour, you clearly haven't been round long! Old fashioned tomatoes were shite I can testify (at least those available in the UK).
Apparently the mechanisms for absorbing it depend on having sufficient B1, and can get "stuck" in a deficient mode if you went through a period of deficiency, which can then be "unblocked" (kickstarted) with a megadose.
Take this with a grain of salt, it's supposedly based in research, but I didn't check any papers about it yet.
And if you aren't eating a lot of enriched flour you might not be consuming it in fortified foods at all.
Supplementing with B12 helps, to a degree (you're providing more input to a broken machine), but you can supplement 5-MTHF (methylfolate) to get what the mutation inhibits your body from producing.
MTHFR has been hijacked by alternative medicine and exaggerated into an "explains everything" diagnosis.
The first red flag is that MTHFR pushers use it to explain ever vague disorder under the sun: Depression, anxiety, stomach issues, being tired, being unhappy, inflammation, etc. If you name it, chances are someone on an alternative health board will spring up and suggest MTHFR as a narrative, or other variations on the theme ("methylation", etc.)
The second red flag is when they moved to diagnosis anyone with any mutation, including heterozygous people, as "having it". This isn't backed by evidence and was purely an attempt to stretch the diagnosis to cover more people,
Internet MTHFR and "methylation" advice is generally terrible. Don't buy into it.
You can actually test for high homocysteine levels in the blood, but most MTHFR proponents skip that step and just assume they "have it" and that B12 and Methylfolate will solve all of their problems (they don't). Alternative medicine has stepped in to provide endless articles, podcasts, and paid advice about supplements to add to deal with MTHFR, which of course never work because MTFHR isn't the root cause of all of their symptoms. It's terrible.