Fungal growth in the intestine is surprisingly common and largely an unavoidable hygiene issue as 15% of the microbiome is fungus, that people need to understand and address.

The term "Candida" has become the buzzword often used to describe this issue by lay persons, though it oversimplifies a more complex problem it does its job and lets people discuss the issue, which is usually straightforward to fix with options like antifungal medications, biofilm disruptors, a carnivore diet, probiotics, and other interventions.

Dismissing these concerns as "crank" or "quackery" , the same school of thought as those who play dumb about fungal overgrowth and mislable issues as crohns, ibs etc etc , comes across as disingenuous and seems aimed at discouraging others from educating themselves about basic hygiene and health.

Look at their username; sounds like a pet theory of theirs

You don't know what you are talking about. Low FODMAP diet for example is advocated by John Hopkins Medicine institute , Yale, Cleveland clinic etc.

Craving sugar is a hallmark symptom of B1 deficiency. Source "Thiamine Deficiency Disease, Dysautonomia, and High Calorie Malnutrition" by Dr Derrick Lonsdale the world expert in b1 deficiency.

B1 is only absorbed in the ileum (small intestine).

The biofilm grown by the fungus (candida) is what covers the skin of the small intestine and it stops the ileum absorbing b1.

There are places that will do a stool analysis for you, but it's a lot of guesswork. Many quacks have also discovered that they can get people to pay a lot of money hoping for relief, and they don't hesitate to take advantage. It's a shame because there are honest people out there trying to help, but sorting the wheat from the chaff is quite the order.

My opinion is that if you're concerned, the best thing is to make sure you aren't overeating carbs (I suggest limiting carbs to 30-40g per meal and 120g per day, and avoid simple carbs) and ideally take a probiotic and/or consume fermented foods such as yogurt, kombucha, etc that naturally provide probiotics. The carb limiting is the most important. If you do nothing else, do that. Even if you don't have an issue with candida, you'll feel better overall and get healthier. Again this is just my opinion as someone who has spent years reading and experimenting on myself, but is not formally educated or trained so take with a grain of salt.

Can you narrow it down to which specific B vitamin does it? If you really wanted to undertake a project, you could do a single blind study with placebo vs real b vitamins and prove if they work (grind up real vitamins and press them back in a way they look like placebo, put them in 30 day packs, and ask a friend to label and mix them up). Then make your guess after several months.

Candida species cause thrush and yeast infections. Afaik they are fairly ubiquitous in the human biome but become problematic when Candida gets out of control.

So if you can test for it chemically there could be positives even if it's not a problem. So it would be a matter of looking under a microscope at the gut microbiome and checking if theres an overgrowth. And then treatment is tricky in the gut - how do you target a single problematic species but keep the rest of the microbiome intact? And if you do knock it out, you still need to create the conditions where it doesnt just bloom again since its ubiquitous.

In the end it might be a thing where you have to follow general gut health advice and try to cultivate a healthy gut microbiome.