If you lose weight but end up with diabetes, or a serious vitamin deficiency, would you still think this research is legit?

Eating only one type of food for weeks will almost always result in losing weight, because it would disrupt the gut flora, as well as deprive one of necessary vitamins/minerals.

In order to be accepted as anything other than an anecdote, you would require a much more rigorous study with a LOT more people and a much higher level of scrutiny. We would want to control for external issues, possibly genetic complications, gut flora, blood glucose levels, liver and pancreas health, illness, infection, cancers, etc...

Anecdotal evidence if fine for discussion, but no one should act upon it without medical supervision.