I am building a dhampir using the stats from Van Richten's Guide to Ravenloft (p. 16-17), which has some interesting entries, such as this paragraph under "Dhampir Hungers":
Those who overindulge their thirst risk losing control and forever viewing others as prey. Those who resist might find exceptional ways of controlling their urges or suppress them through constant, molar-grinding restraint.
and this entry in the "Dhampir Origins" table, listed for a roll of 6 on a d8:
You are a diminished form of an otherworldly being. Slaking your hunger hastens your renewal.
I also noticed that the stats on a dhampir's Deathless Nature trait (which only says "You don't need to breathe") is quite underwhelming compared to the reborn's Deathless Nature trait (p. 20-21). Compared to the reborn's version of the trait, the dhampir's version obviously removes things like the need to eat and drink (endless thirst), and the need to sleep (cause coffins) – but also takes out resistance to poison, and advantage on death saves, which I find peculiar. At any rate, as I was doing a Google search for a dhampir's age/lifespan, I came across many iterations of them in other games that link their abilities to their feeding, which got me thinking of the question in the title:
Can a dhampir survive on blood alone?
Mechanically, if a dhampir was not to overindulge, say by consuming only 1 pint of blood a day (which is roughly 1/12th of a human male a day, so say 1 Vampiric Bite), could that satiate the creature's need for food and drink?
Or on the other end, would a vegan dhampir's gnawing of teeth or rumbling stomach cause it disadvantage to stealth checks?
I saw in the post What is a dhampir's max lifespan? that there might be some lore that I have missed, but I have yet to find the answer on this site.