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Don’t worry about calories. Your first goal is to limit your net carbs. Eat as much protein as possible and use fats to fill you up. After 3-4 weeks, the cravings for carbs will start to fade. As your cravings fade, then start to reduce calories. Read the FAQ; it has a lot of good information in it. Use the calculator it links to so you can calculate your daily calorie target. More on reddit.com

The average adult weighing 150 to 180 pounds should have about 1.2 to 1.5 gallons of blood in their body. This is about 4,500 to 5,700 mL

During a regular donation, you will give around 470ml of whole blood. This is about 8% of the average adult's blood volume. The body replaces this volume within 24 to 48 hours, and replenishes red blood cells in 10 to 12 weeks.

5700/470=12,1276596

≈13 people every day.

That's only if your folk needs to update their blood supply every single day.

That's if they donate the usual amount. If you wanna suck them dry:

It is generally accepted that the volume of whole blood donated should not exceed 13% of blood volume

So 5700/100*13=741 ml per person.

That equates to around 7.6 people, so you just cut a poor guy in two 0.4 and 0.6 parts like if they were gojo satoru. (Or you can round up and just use 8 people but that's boring)

Individual red cells live on average about 120 days, so each day, the normal bone marrow must replace 1/120th of the blood volume. For a 70 kg(around 170 pounds) person, that would be about 40 ml

Overall, if the weird vampires don't require a full blood tank refill every day, that's very plausible, they only need around a 40ml refill every day.

All data sourced from Google searches, so don't expect me to be 100% correct, but tbh, why the fuck you need more scientific data for worldbuilding, overly focusing on realism and physics just ruins the fun of it.

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