If a person eats 700 calories a day for months, well they lose their hair?

most likely but that more a nutrition thing, the real risk is death. you need about 1200cal a day to keep your body ticking over.

If a person eats 700 calories a day for months, well they lose their hair?

It depends on the person, how much they weigh, their age, gender, activity level, and how nutritious the foods are, but the easy answer is... probably. People generally need at least 1200 calories a day to simply survive, so someone so deficient in energy and nutrients will probably become malnourished and begin to lose their hair.

Why do you ask?

If a person eats 700 calories a day for months, well they lose their hair?

I suspect 700 calories a day would put you in the Anorexic category and yes, one of the results of anorexia is severe hair loss (and death, but let's keep our priorities straight) :-P

If weight loss is your goal, please consider a less extreme diet paired with a reasonable amount of exercise. It took a long time to reach your current weight (Apologies if I'm assuming something that isn't true!) and it will take a while to get down to where you want as well. In the end, your goal is to have a healthy body that you love, right? So don't hurt it in the process.