Calories are units of energy that will leave you unenergized if you don’t get enough, which should be at least 1,000 a day just so your body can carry out basic functions.

Even if you eat enough, fatigue from low calorie consumption tends to last for a longer period of time. If your energy improves greatly after eating, you may not be eating enough.

If you get a period, pay attention; severe calorie restriction can cause your body to stop producing the hormones you need to ovulate, a condition called hypothalamic amenorrhea.

By eating at least 2,500 calories and 200 grams of starch per day, ovulation should resume within six months, though it’s best to consult a medical professional to know for sure.

Due to the lack of nutrition and vitamin deficiencies that under-eating can lead to, you may struggle with brittle nails, thinning hair, or unusually sensitive skin.

Though the problems will reoccur (and worsen) if you continue to undereat, you can use topical skin remedies, nail hardeners, and hair products that promote growth and thickness.

When under-eating, your liver isn’t getting enough glycogen to maintain a healthy blood sugar level and instead makes hormones like adrenaline and cortisol, which keep you awake.

To help prevent this, eat a bedtime snack an hour or two before bed, or if you’re not used to late night eating, simply start eating more during the day or at dinner.

Under-eating can actually make it harder for you to lose weight than following a healthy diet because severe under-eating can affect the rate at which your metabolism burns energy.

It sends your body into conservation mode; it stores fat because it believes there's a lack of food available and burns it as slowly as possible to fend off starvation.