You need a certain amount of calories for basic bodily functions, what's referred to as your basal metabolic rate, or BMR. You also need calories to burn for the activities of daily living, such as preparing a meal, folding the laundry or brushing your teeth. Most people who don't do any extra exercise use between 1,800 to 2,600 calories a day depending on their sex and size. So 1,500 calories a day is on the low end -- you will most likely lose weight at that rate. Consult a doctor before beginning such a low-calorie regimen.
Basal Metabolic Rate
Your body needs a certain number of calories to fuel the heart, liver and other organs. Bodily functions such as cell growth and repair, breathing and hormone replacement all require a certain number of calories as well. These calories are measured as your basal metabolic rate, or BMR, and it is your body's caloric needs when at rest. The BMR burns about 60 to 75 percent of your overall calories, according to the Mayo Clinic -- and it varies depending on size, sex and age. For example, a 30-year-old female who is 5-foot 6 inches tall and weighs 110 lb. will require about 1,238 calories to maintain her BMR, according to BMRCalculator.org.
The number of calories you need will depend on your BMR and how much exercise you get. For example, according to the U.S. Department of Agriculture, a sedentary female between the ages of 19 and 30 will need between 1,800 to 2,000 calories a day to maintain her weight, whereas an active female will need 2,400 calories a day. Men require, on average, between 600 calories more than women for that age range. If you are a 19-year-old female who doesn't exercise and you require 1,800 calories a day to maintain your weight, you will create a 2,100 calorie deficit a week if you consume 1,500 calories a day. It takes a 3,500 calorie deficit to lose 1 lb., so you will lose about 2/3 lb. a week at that rate, even before exercise.
Diet and Exercise
Another important factor in determining if caloric consumption is too low is the types of calories you are getting. For example, if you are eating a lot of junk food or fast food, you are eating "empty calories" -- calories without any nutrients. Your body needs nutrient-dense whole foods, such as lean meats, whole grains and fresh fruits and vegetables to provide you with proper nutrition. If you are exercising, you will require more calories to give your body fuel. A 19-year-old male who is moderately active, for instance, will use between 200 to 400 more calories than someone who is sedentary. If you aren't exercising, you are possibly putting yourself at risk for health issues. Exercise helps boost your metabolism, works the muscles, reduces stress and helps you sleep -- all important issues in overall health. Exercise also helps reduce the risk of diseases such as high blood pressure and some forms of cancer.
The recommended minimum caloric intake is 1,500 for men and 1,200 for women, according to MedlinePlus. The numbers are usually only meant to be that low for a short period of time while on a weight-loss program. While in some instances your caloric requirements will be lower than the norm, it's best to consult a doctor to determine the best plan for you. Consuming 1,500 calories over a longer period of time can lead to health issues because you may have difficulty meeting basic requirements for your body.