The Effects of Consuming Fewer Than 1000 Calories Daily

You hear that to lose weight, you should eat fewer calories than you burn. In the simplest analysis, this equation can lead to weight loss, but going too low can actually undermine your weight-loss efforts and leave you with unwanted side effects. If you're eating less than 1,000 calories a day, know the consequences and, if you can, boost your intake to achieve weight and health goals.

The average person needs between 1,600 and 3,000 calories per day, depending on gender, age and activity level, according to the Dietary Guidelines for Americans. These numbers are recommended because they allow you to get optimal nutrients and energy to complete everyday activities, keep your body healthy and maintain your weight.

Eating fewer than 1,000 calories a day can leave you nutritionally deficient. A paper published in 2014 in the journal Obesity reported that this low level of caloric intake will put you at risk of being low in calcium, iron and vitamin E, among other valuable nutrients, such as fat and protein.

Read more: Signs and Symptoms of Low Iron in Women

You may end up with constipation, as it's hard to get enough fiber on so few calories. If you maintain less than 1,000 calories a day for a month or longer, you may also experience gallstones due to the inactivity of the gallbladder from the very low fat in the diet. Gout can also result from rapid weight loss.

It's frustrating to be eating under 1,000 calories a day and not losing weight. As your body adapts to a low calorie intake of 1,000 calories per day, your metabolism slows down. Your metabolism is the energy your body uses to drive basic functions, such as to breathe and digest food, as well as to perform the exercise and movement you do during the day.

When your body senses you're putting less fuel in, it expends less energy than usual for fear that you're starving it. It uses fewer calories to pump blood and operate your internal organs. You also may find yourself lower on energy, so you sit more and are less spontaneously active.

Research published in a 2016 issue of Obesity followed former contestants from the television show, The Biggest Loser. The study confirmed that the body makes metabolic adjustments when you attempt to lose weight by lowering calories. The result is that you may find it harder to lose weight, or may even gain weight, when you're eating less than 1,000 calories a day.

Read more: How to Increase Calorie Intake After Dieting

Calories are fuel for your body's activity. When you're eating less than 1,000 calories a day, you're not giving your body the "gas" it needs to get up and go. You may feel weak or lifeless. With too few calories, your glucose levels drop and so do all your body functions — from your muscles to your brain.

When you're feeling fatigued, it can make it harder to hit the gym. Or if you're an athlete training to get lean and hit a goal weight, low calories can undermine your power and performance, according to the experts at Training Peaks. You may even develop overtraining syndrome.

Eating less than 1,000 calories a day puts your lean body mass at risk. When you lose weight, you lose a combination of fat and some muscle. You want to maximize fat loss and minimize muscle loss to benefit your health and the look of your physique.

Restricting yourself to 1,000 calories per day will invariably mean you'll deny yourself some important nutrients, particularly protein. When you don't have enough protein, your body doesn't have the amino acids necessary to support muscle growth and retention. Even if you're working out, your body's muscles can't be sustained or grow because they don't have the necessary building blocks. Your body will tend to hold onto fat because it feels as if it's starving and needs some reserves to sustain itself.

Losing muscle results in a decreased metabolism, as muscle burns more calories at rest and activity than does fat, and a softer physique.

You've heard of being "hangry?" Well, eating less than 1,000 calories a day puts you in this state — all the time. Research in Current Neuropharmacology published in 2015 noted a connection between depressive symptoms, mood irregularities and calorie restriction.

When you excessively restrict calories, your cognitive abilities are impaired and your mood can become negative. Your body perceives low-calorie intake as stress and responds accordingly. The result is a decrease in the output of a hormone known as leptin, which is associated with mood. Low leptin levels are connected to depression.

Hair loss can result due to the nutrient deficiencies, including iron and protein, likely in a diet of 1,000 calories per day or fewer. Research published in Dermatology Practical and Conceptual in 2017 found that weight loss and nutritional deficiencies can impact hair growth and structure.

You naturally lose up to 100 strands of hair per day, but if it seems like you're losing a lot more, it could be due to your low-calorie diet.

Consistently restricting your calorie intake can affect fertility, especially in women. If you eat 22 to 42 percent fewer calories than you need to maintain your weight, reproductive function can be suppressed, according to a 2015 study published in the American Journal of Physiology, Endocrinology and Metabolism. The research showed that this level of calorie restriction negatively interfered with ovulation, or the release of eggs for fertilization.

An irregular period doesn't just have implications for getting pregnant. If you're not producing enough estrogen, you risk early bone loss.

If you're denying yourself food by eating fewer than 1,000 calories per day, you can easily become preoccupied with thoughts of food. Perceptions of hunger and deprivation can become overwhelming. Obsessing over food interferes with relationships, work and school.

Read more: Low-Calorie Foods That Make You Feel Full

Calorie needs do vary from person to person. Use a reliable formula to determine a baseline appropriate for you. A day or two of eating fewer than 1,000 calories, such as when you're sick, won't have a major impact. However, consistently dipping to such a low level can have many negative effects.