Calories are critical when you're trying to lose weight, but low calorie diets eventually catch up to you. If you're eating less than 1,200 calories a day, you might experience negative side-effects. Your body begins to fight weight loss by lowering your metabolism and releasing hormones that make you hungry.
Recommended Calorie Intake
Eating 1,200 calories per day is most likely not enough. The recommended calorie intake for sedentary females aged 26 to 50 is 1,800 per day, according to the USDA Dietary Guidelines. For sedentary males of the same age, the recommended calorie intake is 2,400, but lowers to 2,200 at age 40.
For athletes or people who work out regularly, those numbers may be higher. A 2015 study published in Sports Medicine in September 2015 explains that energy intake below 1,500 calories per day should be avoided. Even a small female, weighing 110 pounds and standing 60 inches tall, has a metabolism of over 1,300 calories per day.
Those calorie intakes are based on a sedentary lifestyle, but the numbers are even higher if you exercise, because activity burns extra calories.
Risk of Nutrient Deficiency
Restricting carbs, for example, might lead to a dangerously low intake of fruit and vegetables. Most fruit and vegetables, as well as carbohydrates like oats or rice, are high in fiber. Fiber helps your digestive system and can lower your risk for heart disease. Fruits and vegetables contain vitamin C, which is an antioxidant that can boost immunity.
If you're planning on eating a restricted diet, check with a registered dietitian first. They can give you tips for eating 1,200 calories a day, including how to get all the nutrients your body needs.
Reducing Calories Slows Metabolism
When you eat a restricted diet, you initially lose weight. As you lose weight, your body begins to adapt. This is called adaptive thermogenesis, or AT, according to a December 2016 article published in Current Obesity Reports. Given AT, your metabolism can change by 100 to 500 calories per day. If you're eating under 1,200 calories a day and not losing weight, it might be because your metabolism has slowed to match your intake.
Reducing Calories Burns Muscle Mass
Your metabolism can fluctuate wildly and quickly, but there's another factor in your metabolism that changes slowly: muscle mass. Muscles do a lot of work moving you around, which is why they consume a considerable amount of energy.
According to University of New Mexico professors of exercise physiology, one pound of muscle burns about 4.5 to 7 calories per day. Muscle mass makes up about 40 percent of your body, so a 150-pound person's muscles burn up to 420 calories per day without extra activity.
Muscles help you burn calories, so it's important to retain muscle strength when you're trying to lose weight. You're likely to lose muscle mass on a low-calorie diet. According to MedlinePlus, weight loss of 1 to 2 pounds per week can cause muscle loss. If you're losing that much weight or more while eating under 1,200 calories per day, some of it is likely muscle.
Fewer Calories Boosts Hunger
Your body's response to a low-calorie diet is to make you look for food. You'll feel hungrier if you don't eat enough, and that's partially due to a hormone called leptin. Your body releases leptin to reduce hunger, according to the Hormone Health Network. As your calorie intake goes down, your body secretes less leptin, so you'll feel hungrier.
The Female Athlete Triad
Low calorie diets can be used to achieve an unhealthy, slender figure. Low calorie intakes can hurt both males and females, but the dangers are different for females.
While it's called the female athlete triad, you don't have to be an athlete to be affected by it. The triad is comprised of three things: negative energy balance, disruption of the menstrual cycle and low bone density. Negative energy balance can come from too much exercise, not enough food, an eating disorder or a combination of all three.
The menstrual cycle is a useful gauge to monitor health. Missing periods is a sign that you're suffering from the female athlete triad. A sign that you're back to normal is restoration of the menstrual cycle, according to The American College of Obstetricians and Gynecologists.
Bone Loss From Calorie Reduction
Even if you're not experiencing all three parts of the triad, it can still be dangerous to restrict calories. Long-term effects of the triad, such as loss of bone density, can be irreversible. The female athlete triad is a serious health risk, and if you or someone you know is experiencing it, you should seek professional help.
Male Response to Low Calories
Men have a different response to calorie restriction than women. A January 2016 article in the Journal of Sports Sciences showed that men who ate a low calorie diet and exercised regularly, thus putting them in calorie restriction, didn't lose a significant amount of testosterone, which is the main male sex hormone. The researchers note that both exercising and sedentary females experience a drop in their primary sex hormone, estrogen, among others.
While some hormones seem immune to low calorie diets in men, two were affected the same as in women: leptin and insulin are both reduced. Both hormones were reduced during calorie restriction.
Less leptin results in more feelings of hunger, which makes it harder to stick to a diet under 1,200 calories. Less insulin means less glucose is being pulled out of the bloodstream, which could be due to the lack of food eaten on a restricted diet.
The Odds Are Against You
If you're eating under 1,200 calories per day to lose weight, you'll probably lose a lot of weight in the beginning. Over time, this weight loss will probably begin to dwindle. A November 2018 review of extreme weight-loss diets published in the Indian Journal of Medical Research notes that none of the diets worked in the long-term.
Perhaps a better method is to slowly reduce your calories and increase your activity level. A June 2016 study published in The American Journal of Clinical Nutrition shows that increasing activity level was better for weight loss than reducing calories.
- Office of Disease Prevention and Health Promotion: "Dietary Guidelines for Americans, 2015-2020: Appendix 2. Estimated Calorie Needs per Day, by Age, Sex, and Physical Activity Level"
- Colorado State University: "Fat-Soluble Vitamins: A, D, E, and K - 9.315"
- Harvard T.H. Chan School of Public Health: "Fiber"
- The American College of Obstetricians and Gynecologists: "Female Athlete Triad"
- Sports Medicine: "Weight Management for Athletes and Active Individuals: A Brief Review"
- Journal of Sports Sciences: "Low Energy Availability in Exercising Men Is Associated With Reduced Leptin and Insulin but Not With Changes in Other Metabolic Hormones"
- Hormone: "What Is Leptin?"
- Current Obesity Reports: "Changes in Energy Expenditure With Weight Gain and Weight Loss in Humans"
- University of New Mexico: "Controversies in Metabolism"
- MedlinePlus: "Diet for Rapid Weight Loss"
- Indian Journal of Medical Research: "Pros & Cons of Some Popular Extreme Weight-Loss Diets"
- The American Journal of Clinical Nutrition: "Low Energy Intake Plus Low Energy Expenditure (Low Energy Flux), Not Energy Surfeit, Predicts Future Body Fat Gain"