If you're trying to lose weight, it may seem tempting to drastically decrease your daily calorie intake. However, an intake under 1,200 calories per day for women and 1,500 calories per day for men can slow your metabolism and cause muscle loss.
Eating too few calories can contribute to a slower metabolism and losing muscle mass. This can stall weight loss and even contribute to weight gain going forward.
Recommended Calorie Intake
According to Dietary Guidelines for Americans, most adult women need to eat 1,600 to 2,400 calories per day to maintain weight, depending on their age, height and activity level. For adult men, that range is 2,000 to 3,000 calories per day.
If you're trying to lose weight, you can use a calorie calculator to figure out how much you should be eating each day. Generally speaking, burning 3,500 calories is equal to 1 pound of weight loss. The American Council on Exercise says that operating under a calorie deficit of 500 to 1,000 calories each day can cause a safe, steady weight loss of 0.5 to 2 pounds per week.
Some crash diets, which prescribe extremely low daily calorie intakes, can be unhealthy or even dangerous. While these diets might promise to cause rapid weight loss, they typically just cause you to lose retained water which you then gain back. Plus, following a fad diet in the long-term can contribute to harmful nutritional deficiencies.
The Risks of Malnutrition
If you're eating too few calories and entirely cutting out certain food groups, you may find yourself at risk for nutritional deficiencies. These can contribute to a number of health issues.
Iron deficiency can put you at risk for iron-deficiency anemia. Iron is a crucial component of hemoglobin, a substance in red blood cells that helps transport oxygen from your lungs to the rest of your body. A shortage of iron affects the transport of oxygen, causing symptoms like fatigue, dizziness, cold hands and feet, an increased heart rate, trouble remembering things and decreased concentration.
You can also get vitamin-deficiency anemia from a lack of B12 in the diet. This condition, also known as pernicious anemia or megaloblastic anemia, causes red blood cells to be larger than usual and oval-shaped rather than round. The size and shape changes make it more difficult for the red blood cells to transport oxygen around the body.
A lack of vitamin D is associated with increased rates of cancer, heart disease and diabetes, says Indiana University. Plus, low vitamin D levels are associated with fatigue and weight gain, though the exact connections are not clear.
Mental Side Effects of Undereating
Eating too few calories can affect your body in a number of different ways. If you're not eating enough to properly fuel your body, you might feel physically tired or mentally fatigued. That's because your body burns calories for all sorts of functions, not just when you're moving around or working out. Cognition, respiration and digestion all require fuel from calories. Physical and mental fatigue could affect your job performance, social life and relationships.
Long-term undereating can also contribute to depression, panic disorders and social withdrawal. Some people who consistently undereat may become fixated with their calorie intake and inflexible regarding their daily routines.
Physical Side Effects of Undereating
Eating too few calories can also contribute to a slower metabolism. Drastically cutting calories can put your body into "starvation mode," slowing down your metabolism. When you have a slow metabolism, you burn fewer calories when your body is at rest or during physical activity — so workouts where you would previously torch a high number of calories become less effective.
It can also trigger muscle loss. According to Michigan Medicine, when your body is not receiving enough carbohydrates for fuel, it will break down lean tissues like muscles. When you lose lean tissue, your body fat percentage increases and your metabolism slows down. This can contribute to weight gain, even on a reduced calorie intake.
Undereating may contribute to electrolyte imbalances. Electrolytes, which include bicarbonate, calcium, chloride, magnesium, phosphate, potassium and sodium, are crucial for regulating various bodily processes, including hydration and your heartbeat. If levels of a certain electrolyte become too low, this can cause potentially serious health issues.
For example, a chronic shortage of calcium can contribute to osteoporosis, which makes your bones weak and brittle. To prevent osteoporosis, the Mayo Clinic recommends that men and women between the ages of 18 and 50 consume 1,000 milligrams of calcium a day, which increases to 1,200 milligrams per day for women over 50 and men over 70.
Read more: Fatigue While on a Calorie Restricted Diet
Calorie Restriction and Eating Disorders
Severe restriction of calorie intake can be a symptom of disordered eating. According to the National Eating Disorders Association, one diagnostic criteria for anorexia nervosa is restricting your energy intake to the point where your body weight is significantly lower than the expected range for someone of your age, sex and health.
People who have anorexia also intensely fear weight gain and have a distorted perception of their own body and weight. Anorexia can cause a host of symptoms, including:
- Extreme weight loss
- Thinning hair, hair loss or hair breakage
- Downy hair that covers the body
- Dry skin
- Low blood pressure
- The absence of menstruation
Health risks associated with anorexia include heart problems, osteoporosis, anemia, gastrointestinal issues, kidney issues, electrolyte imbalances and muscle loss. Being anorexic and severely malnourished may result in organ or tissue damage that can never be fully reversed. But, eating disorders can be treated by doctors or other professionals, typically using therapy. For some people, residential or inpatient treatment might be the most effective option.
If you believe you might have an eating disorder, you should speak to a doctor about what you're going through. Your physician can help you work out a treatment plan and work with you to ensure you're getting adequate nutrition.
- Dietary Guidelines for Americans: "Needs per Day, by Age, Sex, and Physical Activity Level"
- American Council on Exercise: "How Many Calories Do We Really Need?"
- Michigan Medicine: "Weight Loss by Limiting Calories"
- Rush University Medical Center: "Body Electric"
- Mayo Clinic: "Osteoporosis"
- Indiana University: "Common Nutrient Deficiencies in Millennials"
- National Eating Disorders Association: "Anorexia Nervosa"
- American Council on Exercise: "Slow Metabolism: 8 Things That Slow Down Your Metabolism"
- Mayo Clinic: "Anorexia Nervosa"
- National Centre for Eating Disorders: "The Effects of Under-Eating"