Eating too few calories on a regular basis can lead to serious health consequences. While it may result in short-term weight loss, restricting calories too much over an extended period of time can cause a number of metabolic, physiological and psychological effects.
How many calories do adults need daily?
The number of calories needed each day varies from person to person, depending on factors like age, sex, height, weight and activity level. However, most adults need at minimum:
- Women: 1,200-2,400 calories per day
- Men: 1,800-3,000 calories per day
Eating fewer calories than your body needs can put you at risk of nutrient deficiencies and other issues. The sections below outline some of the potential effects of severe calorie restriction.
Weight Loss Effects
Cutting calories very low will often lead to fast initial weight loss as the body’s glycogen stores become depleted and body water is lost. However, this type of weight loss is not sustainable long-term.
When you severely restrict calories for an extended time, your metabolism eventually slows down to conserve energy. You end up burning fewer calories, which can make it hard to keep losing weight.
Reduced muscle mass is another side effect of crash dieting or eating too little. When your body doesn’t get enough calories, it may break down muscle for energy, resulting in loss of lean tissue.
Nutrient Deficiencies
Eating too few calories can increase your risk of nutrient deficiencies. Even if you’re eating a variety of healthy foods, restrictive diets contain too little energy and micronutrients to fully meet nutritional needs.
Some potential nutrient deficiencies that can develop include:
- Iron: vital for blood and oxygen transport
- Calcium: important for bone health
- Zinc: supports immune function and cell growth
- Vitamin B12: needed to produce red blood cells
- Folate: key for new cell and DNA production
- Vitamin C: aids immune function and iron absorption
Without adequate intake of these and other nutrients, you may be at increased risk of anemia, osteoporosis, heart problems, depression and other health issues.
Gastrointestinal Effects
Restricting calories can also affect your digestive system.
Potential gastrointestinal side effects of crash dieting include:
- Constipation
- Diarrhea
- Abdominal pain
- Acid reflux
- Hemorrhoids
- Irritable bowel syndrome (IBS)
These issues occur because your gut relies on a regular supply of food and energy to function properly. Eating too little disrupts the digestive process.
Hormonal Changes
In women, consuming too few calories can lead to disruptions in the menstrual cycle and reproductive hormone levels.
Potential effects include:
- Missing or irregular periods
- Low estrogen levels
- Decreased sexual desire
- Infertility
Inadequate calorie intake and low body weight may also reduce testosterone levels in men, resulting in reduced muscle mass and sex drive.
Weakened Immune Function
Consuming too few calories can weaken your immune system and ability to fight infection. This occurs due to insufficient intake of energy, protein and micronutrients needed for immune cells to work properly.
Studies show that even short-term calorie restriction may reduce the activity of immune cells and antibodies, impairing your body’s defenses against bacteria and viruses.
Increased Infection Risk
The combination of malnutrition and a weakened immune system significantly raises your risk of various infections.
Potential infections that may occur as a result of crash dieting or eating too little include:
- Common cold and flu
- Strep throat
- Bronchitis
- Pneumonia
- Urinary tract infections
- Yeast infections
- Skin infections
In some cases, fighting these infections will be harder due to diminished immune defenses. This may result in longer, more severe illnesses.
Fatigue and Weakness
When your calorie intake drops below your body’s needs for too long, you’ll start to feel tired and weak.
Fatigue occurs because your body doesn’t have enough energy to get you through the day. Meanwhile, weakness happens as muscles deteriorate due to inadequate calories to sustain them.
Even if you’re losing weight, you may find it harder to complete everyday tasks and exercise due to low energy levels and diminished muscle strength.
Mood Changes
In addition to physical effects, not eating enough calories can also impact your brain and emotions.
Potential mood symptoms of very low calorie intakes include:
- Depression
- Anxiety
- Irritability
- Brain fog and confusion
Research indicates that severe calorie restriction increases levels of cortisol, the stress hormone. Elevated cortisol contributes to mood instability and impaired thinking and memory.
Bone Loss
Osteoporosis and weaker bones may occur as a result of prolonged calorie restriction. This is often tied to inadequate intakes of calcium and vitamin D.
Bone is constantly remodeled and requires sufficient energy, protein and micronutrients like magnesium and phosphorus for maintenance. Eating too little deprives your bones of what they need to stay strong.
Over time, this makes bones more porous and fragile. As a result, even minor stresses like bending over or coughing can lead to fractures.
Heart Problems
Crash dieting and inadequate calorie intake also appears linked to abnormalities in heart structure and function.
Potential heart-related effects may include:
- Abnormally slow heart rate (bradycardia)
- Low blood pressure (hypotension)
- Heart muscle deterioration (cardiomyopathy)
- Irregular heart rhythms (arrhythmias)
- Congestive heart failure
Research indicates that extreme calorie restriction causes heart muscle to waste away, or atrophy, which diminishes its ability to pump blood through your body.
Death
In extreme cases, consuming too few calories for an extended time can result in starvation and eventually death.
Studies show that people with anorexia nervosa, an eating disorder characterized by dangerously low body weight and an extreme fear of gaining weight, have an increased risk of dying. This is especially true if they have other medical complications.
Death most commonly occurs due to complications like heart failure, infections or suicide. Prompt evaluation and treatment for eating disorders can decrease mortality risk.
Who’s at Risk of Eating Too Few Calories?
While anyone can technically consume too little food energy and lose weight, some groups are at a higher risk of negative effects from calorie restriction.
Those more likely to eat too little include:
- People with eating disorders like anorexia or bulimia
- Those following very low-calorie diets
- People who fast for extended periods
- Endurance athletes
- Vegans or vegetarians who poorly plan diets
- Older adults with small appetites
- Those with medical conditions affecting appetite or nutrient absorption
If you fall into one of these high-risk groups, aim for the recommended daily minimum calories for your age, sex and activity level to stay healthy.
Health Consequences of Chronic Calorie Restriction
The health consequences of chronically eating too few calories include:
| System | Effects |
|---|---|
| Gastrointestinal | Constipation, diarrhea, acid reflux, hemorrhoids, IBS |
| Immune | Impaired function, increased infections |
| Musculoskeletal | Loss of muscle and bone mass, fractures |
| Endocrine | Menstrual dysfunction, reduced fertility, low hormone levels |
| Cardiovascular | Abnormal heart rhythms, heart failure, hypotension |
| Psychological | Depression, anxiety, irritability, reduced cognition |
Tips for Avoiding Too Few Calories
To prevent potential problems caused by inadequate calorie intake, aim to meet your body’s needs through a balanced, nutritious diet. Here are some tips:
- Calculate your calorie needs using your age, sex, height, weight and activity level.
- Don’t restrict calories more than 500 calories below your estimated needs for steady, healthy weight loss.
- Include plenty of vegetables, fruits, whole grains, lean proteins and healthy fats at meals.
- Space meals 4-6 hours apart during the day to stabilize energy and hunger.
- Stay hydrated by drinking water when hungry between meals.
- Use a calorie tracking app to ensure you meet daily minimums.
- Get enough calcium and vitamin D for bone health.
- See a doctor if you think you have an eating disorder or malnutrition.
Conclusion
Eating too few calories can cause weight loss in the short term, but poses many health risks if continued long-term. Effects may include nutrient deficiencies, muscle loss, bone loss, fatigue, infections, digestive issues, heart abnormalities and even death.
Those most at risk include people with eating disorders, older adults, endurance athletes and vegans. Consuming the minimum number of calories recommended for your age, sex and activity level can help avoid complications.