Body size and composition vary from person to person, so one single dangerous amount of weight loss doesn’t exist. Instead, the specific amount of weight you can lose before it impacts your health depends on factors including your starting weight and overall health status.
In severe cases, losing too much weight can cause the body to shut down completely. You can learn more about how this happens and warning signs to look for below.
Low Weight and Body Mass Index
In the United States, most health organizations focus on the potential consequences of having a high body mass index (BMI). But being below your healthy weight also causes health concerns, and research suggests this could actually pose more health risks than having a high BMI.
BMI is one way to estimate if someone is underweight. You can calculate your BMI by dividing your weight in pounds by your height in square inches and multiplying this value by 703, according to the Centers for Disease Control and Prevention (CDC).
According to the World Health Organization, an adult BMI below 16 tends to come with a higher risk of lethargy, illness, and even death. Additionally, a BMI under 17 can indicate severe thinness and increased risk of sickness, while BMIs below 18.5 fit into the underweight category.
Keep in mind that BMI doesn’t always tell the full story when it comes to health. For example, BMI doesn’t measure body fat or muscle mass, but it could correlate with other methods for measuring body fat, according to the CDC.
People with the same BMI can have different levels of body fat. In general, women have more body fat than men, and older individuals have more body fat than those who are younger.
What Can Cause Severe Weight Loss?
Severe weight loss has many potential causes. Anorexia nervosa, an eating disorder most common in women during their teens and early adulthood, is one well-known cause of extreme weight loss, according to MedlinePlus.
People with this mental health condition may severely restrict the amount of food they eat in order to lose weight. In addition to weight loss, other symptoms of anorexia include:
- Fear of weight gain
- Obsession with exercise and calorie counting
- Hiding or secrecy around food
- Distorted body image
- Hair loss
- Pale or gray skin tone
- Loss of menstrual cycle
- Low blood pressure
- Feeling cold
- Insomnia
- Mood swings and low self-esteem
Other conditions and circumstances can cause weight loss, too, including malnutrition and lack of available food. Certain medical conditions can also affect your body’s ability to properly absorb nutrients from food, resulting in weight loss, according to MedlinePlus.
Some of these conditions include:
- Celiac disease
- Whipple disease
- Short bowel syndrome
- Lactose intolerance
Certain medications can also prevent nutrient absorption.
If you have symptoms of anorexia or unexplained weight loss, it’s best to contact your healthcare provider right away. They can help you rule out serious medical conditions and connect you with resources, support, and treatment.
What Happens When the Body Goes Into Starvation Mode
As weight loss progresses and reaches a critical level, multiple body systems begin shutting down. According to Cleveland Clinic, some signs of the body shutting down include:
- Fainting
- Dry skin prone to rashes
- Slow heartbeat
- Brittle hair and hair loss
- Inability to regulate body temperature
Other complications of starvation — anorexia in particular — may affect nearly every system in the body, as reported in a research review published in 2021:
- Heart: In addition to decreased heart rate, cardiovascular impacts of anorexia include very low blood pressure and mitral valve prolapse, which can result in irregular heartbeat and difficulty breathing.
- Metabolism: Potential metabolic complications include thyroid disease and hypoglycemia, or extreme low blood sugar.
- Reproductive health: Prolonged starvation can cause irregular periods or period loss, as well as infertility in severe cases.
- Skin and hair: Increased body hair, called lanugo, can be a sign of late-stage anorexia, as well as itching, fissures, and bleeding, according to Cleveland Clinic.
- Digestion: Gastrointestinal complications of anorexia can include constipation, diarrhea, nausea, and heartburn.
- Bones: People with anorexia may experience reduced bone mineral density and bone loss.
As the body starts to shut down due to lack of energy, symptoms may become more severe.
Amenorrhea, or loss of period, is one warning sign that you’ve lost a dangerous amount of weight. But if you already don’t get a regular period (or have one at all), there isn’t a comparable warning sign.
Treatment for Starvation and Anorexia
In cases where someone is severely underweight and malnourished, hospitalization is usually necessary to stabilize them. Medical supervision and nutritional counseling can provide important support during the process of reintroducing food.
A condition called refeeding syndrome sometimes occurs during treatment, according to Cleveland Clinic. Untreated refeeding syndrome can cause electrolyte imbalances and deficiencies that may lead to respiratory failure, coma, or death, so it’s important to reintroduce food slowly with medical supervision.
No standard treatment exists for refeeding syndrome, but options could include a slower increase in calories as well as electrolyte monitoring and replacement.
Your healthcare team will also look for the underlying cause of weight loss to treat it. For example, treatment for anorexia might involve therapy and medications such as antidepressants to address the root cause of the eating disorder.
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