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What Happens When Women Drop Below 5% Body Fat?

author image Becky Bell, MS, RD
Becky Bell is a registered dietitian with experience in the areas of diabetes, chronic kidney disease and general nutrition. Bell holds a Bachelor of Science in dietetics from Olivet Nazarene University and a Master of Science in human nutrition from the University of Alabama.
What Happens When Women Drop Below 5% Body Fat?
Women who are at the highest risk for low body fat are athletes and those with a chronic disease. Photo Credit Chad Riley/OJO Images/Getty Images

Many women have some unwanted body fat they would like to eliminate. If you're very slim, though, you may be worried that you have too little fat on your frame. A certain amount of body fat is necessary for your body to maintain proper function and sustain life. If a woman's body fat percentage drops below 5 percent, severe health consequences may result, potentially even death. It is nearly impossible to attain a body fat percentage below 5 percent, as female athletes, who have the lowest body fat, generally have between 14 and 20 percent body fat, according to the American Council on Exercise. The council states that a healthy body fat percentage ranges from 14 to 31 percent.

Body Fat's Role in Women's Health

You may think of fat in a negative light, as a nuisance and cosmetic problem, but it actually serves several very important roles in your body. Fat protects your vital organs, surrounding them with a layer of cushion in case of sudden movement or trauma. Your subcutaneous fat -- the layer of fat directly beneath the skin -- helps to regulate your body's core temperature.

Fat plays a role in nutrition and metabolism, too. While the fat-soluble vitamins -- A, D, E and K -- require dietary fat in order to be absorbed, these vitamins are stored in your body's fat tissue. Your body also uses fat stores as a backup energy source when all other fuel sources have been depleted. The amount of body fat that's absolutely necessary for the body to function properly is called essential fat. The American Council on Exercise estimates that 10 to 13 percent of body fat is essential in women; therefore, a drop below 5 percent body fat is extremely dangerous to basic metabolic function.

The Initial Symptoms of Low Body Fat

Women who are at the highest risk for low body fat are athletes and those with a chronic disease, such as cancer. The first noticeable symptom of low body fat percentage in women is the loss of the menstrual cycle. The production of estrogen in the body depends on fat, so when there isn't enough body fat, estrogen levels become deficient. As a result of low estrogen, menstruation ceases, causing infertility and a cascade of other health problems. If you are thin and have missed three consecutive menstrual cycles or have had more than 35 days between cycles, you should see a physician. The good news is that amenorrhea can usually be corrected by increasing body fat.

Other early symptoms that may indicate your body fat percentage is too low are hair loss, chronic fatigue and anemia. See a physician if you are thin and are experiencing these symptoms.

Bone Loss Due to Inadequate Body Fat

Estrogen plays a role in women's bone health. So when estrogen levels drop due to low body fat percentage, calcium leeches out of the bones, decreasing bone mineral density and significantly increasing a woman's risk for osteoporosis. The longer amenorrhea and a low estrogen level persist, the lower the bone mineral density becomes. Although menses usually resumes when body fat is gained, bone density may never recover, according to an article published in the Journal of Clinical Endocrinology and Metabolism. The journal also reports that women with low body fat and amenorrhea, such as those with anorexia nervosa, are seven times more likely to develop a fracture than women of the same age with a healthy weight.

Nutrient Deficiencies and Organ Damage

The consequences of very low body fat levels reach far beyond reproductive health. For a woman to achieve 5 percent body fat, it would require an extreme restriction of caloric intake. Food restriction of that magnitude will almost certainly lead to nutrient deficiencies, hair loss, anemia, electrolyte imbalance, dehydration, starvation, loss of muscle mass and fatigue.

Extremely low body fat can hinder blood vessel dilation and increase low-density lipoprotein cholesterol, both of which increase risk for cardiovascular disease. When a woman's body fat percentage drops below 5 percent, it can ultimately result in heart damage, bone fractures, gastrointestinal problems, shrinkage of internal organs, immune system dysfunction, damage to the nervous system and possible death.

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