Being extremely skinny is typically defined as having a body mass index (BMI) of less than 17.5. BMI is a measure of body fat in adults that takes into account a person’s height and weight. A BMI below 18.5 is considered underweight. So someone who is extremely skinny would fall into the more severe end of being underweight.
What are the causes of being extremely skinny?
There are several potential causes of being extremely skinny:
- Eating disorders like anorexia nervosa or bulimia can lead to extreme thinness due to severely limiting food intake and/or purging food that is eaten.
- Hyperthyroidism is an overactive thyroid gland that can speed up metabolism and cause weight loss.
- Cancer or chronic infections can result in cachexia, which is severe weight loss and muscle wasting.
- Malnutrition from poverty, food insecurity, or health conditions that impair nutrient absorption can lead to an extremely low body weight.
- High levels of physical activity without adequate calorie intake to fuel the exercise can also contribute to low BMI.
- Genetics may play a role for some people who are naturally very lean.
Eating disorders are one of the most common reasons behind being extremely underweight. Anorexia nervosa is an eating disorder characterized by an abnormally low body weight, an intense fear of gaining weight, and a distorted perception of body image. People with anorexia nervosa severely restrict their food intake, often through extreme dieting, fasting, and excessive exercise. Bulimia involves cycles of binge eating followed by purging behaviors like self-induced vomiting to avoid weight gain.
What are the health risks of being extremely skinny?
Being extremely underweight can negatively impact health in the following ways:
- Weakened immune system – not getting adequate nutrition can impair immune function and increase susceptibility to infections.
- Anemia – a lack of iron and certain vitamins can lead to low red blood cell counts (anemia).
- Bone loss – low body weight and inadequate calcium/vitamin D intake can cause osteopenia or osteoporosis.
- Growth and development issues – being underweight can impair growth in children and adolescents.
- Reproductive health issues – women may stop menstruating and have fertility problems.
- Organ damage – the heart, brain, and other organs can be affected by malnutrition.
- Mental health issues – underweight individuals have higher rates of anxiety, depression, and suicide.
In severe cases, the health consequences of extremely low BMI can be fatal. Being underweight impacts nearly every system in the body and increases mortality risk. Proper treatment of any underlying medical or mental health conditions is important to help restore a healthy body weight.
What BMI is considered extremely skinny for women?
For adult women, a BMI below 17.5 is categorized as extremely underweight. Here are the BMI classifications for women:
| BMI | Weight Status |
|---|---|
| Below 17.5 | Extremely underweight |
| 17.5 – 18.49 | Underweight |
| 18.5 – 24.9 | Healthy weight |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obese |
A woman who is 5′ 4″ (163 cm) would be considered extremely skinny at a weight of less than 91 lbs (41 kg). That corresponds to a BMI of 15.4, which falls well below the 17.5 extremely underweight threshold. Such a low body weight would likely impair health and require prompt medical attention.
What BMI is extremely skinny for men?
Just as with women, a BMI below 17.5 is classified as extremely underweight for men. Here are the BMI weight status categories for adult men:
| BMI | Weight Status |
|---|---|
| Below 17.5 | Extremely underweight |
| 17.5 – 18.49 | Underweight |
| 18.5 – 24.9 | Healthy weight |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obese |
A man who is 5′ 10″ (178 cm) would be extremely underweight at a BMI of less than 15.5. That equates to weighing around 105 lbs (48 kg) or less, which is dangerously low. Medical evaluation would be recommended for men with BMIs this low in order to treat any underlying condition contributing to the extreme thinness.
What are visible signs of being extremely skinny?
There are certain visible cues that someone may be extremely underweight. These include:
- Prominent bones – ribs, shoulder blades, collarbones, vertebrae, hip, and other bones protruding visibly.
- Sunken cheeks and hollows around temples and eyes.
- Thin limbs with very little muscle or fat.
- Fragile, bony appearance of joints and hands.
- Prominent veins due to lack of subcutaneous fat.
- Fine, brittle hair or hair loss.
- Lanugo – fine body hair that can grow to keep the body warm.
- Poor skin integrity with visible capillaries.
- Blue-tinged lips and dark circles under eyes.
These physical signs stem from an exceptionally low percentage of body fat. They signify that a person’s weight has dropped to a point where it is compromising their health and bodily functions.
What percentage of body fat is extremely skinny?
There is no definitive body fat percentage that signifies being extremely underweight. However, below are some general guidelines:
- Women: Body fat below 10% is generally considered extremely low for females. Essential body fat for women is around 10-13%.
- Men: Men’s essential fat is around 2-5%. Body fat below 5% can be dangerously low for males.
- Athletes: Extremely low fat levels of under 5% body fat for men and under 10% for women may only be safe for elite athletes under medical supervision.
Body fat percentages below these minimal levels typically indicate an undernourished state. Bodily functions like menstruation, hormonal balance, body temperature regulation, and immune function can be disrupted when body fat drops too low.
How can you gain weight healthily if extremely underweight?
If someone is extremely underweight due to an underlying medical issue or eating disorder, professional treatment of the root cause is crucial. With proper care, the following strategies may help support healthy weight gain:
- Eat 5-6 smaller meals throughout the day rather than 1-2 large meals.
- Choose nutrient-dense foods like whole grains, proteins, dairy, fruits and vegetables.
- Drink high-calorie smoothies or protein shakes as supplements.
- Consume healthy fats from nuts, seeds, avocados, olive oil.
- Stay hydrated – drink water, milk, juices throughout the day.
- Exercise lightly – walking helps build appetite without burning many calories.
- Keep a food log to ensure adequate calorie and nutrient intake.
- Seek counseling for body image, food relationships, and coping skills.
- Get bloodwork done to check for deficiencies or conditions.
Gaining 1-2 pounds per week is a reasonable goal. Working with dietitians, therapists, and doctors provides essential support for healthy, sustainable weight restoration.
Conclusion
Being extremely underweight with a BMI below 17.5 raises severe health risks. Extreme thinness has many possible causes including eating disorders, hyperthyroidism, cancer, malnutrition, genetics, and excessive activity without fuel. Restoring a minimally healthy body weight is crucial to support bodily functions and reduce mortality risk. With proper treatment and monitoring, it is possible to regain weight safely by starting with small, frequent meals and nutrient-dense foods.