Your bone density is directly correlated to your body fat, so if you're very slender or exercise too much, your bones may suffer. Girls and young women are susceptible to the "female athlete triad" – a combination of inadequate nutrition, hormone disruption and low bone density. Your family and friends probably won't know you have this condition, so it's up to you to seek help. If the problem isn't corrected early, you risk long-term damage to your bones. A healthy diet and exercise routine can get your body fat and hormones back to where they should be.
Body Fat Percentage and Your Bones
Your body fat percentage can drop dangerously low if you lose too much weight, whether it's from a severe calorie restriction, excessive exercise or abuse of diet pills, laxatives or diuretics. Women need at least 10 to 13 percent body fat for good health, according to the American Council on Exercise. The average body fat percentage for females athletes is 14 to 20 percent, with fit women -- those who keep in shape but aren't professional athletes -- averaging 21 to 24 percent.
If you have less than 10 percent body fat, you're probably not consuming enough calories and nutrients, including calcium. Calcium is vital for your bone structure and function, and if your body doesn't get enough from your diet, it steals it from your bones, making them weak. Bone breakdown is especially concerning if you're a teen or young adult, because your peak bone mass is achieved by age 30, and 40 percent of that is acquired during your teen years, according to a 2006 article in Pediatrics
Hormone Changes and Your Bones
Your bones are constantly remodeling themselves, with two kinds of special cells, whose job is to either break down or build new bone. The hormone estrogen, that you produce each menstrual cycle, puts a stop to the cells that break down your bones.
When your body fat percentage dips below the essential amount, your hormones become disrupted and amenorrhea, or missed periods, ensues. Your estrogen levels decrease, and the cells that break down your bones live longer, giving them time to destroy more bone. More bone breakdown leads to premature osteoporosis – a term used to describe low bone mineral density for your age -- which makes you susceptible to broken bones. Normally, women aren't at risk for osteoporosis until menopause, which occurs later in life, when estrogen levels naturally drop.
Even though you may not have symptoms of osteoporosis, a 20-year-old woman who had amenorrhea during her teen growth spurt can have the bone mass of a 70-year-old, according to the American College of Sports Medicine. Osteoporosis is typically diagnosed with a DEXA scan -- a machine that uses low levels of radiation to measure your bone density. Speak to your physician, psychologist, nutritionist or coach if you're concerned you're not eating properly, haven't gotten your period by age 16, or have missed three periods in a row.
Foods to Increase Your Bone Density
The 206 bones in your body help you move and provide a strong shield for your organs, so it's your job to eat well and exercise to keep them healthy. Eat a variety of foods from all four food groups each day so you're getting the nutrients your body needs. Choose calcium-rich foods -- mainly found in dairy products, tofu and green, leafy vegetables -- to protect your bones. Teen girls need 1,300 milligrams of calcium a day, and young women over 19 need 1,000 milligrams a day. An 8-ounce glass of milk contains 300 milligrams of calcium, about a quarter of your daily needs. Milk is also fortified with vitamin D, about 100 international units per cup, which is also essential for bone health. Adolescents and young adults need 600 IU of vitamin D a day.
Your body only absorbs so much calcium at once, so space out your dairy products throughout the day. Make a smoothie with milk, yogurt and berries for breakfast. Dip fruits in Greek yogurt mixed with a touch of honey for a snack. Add cheese to your sandwiches or salad at lunch. Top whole-grain pasta with tofu and sauteed spinach or kale for dinner. Vitamin D is naturally found in only a handful of foods, such as fatty fish, like salmon and mackerel, and fish liver oil, so getting it from milk, so it's paired with calcium, is probably your best bet for increasing your bone density.
Exercise to Strengthen Your Bones
If your body fat percentage is low, you may not have much energy, but don't stop exercising altogether, recommends a 2010 article in American Family Physician. Your bones get stronger in response to exercise. Weight-bearing exercises – jogging, walking, dancing, resistance training and tennis -- are most beneficial for improving bone density. To make up for calories lost through physical activity, increase the amount you're eating on the days you exercise. Track your eating and exercise to stay on track, and involve coaches, parents and friends who will support you. Rather than your weight, focus on your health and performance.
- American Academy of Orthopaedic Surgeons: Female Athlete Triad: Problems Caused by Extreme Exercise and Dieting
- American Council on Exercise: Fit Life
- Pediatrics: Optimizing Bone Health and Calcium Intakes of Infants, Children and Adolescents
- American College of Sports Medicine: The Female Athlete Triad
- Medline Plus: Osteoporosis
- University of Washington: Estrogen -- Mechanisms of Action on Bone
- Dairy Council of California: Preventing Fractures Through a Commitment to Healthy Bones
- Linus Pauling Institute: Calcium
- Linus Pauling Institute: Vitamin D
- American Family Physician: The Female Athlete Triad