Body mass index, or BMI, and body composition are ways to determine whether you're at a healthy weight -- and, by extension, if you're facing a higher risk of obesity-related illnesses, like type 2 diabetes and heart disease.

It’s not uncommon to question whether your weight is normal when you’re growing so rapidly during your teen years. However, the answer isn’t always as simple as it might seem. Teens have different bodies that grow at different rates, which means that you and a friend could be the same height but 25 lbs.

General guidelines exist to help determine the ideal body weight range for adult men and women of all frame sizes, including large-boned – or large-framed -- individuals. If you have a large frame, your ideal body weight is higher than that for individuals with small or medium frames.

The notion that an ideal weight exists for every age and gender fails to take into account differences in body fat percentage, height and body shape. An ideal weight for your age really isn't relevant unless you're measuring growth rates of a child.

For many years, experts have investigated the effects of low body fat on menstrual cycles in women. Some women with low body fat percentages report several irregularities, including infrequent periods, abnormally painful periods and even no period at all.

The body mass index, or BMI, is commonly used in doctors' offices as a way to estimate your body fat level. It provides a quick and easy way to evaluate obesity trends in the general population, but the equation can overestimate or underestimate body fat levels in many people.

Body Mass Index, or BMI, measures the relationship between a person’s height and weight. Your BMI indicates whether you are underweight, overweight, obese or at a healthy weight. You can use the same formula to calculate an infant’s BMI that you would use to calculate an adult’s BMI.

Neurotransmitters are the chemical communicators that are shared between neurons in your body, causing an action or reaction of a specific nerve or group of nerves. The neurotransmitters norepinephrine and serotonin play an important role in your psychological wellness.

You can use one of a number of ways to calculate a healthy size for any given weight, including ideal height calculations, body mass index and waist-for-height measurements.

Call it your "muffin top," "middle-age spread," "jelly rolls" or "apron," but there's nothing harmless about belly fat. Excessive belly fat puts you at a high risk of developing chronic disease. Men with a waist larger than 37 inches and women with one larger than 31.

At 6-foot-2 your ideal weight can fall into a nearly 50-pound ideal range. Even outside of this range your weight may still be healthy if your body fatness is within the ideal range.

Too much body fat puts you at risk for chronic disease, but having too little can also endanger your health and well-being. Older adults or those recovering from illness sometimes experience unintentional weight loss that leads to very low body fat levels.