What does body fat percentage mean?

Originally Published: April 25, 2003 - Last Updated / Reviewed On: February 3, 2011
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Dear Alice,

I'm a vegetarian with 'wanna-be vegan tendencies' (i.e., I don't eat eggs or milk as a substance itself, but do it 'hidden' in other foods, like bread, pasta, etc.)

I've been advised by my fitness instructor that my 'body fat' percentage is too low, and I need to consider eating oily fish, milk, eggs, etc. in order to gain weight.

A strict vegan friend of mine has just suggested that I eat extra nuts, rice, and veg, and the extra calories will be converted to fat if I don't 'use them up,' but I'm not convinced. As a woman, I'm sure I need 'fats,' but how to get them when my choices seem limited?

Also, could you explain 'body fat percentage,' and what is safe and unsafe?

Thanks, Alice.

Dear Reader,

Your choices for increasing fat are not as limited as you may think. First off, know that body fat is essential to normal body functioning. What is referred to as essential fat is the type of fat needed to do just that — help the body function well. Essential fat is found in the bone marrow and spinal cord; it also surrounds the liver, spleen, heart, kidneys, and other organs. We also have fat in our breasts, genitals, and muscle tissue. External layers of body fat offer insulation and protect us from the cold. In addition to this, most of us have some storage fat.

Body fat percentage indicates how much of your total body composition is fat. How much is healthy or unhealthy is determined by your body and its needs. Too low a body fat percentage results in disrupted metabolism, fatigue, and lowered cognitive function, among other things. Women with "too low" body fat will develop amenorrhea (absence of menstrual periods), because the body senses inadequate energy reserves or high physical stress — and won't sustain a pregnancy, for example. Some experts believe that 17 percent body fat is needed for the onset of menses and that 22 percent body fat is needed to maintain normal menstrual cycles. Of course, some people are healthy outside of these parameters. A gynecologist or endocrinologist can better evaluate your specific situation; you can start with your primary care provider.

Body fat is measured in terms of percentage, and you can get your body fat measured at your gym, for example, but what are you going to do with the number? Getting a body fat measurement can be anxiety-provoking. Make sure you go for an assessment with a qualified health professional. Most of the measurement techniques for assessing body fat percentage fall short in terms of accuracy. A good rule of thumb is to expect a standard error of 3 percent; meaning, whatever percentage you are measured at, consider that you could, in reality, have 3 percent less or 3 percent more than that measurement. Body fat percentage is more useful as a measure to track how your body changes over time.

In terms of ways to increase body fat, you can do so by taking in more calories than you expend. One food specifically won't increase your body fat. If your eating plan is low in fats, though, you will have difficulty absorbing vitamins A, D, E, and K and a variety of valuable plant chemicals, known as phytochemicals. Your friend and/or fitness instructor may suggest high fat foods because they are denser in calories than low fat foods. This means they will provide you with more calories for a smaller amount of food. Calories supply energy, and fat has a higher number of calories per gram than other nutrients:

Nutrient Calories per gram
Fat 9
Carbohydrate 4
Protein 4

This table gives you an idea of why calories from fat may be a smart choice for you. Good choices for a vegetarian are avocados, olive and canola oil, nuts, peanut butter, and olives. If you're willing to relax your vegetarianism a bit, fatty fish are also a good option, but aren't as calorie dense as the first group of foods mentioned. If you're avoiding dairy foods, include other rich sources of calcium, such as collard greens, turnip greens, kale, or calcium-fortified juices, to strengthen bones, among other functions.

Hope this helps you understand your body a little better.

Alice