November 22, 2011

body fat too low?

I had my body fat tested at the UNM physiology lab late last month. I had 6.8 percent body fat. The person who ran the lab told me it wasn't a good idea to get below 5 percent. I googled the reasons why. The net didn't have much to say. What information I was able to find was very basic. I posted some of the info the web site's had posted (see 3rd paragraph and below).

After giving up on getting the information on the net I contacted a dietitian. He told me essential body fat is necessary to regulate my core body temperature. Fat is necessary to create hormones like testosterone. Eating fat and having a minimum amount of essential body fat is also necessary for absorption of fat soluble vitamins. Vitamins A, D, E and K are all classified as fat soluble vitamins - since they are soluble in fat and are absorbed by the body from the intestinal tract. They follow the same path of absorption as fat and any condition interfering with the absorption of fats or not having enough fat in storage would result in poor absorption of these vitamins.

Wikipedia says:
A person's percentage is the total weight of the person's fat divided by the person's weight and consists of essential body fat and storage body fat. Essential body fat is necessary to maintain life and reproductive functions. The percentage for women is greater than that for men, due to the demands of childbearing and other hormonal functions. Essential fat is 3%–5% in men, and 8–12% in women. Storage body fat consists of fat accumulation in adipose tissue, part of which protects internal organs in the chest and abdomen. The minimum recommended total body fat percentage exceeds the essential fat percentage value reported above.

ask.com says:
Men can get down to around 5% and women to about 12% body fat. Below those numbers you really have to be careful that some basic physiological and hormone systems aren't disrupted to the extent that you get ill. The immune system can suffer, and in women, periods can go missing and bone health can be affected adversely.

An article written by a UNM exercise physiology student says:
Body Composition
The body is composed of water, protein, minerals, and fat. A two-component model of body composition divides the body into a fat component and fat-free component. Body fat is the most variable constituent of the body. The total amount of body fat consists of essential fat and storage fat. Fat in the marrow of bones, in the heart, lungs, liver, spleen, kidneys, intestines, muscles, and lipid-rich tissues throughout the central nervous system is called essential fat, whereas fat that accumulates in adipose tissue is called storage fat. Essential fat is necessary for normal bodily functioning. The essential fat of women is higher than that of men because it includes sex-characteristic fat related to child-bearing. Storage fat is located around internal organs (internal storage fat) and directly beneath the skin (subcutaneous storage fat). It provides bodily protection and serves as an insulator to conserve body heat. The relationship between subcutaneous fat and internal fat may not be the same for all individuals and may fluctuate during the life cycle.
Lean body mass represents the weight of your muscles, bones, ligaments, tendons, and internal organs. Lean body mass differs from fat-free mass. Since there is some essential fat in the marrow of your bones and internal organs, the lean body mass includes a small percentage of essential fat. However, with the two-component model of body composition, these sources of essential fat are estimated and subtracted from total body weight to obtain the fat-free mass. Practical methods of assessing body composition such as skinfolds, bioelectrical impedance analysis (BIA), and hydrostatic weighing are based on the two-component (fat and fat-free mass) model of body composition.


Standards of Body Fat nessary
Our bodies require essential fat because it serves as an important metabolic fuel for energy production and other normal bodily functions. Referring to Table 1, you can see that the essential fat requirements are < 5% for men and < 8% for women. Normal body functions may be disrupted if body fat falls below the minimum level recommended for men (5%) and women (15%). The body fat ranges for optimal health (18%-30% for women and 10%-25% for men) are based on several epidemiological studies of the general population. Body fat percentages for optimal fitness and for athletes tend to be lower than optimal health values because excess fat may hinder physical performance and activity.

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