Fit or Fat?
Q: What is the difference between BMI, body fat and fat-free mass?
A: Thank you to my father for this thoughtful question. Body weight and body composition are not the same thing but are often times used interchangeably. Body weight is the total mass of a person. Body composition is different substances or tissues that make up that person's mass. Often times people measure their leanness by body weight, however, this is not entirely accurate. Although, generally people who weigh more do have a higher percent of body fat.
BMI is the body mass index. This was once considered an accurate way to determine if a person is at an increased risk for health issues depending on which category they fall into. A BMI < 18.5 kg/m2 is considered underweight, BMI 18.5 - 24.9 is considered "normal", BMI 25-29.9 is considered "overweight" and anything >30 is considered "obese." To figure out your BMI, take your weight in kg (wt in lbs /2.2) and divide by your height in meters squared i.e. someone who is 5'4 and weighs 120 lbs has a BMI of 54.5 kg/2.62 m = 20.8. However, we are now moving towards more accurate ways to determine these ranges as BMI is not entirely accurate. Take for instance a man who is 5'9 and weighs 180 lbs. His BMI is 26.7 kg/m2 which puts him in the "overweight" category. Now, take a pro-athlete with the exact same measurements. He, too, is in the "overweight" category, but his body composition may be completely different. The athlete likely has more muscle which increases his overall mass but has a low body fat percentage, so he is not at as high of a risk for health issues as the former.
The body is made up of about 60% water, 14-16% of protein and fat, 4-6% of minerals, and less than 1% of carbohydrates. These components are usually identified as fat mass (FM), lean body mass (LBM), fat-free mass (FFM) and bone mineral mass (BMM). FFM includes only nonfat components of the body whereas LBM includes essential fat depots as well as FFM. Essential fat is found in bone marrow, central nervous system and organs. Nonessential fat is found in adipose tissue. Body fat deserves the most attention because excessive fatness leads to chronic health issues. Higher FFM can be associated with greater bone density and greater skeletal muscle whereas lower levels of FFM can result in lower energy expenditure and more prone to weight gain, reduced glucose tolerance and decreased strength. For men, a level of body fat > 25% is considered the lower threshold for obesity. Women are considered obese when their body fat exceeds 33%. There are several methods used to estimate body composition including under water weighing, bioelectrical impedance analysis (BIA), and dual-energy X-ray absorptiometry (DXA or DEXA). These methods require machines and sometimes a lab which can get pricey. Skin-fold tests are another way to measure body fat percentage which does not require an expensive tool, but does require an expert to perform for accurate results. BIA separates body composition into FM and FFM. BIA passes a small electrical current from one body extremity to another. Electrical current is transmitted through body tissue. Adipose tissue (fat) provides resistance to electrical current and fluids (found in lean tissue) conduct electrical current. Therefore percentage of body fat can be estimated from resistance. Most athletes have a body fat percentage of 12-22% for women and 5-13% for men. For optimal health, the ranges are 18-30% for women and 10-25% for men. For optimal fitness the ranges are 16-25% for women and 12-18% for men. The average body fat percentages are 15-18% for men and 22-25% for women. Accuracy of this test may be skewed depending on hydration status, recent exercise, recent food/beverage intake and diuretics. Say a man weighs 175 lbs with a body fat percent of 18, 175 x 0.18 = 31.5 lbs. His fat free mass would then be 175-31.5 = 143.5 lbs. His goal is to have 15% body fat, so his goal body weight = (15% body fat = 85% fat free mass) 143.5 lbs/ 0.85 = 168.8 lbs.
There are many other ways to measure body fat percentage, but that would take much more detail to discuss and I can only hold your attention for so long....
Until next time, lift the dumbells more than the ice-cream.
BMI is the body mass index. This was once considered an accurate way to determine if a person is at an increased risk for health issues depending on which category they fall into. A BMI < 18.5 kg/m2 is considered underweight, BMI 18.5 - 24.9 is considered "normal", BMI 25-29.9 is considered "overweight" and anything >30 is considered "obese." To figure out your BMI, take your weight in kg (wt in lbs /2.2) and divide by your height in meters squared i.e. someone who is 5'4 and weighs 120 lbs has a BMI of 54.5 kg/2.62 m = 20.8. However, we are now moving towards more accurate ways to determine these ranges as BMI is not entirely accurate. Take for instance a man who is 5'9 and weighs 180 lbs. His BMI is 26.7 kg/m2 which puts him in the "overweight" category. Now, take a pro-athlete with the exact same measurements. He, too, is in the "overweight" category, but his body composition may be completely different. The athlete likely has more muscle which increases his overall mass but has a low body fat percentage, so he is not at as high of a risk for health issues as the former.
The body is made up of about 60% water, 14-16% of protein and fat, 4-6% of minerals, and less than 1% of carbohydrates. These components are usually identified as fat mass (FM), lean body mass (LBM), fat-free mass (FFM) and bone mineral mass (BMM). FFM includes only nonfat components of the body whereas LBM includes essential fat depots as well as FFM. Essential fat is found in bone marrow, central nervous system and organs. Nonessential fat is found in adipose tissue. Body fat deserves the most attention because excessive fatness leads to chronic health issues. Higher FFM can be associated with greater bone density and greater skeletal muscle whereas lower levels of FFM can result in lower energy expenditure and more prone to weight gain, reduced glucose tolerance and decreased strength. For men, a level of body fat > 25% is considered the lower threshold for obesity. Women are considered obese when their body fat exceeds 33%. There are several methods used to estimate body composition including under water weighing, bioelectrical impedance analysis (BIA), and dual-energy X-ray absorptiometry (DXA or DEXA). These methods require machines and sometimes a lab which can get pricey. Skin-fold tests are another way to measure body fat percentage which does not require an expensive tool, but does require an expert to perform for accurate results. BIA separates body composition into FM and FFM. BIA passes a small electrical current from one body extremity to another. Electrical current is transmitted through body tissue. Adipose tissue (fat) provides resistance to electrical current and fluids (found in lean tissue) conduct electrical current. Therefore percentage of body fat can be estimated from resistance. Most athletes have a body fat percentage of 12-22% for women and 5-13% for men. For optimal health, the ranges are 18-30% for women and 10-25% for men. For optimal fitness the ranges are 16-25% for women and 12-18% for men. The average body fat percentages are 15-18% for men and 22-25% for women. Accuracy of this test may be skewed depending on hydration status, recent exercise, recent food/beverage intake and diuretics. Say a man weighs 175 lbs with a body fat percent of 18, 175 x 0.18 = 31.5 lbs. His fat free mass would then be 175-31.5 = 143.5 lbs. His goal is to have 15% body fat, so his goal body weight = (15% body fat = 85% fat free mass) 143.5 lbs/ 0.85 = 168.8 lbs.
There are many other ways to measure body fat percentage, but that would take much more detail to discuss and I can only hold your attention for so long....
Until next time, lift the dumbells more than the ice-cream.
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