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Tuesday, November 8, 2011

Body Fat... Why Measure It?

There are two good reasons to measure body composition.  One, knowing body composition is a great way to identify and track progress towards better health or fitness.  Two, an optimal body composition affects sport performance positively.  Whether your goal is related to fitness, sport or both, body fat and bone density are some of the key physiological factors that definitely should be monitored throughout an exercise program.

Fat cells aka adipocytes fall under 
two categories based on how lipid 
is stored.  WF cells store lipid in 
one giant mass and BF cells store 
lipids in groups of many little sizes. 
Humans carry more WFC's than 
BFC's (5).
There are short term and long term changes that occur with the fat cell.  Think of the fat cell as a balloon that calls for back up when it fills up with too much air or "lipids".  When fat intake rises, the first physiological change that occurs is an increase in the size of the fat cell (up to 10x larger) caused by the storage of lipids (3).  This is a short term change which can be easily corrected through dietary and exercise interventions.  If nothing is done to reduce the amount of lipids stored in each fat cell, eventually the fat cell will call for help and stimulate cell division as well as the maturation of precursor cells to fat cells (2,3).  Basically, you'll end up with more fat cells than you started with.  Generally, someone with a normal percentage of body fat has about 30 to 50 billion fat cells whereas an obese individual can have 75-80 billion fat cells (3).  That's a lot more cells!

After the original cell undergoes
hypertrophy (enlargement), it remains
the same size even when emptied.
Things get worse...  Once the new fat cells mature, the cells itself will permanently remain the same size despite a significant loss of body fat (4).  In other words, the balloon deflates, but doesn't shrink.  This is a major reason why many of the obese who successful loses weight cannot maintain the loss easily- they become extremely efficient at storing fat.  This is why early detection is extremely important.

Just as important as it is to prevent excess body fat, it's also important to prevent body fat from getting too low.  Young women and athletes who benefit from a low body weight are particularly at risk for eating disorders (1).  Pay attention to the fine line between attention and obsession with regards to body weight or composition.

Changing body composition affects the metabolic
systems.  If less fat is available to use as energy,
more carbohydrates will be fed into the LA system.
The goal for endurance is to use more fat and save
carbs for the harder or faster parts of a race.
Because the relative proportion of bone, muscle and fat are directly affected by changing body composition, performance may decrease due to a shift from homeostasis or equilibrium.  Remember that both anaerobic and aerobic metabolic systems are used simultaneously, but at different percentages.  Because the mitochondria are located in fat and muscle, reducing fat mass will leave the mitochondria with less accessible fat to use as energy.  with a healthy diet, the body will naturally take on the optimal body fat percentage- forcing the body into extremely low body fat percentages is the goal should never be to lose as much fat as possible to get lighter.

I'm probably stating the obvious, but the older population will need to worry about a bone density condition called sarcopenia which is just a fancy word to say that an individual has lower than normal bone density.  The second group of people that should worry involves a group of people that many would not expect to have low bone density- all levels of road cyclists, including professional cyclists!  See my post that covers this topic separately, Low Bone Mass in ROAD Cyclists and Ways to Fix it.

There are six popular methods that gyms use to measure body fat and are ranked below.  In a clinic, an MRI or a CT scan can be used to get an actual visual representation of the adipose tissue.  Some methods are more accurate than others and some can be absolutely inaccurate when used on the wrong person.  Each method has its pros and cons and are discussed in detail separately.  I ranked the assessments based on most accurate (#1) to least accurate (#6).  Know your options and make sure you're getting the right assessment based on your personal preferences.
  • Body Fat Assessment #1: Hydrostatic weighing
  • Body Fat Assessment #2: Skinfold Meaurements
  • Body Fat Assessment #3: Bioelectrical Impedance
  • Body Fat Assessment #4: Body Circumference Measures
  • Body Fat Assessment #5: Waist to Hip / Waist Circumference
  • Body Fat Assessment #6: Body Mass Index "BMI

  1. Kaminsky, Leonard A..ACSM's health-related physical fitness assessment manual. 3rd ed. Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins Health, 2010. Print.
  2. Malina, R. M., C. Bouchard, O. Bar-Or (2nd ed.): Growth,  Maturation and Physical Activity. Champaign, IL: Human Kinetics (2004).
  3. Plowman, Sharon A., and Denise L. Smith. Exercise physiology for health, fitness, and performance. 3rd ed. Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins, 2011. Print.
  4. Sjöström, L., & P. Björntorp: Body composition and adipose tissue cellularity in human obesity. Acta Medica Scandinavica. 195:201–211 (1974)
  5. Malina, R. M., C. Bouchard & O. Bar-Or: Growth, Mat-uration and Physical Activity (2nd ed.) Champaign, IL: Human Kinetics, 163 (2004). Reprinted by permission.