Regional Fat Deposition (WHR)

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Abdominal Body FatRelationships with CHD RisksAbdominal obesity predicts CHD risk independent of BMI, smoking, cholesterol and hypertension (Kannel et al., J. Clin Epid., 44, 183-190, 1991). Abdominal obesity predicts CHD risk independent of total body fatness. (Larsson et al. ,Appetite, 13, 37-44, 1989). Abdominal obesity statistically accounts for the difference in CHD rates between men and women (Larsson et al., Am. J. Epi., 135: 266-273, 1992).

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Abdominal Body FatRelationships with other risk factorsAbdominal obesity is strongly influenced by genetics - similar gain among twins (r=.72). (Bouchard, NEJM, 322, 1477-1482, 1990). Abdominal obesity is greater in smokers than non-smokers due to the presence of androgens (Barrett-Conner, Ann. Int. Med. 111, 783-787, 1989). Abdominal body fat is preferentially lost during a physical activity program (Kohrt, J. Gerontology, 47: M99-M105, 1992)

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Body Composition EstimationBMICircumference MeasuresSkinfoldsBioelectric impedanceUnderwater WeighingImaging techniques (DEXA, MRI)

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BMIs for Adults

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Underwater Weighing Technique Body fat provides more buoyancy so a fatter person weighs less (on a relative basis) than a lean person

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Body Composition AssessmentImplications of ResultsValues are estimates (+/- 2-3% at best)Values are personal and confidential

Proper uses of results:- Serve as baseline data for repeated testing- Provide motivation for goal setting- Provide awareness about health risks

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Calculating Desired Body Weight (Example)

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Fundamental Concepts 2e2This lecture will cover the subject of body composition. Students will learn about the different assessment techniques and how body composition influences health.Concept 12Fundamental Concepts 2e5Many health problems are associated with excess levels of body fatness

Obesity is considered to be a secondary risk factor for coronary heart disease mainly because the effect of body fatness is manifested in other risk factors. These data show the relative risk of other risks if you are overfat (data from NHANES II data cited in VanIttallie (1992):Hypertension (RR = 2.9x)Hypercholesterolemia (RR = 1.5xDiabetes (RR = 2.9x) VanIttallie, T. B. (1992) Body Weight, Morbidity, and Longevity. IN: Bjorntorp, P. & Brodoff, B.N. (Eds.) Obesity. Lippincott Co.., Philadelphia.

Concept 12Fundamental Concepts 2e6Discuss the 2 compartment model of body composition.Fat Mass (FM)Lean Body Mass (LBM) or Fat Free Mass (FFM)

Concept 12Fundamental Concepts 2e9The site of fat deposition is also an important consideration for health. Fat stored in the abdominal region presents more risk than fat stored in the lower or upper extremities

Concept 12Fundamental Concepts 2eThere are many studies that document the health risks associated with abdominal obesity.Concept 12Fundamental Concepts 2eThese are some additional studies that document the health risks of abdominal obesityConcept 12Fundamental Concepts 2e5Other body fat assessment techniques are available.

Bioelectric Impedance:Electrical conduction is different in different tissues. Muscle has water and is a good conduction. Fat has less water and is a poor conductor. It tends to overestimate %fat in lean people and underestimate %fat in fat people.

Infra RedAbsorption of light is different in different tissues.

UltrasoundSound absorbence is different in different tissues (muscle: sounds bounces off; fat: sounds pass through)

Imaging Techniques (DEXA, MRI)Considered to be highly accurate but expensive

Chemical measures (3 methyl histidine - waste product of muscle - corr with LBM

Concept 12Fundamental Concepts 2e4The gold standard measurement for body composition assessment is currently underwater weighing. It is based on the fact that muscle is more dense than fat- muscle is like a rock (it sinks)- fat is like styrofoam (it floats)

By weighing a person underwater you can estimate body density. The procedure is based on Archimedes Principle which states that the buoyant force is equal to the weight of the volume of water that is displaced. Fat because it is less dense occupies a larger volume which gives it a larger buoyant force

NOTE: The story of Archimedes and the gold crown is effective for explanation (muscle = gold and fat = silver)

Concept 12Fundamental Concepts 2e11Body Fat estimates from calipers must be interpreted correctly. It is important to keep the following factors in mind:

1. The estimates have 2-3% error so the value that results is not "exact". It is more important to look at trends over time.

2.Values serve as baseline for goal setting. You need to know where you are to set objective goals. Book has a chart to calculate desired weight based on current level and desired level (formula available from instructor).

3. Values are individual. People should not compare values with other people or be embarrassed about their numbers. Each person is different and it may not be possible for all people to achieve the ideal percent body fat.

Concept 12Fundamental Concepts 2e19This slide shows the calculations used to calculate desired body weight based on current body fat percentage and desired body fat percentage

A chart in the book simplifies this calculation

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