Untitled lesson

Decoding Body Composition

Jana Jabbour PhD, MPH, LD

NUT 623: Advanced MNT

Learning Outcomes

•Appraise body composition assessment protocols.

•Compare and contrast the accuracy, precision,

cost, and practicality of different body composition

assessment methods.

•Propose research questions related to body

composition and its impact on health and

performance.

Body Composition

• The proportion of various components that make up the human body

• Main components:

• Fat Mass

• Lean body mass (muscles, bones, and organs)

• Water

• Focuses on the quality of the weight

Epidemiology

• Obesity

• Low body fat percentage

• Wasting

Sarcopenia

Obesity

Sarcopenic Obesity

Body Composition Techniques

• Magnetic Resonance Imaging (MRI)

• Computed Tomography (CT)

• Dual-Energy X-Ray Absorptiometry (DXA)

• Bioelectrical Impedance Analysis (BIA)

• Skinfold Thickness Measurements

MRI

• Description

• Provides high-resolution

images of fat and muscle
distribution.

• Gold standard for assessing

muscle quality and organ fat.

• Site of measurememnts

• Key Terms

• Resolution: The ability to

distinguish between tissues.

• Fat Fraction: The proportion

of fat in a specific area.

•Strengths

• Precise and non-invasive.
• Effective for measuring

intramuscular and visceral fat.

•Limitations

• Expensive, time-consuming,

and requires trained
personnel.

•Correlation

• High correlation with other

gold standard techniques like
CT and DXA (r > 0.9).

CT

• Description

•Uses X-rays to produce cross-sectional
images of the body.

•Quantifies visceral and subcutaneous fat.

• Key Terms

•Hounsfield Units (HU): Measurement
scale for tissue density.

•Visceral Fat Area (VFA): Fat located
around internal organs.

•Strengths

• Accurate for assessing visceral fat.
• High correlation with metabolic health

markers.

•Limitations

• Radiation exposure.
• High cost.

•Correlation

• High correlation with MRI for fat

distribution and tissue density (r >
0.9).

DXA

• Description

•Uses X-rays to measure body composition,
including fat mass, lean mass, and bone
mineral density (BMD).

• Key Terms

•Bone Mineral Density (BMD): A measure
of bone strength.

•Regional Fat Analysis: Fat distribution
across specific areas of the body.

•Strengths

• Relatively quick and non-invasive.
• High precision for bone and fat mass

measurement.

•Limitations

• Limited accessibility.
• Cannot distinguish visceral fat from

subcutaneous fat.

•Correlation

• Moderate to high correlation with MRI

and CT for total and regional fat (r =
0.8–0.9).

DXA

• Description

•Measures body composition by sending a
small electrical current through the body.

• Key Terms

•Resistance: Opposition to the electrical
current through body tissues.

•Reactance: Delay in the current due to cell
membranes.

•Impedance: Combined measure of
resistance and reactance.

•Phase Angle: Reflects cell membrane
integrity and hydration status.

•Strengths

• Portable, inexpensive, and easy to

use.

• Suitable for field studies.

•Limitations

• Results affected by hydration, food

intake, and device quality.

• Less accurate in very obese or very

lean individuals.

•Correlation

• Moderate correlation with DXA and

MRI for fat-free mass (r = 0.7–0.9).

DXA

•Strengths

• Relatively quick and non-invasive.
• High precision for bone and fat mass

measurement.

•Limitations

• Limited accessibility.
• Cannot distinguish visceral fat from

subcutaneous fat.

•Correlation

• Moderate to high correlation with MRI

and CT for total and regional fat (r =
0.8–0.9).

Computed Tomography

DXA

BIA

• Reactance

• Resistance

Body Composition Derived Measures

•Skeletal Muscle Mass (SMM):
•Reflects the total muscle mass in the body.
•Important for assessing sarcopenia and functional capacity.
•Measured by techniques like DXA, BIA, or MRI.
•Lean Body Mass (LBM):
•Composed of all non-fat components, including muscle, water, bone, and organs.
•Significant in evaluating metabolic health and energy expenditure.
•Body Fat Percentage (BF%):
•Total body fat expressed as a percentage of total body weight.
•A primary marker of obesity and overall metabolic health.
•Bone Mineral Content (BMC):
•Indicates the weight of minerals in the bones.
•Used to assess osteoporosis risk, commonly measured using DXA.

Body Composition Derived Measures

•Extracellular Water (ECW) vs. Intracellular Water (ICW):
•ECW: Water outside cells, reflects hydration status and edema.
•ICW: Water within cells, associated with cell function and muscle health.
•Measured via BIA and segmental BIA.
•Visceral-to-Subcutaneous Fat Ratio (V/S Ratio):
•Indicates fat distribution, with a high ratio associated with increased cardiometabolic risks.
•Measured through imaging techniques like MRI or CT.
•Phase Angle (PhA):
•Reflects the integrity and function of cell membranes.
•A higher phase angle is indicative of better health and nutritional status.
•Calculated from BIA-derived resistance and reactance.

Compartment Models of Body
Composition

•2-Compartment Model

•Divides the body into fat mass and fat-free mass.

•Common techniques: BIA, Skinfolds.

•Limitation: Does not account for water, bone, or specific tissue types.

•3-Compartment Model

•Divides the body into fat mass, water, and fat-free dry mass.

•Common techniques: DXA with additional hydration measurements.

•Advantage: Better accuracy than 2-compartment models.

•4-Compartment Model

•Divides the body into fat mass, water, bone mineral content, and residual (protein).

•Combines data from multiple techniques (DXA, BIA, densitometry).

•Gold standard for accuracy.

The power of
communicatio
n

Overcoming
nervousness
Confidence-building
strategies

Thank you