2.16 Body Composition and Energy Balance Flashcards
What is body composition
A branch of human biology focusing on in vivo quantification of body components and how they interact.
What are some reasons for measuring body composition
- to assess nutrition quality and any specific nutritional problems
- to look for significant decreases in body composition which can indicate undernutrition - disease related undernutrition with inflammation (e.g chronic kidney disease, cancer or cachexia), disease related undernutrition without inflammation (e.g dysphagia or anorexia) or undernutrition without disease (e.g food insecurity or poverty)
- there are strong relationships such as between body composition and chronic disease and elevated fat mass and cardiometabolic disease
- there is a relationship between fat free mass and functional capacity, improving strength, balance and reducing mortality risks
- to help categorise a sample given for any scientific study
- to assist in energy balance and give an estimation for energy expenditure
What are the two different components of body composition
Fat mass and fat free mass
What is fat mass made up of
It is loose connective tissue mostly made up of adipocytes. Different types of fat include;
-loose connective tissue mostly made of adipocytes
-essential fats are in tissues and organs (e.g bone marrow, nervous system and muscle), 3% average for men 12% for women
-storage fats are energy reserves as adipose tissue beneath skin and in visceral depots- accumulates when energy input exceeds expenditure (influenced by lifestyle and genetic)
-android (specifically visceral) fat is found in central abdominal areas (associated with many metabolic conditions)
-gynoid fat is found in hip and gluteal regions, is not associated with metabolic health, women have more for child bearing reasons
Where can fat mass cause damage
Fat mass around organs can cause damage, e.g liver and pancreas fat is associated with insulin resistance
What is fat free mass
Fat free mass is mass that does not have adipose tissue. It is made up of lean tissue, which is protein and body water, as well as bone.
What is fat free mass hydration
The proportion of fat free mass made of water, including intracellular and extracellular water (the extracellular to intracellular ratio stays fairly constant unless there is disease).
Describe changes in bone mass over time
Bone mass increases early in life and peaks early in adulthood, it then decreases from then onwards. Bone density is a determinant of bone strength, the minerals that determine density are primarily calcuim and phosphate
Describe changes in skeletal muscle mass over time
Skeletal muscle mass increases during adolescence, is stable from 30-40 and then decreases after, during old age rapid decrease can cause sarcopenia.
What factor can slightly modify organ size
Nutrition
What are the average changes in fat mass and fat free mass every year during adulthood
During adulthood the average person gains 0.5kg of FM and looses 0.2kg of FFM per year
Describe changes in bodyweight and BMI as you age
Body weight and BMI increase up until 70-80 when it declines due to hormonal and lifestyle factors
Describe some different body composition assessment methods
Body mass index (BMI):
-BMI (kg/m2) = weight (kg) / [height (m)]^2
-used as a screening tool to see if a person is underweight, healthy weight, overweight, class 1 obese, class 2 obese or class 3 obese (morbid) in clinical settings, field surveys and large scale population studies
Skinfolds:
-pull skin and fat away from muscles and place skin callipers estimate thickness in mm of skinfolds at different body sites
-based on principle that subcutaneous fat is proportional to total fat
-uses equations to give a body density estimate
Hydrostatic weighing:
-weight in air compared to weight in water (whilst holding breath), provides volume (via archimides principle) which can be used to estimate density
-FM and FFM can be calculated from this
-residual volume of air in lungs and GI tract is taken into account, Volume = ((Weight [air] – weight [water])/density of water) – (RV)
-a person with a larger percentage of FFM will weigh more in water
Body volume measurement by air displacement:
-volume measured when a person sits in an enclosed chamber (BODPOD) and then the amount of air that is displaced
-can quantify density and then body fat
Bioelectrical Impedance Analysis (BIA):
-measures impedance (opposition to a flow) by body tissues when exposed to a small alternating electric current
-regression can provide FM and FFM estimates as non-aqueous mass gives a greater resistance than aqueous so current flows more freely through FFM (as lean mass has a lot of water but FM has little)
Dual energy x-ray absorptiometry (DEXA):
-imaging technique with high energy and low energy beams
-different masses reduce the signal at different extents
Magnetic Resonance Imaging (MRI):
-strong magnetic fields and radio frequency signals interact with protons of the tissues to produce cross sectional areas and 3D images of tissues
Digital Image Analysis:
-3D optical body scanners are a recent tool to estimate body volume, circumferences and size at body parts
