Body Composition Over the Lifecourse

Question 1

What factors influence body composition and should be considered in a nutritional assessment?

Answer 1

• nutrient intake
• energy metabolism
• physical activity
• hormonal regulation of metabolism

Question 2

What are the compartments of body composition?

Answer 2

• Fat mass = subcutaneous and visceral fat, functional/ essential fat
• FFM = skeletal mass, organs, bone, extracellular fluid
• Body cell mass = skeletal muscle and organs

Question 3

What is considered normal?

Answer 3

this can vary tremendously within and between individuals with the separation between age-related normal and disease related normal where genes, environment and behaviour interact

Question 4

2 compartment models of body composition

Answer 4

Can measure fat mass and fat free mass: skinfolds, underwater weighing, air displacement, BIA
* strength: convenient, low cost, simple
* limitation: 2 compartment model does not distinguish components of fat free mass

Question 5

Golden standard for measuring body composition

Answer 5

DXA
* 3 compartment model for fat mass, lean body mass and bone mass (density measures)
* can assess skeletal muscle mass: appendicular lean body mass
* limitation: difficult to access and costy

Question 6

What scans can be used for body composition?

Answer 6

MRI, CT, PET which are mostly used for abnormalities in body composition in a clinical setting
* body fat regions: subcutaneous, visceral, intra-fat
* skeletal muscle and organs
* limitation: inaccesible unless have a diagnosis which requires a scan and very costly

Question 7

How does general body composition change over the lifecourse?

Answer 7

subtle and gradual changes beginning from the moment of conception to death

Question 8

What are the 3 main phases of body composition changes over the lifecourse?

Answer 8

• growth and development
• maturity
• aging

Question 9

General treands of body composition changes during growth and development

Answer 9

• gain all components during growth
• sex differences starting at ~5 years, but minor until puberty
• fat mass and percent body fat are highly variable throughout

Question 10

How is body fat variable during growth and development?

Answer 10

at birth 14-16% BF but by 1 year can be 22-24%. This can then decrease in early childhood following by a rebound adipositiy and continual gain.

Question 11

BMD changes during growth and development

Answer 11

BMD increases but tapers at approximately the end of adolescence for boys and a bit sooner for girls

Question 12

LBM changes during growth and development

Answer 12

• boys see gradual increase but then a jump between 13 and 15 followed by further gradual increase
• girls see gradual increase but this tapers slightly arounf puberty

Question 13

How does percent body changes during growth and development differ between boys and girls?

Answer 13

• boys it stays pretty much stable
• girls see a gradual increase

Question 14

Fat mass changes during maturity and aging

Answer 14

remains the most variable component (certain life points may see more such as getting married, pregnancy, university) but total fat increase slowly with age although the rate differs by sex and possibly race/culture
* men ~0.37 kg/yr; starts to decrease around 60 yrs, except puerto ricans continue increase
* women ~0.41 kg/yr; starts to decrease around 60 yrs although

Question 15

FFM (LBM) changes during maturity and aging

Answer 15

Generall this declines with aging with mainly skeletal muscle mass which is a part of body cell mass and is the most metabolically active FFM (bone density also decreases).
* Ex. body cell mass in men 20-29 is 59% of FFM and 80-89 is only 46%.

Question 16

How does BMD change with aging and maturity?

Answer 16

BMD peaks between 20-30 years of age and then begins to decrease (final height is reacher slightly before peak BMD)
* The more you have the longer it takes to get to the fracture zone which starts around age 50

Question 17

Skeletal muscle mass changes during maturity and aging

Answer 17

skeletal muscle mass is the second most variable component within and between individuals after fat mass. It stays relatively stable within individuals during younger adult years up to to ~30, after which this mass begins to decrease (and fat mass increase).
* the rate of decrease is greater in men then women and accelerates >65 years
* The more you can retain the longer it takes to reach the disability threshold in later years

Question 18

What factors contribute to skeletal muscle mass change during aging?

Answer 18

• age-related decrease in muscle area/volume
• age-related reduction in muscle protein synthesis rate
• loss of skeletal muscle fibre
• reduction in skeletal muscle fibre quality
• reduction in anabolic hormones

Question 19

Describe age-related decrease in muscle area/volume

Answer 19

decrease in muscle area/volume is associated with a functional reduction in strength and muscle oxygen uptake
* starts mid-40s
* more lower body than upper body for both men and women
* Men see more drastic decrease then women for both (but women overall low skeletal muscle)
* Also see a loss in functionality (strength) of muscle

Question 20

Describe age-related reduction in muscle protein synthesis rate

Answer 20

This is the progressive decrease in the the synthesis rate of the myosin heavy chain fibres AND decreased stimulation of muscle protein synthesis by AA
* More AA are needed to stimulate muslce protein synthesis (requires more substrate to evoke same amount of synthesis that would occur in a young person)

Question 21

Describe the loss of skeletal muscle fibre with aging

Answer 21

This begins with the loss or impairment of motor neurons (denervation) which causes the muslce fibre to atrophy and eventually die since it is not being stimulated.
* absolute reduction in type II (fast twitch) muscle fibre area with relative preservation of type I

Question 22

What is the different between type I and II muscle fibres?

Answer 22

• Type I are slow twitch, red, slow oxidative and fatigue resistant which have lots of mitochondria and therfore depend upon cellular respiration for ATP. Dominant in muscles for posture and endurance (sustained activities) Hence individuals are typically always using these muscle in every day activities.
• Type II are fasr twitch, whitem fast glycolytic and quick to fatigue with few mitochondria but rich in glycogen so depend on glycolysis for ATP production. Dominant in rapid movement muslce (fight or flight/ anaeorobic). In order to maintain these muscle would have to be more intentional through strength training.

Question 23

Describe the reduction in skeletal muscle fibre quality with aging

Answer 23

In vitro studies of type I and type IIA muscle fibres (aging compared to younger adults) have showed
* lower maximal force
* reduced shortening velocity

Question 24

Describe the reduction of anabolic hormones that occurs with aging

Answer 24

Decrease in growth hormone, insulin-like growth factor-1, estrogen/progesterone, testosterone, etc.
* linked to decrease in muscle mass but increase in fat mass and can result in insulin resistance

Question 25

What are the body composition phenotypes with muscle mass:fat mass?

Answer 25

• healthy
• obese
• sarcopenia
• sarcopenic obesity

Question 26

What is sarcopenia

Answer 26

Loss of muscle mass and strength (often age-related but not always).
* appendicular skeletal muscle is 2SD below the mean for young healthy adults
* mass ↓ = ~0.8% per year
* strength ↓ = ~2-4% per years

Question 27

What is the impact of sarcopenia on health?

Answer 27

ultimately an increase in mortality and morbidiy

• Functional limitation (impairment such as standing up from sitting position, balance, walking ability) and disability with decreased strength and power of muscle
• Increased risk for falls and bone fractures
• Increased risk of infections
• Increased length of hospital stay
• decreased response to treatments

Question 28

How does the criterion for sarcopenia differ?

Answer 28

Everyone has a different definition of what sarcopenia means, ours is 2 SD below
* Groups try to define cuts points of what level of muscle mass is associated with the poor outcome but controversial people
* Typically standardized by DXA, or BMI and all include functionality to some capacity.

Question 29

prevalence of sarcopenia during aging

Answer 29

• men see a jump around 75-80 and another jump >80
• women see a jump around 70-74 and another jump >80

Question 30

What is SO?

Answer 30

sarcopenia obesity (an emergency syndrome) that combines low muscle mass with greater amounts of adiposity that has occured relatively recently due to the aging population and higher prevalence of obesity
* influenced by food environment and less physical activity

Question 31

How does SO compare to sarcopenia or obesity alone?

Answer 31

worse outcomes than obesity or sarcopenia alone with a high metabolic load but low metabolic capacity.
* More weight but less ability to hold it with fragile bone and not metabolically active weight

Question 32

Why is SO a new emerging syndrome?

Answer 32

obesity acts synergistically with sarcopenia to maximize disability

Question 33

What is the prevalance of SO?

Answer 33

about 25% of the population ranging from mild, moderate and severe.
* males moreso than females

Question 34

How can sarcopenia and obesity be assessed in older adults?

Answer 34

• BMI classifications but not useful for assessing sarcopenia or muscle mass
• measure skeletal muscle mass through DXA but not always practical or accessible
• In clinical setting can do antropometric measures, handgrip tests, chair standing test

Question 35

What nutrients are currently being researched which may have a benefical effect for retainin muscle?

Answer 35

• vitamin D: increase protein synthesis and anti inflammatory effects
• Leucine: increase protein synthesis and attenuate protein degradation
• hydroxy methyl butyrate (HMB): increase protein synthesis and protective effects on muscle cells