Ricki Colman (UW) - Body composition in CR monkeys
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Components: Fat, water, protein, bone/mineral

Many body composition models:
o     chemical analysis of cadavers
o     Two, three and four compartment models

Many ways of measuring body composition: weight, size measurements (skinfolds,
BMI, abdominal circumference, etc), impedence, MRI, CXT, dissection, etc.

All except dissection are in vivo, and are approximations.

DEXA measurements are gold standard for body composition, and particularly
bone mass measurement.

Trying to use MRI imaging to measure muscle mass directly, and distinguish 
visceral from subcutaneous fat.

Body composition important indicator of energy economy. Important marker 
for risk of many diseases.

Serious loss of muscle mass (sarcopenia) can be very dangerous in of itself, 
not just a correlate with morbidity.

Too low body weight (BMI less than 18) , mortality goes up. Mortality appears 
U-shaped with BMI. Could be due to poor nutrition in low weight people, or 
because we dont have reserves to fight disease, or because terminal illnesses 
result in loss of body weight.

In "wild" monkeys that eat from human garbage dumps, you see obesity and 
diabetes. Monkeys protected in Indian temples, and fed, also develop obesity 
- like overfed lab monkeys.

Osteoporosis: Affects 8 million American women, and 2 million American men.

Females suffer more than males for several reasons:
o     lower body weight means lower total bone mass
o     Greater dip due to hormone changes around time of menopause

Bone is not a static tissue - Osteoclasts break down (resorb) bone, and 
Osteoclasts build up (deposition) bone. When these are in balance, bone 
mass is stable.

Bisphophonates (like Fosamax and Actonel) decrease bone resorption. Data on 
the bone quality as a result of Bisphophonate treatment still unclear.

Weight loss doesnt affect bone turnover, or our ability to form new bones.

Decrease in fat mass may affect estrogen levels, which alters bone formation
rate.

Impact on bone loss weight loss vs. weightlessness (in space). Weight loss 
in weightlessness very much higher than that seen in weight loss.

If youve already lost bone mass - high impact training can help increase bone 
mass. But in older people, and people with lower hormones, there may not be 
enough anabolic factors to increase bone mass, even with exercise.

Lots of factors impact bone density:
o     calcium
o     every hormone the body produces impacts calcium metabolism, and 
      therefore bone density.

DEXA measures bone mass, then it uses area (approximation for volume) analysis 
to figure out bone density (bone mass / cm3).

Factors influencing factor risk:
o     bone factors
o       bone mass
o       bone quality
o     trauma
o       impact - fat padding
o       frequency - coordination, ability to avoid falls via quick reactions

Rhesus monkey very good model for human bone loss. Rats and small mammals dont 
do bone remodeling (turnover) - so rats arent good model. Example, fluoride 
helps build rats bone density, but hurts human bone density.

Bone density decreases with age in male AL-fed Rhesus monkeys - peaks at 10 
years and goes down from there.

Bone density decreases after menopause in female AL monkeys.

Longitudinal drop in pre-menopausal female AL-fed monkeys with age.

Visceral fat went up, and thigh muscle mass went down with age in AL monkeys.

Lots of measures done one a year in the CR and AL monkeys in Wisconsin primate 
lab.

Restricted animals have 30% lower food intake (via individual calorie intake 
baseline).

AL-fed monkeys given 40g more food per day than their (individual) average intake.

Control and restricted animals originally received same food (just less for CR). 
Changed to give CR animals extra nutrients to match nutrient intake of controls. 
She didnt think prior to this switch that the CR animals were deficient due to 
excess in the standard diet, but cant be certain.

AL monkeys in Wisconsin are eating less now. There is a question about whether 
they will need to restrict CR animals more, in order to maintain 30% restriction 
relative to AL monkeys. Tough question, leaning against it. Leaning towards 
basing feed level on animals individual health requirements.

Another weirdness, all the groups are gaining fat mass lately.  It is *possible* 
that control animals are handing food to CR animals.

Arent seeing longitudinal skeletal muscle loss in CR monkeys.

Insulin sensitivity - much better on CR monkeys. After their recent (unexplained) 
fat mass gain, their insulin sensitivity went down.

C-Reactive Protein lower in CR monkeys than AL.

See decreased bone mass in CR monkeys - due lower body size, or something more 
insidiously?

Human data from NHANES study - very strong correlation between weight and bone
mass.

New Data - Looked at correlation between weight and bone mass within monkey
groups. In males CR monkeys looks like all of bone loss can be explained by
simple drop in total body weight, which results in bone loss as well as other
tissue loss.  Appears nothing extra (bad) is happening with CR in monkeys.

DEXA may chronically underestimate bone density and mass in skinny people.
Calibrated for heavy people. They carefully calibrate their DEXA machine for
low body weight monkeys. May not be done in human DEXAs.

Bone turnover rate (NtX) not different between CR and AL.

Havent measured bone quality - looking into it.