Differential effects of casein versus whey on fasting plasma levels of insulin, IGF-1 and IGF-1/IGFBP-3: results from a randomized 7-day supplementation study in prepubertal boys.
OBJECTIVE
Milk increases both fasting insulin and insulin-like growth factor 1 (IGF-1), and thereby growth, in healthy prepubertal boys. It is, however, unknown which components in milk are responsible for milk's growth-stimulating effect.


METHODS
To get closer to the identification of which components in milk that stimulate growth, we have performed an intervention study with 57 eight-year-old boys in which we examined the effects of the two major milk protein fractions, whey and casein, and milk minerals (Ca and P) in a 2 x 2 factorial design on IGFs and glucose-insulin metabolism. The amounts of whey and casein were identical to the content in 1.5 l skim milk. The amounts of Ca and P were similar to 1.5 l skim milk in the high-mineral drinks, whereas the amounts of Ca and P were reduced in the low-mineral drinks.


RESULTS
There were no interactions between milk mineral groups (high, low) and milk protein groups (whey, casein). Serum IGF-1 increased by 15% (P<0.0001), whereas there was no change in fasting insulin (P=0.36) in the casein group. In the whey group, fasting insulin increased by 21% (P=0.006), with no change in IGF-1 (P=0.27). There were no independent effects of a high milk mineral intake on IGF-1 and insulin.


CONCLUSIONS
The main milk protein fractions exhibit important but different growth-promoting effects by increasing either fasting insulin (whey) or IGF-1 (casein) levels.
Hoppe
C
C
Department of Human Nutrition, Faculty of Life Sciences, University of Copenhagen, Frederiksberg, Denmark. cahop@food.dtu.dk
Mølgaard
C
C
Dalum
C
C
Vaag
A
A
Michaelsen
K F
KF
D002118:Calcium / Q000494:pharmacology; D002136:Calcium, Dietary / Q000008:administration & dosage; D002364:Caseins / Q000494:pharmacology*; D002648:Child; D004044:Dietary Proteins / Q000008:administration & dosage*; D004311:Double-Blind Method; D006801:Humans; D007328:Insulin / Q000097:blood*; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000097:blood*; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D008297:Male; D008894:Milk Proteins / Q000494:pharmacology*; D010758:Phosphorus / Q000494:pharmacology; D016226:Phosphorus, Dietary / Q000008:administration & dosage; D000067816:Whey Proteins
D002136:Calcium, Dietary; D002364:Caseins; D004044:Dietary Proteins; D007328:Insulin; D018972:Insulin-Like Growth Factor Binding Protein 3; D008894:Milk Proteins; D016226:Phosphorus, Dietary; D000067816:Whey Proteins; D010758:Phosphorus; D007334:Insulin-Like Growth Factor I; D002118:Calcium