Biology Reference
In-Depth Information
12 g from ingesting 50 g of lean beef meat protein. However, the amount of
glucose appearing in the circulation of this group of people was only 2 g.
The peripheral plasma glucose concentration decreased by about 1 mM after
ingestion of either protein or water, confirming that ingested protein does
not result in a net increase in glucose concentration, and results in only a
modest increase in the rate of glucose disappearance in type 2 diabetics
(
Gannon et al., 2001
)
. A much lower amount of glucose was entering the
circulation of normal and type 2 diabetic subjects from ingesting protein
and the fate of the remaining metabolized amino acids was unknown.
The metabolic response of two different protein sources was compared
by
Nuttall and Gannon (1990)
, who looked at the ingestion of egg white
and cottage cheese alone on glycemia. Egg white stimulated a slight increase,
whereas cottage cheese stimulated a slight decrease in serum glucose concen-
tration in healthy subjects. Both stimulated an increase in serum insulin,
C-peptide, and glucagon concentrations. Although the role of individual
amino acids on these parameters was not determined, the increase in circu-
lating amino acid concentrations appeared to have stimulated these effects.
Nuttall and Gannon (1991)
critically reviewed studies investigating
plasma glucose and insulin response to macronutrients in nondiabetics
and type 2 diabetics. Protein generally was identified as not affecting glucose
concentrations in both groups but protein stimulated insulin secretion, with
it being more pronounced in type 2 diabetics. The null effect of proteins on
blood glucose was ascribed to an early hypothesis stating that increased pro-
duction and release of glucose from the liver led to a concomitant increased
uptake and utilization of glucose by peripheral tissues (
Unger &Orci, 1976
)
.
Ingestion of protein results in an increased glucagon concentration that
would stimulate gluconeogenesis from amino acids in the liver. The
increased insulin concentration would also stimulate peripheral tissues to
remove glucose produced and to store it as glycogen (
Unger & Orci,
1976
). Studies carried out afterward, however, have shown the picture to
be more complex. For example, protein quality has been demonstrated to
affect glucagon and insulin expression.
In summary, controlled feeding studies of known amounts of proteins
did not result in the predicted increase in peripheral glucose concentration
in normal and type 2 diabetic subjects. In fact, there were decreases in blood
glucose even though amino acids can be potentially used for gluconeogen-
esis. These studies showed lower glucose concentrations in diabetic subjects
than in nondiabetics. Therefore, protein ingestion collectively appears to
have a limited effect on glycemia. Reasons for this remain unclear and
