Role of Proteins in Insulin Secretion and Glycemic Control - Advances in Food and Nutrition Research - page 31

With glucose present in the protein meal, there was no significant rise
in glucagon concentration for 60 min, regardless of protein dose
( Westphal et al., 1990 ) . This data support previous studies showing that
the ingestion of either protein or glucose results in glucagon stimulation
and suppression, respectively ( Muller, Faloona, Aguilarparada, & Unger,
1970 ). Circulating glucagon concentrations also appear to depend on the
ratio of protein to carbohydrate in the meal ( Ahmed, Nuttall, Gannon, &
Lamusga, 1980 ) .
Some studies have shown that protein hydrolysates enhance postprandial
insulin response and reduce postprandial serum glucose levels in type 2
diabetics ( Jonker et al., 2011; Manders, Koopman, et al., 2006; Manders,
Praet, et al., 2006; Manders et al., 2005; van Loon et al., 2003 ) .These studies
showed that although the b -cell response to glucose is impaired in this
group, the insulin secretory response to amino acids remains functional.
In addition, hydrolysates are advantageous in that they have faster digestion
and quicker availability of amino acids than whole proteins ( Koopman
et al., 2009 ) .
Overall, the metabolic response to ingested protein alone either results in
little or no increase in blood glucose concentrations. Protein coingested with
glucose increases insulin secretion and reduces plasma glucose rise and this is
more apparent in diabetics than healthy individuals. Protein ingestion stim-
ulates a rise in glucagon secretion and is suppressed in the presence of glucose
ingestion. Proteins could stimulate a rise in insulin and glucagon, but these
effects depend on protein type and quantity. The glucose and insulin
responses also appear to have a dose-dependent relationship with the quan-
tity of protein (and carbohydrate) ingested. However, there is inadequate
data regarding the extent and limits of this relationship.
5.2. Effect of amino acids on glycemia
Studies on dietary proteins have made it clear that they have different effects
on circulating glucose, insulin, and glucagon concentrations both when
consumed alone or with glucose. Similarly, amino acid type has also been
shown to significantly affect insulin secretion (section 4). This section will
focus on the effects of amino acids on glycemia.
Amino acids released from proteins can be gluconeogenic, insulinogenic,
or both. Gluconeogenic amino acids directly contribute to de novo synthesis of
glucose and participate in recycling of glucose carbon via the glucose-amine
cycle. These amino acids give rise to a net production of pyruvate or TCA