The rate of intestinal glucose absorption is correlated with plasma glucose-dependent insulinotropic polypeptide concentrations in healthy men

Glucagon-like pepticle-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) both play a role in the control of glucose homeostasis, and GIP is implicated in the regulation of energy storage. The capacity of carbohydrates to induce secretion of these incretin hormones could be one of the factors determining the metabolic quality of different types of carbohydrates. We analyzed the correlation between the rate of intestinal absorption of (starch-derived) glucose and plasma concentrations of GLP-1 and GIP after ingestion of glucose and starchy foods with a different content of rapidly and slowly available glucose. In a crossover study, glucose, insulin, GLP-1, and GIP concentrations were monitored for 6 h after consumption of glucose, uncooked cornstarch (UCCS) or corn pasta in 7 healthy men. All test meals were naturally labeled with C-13. Using a primed, continuous D-[6,6-H-2(2)]glucose infusion, the rate of appearance of exogenous glucose (RaEx) was estimated, reflecting the rate of intestinal glucose absorption. GLP-1 concentrations increased significantly from 180 to 300 min after ingestion of UCCS, the starch product with a high content of slowly available glucose. A high GIP response in the early postprandial phase (15-90 min) occurred after consumption of glucose. There was a strong positive within-subject correlation between RaEx and GIP concentrations (r=0.73, P &lt;0.01) across the test meals. Rapidly and slowly digestible carbohydrates differ considerably in their ability to stimulate secretion of incretin hormones; the metabolic consequences of such differences warrant exploration.</p

An explorative study of in vivo digestive starch characteristics and postprandial glucose kinetics of wholemeal wheat bread

&lt;p&gt;&lt;b&gt;Background&lt;/b&gt;&lt;/p&gt; &lt;p&gt;Based on in vitro measurements, it is assumed that starch in wholemeal bread is rapidly digestible, which is considered to be less desirable for health.&lt;/p&gt; &lt;p&gt;&lt;b&gt;Aim of the study&lt;/b&gt;&lt;/p&gt; &lt;p&gt;To evaluate the in vitro prediction, we characterized starch digestion of wholemeal wheat bread (WB) and postprandial glucose kinetics in healthy volunteers.&lt;/p&gt; &lt;p&gt;&lt;b&gt;Methods&lt;/b&gt;&lt;/p&gt; &lt;p&gt;In a crossover study 4 healthy men ingested either intrinsically &lt;sup&gt;13&lt;/sup&gt;C-enriched WB (133 g) or glucose (55 g) in water. Plasma glucose and insulin concentrations were monitored during 6 h postprandially. Using a primed continuous infusion of D-[6,6-&lt;sup&gt;2&lt;/sup&gt;H2] glucose, the rate of systemic appearance of glucose was estimated (reflecting glucose influx) and the endogenous glucose production calculated.&lt;/p&gt; &lt;p&gt;&lt;b&gt;Results&lt;/b&gt;&lt;/p&gt; &lt;p&gt;The glucose influx rate after WB was comparable with that after glucose in the early postprandial phase (0–2 h) (&lt;i&gt;P&lt;/i&gt; = 0.396) and higher in the late postprandial phase (2–4 h) (&lt;i&gt;P&lt;/i&gt; = 0.005). Despite the same initial glucose influx rate the 0–2 h incremental area under the curve (IAUC) of insulin after WB was 41% lower than after glucose (&lt;i&gt;P&lt;/i&gt; = 0.037). Paradoxically endogenous glucose production after WB was significantly more suppressed than after glucose (0–2 h IAUC: &lt;i&gt;P&lt;/i&gt; = 0.015, 2–4 h IAUC: &lt;i&gt;P&lt;/i&gt; = 0.018).&lt;/p&gt; &lt;p&gt;&lt;b&gt;Conclusions&lt;/b&gt;&lt;/p&gt; &lt;p&gt;Starch in WB seems to be partly rapidly and partly slowly digestible. Postprandial insulin response and endogenous glucose production after WB ingestion might not solely be determined by the digestive characteristics of starch; other components of WB seem to affect glucose homeostasis. In vitro measurements might not always predict in vivo starch digestion precisely.&lt;/p&gt