Effect of meal frequency on glucose and insulin excursions over the course of a day
Background & aimsThis study characterized the glucose and insulin responses to temporal alterations in meal frequency, and alterations in the macronutrient composition.
MethodsEight subjects underwent three separate 12-h meal tests: three high carbohydrate (3CHO) meals, 6 high carbohydrate meals (6CHO), 6 high-protein meals (6HP). Blood samples were taken at 15-min intervals. Integrated area under the curve (AUC) concentrations for glucose and plasma insulin were determined (total, 4-h, and 2-h blocks) for each meal condition.
ResultsBaseline glucose and insulin values were not different between study days. Peak glucose levels were highest on the 3CHO day; however the 12 h glucose AUC was higher during the 6CHO condition (p = 0.029) than 3CHO condition, with no difference in the insulin response. The 6HP condition resulted in a decreased glucose AUC (p = 0.004) and insulin AUC (p = 0.012) compared to 6CHO.
ConclusionsIn non-obese individuals, glucose levels remained elevated throughout the day with frequent CHO meals compared to 3CHO meals, without any differences in the insulin levels. Increasing the protein content of frequent meals attenuated both the glucose and insulin response. These findings of elevated glucose levels throughout the day warrant further research, particularly in overweight and obese individuals with and without type 2 diabetes.
Human insulinotropic response to oral ingestion of native and hydrolysed whey protein.
Human Science Research Unit, Department of Physical Education and Sports Science, University of Limerick, Limerick, Ireland. email@example.com
The insulinotropic response to the ingestion of whey protein and whey protein hydrolysate, independent of carbohydrate, is not known. This study examined the effect of protein hydrolysis on the insulinotropic response to the ingestion of whey protein. Sixteen healthy males ingested a 500 mL solution containing either 45 g of whey protein (WPI) or whey protein hydrolysate (WPH). The estimated rate of gastric emptying was not altered by hydrolysis of the protein [18 (3) vs. 23 (3) min, n = 16; P = 0.15]. Maximum plasma insulin concentration (Cmax) occurred later (40 vs. 60 min) and was 28% [234 (26) vs. 299 (31) mM, P = 0.018] greater following ingestion of the WPH compared to the WPI leading to a 43% increase [7.6 (0.9) vs. 10.8 (2.6) nM, P = 0.21] in the AUC of insulin for the WPH. Of the amino acids with known insulinotropic properties only Phe demonstrated a significantly greater maximal concentration [C (max); 65 (2) vs. 72 (3) microM, n = 16; P = 0.01] and increase (+22%) in AUC following ingestion of the WPH. In conclusion, ingestion of whey protein is an effective insulin secretagogue. Hydrolysis of whey protein prior to ingestion augments the maximal insulin concentration by a mechanism that is unrelated to gastric emptying of the peptide solution.
Protein ingestion prior to strength exercise affects blood hormones and metabolism.
The effects of protein consumption before strength training session on blood hormones, energy metabolites, RER, and excess postexercise oxygen consumption (EPOC) were examined.
Ten resistance-trained young men consumed either a 25 g of whey and caseinate proteins (PROT) or a noncaloric placebo (P) in a liquid form 30 min before a heavy strength training session (STS) in a crossover design separated by at least 7 d. STS lasted 50 min and included 5 x 1 RM squats, 3 x 10 RM squats and 4 x 10 RM leg presses with 2-, 3-, and 2-min recoveries, respectively. A protein-carbohydrate supplement was consumed after STS in both trials. Venous blood samples were collected before, during, and after STS and oxygen consumption before and after STS.
Serum growth hormone (GH), testosterone, and free fatty acids (FFA) were significantly (P < or = 0.05) higher in P compared with PROT 5 min after an STS. The calculated area under curve (AUC) of the serum insulin response during an STS was significantly (P < 0.001) higher in PROT compared with P. The EPOC value from 90 to 120 min after an STS was significantly greater in the PROT condition compared with P (P = 0.01), and PROT treatment had a significantly higher RER 2 h postexercise (P = 0.04). The AUC of serum FFA during STS correlated significantly and negatively with RER 10-30 min after STS (r = -0.53, P = 0.02).
Consuming 25 g of whey and caseinate proteins 30 min before an STS significantly decreases serum GH, testosterone, and FFA levels, and increases serum insulin during an STS. Furthermore, the pre-STS protein increased EPOC and RER significantly during 2-h recovery after STS.
Food insulin index: physiologic basis for predicting insulin demand evoked by composite meals.
BACKGROUND:Diets that provoke less insulin secretion may be helpful in the prevention and management of diabetes. A physiologic basis for ranking foods according to insulin "demand" could therefore assist further research.
OBJECTIVE:We assessed the utility of a food insulin index (FII) that was based on testing isoenergetic portions of single foods (1000 kJ) in predicting the insulin demand evoked by composite meals.
DESIGN:Healthy subjects (n = 10 or 11 for each meal) consumed 13 different isoenergetic (2000 kJ) mixed meals of varying macronutrient content. Insulin demand predicted by the FII of the component foods or by carbohydrate counting and glycemic load was compared with observed insulin responses.
RESULTS:Observed insulin responses (area under the curve relative to white bread: 100) varied over a 3-fold range (from 35 +/- 5 to 116 +/- 26) and were strongly correlated with insulin demand predicted by the FII of the component foods (r = 0.78, P = 0.0016). The calculated glycemic load (r = 0.68, P = 0.01) but not the carbohydrate content of the meals (r = 0.53, P = 0.064) also predicted insulin demand.
CONCLUSIONS:The relative insulin demand evoked by mixed meals is best predicted by a physiologic index based on actual insulin responses to isoenergetic portions of single foods. In the context of composite meals of similar energy value, but varying macronutrient content, carbohydrate counting was of limited value.
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