Level of dietary protein intake affects glucose turnover in endurance-trained men
Journal of the International Society of Sports Nutrition
Level of dietary protein intake affects glucose turnover in endurance-trained men
Stefan M Pasiakos 0
William F Martin 0
Charu S Sharma 0
Matthew A Pikosky 0
Patricia C Gaine 0
Douglas R Bolster 0
Brian T Bennett 0
Nancy R Rodriguez 0
0 Department of Nutritional Sciences, University of Connecticut , Storrs, CT , USA
Background: To examine the effects of higher-protein diets on endogenous glucose metabolism in healthy, physically active adults, glucose turnover was assessed in five endurance-trained men (age 21.3 ± 0.3 y, VO2peak 70.6 ± 0.1 mL kg-1 min-1) who consumed dietary protein intakes spanning the current dietary reference intakes. Findings: Using a randomized, crossover design, volunteers consumed 4 week eucaloric diets providing either a low (0.8 g kg-1 d-1; LP), moderate (1.8 g kg-1 d-1; MP), or high (3.6 g kg-1 d-1; HP) level of dietary protein. Glucose turnover (Ra, glucose rate of appearance; and Rd glucose rate of disappearance) was assessed under fasted, resting conditions using primed, constant infusions of [6,6-2H2] glucose. Glucose Ra and Rd (mg kg-1 min-1) were higher for MP (2.8 ± 0.1 and 2.7 ± 0.1) compared to HP (2.4 ± 0.1 and 2.3 ± 0.2, P < 0.05) and LP (2.3 ± 0.1 and 2.2 ± 0.1, P < 0.01) diets. Glucose levels (mmol/L) were not different (P > 0.05) between LP (4.6 ± 0.1), MP (4.8 ± 0.1), and HP (4.7 ± 0.1) diets. Conclusions: Level of protein consumption influenced resting glucose turnover in endurance athletes in a state of energy balance with a higher rate of turnover noted for a protein intake of 1.8 g kg-1 d-1. Findings suggest that consumption of protein in excess of the recommended dietary allowance but within the current acceptable macronutrient distribution range may contribute to the regulation of blood glucose when carbohydrate intake is reduced by serving as a gluconeogenic substrate in endurance-trained men.
Introduction
Increasing dietary protein at the expense of
carbohydrate in either Type 2 diabetics or in overweight adults
in response to energy restriction improves insulin
sensitivity and glycemic control [
1-5
]. Studies have shown
that protein intake in excess of the current
recommended dietary allowance (RDA: 0.8 g kg-1 d-1)
stabilizes blood glucose and reduces the postprandial insulin
response after weight loss [
2,3
]. The metabolic
advantage of a diet which provides dietary protein above the
RDA specific to glucose utilization in healthy, physically
active adults is unclear [6].
Higher-protein intakes are recommended for
physically active adults who routinely participate in
endurance exercise [
7-9
]. To date, no studies have
investigated the impact of dietary protein intake on
glucose homeostasis in endurance-trained adults. The
objective of our study was to examine the effects of
consuming dietary protein intakes spanning the current
Acceptable Macronutrient Distribution Range (AMDR)
on resting glucose turnover in endurance-trained men
[
10
]. We hypothesized that protein availability would
influence glucose turnover during a eucaloric state such
that glucose rate of appearance (Ra) would be greater
when the proportion of energy derived from dietary
protein was increased with a simultaneous reduction in
carbohydrate consumption.
Methods
Using a randomized, crossover design, five
endurancetrained men (21.3 ± 0.3 y, 179.1 ± 1.6 cm, 70.6 ± 0.1 kg,
8.7 ± 0.4% fat, VO2peak 70.6 ± 0.1 mL kg-1 min-1) were
assigned to a diet providing 0.8 (Low Protein; LP), 1.8
(Moderate Protein; MP) or 3.6 (High Protein; HP)
grams of protein per kilogram body mass per day for
four weeks. Participants crossed over and consumed
each of the remaining diets in randomized order
following a 2 wk wash out period between each diet
intervention. Actual macronutrient composition of the
each diet was 48% carbohydrate (5.4 g kg-1 d-1), 26% fat,
and 26% protein (3.1 g kg-1 d-1) for HP, 60%
carbohydrate (7.4 g kg-1 d-1), 26% fat, and 14% protein (1.8 g
kg-1 d-1) for MP, and 66% carbohydrate (8.3 g kg-1 d-1),
27% fat, and 7% protein (0.9 g kg-1 d-1) for LP. Extended
details of the diet intervention have been previously
reported [
8
]. Volunteers maintained their normal level
of training throughout the study. However, exercise was
restricted for 24 h before glucose turnover assessments
to minimize the potential influence of previous exercise
on study measures.
Glucose turnover was assessed after 3 wks of each 4
wk diet intervention using a 120 min primed, constant
infusion of [6,6-2H2] glucose (17 μmol kg-1; 0.2 μmol
kg-1 min-1; Cambridge Isotope Laboratories, Andover,
MA) at 0700 h after an overnight fast (≥ 10 h).
Arterialized blood samples were obtained from a dorsal hand
vein at baseline, 60, 75, 90, 105 and 120 min to
determine glucose turnover, insulin, and glucose
concentrations. Plasma enrichment of [6,6-2H2] glucose was
determined in duplicate with a precision of ± 0.2% SD
using a Hewlett Packard 5989A GC-MS (Metabol (...truncated)