Effect of Glycemic Index of a Pre-exercise Meal on Endurance Exercise Performance: A Systematic Review and Meta-analysis.
BACKGROUND
Low glycemic index (GI) pre-exercise meals may enhance endurance performance by maintaining euglycemia and altering fuel utilization. However, evidence for performance benefits is equivocal.


OBJECTIVE
To evaluate the effect of a low GI (LGI) versus a high GI (HGI) pre-exercise meal on endurance performance using meta-analyses.


METHODS
Data sources included MEDLINE, SPORTDiscus, AUSPORT, AusportMed, Web of Science, and Scopus. Eligibility criteria were randomized, crossover trials with an endurance exercise (≥60 min) component, e.g., time trial (TT), time to exhaustion (TTE) test, or submaximal bout followed by TT or TTE. Participants were healthy, active individuals aged ≥16 years. Interventions included a LGI (≤55) and HGI (≥70) meal ingested 30-240 min before exercise. Study quality was assessed using an adapted version of the validated Downs and Black tool. Effect size (ES) and 95 % confidence interval were calculated for each study and pooled according to performance test type and whether exogenous carbohydrate (CHO) was given during exercise. Potential effect modifiers including exercise duration, pre-exercise meal timing, glycemic load (GL), and fitness were assessed using meta-regression.


RESULTS
The search netted 3431 citations with 19 studies eligible for inclusion (totaling 188 participants; 91 % male; VO2max: >50 ml/kg/min). Meals with 0.18-2 g CHO/kg body mass, and a mean GI and glycemic load of 82 (GL: 72) and 35 (GL: 32) for HGI and LGI, respectively, were given between 30 and 210 min before exercise. All test types without CHO ingestion during exercise showed slightly improved performance with LGI, but no significant pooled effects were observed (ES: -0.17 to -0.36; p > 0.05). Studies where exogenous CHO was ingested during exercise showed conflicting results (ES: -0.67 to 0.11; p = 0.04 to 0.94). No significant relationship was observed with any of the effect modifiers (p > 0.05). No consistent metabolic responses (glucose, insulin, lactate, respiratory exchange ratio) during exercise were observed with either meal type.


CONCLUSIONS
There were small numbers of studies within each exercise testing protocol and limited statistical power within studies. Pre-exercise meal timing, GL, meal composition and participant fitness varied across studies, limiting the capacity to assess the influence of these factors on study outcomes.


CONCLUSIONS
There was no clear benefit of consuming a LGI pre-exercise meal for endurance performance regardless of carbohydrate ingestion during exercise.
Discipline of Exercise and Sport Science, Faculty of Health Sciences, The University of Sydney, 75 East Street, Lidcombe, Sydney, NSW, 2141, Australia.|School of Medicine, University of Wollongong, Wollongong, NSW, Australia.
Catriona A
CA
Burdon
Wageningen University, Wageningen, The Netherlands.
Inge
I
Spronk
Discipline of Exercise and Sport Science, Faculty of Health Sciences, The University of Sydney, 75 East Street, Lidcombe, Sydney, NSW, 2141, Australia.|Academic Department of Adolescent Medicine, The Children's Hospital at Westmead, Westmead, Sydney, NSW, Australia.|Discipline of Child and Adolescent Health, Sydney Medical School, The University of Sydney, Westmead, Sydney, NSW, Australia.
Hoi Lun
HL
Cheng
Discipline of Exercise and Sport Science, Faculty of Health Sciences, The University of Sydney, 75 East Street, Lidcombe, Sydney, NSW, 2141, Australia. helen.oconnor@sydney.edu.au.|Charles Perkins Centre, The University of Sydney, Camperdown, Sydney, NSW, Australia. helen.oconnor@sydney.edu.au.
Helen T
HT
O'Connor
D001786:Blood Glucose / Q000378:metabolism; D004040:Dietary Carbohydrates; D015444:Exercise; D005080:Exercise Test; D038321:Glycemic Index; D006801:Humans; D007328:Insulin; D008297:Male; D062407:Meals; D010807:Physical Endurance / Q000502:physiology*
D001786:Blood Glucose; D004040:Dietary Carbohydrates; D007328:Insulin
Int J Sports Med. 1991 Apr;12(2):180-6
1860741
Int J Sport Nutr Exerc Metab. 2010 Dec;20(6):447-56
21116017
Am J Clin Nutr. 1985 Dec;42(6):1192-6
4072954
Diabetes Care. 2004 Sep;27(9):2266-71
15333500
Int J Sports Med. 1981 May;2(2):114-8
7333741
Am J Clin Nutr. 1991 Nov;54(5):846-54
1951155
Stat Med. 2002 Jun 15;21(11):1539-58
12111919
Sports Med. 2010 Jan 1;40(1):27-39
20020785
J Acad Nutr Diet. 2016 Mar;116(3):501-528
26920240
J Epidemiol Community Health. 1998 Jun;52(6):377-84
9764259
Br Med J (Clin Res Ed). 1981 Mar 28;282(6269):1032
6783232
J Nutr. 2003 Sep;133(9):2728-32
12949357
Br J Nutr. 2012 Aug;108 Suppl 1:S81-90
22916819
Int J Sports Med. 2010 Mar;31(3):207-12
20175040
Am J Clin Nutr. 2002 Jul;76(1):266S-73S
12081850
Am J Clin Nutr. 2006 Aug;84(2):354-60
16895883
Med Sci Sports Exerc. 1999 Jan;31(1):164-70
9927025
Int J Sport Nutr Exerc Metab. 2008 Jun;18(3):281-300
18562775
Br J Nutr. 2003 Dec;90(6):1049-56
14641964
J Appl Physiol (1985). 1996 Sep;81(3):1115-20
8889742
Scand J Med Sci Sports. 2010 Feb;20(1):112-21
19000102
J Appl Physiol (1985). 2005 Aug;99(2):707-14
15831796
Am J Clin Nutr. 1981 Mar;34(3):362-6
6259925
J Appl Physiol (1985). 1998 Dec;85(6):2220-6
9843546
J Sci Med Sport. 2009 Nov;12(6):697-703
18789762
Med Sci Sports Exerc. 2009 Mar;41(3):709-31
19225360
Int J Sports Med. 2012 Sep;33(9):756-62
22706944
J Appl Physiol (1985). 2000 Nov;89(5):1845-51
11053335
Nutrients. 2014 Apr 29;6(5):1782-808
24787031
Int J Sport Nutr Exerc Metab. 2009 Oct;19(5):485-503
19910651
Diabetes Care. 2008 Dec;31(12):2281-3
18835944
Sports Med. 2001;31(3):211-34
11286357
Int J Sports Physiol Perform. 2009 Sep;4(3):367-80
19953824
Med Sci Sports. 1979 Spring;11(1):1-5
582616
Diabetes. 1976 Sep;25(9):741-7
955301
J Sci Med Sport. 2010 Jan;13(1):182-8
19230767
Int J Sport Nutr Exerc Metab. 2010 Apr;20(2):154-65
20479489
Eur J Appl Physiol Occup Physiol. 1988;57(1):70-4
3342797
J Appl Physiol (1985). 2000 Dec;89(6):2413-21
11090597
Int J Sport Nutr Exerc Metab. 2009 Jun;19(3):222-42
19574611
Diabetes Care. 1984 Sep-Oct;7(5):465-70
6389060
Diabetes Care. 2005 Dec;28(12):2832-8
16306541
J Appl Physiol (1985). 2004 Apr;96(4):1277-84
14657042
Behav Res Methods. 2007 May;39(2):175-91
17695343
Sports Med. 2000 Jun;29(6):407-24
10870867
Int J Sport Nutr Exerc Metab. 2006 Oct;16(5):510-27
17240783
Int J Sports Physiol Perform. 2013 Mar;8(2):111-22
23428482
J Am Diet Assoc. 2002 Mar;102(3):415-7
11902378
J Appl Physiol (1985). 1994 Sep;77(3):1537-41
7836162
Int J Sports Physiol Perform. 2009 Sep;4(3):331-44
19953821
Int J Sports Med. 2009 Dec;30(12):898-905
20013559
Med Sci Sports Exerc. 1998 Jun;30(6):844-9
9624641
PLoS Med. 2009 Jul 21;6(7):e1000097
19621072