Glycemic Index in Sport Nutrition

Abstract

Carbohydrates (CHO) can be classified on the basis of their glycemic index (GI), and the use of this classification has been increasingly supported by science. Because of its impact on blood glucose and insulin responses following the ingestion of CHO foods, the GI has been studied in many fields of medicine, including sport nutrition. As a new tool in sport nutrition, glycemic index manipulation has been evaluated to improve the first and second phases of glycogen recovery, glycogen load, and exercise metabolism, including control of rebound hypoglycemia and, it is interesting to note, stimulation of lipid oxidation for longer availability of glucose sources during endurance exercise. Although attractive, the use of GI in sport nutrition has received only partial support from available experimental evidence. At the biochemical level, consistent evidence has been attained to suggest that GI manipulation can determine variations in adipocyte lipolysis, plasma free fatty acids levels, and lipid and CHO oxidation rates during exercise. However, when the effects of GI manipulation have been assessed at the functional level, the results have been inconsistent, with evidence of improved exercise performance in some studies, but not in many others. The purpose of the current article is to review the effects and limits of GI manipulation in sport nutrition, and to propose an overall strategy for its application.

Índice glicêmico da refeição pré-exercício e metabolismo da glicose na atividade aeróbica

“…Apesar de 15 minutos pré-exercício para ingestão alimentar ser um tempo que mais se aproxima da realidade do praticante de atividade física matinal, era esperado uma redução acentuada na glicemia na fase inicial do exercício, normalmente 15 minutos, devido ao efeito somatório da ação da insulina e da contração muscular no consumo da glicose 3,7 . Porém, não foi o que ocorreu nesse estudo 26 , o que sugere que esse período de 15 minutos entre a refeição e o exercício pode não ser suficiente para aumentar a insulina a seu nível máximo de ação, que ocorre entre 20 a 40 minutos 3 .…”

“…Este índice tem sido amplamente estudado, compondo estraté-gias dietéticas para prevenção e intervenção de doença cardiovascular, diabetes, e obesidade, entre outros [4][5][6] , e principalmente no ramo da nutrição esportiva 7,8 , pois a última refeição antes do exercício pode ter influência nos níveis de glicose e insulina no sangue, ácidos graxos livres, na taxa de oxidação de CHO e gordura, além do conteúdo de glicogênio muscular 7 . Esta refeição também tem influência funcional, expressa pelo desempenho no exercício 7 .…”

“…Dessa forma, quando o exercício é iniciado com níveis altos de insulina, a captação de glicose pelo músculo é aumentada em virtude da translocação da proteína transportadora de glicose (GLUT-4) para a superfície das fibras musculares, provocada pelas suas contrações, portanto, através de um mecanismo independente da insulina 3,7 .…”

Influence of Glycemic Index-Based Menu on Endurance Performance of Athletes

“…In consuming a high-GI meal before practicing sport, the concentration of blood glucose will rise and lower sharply and attain a higher level at peak times than in consuming low-GI meal with similar number of carbohydrates (Mondazzi et al, 2009). This finding is confirmed by Burke et al (1998) and Cocate et al (2011) suggesting that the rate of glucose oxidation is higher after consuming high-GI meal.…”

Comparison between Preexercise Meals Intake Effect with Different Glycemic Load on Exercise Performance in Female Athletes

“…In addition to the beneficial effects of low GI (LGI) foods in controlling blood glucose levels; these days, useful roles of these foods find wider applications such as athletics' performance [9]. Manipulation of GI from different sources of CHO in order to optimizing athletic performance has been investigated in different studies [8,10]. Researches show that a CHO-rich meal with LGI level is a suitable choice before prolonged exercises plan, because it causes blood glucose being more stable and maintains free fatty acids (FFA) at higher levels during exercises [11,12].…”