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Glycemic Index and Adult Health
By Dr Shashikala (UCSI University)
Dietary carbohydrates have received negative publicity in the last decade following the popularity of high protein diets for weight loss, and the more recent findings that carbohydrates may be worse than saturated fats for cardiovascular disease (CVD) risk 1,2. These landscape changes have raised questions about the amount and type of carbohydrate to be recommended in healthy diets. Now the majority of carbohydrate-containing foods consumed in industrialized nations are of poor quality (e.g., higher in GI (glycemic index) and GL (glycemic load) as well as low in dietary fiber and calorie-dense). Generally, foods are now of the kind that are quickly digested, absorbed, and give rise to high blood glucose and insulin spikes. As overweight, obesity and insulin resistance have become more prevalent, concerns for the amount and type of carbohydrate consumed have increased because of the changed view that carbohydrate nutrition can increase rather than (as originally perceived) only decrease cardiometabolic risk. Thus, evidence has supported that some carbohydrate sources can be beneficial while others are not, depending on both their glycemic index and fiber content 2-6.
GR (glycemic response) is the post-prandial blood glucose response (change in concentration) elicited when a food or meal that contains carbohydrate is ingested. Available carbohydrate is the carbohydrate in foods that is digested, absorbed and metabolized as carbohydrate and it is sometimes referred to as net carbohydrate or glycemic carbohydrate (expressed as the monosaccharide equivalent for optimal comparability between carbohydrates) 7. The GI is conceptually the GR elicited by a portion of food containing 50 g (or in some cases 25 g) of available carbohydrate and is expressed as a percentage of the GR elicited by 50 g (or 25 g) of the reference carbohydrate (i.e., either a glucose solution or white wheat bread, defined respectively as the glucose scale or the bread scale). The GI is therefore both a standardized GR (based on an equal amount of available carbohydrate) and a relative GR (relative to a referent food). It is a property of the food itself, an index or percentage representing a quality of carbohydrate foods. Foods having carbohydrate that is digested, absorbed and metabolized quickly are considered high GI foods (GI ≥70 on the glucose scale) whereas those that are digested, absorbed and metabolized slowly are considered low GI foods (GI≤55 on the glucose scale). The GL is the product of GI and the total available carbohydrate content in each amount of food (GL=GI x available carbohydrate/given amount of food). Available carbohydrates can have different modes of expression, for example: gram (g) per serving, g per 100 g food, g per day’s intake, and g per1000 kJ or 1000 kcal (1 kcal = 4.184 kJ). Thus, depending on the context in which GL is used, the GL has corresponding units of g per serving, g per 100 g food, and g per1000 kJ or 1000 kcal 1,2,7.
Postprandial glycemia as a relevant factor in overall health, considers dietary approaches that slow carbohydrate absorption to be useful tools in lowering the risk of major chronic diseases and related risk factors. One of these tools is represented by the low GI aspect of carbohydrate foods where the GI methodology is reproducible and valid to express the glycemic response of foods in a standardized fashion. Strong evidence from clinical trials showed that low GI diets moderately improved glycemic control in type 1 and 2 diabetes, with evidence for benefits in blood lipids and inflammatory markers in people with and without diabetes. A strong association between lower dietary GI/GL in reducing the risk of developing T2DM in men and women and CHD risk mainly in women was found. These health advantages may be of greater relevance in individuals who are sedentary, overweight and in those with insulin resistance condition. Despite the lack of clinical trials investigating the role of low GI in reducing the risk of developing T2DM and heart disease, the experience with alpha-glucosidase inhibitors, which convert meals into low GI meals, suggests a potential role of low GI in disease risk reduction end points. The evidence was found to be moderate to weak for a possible protective role of low GI/GL diets in cancer risk and in metabolic outcomes in childhood and adolescence although some benefits may be seen in individuals with insulin resistance. However, low GI diets may have health advantages in youth since they are related to overall improvements in nutrient profiles 9-10.
There might be probable role of low GI and GL diets in bodyweight management. In adults, low GI diets tended to have a greater impact on reducing body fat mass than bodyweight while weight loss was mainly observed in over-weight people with high insulin levels. However, after weight loss, the combination of low GI and higher protein may prevent weight regain. Only Scandinavian countries and Italy suggested the use of low GI diets but in selected groups, i.e. in overweight and obese people and in those whose dietary carbohydrate intakes reach 60% of total calories, with a warning regarding foods where low GI is a consequence of high levels of fructose or fats. However, the concern that the low GI sugar fructose may adversely affect metabolic makers when in substitution for equivalent amounts of other sources of carbohydrate likely to replace it (mainly refined starch, glucose, or sucrose) was not supported by the Scientific consensus on glycemic index and load scientific evidence particularly if the quantity of fructose is moderate 8.
The use of the dietary GI and GL labeling in the context of a healthy diet complementing other healthy dietary attributes (e.g. high fiber) is recommended. A front-of-pack label could be used that also requires foods to meet healthy nutrient criteria in line with international dietary guidelines. In light of the epidemic of conditions affecting glucose metabolism, the dietary GI and GL should be communicated to the general public and health professionals through dietary guidelines, country-specific GI databases, food composition tables and food labels.
References :
- Jakobsen MU, O’Reilly EJ, Heitmann BL, Pereira MA, Balter K,Fraser GE, et al. 2009. Major types of dietary fat and risk of coronary heart disease: a pooled analysis of 11 cohort studies. The American Journal of Clinical Nutrition 89:1425e32.
- Jakobsen MU, Dethlefsen C, Joensen AM, Stegger J, Tjonnel and A,Schmidt EB, et al. 2010. Intake of carbohydrates compared with intake of saturated fatty acids and risk of myocardial infarction: importance of the glycemic index. The American Journal of Clinical Nutrition 91:1764e8.
- Ludwig D. 2002. The glycemic index: physiological mechanisms relating to obesity, diabetes, and cardiovascular disease.,”. JAMA 287:2414e23.
- Jenkins DJ, Kendall CW, McKeown-Eyssen G, Josse RG,Silverberg J, Booth GL, et al. 2008. Effect of a low-glycemic index or ahigh-cereal fiber diet on type 2 diabetes: a randomized trial. JAMA 300:2742e53.
- Astrup A, Dyerberg J, Elwood P, Hermansen K, Hu FB,Jakobsen MU, et al. 2011. The role of reducing intakes of saturated fat in the prevention of cardiovascular disease: where does the evi-dence stand in 2010? The American Journal of Clinical Nutrition 93:684e8.
- Mirrahimi A, de Souza RJ, Chiavaroli L, Sievenpiper JL, Beyene J,Hanley AJ, et al. 2012 Associations of glycemic index and load withcoronary heart disease events: a systematic review and meta-analysis of prospective cohorts. Journal of the American Heart Association 1: e000752.
- Food and Agriculture Organisation (FAO). 2003. Food energy methods of analysis and conversion factors. Rome: Food and Agriculture Organisation; Food and nutrition paper 77.
- Ludwig D. 2014. Dietary glycemic index and obesity. Journal of Nutrition 130(Suppl.):280Se3S.
9.Jenkins DJ, Taylor RH, Goff DV, Fielden H, Misiewicz JJ, Sarson DL, et al. 2012. Scope and specificity of acarbose in slowing carbohydrate absorption in man. Diabetes 30:951e4.
