Glycaemic index (GI) and glycaemic load

• glycaemic index of a food is the capacity of a portion of that food containing 50 g available carbohydrate to raise blood glucose compared with 50 g glucose in normal glucose-tolerant individuals
  • differences between foods are likely to be exaggerated in individuals with any degree of impairment of glucose tolerance
  • a diet with a low glycaemic index will involve choosing starch foods, such as basmati rice or spaghetti, as a substitute for foods with a high glycaemic index, such as potato (especially when hot and freshly cooked)
  • a diet with a low glycaemic index can still be high in total carbohydrates
    
    
• glycaemic load of a food is essentially a product of the glycaemic index of the food and the available carbohydrate
  
  
  • glycaemic load is an attempt to give a quantitative means of comparing meals, foods, or diets for their glycaemic effects
  • a diet with a lower glycaemic load can be achieved by choosing foods with a low glycaemic index or by reducing the quantities of carbohydrate consumed, or both.
  • diets with a low glycaemic index have been associated with improvements in insulin sensitivity, and the glycaemic index of diets on a population level inversely correlates with HDL cholesterol

For those clinicians seeking to give advice about diets:

• for lowering the glycaemic index of a diet:
  • use breakfast cereals based on oats, barley, and bran
  • use grainy breads made with whole seeds
  • reduce the amount of potatoes
  • enjoy all types of fruit and vegetables (except potatoes)
  • eat plenty of salad vegetables with vinaigrette dressing

Notes:

• a systematic review compared (2) the use of low glycaemic index or load diets with higher glycaemic index or load diets or other weight reduction diets
  • overweight or obese people on a low glycaemic index lost more weight and had more improvement in lipid profiles than those receiving other weight reduction diets
    • body mass, total fat mass, body mass index, total cholesterol and LDL-cholesterol all decreased significantly more in the low glycaemic index group
    • the study authors concluded that lowering the glycaemic load of the diet appears to be an effective method of promoting weight loss and improving lipid profiles and can be simply incorporated into a person's lifestyle
• a low glycaemic diet in patients with type 2 diabetes
  • study of patients with type 2 diabetes, 6-month treatment with a low-glycaemic index diet resulted in moderately lower HbA1c levels compared with a high-cereal fiber diet
  • the authors concluded that low-glycaemic index diets may be useful as part of the strategy to improve glycemic control in patients with type 2 diabetes taking antihyperglycemic medications
    • the study revealed a reduction of 0.50% absolute HbA(1c) units (95% CI, -0.61% to -0.39%) in the low-glycemic index diet (P < .001) treatment group
• a systematic review and meta-analysis of randomised controlled trials investigated the effect of diets with low glycaemic index (GI)/glycaemic load (GL) in diabetes (4):
  • low GI/GL dietary patterns reduced HbA1c in comparison with higher GI/GL control diets (mean difference - 0.31%
  • reductions occurred also in fasting glucose, LDL-C, non-HDL-C, apo B, triglycerides, body weight, BMI, and CRP (P<0.05), but not blood insulin, HDL-C, waist circumference, or blood pressure
  • a positive dose-response gradient was seen for the difference in GL and HbA1c and for absolute dietary GI and SBP (P<0.05). The certainty of evidence was high for the reduction in HbA1c and moderate for most secondary outcomes, with downgrades due mainly to imprecision
  • suggests that low GI/GL dietary patterns result in small important improvements in established targets of glycaemic control, blood lipids, adiposity, and inflammation beyond concurrent treatment with hyperglycaemia drugs or insulin, predominantly in adults with moderately controlled type 1 and type 2 diabetes
    
• a meta-analysis of 48 studies suggests that consumption of high glycaemic index food is linked to increased incidence of type 2 diabetes (RR 1.27; p<0.0001), total CVD (1.15; p<0.0001), diabetes-related cancer (1.05; p=0.0010) and all-cause mortality (1.08; p<0.0001) (5)

Reference:

• (1) Lancet. 2004;364(9436):736-7
• (2) Thomas DE et al. Low glycaemic index or low glycaemic load diets for overweight and obesity.Cochrane Database Syst Rev. 2007 Jul 18;(3):CD005105.
• (3) Jenkins DJ et al.Effect of a low-glycemic index or a high-cereal fiber diet on type 2 diabetes: a randomized trial. JAMA. 2008 Dec 17;300(23):2742-53
• (4) Chiavaroli L et al. Effect of low glycaemic index or load dietary patterns on glycaemic control and cardiometabolic risk factors in diabetes: systematic review and meta-analysis of randomised controlled trials. BMJ 2021;374:n1651
• (5) Jenkins DJA et al. Association of glycaemic index and glycaemic load with type 2 diabetes, cardiovascular disease, cancer, and all-cause mortality: a meta-analysis of mega cohorts of more than 100 000 participants. Lancet Diabetes and Endocrinology 2024;12 (2): 107-118.