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Glycaemic index and glycaemic load: current concepts and future challenges for the industry

Glycaemic index and glycaemic load: current concepts and future challenges for the industry. Jeya Henry Professor of Human Nutrition 22 June 2005. Slow realisation of differences in CHO metabolism. All foods are composed of protein, fat and carbohydrate

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Glycaemic index and glycaemic load: current concepts and future challenges for the industry

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  1. School of Biological and Molecular Sciences Glycaemic index and glycaemic load: current concepts and future challenges for the industry Jeya Henry Professor of Human Nutrition 22 June 2005

  2. Slow realisation of differences in CHO metabolism • All foods are composed of protein, fat and carbohydrate • By 1911 the importance of protein quality identified (Osborne & Mendel) • By 1932 the effect of differences in fat composition were identified (Burr & Burr) • It was not until 1981 that metabolic differences in carbohydrates were recognised (Jenkins et al, 1981) • Why? School of Biological and Molecular Sciences

  3. Plasma glucose response to ingestion of 50 g CHO (Krezowski et al. 1987) School of Biological and Molecular Sciences

  4. Glycaemic index • The glycaemic index (GI) is a method of ranking foods on a scale according to the extent to which foods raise blood glucose levels after ingestion • Carbohydrate foods that break down quickly during digestion have the highest GI values - their blood glucose response is fast and high • Carbohydrates which break down slowly, releasing glucose gradually into the bloodstream, have low GI factors School of Biological and Molecular Sciences

  5. GI calculation GI of a food: Incremental area under the blood glucose response curve for the test food containing 50 g available carbohydrate Corresponding area after equi-carbohydrate portion of a standard food X 100 School of Biological and Molecular Sciences

  6. How is GI determined? • Typical testing routine involves 12-15 subjects (age range 18-40 years) • Subjects arrive at the laboratory after an overnight fast • Finger-prick blood sample taken at time zero • Subjects consume 50 g glucose in 200 ml water and blood samples taken at 15, 30, 45, 60,90 and 120 mins • This procedure is done three times on each subject (on separate days with a minimum gap of 1 day between tests) • Subjects then consume 50 g available carbohydrate from the test sample and blood samples are taken at time intervals as above School of Biological and Molecular Sciences

  7. GI testing of foods at Oxford Brookes • FAO/WHOprotocol (Carbohydrates in Human Nutrition, 1998) • The GI rating of a food must be tested physiologically in recognised laboratories • Oxford Brookes University is working with Tesco and several food companies globally to study the effects of low- and high-GI foods and to develop products that have lower GI ratings • Tesco has commissioned Oxford Brookes University to develop QC for GI testing School of Biological and Molecular Sciences

  8. Classification • Low GI 55 or less • Medium GI 56-69 inclusive • High GI 70 or more • Does this classification have any biological significance? School of Biological and Molecular Sciences

  9. Continuous glucose monitoring • Brynes et al. (Br J Nutr, 2005) showed that a low GI diet reduced glucose concentrations by 5% in the daytime and by 16% overnight Mean 24 h area under the curve for glucose at baseline (——) and in response to a diet with low glycaemic index (- - - - -) for eight subjects School of Biological and Molecular Sciences

  10. Are foods low in carbohydrate are also low in GI value – NO! • Amount of carbohydrate does not predict GI • At carbohydrate levels of 10-60% food products show a wide range of GI values • At 25% carbohydrate, GI can be between 10 and 95 School of Biological and Molecular Sciences

  11. Food factors that influence glycaemic response • Nature and amount of carbohydrate • Nature of the monosaccharide components - glucose - fructose - galactose • Nature of the starch - amylose - amylopectin - resistant starch • Cooking or food processing - degree of gelatinisation of starch - particle size - food form - cellular structure • Other food components - fat and protein - dietary fibre - antinutrients - organic acids School of Biological and Molecular Sciences

  12. Food ingredient/macronutrient effect Henry et al. (unpublished data) School of Biological and Molecular Sciences

  13. Rate of starch breakdown will influence GI Three main factors influence glucose release • Access of enzymes to starch • cell wall as a barrier • protein matrix • Susceptibility of starch to hydrolysis • structural breakdown • molecular breakdown • Presence of other specific nutrients which affect stomach emptying and viscosity of gut contents School of Biological and Molecular Sciences

  14. Peanuts: very low GI (14). Why? • Thick, resilient cell walls enclose limited amount of starch School of Biological and Molecular Sciences

  15. Three examples of newly developed foods with low-GI School of Biological and Molecular Sciences

  16. Glycemic load • Glycemic load (GL) assesses the total glycaemic effect of a food/diet • Calculated by multiplying the GI by the amount of available CHO in a serving/100 • E.g. • GI of food item = 40 • 1 serving = 12 g available CHO • Therefore GL = 12 x 40 / 100 = 4.8 (rounded to 5) School of Biological and Molecular Sciences

  17. Glycemic load • Glycaemic load represents both the quality and quantity of carbohydrate GL = (GI x amount of CHO in serving [g])/100  ‘QUALITY’ ‘QUANTITY’ • Similar to: NDPE% = NPU x P:E%  ‘QUALITY’ ‘QUANTITY’ School of Biological and Molecular Sciences

  18. GL classification • Low GL <10 • Medium GL 10-20 • High GL >20 • We currently have no strong biological basis for this classification • In contrast, we do have a strong biological basis for GI classification School of Biological and Molecular Sciences

  19. Glycaemic INDEX vs Glycaemic LOAD School of Biological and Molecular Sciences

  20. The role of GI and GL on health and well-being • Three major diseases in the UK: • Diabetes • Obesity • Cardiovascular disease • How does a low-GI/GL diet affect these? School of Biological and Molecular Sciences

  21. Global estimates of diabetes (1997) (Amos et al. 1997) School of Biological and Molecular Sciences

  22. % population with diabetes in Europe (1997) (Amos et al. 1997) School of Biological and Molecular Sciences

  23. Potential mechanism for the relationship between high-GI foods and insulin resistance (Augustin et al. Eur J Clin Nut 2002;56:1049-71) School of Biological and Molecular Sciences

  24. Low-GI diets in the management of diabetes • Meta-analysis of randomised controlled trials [Brand-Miller et al. Diabetes Care 2003;26:2261-7] • 14 studies included in the final analysis (356 subjects) -203 type 1 diabetes; 153 type 2 diabetes • After an average duration of 10 weeks, subjects with type 1 and type 2 diabetes who followed a low-GI diet had lower levels of HbA1c (0.4%) and fructosamine (0.2 mmol/l) • Clinically important reduction in HbA1c School of Biological and Molecular Sciences

  25. High-GI vs low-GI - % change in HbA1c or fructosamine Favours low-GI Favours high-GI School of Biological and Molecular Sciences

  26. Effect of low-GI diet on blood glucose control in type 2 diabetes (Augustin et al. Eur J Clin Nut 2002;56:1049-71) School of Biological and Molecular Sciences

  27. Glycaemic index (carbohydrate type) Macronutrient composition (carbohydrate amount) Glycaemic load Alterations in the endocrine profile Independent mechanism (insulin demand, insulin sensitivity) Partitioning of metabolic fuels Regulation of food intake Body weight Risk for obesity-related morbidities Proposed model linking dietary GI and GL to body weight and obesity-related morbidities Source: Ebbeling & Ludwig (2001)

  28. Energy balance Energy balance = Energy Intake - Energy Expenditure • You will only be in positive energy balance when energy intake exceeds energy expenditure • Positive energy balance leads to obesity School of Biological and Molecular Sciences

  29. Yugoslavia Greece Romania Czech Rep. England Finland Germany Scotland Slovakia Portugal Spain Denmark Belgium Sweden France Italy Netherlands Norway Hungary Switzerland 40 30 20 10 0 10 20 30 40 % BMI >30 Male and female obesity levels in selected European countries Collated by the IOTF from recent surveys

  30. Are low-GI diets effective for weight loss? School of Biological and Molecular Sciences

  31. Low-GI diet in the treatment of paediatric obesity (Spieth et al. 2000) • 107 obese, but otherwise healthy children • 43 subjects received hypo-energetic, reduced-fat diet (4.2 months) • 64 subjects received low-GI diet (4.3 months) • Low-fat group: energy restriction of approximately 250-500 kcal per day compared to their usual intake • Low-GI group: emphasis on food selection not energy restriction School of Biological and Molecular Sciences

  32. Mean change in BMI by dietary treatment according to tertiles at baseline (Spieth et al. 2000) School of Biological and Molecular Sciences

  33. Sloth et al. AJCN 2004;80:337-47 • Methods • 45 healthy overweight women • 10-wk parallel, randomised, intervention with 2 groups: high-GI or low-GI • High or low-GI foods (identical in energy, energy density, dietary fibre and macronutrient composition) replaced subject’s usual carbohydrate-rich foods • Results • No significant between-group difference in body weight (P=0.31) • 10%  LDLc in low-GI group (P<0.05) • Larger decrease in TC in low-GI group School of Biological and Molecular Sciences

  34. Mean (SEM) body weight changes during 10-wk ad libitum intake of high- or low-GI diet Body weight and body composition changes after 10-wk ad libitum intake of high- or low-GI diet

  35. Pawlak DB, Kushner JA & Ludwig DS. Lancet 2004;364:778-85 • Male rats • High-GI diet (n = 11) • Low-GI diet (n = 10) • Controlled diet to maintain bodyweight between the groups for 18 weeks • Identical macronutrient composition (69% CHO, 20% protein, 11% fat as percentage of energy) • Type of starch • High-GI 100% amylopectin • Low-GI 60% amylose / 40% amylopectin School of Biological and Molecular Sciences

  36. Body composition changes (week 17) • Consumption of a high-GI diet per se adversely affects body composition and risk factors for diabetes and CVD in animal models • Adiposity was significantly greater in the high-GI group than in the low-GI group • At 18 weeks, high-GI animals had more abdominal fat or “central adiposity” compared to the low-GI animals School of Biological and Molecular Sciences

  37. Do low-GI foods reduce food intake at subsequent meals? School of Biological and Molecular Sciences

  38. Effect of altered GI breakfasts on subsequent food intake (Warren, Henry & Simonite, 2003) • Low-GI • All-Bran • non-Swiss-style toasted muesli • traditional porridge • soya and linseed bread • Low-GI and added sucrose • sucrose added to provide additional 10% energy • High-GI • Corn Flakes • Coco Pops • Rice Krispies • White bread School of Biological and Molecular Sciences

  39. Effect of altered GI breakfasts on subsequent food intake (Warren, Henry & Simonite, 2003) School of Biological and Molecular Sciences

  40. Effect of altered GI breakfasts on subsequent food intake (Warren, Henry & Simonite, 2003) Lunch intake was significantly lower than after high-GI breakfast: **P<0.01 School of Biological and Molecular Sciences

  41. The role of low- and high-glycaemic index breakfasts on food intake, appetite and satiety School of Biological and Molecular Sciences

  42. Low-GI breakfast Soya & linseed bread (with low fat spread and diabetic jam) All-Bran® Porridge cereals served with either skimmed, semi-skimmed or whole milk All breakfasts served with 190ml unsweetened fruit juice High-GI breakfast Wholemeal bread (with low fat spread and jam) Weetabix® Shreddies® cereals served with whole milk All breakfasts served with 190ml of low sugar squash + teaspoon of glucose powder (to increase the GI) Test breakfasts School of Biological and Molecular Sciences

  43. Nutritional composition of test breakfasts School of Biological and Molecular Sciences

  44. Mean 24-hour energy intake for the low- and high-GI breakfasts 24-hour energy intake was significantly lower than after high-GI breakfast: *P<0.05 School of Biological and Molecular Sciences

  45. Controversies • Many of the studies to date have been short-term single meal effects • Some studies have failed to match the macronutrient composition of test meals • Measures of hunger/satiety are variable • The effect of GI in the context of a mixed meal must be considered School of Biological and Molecular Sciences

  46. 8-week weight loss study on low-GI diets -foods provided School of Biological and Molecular Sciences

  47. 8-week weight loss study on low-GI diets -foods provided School of Biological and Molecular Sciences

  48. Measurements at baseline and week 4 No. subjects: 12 Age: 46  11 yrs School of Biological and Molecular Sciences

  49. Weight profile for the study population School of Biological and Molecular Sciences

  50. Glycaemic load • GL used widely in epidemiological studies (e.g. Salmeron et al. 1997; Schulze et al. 2004; Willet et al. 2002) • Recent studies: • BMI positively associated with GI but not with daily carbohydrate intake or GL (Ma et al. 2005) • GL, fructose and sucrose related to an elevated colorectal cancer risk among men, but not women (Michaud et al. 2005) • GL an important independent predictor of HDL cholesterol, accounting for more than 20% of its variation in young people (Slyper et al. 2005) School of Biological and Molecular Sciences

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