The glycaemic index (GI) is a rating system established in 1981^[1] for foods containing carbohydrates. A corresponding number is given to a food depending on how quickly it causes sugar levels (glucose) to rise when it is eaten in isolation, relative to a referent carbohydrate, generally pure glucose^[2]. The principle is that the slower the carbohydrate is digested and absorbed, the lower the rise in blood glucose and the lower the corresponding GI value^[3]. Conversely, high glycaemic foods are digested and absorbed into the bloodstream quickly, which causes a large, rapid change in blood glucose levels.  The GI rating system is between 1 and 100, with glucose having a score of 100. A high GI value is considered as ≥70, a value between 56 and 69 is medium and a GI value ≤55 is low.

Low and High GI

Generally, we are advised to choose low GI sources of complex carbohydrates (starchy carbs) as they are digested slowly and thus raise blood glucose in a controlled and regulated way. Examples include brown rice, oats, potatoes, couscous and quinoa. In contrast, sources that are categorised as high GI can cause a rapid increase in blood glucose, which signals β-cells of the pancreas to increase insulin secretion^[4]. Over the next few hours, insulin, which regulates blood glucose levels by moving glucose molecules from the blood into cells, will cause a sharp decrease in the concentration of blood glucose, resulting in hypoglycaemia.

A chronic intake of high GI carbohydrates has been linked to several health issues including obesity^[5], metabolic syndrome^{[6, 7]}, type 2 diabetes^[8] and cardiovascular disease (CVD)^[9]. There is a growing body of literature to support the therapeutic potential of low GI diets for diabetes^[9-13] and cardiovascular disease^[14-17].

See the table below for a list of foods and their corresponding GI value^[18].

Table 1. GI and GL Values for Selected Foods

* Amount of available carbohydrate in a food serving that excludes indigestible carbohydrates, i.e. dietary fibre

GI Short falls

Although glycaemic index should be considered when choosing carbohydrate sources, this rating system has several shortfalls.

Firstly, the GI scale does not consider the nutritional value of foods. Foods that are high GI are not necessarily unhealthy, and not all low GI foods are healthy. Many fruits and vegetables, for example, are high GI, such as watermelons and parsnips, which are both good sources of vital vitamins and minerals. Some low GI foods may also be high in calories and should be consumed in small portions.

The GI value of a food does not take real-life application into consideration. Generally speaking, we eat meals that are made up of numerous different foods, and the nutritional composition of one food may influence how another food is digested and absorbed. For example, foods that contain or are cooked with fat and protein slow down the absorption of carbohydrate, thus lowering their GI. For example, crisps have a lower GI than plain boiled potatoes, but we’re recommended to eat crisps in moderation due to their high fat content.

The rate at which your body processes carbohydrates can also be influenced by the total amount of food eaten, the processing of food and the ripeness of the food. A banana's GI value, for example, will increase as it ripens. When a banana is under-ripe, with a greenish colour and firm texture, the GI is relatively low (GI = ~30)^[19]. Over time, as the starch breaks down into simple sugars, the banana will turn yellow and eventually to brown. The GI of a ripe banana is ~62^[20].

Glycaemic Load

Glycaemic load (GL) is the total glycaemic effect of the diet. It is the product of dietary GI and total dietary carbohydrates consumed. GL measures how much a single serving of food influences the blood glucose response and therefore takes into consideration some of the short falls of GI.

To calculate the GL of a single serving of food, multiply the GI number by the grams of carbohydrate in one serving, then divide the total by 100^[21-23].

The GI and GL of Huel Products

Huel Powder v3.0 (Vanilla) has a glycemic index of 16^[24], Huel Ready-to-drink has a GI of 25^[25] and Ready-to-drink v2.0 Salted Caramel has a GI of 30.7^[26] and Huel cocoa and orange bars have a GI of 29^[27]. Huel Black Edition has a GI of 19. Additionally, Huel powder is also high in chromium which supports the maintenance of normal blood sugar levels.

Huel Black Edition (Vanilla) has a GI of 19^[28]. Huel Hot & Savoury flavours have the following GI values: Tomato & Herb - 23^[29], Thai Green Curry - 19^[30], Mexican Chilli - 31^[31], Mac & Cheeze - 34^[32]. Huel Essential (Vanilla) has a GI of 26.7^[33] 

Note that we are unable to obtain GI results for products such as Huel Complete Protein because the total carbohydrates per serve are too low.

Based on the aforementioned GL calculation, the GL of Huel Vanilla Powder v3.0 equates to 6, based on a 100g serving.

As Huel is a complete food designed to be ingested in isolation, the issues with GI and co-ingestion short-falls are not applicable to Huel.

References

1. Jenkins DJ, et al. Glycemic index of foods: a physiological basis for carbohydrate exchange. Am J Clin Nutr. 1981; 34(3):362-6.
2. Brouns F, et al. Glycaemic index methodology. Nutr Res Rev. 2005; 18(1):145-71.
3. Esfahani A, et al. The glycemic index: physiological significance. J Am Coll Nutr. 2009; 28 Suppl:439S-45S.
4. Ludwig DS. The glycemic index: physiological mechanisms relating to obesity, diabetes, and cardiovascular disease. JAMA. 2002; 287(18):2414-23.
5. Ludwig DS. Dietary glycemic index and obesity. J Nutr. 2000; 130(2S Suppl):280S-3S.
6. Liu S, et al. Dietary glycemic load assessed by food-frequency questionnaire in relation to plasma high-density-lipoprotein cholesterol and fasting plasma triacylglycerols in postmenopausal women. Am J Clin Nutr. 2001; 73(3):560-6.
7. McKeown NM, et al. Carbohydrate nutrition, insulin resistance, and the prevalence of the metabolic syndrome in the Framingham Offspring Cohort. Diabetes Care. 2004; 27(2):538-46.
8. Willett W, et al. Glycemic index, glycemic load, and risk of type 2 diabetes. Am J Clin Nutr. 2002; 76(1):274S-80S.
9. Ma XY, et al. Glycemic load, glycemic index and risk of cardiovascular diseases: meta-analyses of prospective studies. Atherosclerosis. 2012; 223(2):491-6.
10. Barclay AW, et al. Glycemic index, glycemic load, and chronic disease risk-a meta-analysis of observational studies. Am J Clin Nutr. 2008; 87(3):627-37.
11. Jenkins DJ, et al. Glycemic index: overview of implications in health and disease. Am J Clin Nutr. 2002; 76(1):266S-73S.
12. Riccardi G, et al. Role of glycemic index and glycemic load in the healthy state, in prediabetes, and in diabetes. Am J Clin Nutr. 2008; 87(1):269S-74S.
13. Solomon TP, et al. A low-glycemic index diet combined with exercise reduces insulin resistance, postprandial hyperinsulinemia, and glucose-dependent insulinotropic polypeptide responses in obese, prediabetic humans. Am J Clin Nutr. 2010; 92(6):1359-68.
14. Sloth B, et al. No difference in body weight decrease between a low-glycemic-index and a high-glycemic-index diet but reduced LDL cholesterol after 10-wk ad libitum intake of the low-glycemic-index diet. Am J Clin Nutr. 2004; 80(2):337-47.
15. 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; 300(23):2742-53.
16. Hermansen ML, et al. Can the Glycemic Index (GI) be used as a tool in the prevention and management of Type 2 diabetes? Rev Diabet Stud. 2006; 3(2):61-71.
17. Burani J, et al. Low-glycemic index carbohydrates: an effective behavioral change for glycemic control and weight management in patients with type 1 and 2 diabetes. Diabetes Educ. 2006; 32(1):78-88.
18. Linus Pauling Institute; Oregon State University. Glycemic Index and Glycemic Load. Date Accessed: 06/09/19 [Available from: https://lpi.oregonstate.edu/mic/food-beverages/glycemic-index-glycemic-load#table-1].
19. Hermansen K, et al. Influence of ripeness of banana on the blood glucose and insulin response in type 2 diabetic subjects. Diabet Med. 1992; 9(8):739-43.
20. Harvard T.H. Chan. Bananas. Date Accessed: 06/09/19. [Available from: https://www.hsph.harvard.edu/nutritionsource/food-features/bananas/
21. Salmeron J, et al. Dietary fiber, glycemic load, and risk of NIDDM in men. Diabetes Care. 1997; 20(4):545-50.
22. Salmeron J, et al. Dietary fiber, glycemic load, and risk of non-insulin-dependent diabetes mellitus in women. JAMA. 1997; 277(6):472-7.
23. Liu S, et al. A prospective study of dietary glycemic load, carbohydrate intake, and risk of coronary heart disease in US women. Am J Clin Nutr. 2000; 71(6):1455-61.
24. Lightowler H, et al. Glycaemic Index Value for Huel Vanilla Powder v3.0. Oxford Brookes Centre for Nutrition and Health, Oxford Brookes University; 2019.
25. Lightowler H, et al. Glycaemic Index Value for Huel Vanilla Ready-To-Drink. Oxford Brookes Centre for Nutrition and Health, Oxford Brookes University; 2018.
26. Lightowler H and Sangeetha T. Glycaemic Index Value for Huel Salted Caramel Ready-To-Drink. Oxford Brookes Centre for Nutrition and Health, Oxford Brookes University; 2022.
27. Lightowler H and Sangeetha T. Glycaemic Index Value for Huel Cocoa and Orange Bar v3.0. Oxford Brookes Centre for Nutrition and Health, Oxford Brookes University; 2019.
28. Lightowler H and Sangeetha T. Glycaemic Index Value for Huel Black Edition Vanilla Flavour Powder v1.0. Oxford Brookes Centre for Nutrition and Health, Oxford Brookes University; 2020.
29. Lightowler H and Sangeetha T. Glycaemic Index Value for Huel Tomato and Herb v1.0. Oxford Brookes Centre for Nutrition and Health, Oxford Brookes University; 2021.
30. Lightowler H and Sangeetha T. Glycaemic Index Value for Huel Thai Green Curry v1.0. Oxford Brookes Centre for Nutrition and Health, Oxford Brookes University; 2021.
31. Lightowler H and Sangeetha T. Glycaemic Index Value for Huel Mexican Chilli v1.0. Oxford Brookes Centre for Nutrition and Health, Oxford Brookes University; 2021.
32. Lightowler H and Sangeetha T. Glycaemic Index Value for Huel Mac & Cheeze v1.0. Oxford Brookes Centre for Nutrition and Health, Oxford Brookes University; 2022.
33. Lightowler H and Sangeetha T. Glycaemic Index Value for Huel Essential Vanilla. Oxford Brookes Centre for Nutrition and Health, Oxford Brookes University; 2022.