Glycemic Index – A Canadian Success Story

Growing interest in personal health and wellbeing is driving consumer demand for nutritious foods that also offer a consistent pleasurable eating experience and are convenient to both prepare and consume in numerous ways. The Glycemic Index was first proposed in 1991 by Dr. David Jenkins at the University of Toronto, as a physiological way to differentiate foods by their rate of digestion and communicate their effect on blood sugar (glucose) levels for at least two hours following their consumption. The GI rating system has an indexed rating scale of 0 – 100 and a food’s GI is determined using ISO 26642:2010 testing protocols. High GI foods have a rating of 70 or more, moderate GI foods have a rating of 56-60, and low GI foods have a rating of 55 or less.

Multiple studies, led by Dr. Jenkins and other researchers have shown that low GI foods, as part of a long-term healthy diet, may reduce individuals’ risk of developing type 2 diabetes and other chronic health conditions. With subsequent research showing that processing, ripeness, accompanying foods and genetics can influence foods’ effect on blood sugar levels, measures including glycemic load (GL) and glycemic response (GR) have been proposed as preferred alternatives to GI. Leading glycemic researchers argue, however, that due to its ease of interpretation, and the fact that both GL and GR refer to GI in their calculation, GI remains the most valuable consumer guide for assessing foods’ likely effect on blood sugar and in maintaining a healthy diet (Barclay, Brand-Miller, Wolever, 2005; Jenkins et al, 2013).

Canadian and Australian researchers remain at the forefront of evaluating foods’ glycemic characteristics and their role in maintaining a healthy balanced diet. Other glycemic research centres include Harvard University’s Glycemic Research Institute. Canadian primary glycemic research centres include the University of Toronto’s Department of Nutrition Sciences (DNS) and GI Labs , which is located at the University of Toronto and led by Dr. Thomas Wolever. Australian research centres include the University of Sydney’s School of Molecular Bioscience, whose glycemic research is led by Professor Jennie Brand-Miller . EarthFresh (who grow and market Carisma™ in Canada) and Agrico (the breeders of Carisma™) work closely with Dr. Wolever and Professor Brand-Miller to ensure that Carisma™ potatoes reach you with the lowest possible GI and GR, the latter being the measure Health Canada recognizes for communicating foods’ glycemic characteristics.

Production Practices

Australia saw the initial launch of Carisma™ as a low GI potato, in 2010. Research has shown that it is not only Carisma’s glycemic characteristics that set it apart from other lower GI potato cultivars; it is the ability of growers and distributors to manage factors that determine Carisma’s lower glycemic characteristics from production to consumption that set it apart from other varieties of potatoes. Consumers can further reduce some potato varieties’ GI/GR by cooling then reheating prior to serving.

Research by Dr. Kai Lin Ek , Sydney University’s Glycemic Index Research Service (GIRS), Agrico, along with results from over four years of field and storage trails conducted by EarthFresh, enabled the development of strict production and handing protocols that include the following:

• As environmental conditions can impact the GI of potatoes, growing locations are carefully chosen to ensure their suitability for Carisma™.
• Carisma is supplied to you direct from the field to prevent changes in starch content that can occur in storage.
• To maintain supply throughout the year, Carisma™ is grown in Ontario and US states, including Idaho, California and Texas.

Each crop of Carisma™ is tested at time of harvest by GI Labs to verify its glycemic characteristics. The graph shown below is taken from GI Labs’ analysis of Carisma and chosen varieties in 2015. The graph illustrates differences in the post-prandial glycemic response of Carisma™ versus a standard* potato variety. Consuming Carisma™ produces a lower and shorter-term spike in blood glucose compared to consuming the same serving size of a standard potato variety.

* Standard potato equals one serving of the Russet Burbank variety.

Why Carisma™ Expresses Consistently Lower GI/GR Compared to Other Potato Varieties

Potato varieties’ genetic and morphological characteristics differ widely, as does their starch content . While potato varieties’ GI/GR also differ widely, no direct correlation exists between their total starch content and glycemic characteristics . Sydney University’s GIRS and Toronto University’s DNS has conducted the majority of peer-reviewed research on potato varieties’ GI characteristics. Other research on potato varieties’ GI characteristics has also been published in peer-reviewed journals by Canadian and UK researchers, amongst others. Potatoes’ GI characteristics have also been the subject of Masters and PhD studies. Research has typically found that floury potatoes have high GI levels (>70) compared to waxy potatoes, which typically have medium GI (56-69) or low GI levels (55). Carisma™ has a waxy skin, resulting in a creamy consistently good eating experience and is perfect boiled, mashed or baked.

Foods that mainly contain rapidly digestible starch will be metabolized comparatively quickly, leading to more sudden and higher spikes in blood sugar. These high spikes are proceeded by a similarly steep decline in blood sugar, which increases our appetite and stimulates a desire to eat. This cycle results in high GI foods leaving people feeling full for a shorter period of time compared to low GI foods.

Why no direct correlation exists between potato varieties’ starch content and their GI/GR characteristics is due to differences in how each varieties’ internal starch is structured. The structure of potato varieties’ starch cells differ in granule size and shape, as does their amylose versus amylopectin content. Amylose and amylopectin are polysaccharides, which determine potatoes’ starch digestibility and typically occur in a 1:3 ratio respectively. Research conducted at the University of Sydney also identified other starch characteristics , which differentiate Carisma™ from other commonly grown potato cultivars. They include more tightly packed growth rings, a stronger florescence at the hilum and a lack of internal imperfections found to exist in higher GI cultivars. These factors are believed to explain why Carisma’s starch cells swell considerably less in size and appear more resistant to gelatinization during cooking. A correlation exists between gelatinized starch granules, the rate at which starch is digested, and foods’ GI characteristics. As amylopectin is more readily gelatinized in cooking than amylose, the higher a potato variety’s ratio of amylose to amylopectin, the less gelatinization may occur. These findings strengthen the hypothesis that a potato varieties’ GI level is primarily a function of the physical and molecular structure structure of its starch cells, not total starch or carbohydrate content. That growing conditions influence potatoes’ internal attributes and subsequent GI level highlights the importance of production practices.

Bibliography

Agrico (Undated). Agrico Homepage; Accessible at: http://en.agrico.nl/

Aziz , A., Dumais , L., Barber , J. (2013). Health Canada’s evaluation of the use of glycemic index claims on food labels; The American Journal of Clinical Nutrition; August 2013; vol. 98 no. 2 269-274 http://ajcn.nutrition.org/content/98/2/269.long

Bach, S., Yada, R.Y., Bizimungu, B., Fan, M., Sullivan, J.A. (2013). Genotype by Environment Interaction Effects on Starch Content and Digestibility in Potato (Solanum tuberosum L.); Journal of Agricultural and Food Chemistry; V61, Issue 16, pages 3941-3948. Accessible at: http://www.ncbi.nlm.nih.gov/pubmed/23484744

Barclay, A.W., Brand-Miller, J.C., Wolever, T.M.S. (2005). Glycemic Index, Glycemic Load, and Glycemic Response Are Not the Same; Diabetes Care 2005 Jul; 28(7): 1839-40; Accessible at: http://care.diabetesjournals.org/content/28/7/1839

Best Health (2016). 4 reasons to eat low GI foods; Best Health; Readers Digest; Accessible at: http://www.besthealthmag.ca/best-eats/healthy-eating/4-reasons-to-eat-low-gi-foods/

Brand-Miller, J., C. (2004). Postprandial glycemia, glycemic index, and the prevention of type 2 diabetes; American Journal of Clinical Nutrition; 2004; 80:243-4; Accessible at: http://ajcn.nutrition.org/content/80/2/243.long

Carisma Australia (Undated). Australian First: The only certified low GI potato; The Matilo Group; Accessible at: http://www.carismapotatoes.com.au/

CDA 1 (Undated). The Glycemic Index; Canadian Diabetes Association; Accessible at: /diabetes-and-you/healthy-living-resources/diet-nutrition/the-glycemic-index

CDA 2 (2016). Prediabetes; Canadian Diabetes Association; Accessible at: /about-diabetes/prediabetes

EatRight Ontario (2016). Getting to Know the Glycemic Index. Dieticians of Canada; Accessible at: http://www.eatrightontario.ca/en/Articles/Carbohydrate/Getting-to-know-the-Glycemic-Index.aspx#.V9Caau_ruNJ

Fajardo, D., Haynes, K.G., Jansky, S. (2013). Starch Characteristics of Modern and Heirloom Potato Cultivars; American Journal of Potato Research; V.90, pages 460-469; Accessible at: http://link.springer.com/article/10.1007/s12230-013-9320-5

GI Labs (2015). Final Report: Determination of Glycemic Index (GI) and Glycemic Response (GR) of: including Texas (grown) Almera, Washington (grown) Almera, Aberdeen (grown) Almera, Idaho (grown) Almera, Idaho Russet #1, Idaho Russet #2.

GI Labs. (Undated). Homepage, Glycemic Index Laboratories Inc. Accessible at: http://www.gilabs.com/index.php

GIF (2016). Glycemic Index Foundation; University of Sydney; Last updated May 3, 2016; Accessible at: http://www.glycemicindex.com/index.php

Haase, N. U., & Plate, J. (1996). Properties of potato starch in relation to varieties and environmental factors. Starch/Staerke, 48 (5), 167-171; Accessible at: http://onlinelibrary.wiley.com/doi/10.1002/star.19960480503/pdf

Harvard Health Publications. (2016). The lowdown on glycemic index and glycemic load; Harvard Medical School; May 2016; Accessible at: http://www.health.harvard.edu/diseases-and-conditions/the-lowdown-on-glycemic-index-and-glycemic-load

Health Canada. (2013). Technical Consultation on Health Canada’s Draft Guidance Document on Food Health Claims Related to Post-Prandial Glycaemia; Health Canada; Accessible at: http://www.hc-sc.gc.ca/fn-an/consult/glyc-postprandial/index-eng.php

ISO (2010). Food products — Determination of the glycaemic index (GI) and recommendation for food classification – ISO 26642:2010; Accessible at: http://www.iso.org/iso/catalogue_detail.htm?csnumber=43633

Jenkins , D.J.A., Willett , W.C., Astrup , A., Augustin , L.S.A., Baer-Sinnott , S., Barclay , A.W., Björck , I., Brand-Miller , J.C., Brighenti , F., Buyken , A.F., Ceriello , A., Kendall , C.W.C., La Vecchia , C., Livesey , G., Liu , S., Poli , A., Riccardi , G., Rizkalla , S.W., Sievenpiper , J.L., Trichopoulou , A., Wolever , T.M.S. (2014). Glycaemic index: did Health Canada get it wrong? Position from the International Carbohydrate Quality Consortium (ICQC); British Journal of Nutrition, 111:2, January 2014, pp.380-382; Accessible at: https://www.cambridge.org/core/journals/british-journal-of-nutrition/article/glycaemic-index-did-health-canada-get-it-wrong-position-from-the-international-carbohydrate-quality-consortium-icqc/057DC30F604D1BC757B5B083B4525BE5

Jenkins , D.J., Wolever , T.M., Taylor , R.H., Barker , H., Fielden , H., Baldwin , J.M., Bowling , A.C., Newman , H.C., Jenkins , A.L., Goff , D.V. (1981). Glycemic index of foods: a physiological basis for carbohydrate exchange; American Journal of Clinical Nutrition; March 1981; 34:3, pp 362-366; Accessible at: http://www.ncbi.nlm.nih.gov/pubmed/6259925

Jeya, C., Henry, K., Lightowler, H.J., Strik, C.M., Storey, M.; (2005). Glycemic index values for commercially available potatoes in Great Britain; British Journal of Nutrition, V.94, pages 917-921. Accesible at: https://www.cambridge.org/core/journals/british-journal-of-nutrition/article/glycaemic-index-values-for-commercially-available-potatoes-in-great-britain/795D0FB6AAD106D347469554741978A1

Kinnear, T. (2010).  Interaction Between the Effects of Preparation Method and Variety on the Glycemic Index of Novel Potato Varieties; University of Toronto; Maters Thesis; Accessible at: https://tspace.library.utoronto.ca/bitstream/1807/25731/1/Kinnear_Tara_S_201011_MAST_thesis.pdf

Kinnear , T.S., Wolever , T.  (2010). The effects of cooking, cooling and reheating on the Glycemic Index depends on potato variety; Federation of American Societies for Experimental Biology ( FASEB) journal 2010 vol:24; Accessible at: http://www.fasebj.org/content/24/1_Supplement/553.2

Lin Ek, K.L. (2014). The Characteristics of Potatoes Differing in Glycemic Index; PhD Thesis, University of Sydney; Accessible at: https://ses.library.usyd.edu.au/handle/2123/12330

Lin Ek, K.L, Wang, S., Copeland, L.; Brand-Miller, J.C.; (2014). Discovery of a low-glycemic index potato and relationship with starch digestion in vitro ; British Journal of Nutrition, V. 111, pages 699-705; Accessible at: http://www.ncbi.nlm.nih.gov/pubmed/24103358

Lin Ek, K., Wang, S., Brand-Miller, J., Copeland, L. (2014) Properties of starch from potatoes differing in glycemic index; Food and Function; 2014, Issue 10, pp. 2509-15; Accessible from http://www.ncbi.nlm.nih.gov/pubmed/25124366

Lin Ek, K., Brand-Miller, J., Copeland, L.; (2011). Glycemic Effect of Potatoes; Food Chemistry; Volume 133, Issue 4 , 15 August 2012, Pages 1230–1240; Accessible at: physical and molecular structure

Lynch, D.R., Liu, Q., Tarn, T.R., Bizimungu, B., Chen, Q., Harris, P, Chik, C.L., Skjodt, N.M.; (2007). Glycemic Index – A Review and Implications for the Potato Industry; American Journal of Potato Research; V. 84, pages 179-190. Accessible at: http://search.proquest.com/openview/cc7da0f9b245e4c7cf0fefeeac2f0259/1?pq-origsite=gscholar&cbl=25213

Media reports of Carisma’s 2010 Australia launch: http://blog.doyoueat.com.au/2010/11/low-gi-potato-world-first.html ; http://foodwatch.com.au/reviews/item/product-review-carisma-cutting-the-gi-of-potatoes.html

Najjar, N., Adra, N., Hwalla, N. (2004). Glycemic and insulinemic responses to hot vs cooled potato in males with varied insulin sensitivity; Journal of Nutrition Research; 24: 993–1004

Randolph, J.M., Edirisinghe, I., Masoni, S.M., Kappagoda, T., Burton-Freeman, B.; 2014) Potatoes, Glycemic Index, and Weight Loss in Free-Living Individuals: Practical Implications; Journal of the American College of Nutrition, Vol 33, No. 5, 375-384. Accessible at: http://www.tandfonline.com/doi/abs/10.1080/07315724.2013.875441

Singh, G. (1969). A review of the soil-moisture relationship in potatoes; American Potato Journal, V.46, Issue 10, pages 398-403. Accessible at: http://link.springer.com/article/10.1007/BF02869560?no-access=true

SUGiRS (2016). Sydney University Glycemic Index Research Service; University of Sydney; Accessible at: http://www.glycemicindex.com/testing_research.php

The Nutrition Source (Undated). Carbohydrates and Blood Sugar; Harvard, T H Chan School of Public Health; Available at: https://www.hsph.harvard.edu/nutritionsource/carbohydrates/carbohydrates-and-blood-sugar/

Venn, B.J., Wallace, A.J., Monro, J.A., Perry, T., Brown, R., Frampton, C., Green, T.J. (2006). The Glycemic Load Estimated from the Glycemic Index Does Not Differ Greatly from That Measured Using a Standard Curve in Healthy Volunteers; Journal of Nutrition; 2006 May;136(5):1377-81; Accessible at: http://jn.nutrition.org/content/136/5/1377.long

Whelan, W.J., Hollar, D., Agatston, A., Dodson, H.J., Tahal, D.S. (2010). The Glycemic Response is a Personal Attribute; IUBMB Life, 62(8): 637–641, August 2010; Accessible at: http://onlinelibrary.wiley.com/doi/10.1002/iub.365/epdf

Wikipedia (2016). Glycemic Index; Wikipedia; Accessible at: https://en.wikipedia.org/wiki/Glycemic_index