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.
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.
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