Over the past 25 years, rates of type 2 diabetes have increased significantly, while stroke and coronary heart disease continue to claim thousands of lives each year [1]. Evidently, cardiovascular disease (CVD) is a major global cause of death [2]. Because of the link between CVD and diet, many studies have investigated dietary choices that can prevent CVD. Recent research has indicated a link between glycemic index (GI) and cardiovascular disease [3]. While this research is not robust, it is worth exploring whether low-GI diets could significantly reduce rates of cardiovascular disease [3].
Glycemic index measures how much a certain carbohydrate-containing food increases blood sugar levels [1]. By comparing foods according to their GIs, measured on a scale from 0 to 100, one can rank foods in terms of their glycemic potential physiologically [1]. People digest and absorb foods with lower glycemic indices more slowly [1]. Meanwhile, diets centered around more quickly absorbed, high-GI foods may interact with insulin resistance to produce an elevated glycemic response (change in blood sugar) after eating [3]. As such, some researchers have had cause to investigate whether lower GI foods contribute to lower risks of CVD.
There is convincing evidence that glycemic index and cardiovascular disease are closely associated. Jenkins et al. analyzed the conditions of 137,851 participants, aged anywhere from 35 to 70, across five different continents [3]. The median follow-up in the experiment was 9.5 years [3]. Subjects completed food-frequency questionnaires to estimate their glycemic index and glycemic load [3]. The researchers identified that patients with high-GI diets tended to experience a higher risk of major cardiovascular events or deaths, regardless of whether they had previously suffered from cardiovascular disease or not [3]. Similar results were reported by Brandhorst et al., who conducted a meta-analysis with 220,005 participants and also found an association between GI and CVD [2]. While the mechanism explaining this relationship remains unclear, these findings are nevertheless promising [4].
Despite the association between GI and CVD, experiments have struggled to demonstrate that lowering the GI in subjects’ diets lowers their risk of CVD and CVD-related death [5, 6]. Sacks et al. placed 163 overweight adults on a five-week controlled feeding study, in which the different experimental groups were placed on diets with either high or low carbohydrate content, and high or low glycemic index [5]. At the end of the study, there was no significant difference between low and high glycemic index participants in terms of lipid levels, insulin sensitivity, or systolic blood pressure [5]. Slavin et al. also found that, among even the strongest intervention studies, there was little evidence to suggest that lower GI contributed to a decreased CVD risk [6].
One explanation for these contradictory findings could be the difference between how men’s and women’s bodies tend to react to carbohydrate consumption. Brandhorst et al. reported that women exhibited a greater positive association between GI and CVD, which could have influenced studies in which there was a greater sex disparity in either direction [2]. Alternatively, the association between GI and CVD may just be that: an association without any form of causation, explaining why lowering a diet’s overall glycemic index may not contribute to reduced risk of cardiovascular disease.
While some studies suggest that low-GI diets reduce the risk of cardiovascular disease, others suggest that the link between GI and CVD is not so strong [4]. As a result, the association between glycemic index and cardiovascular disease warrants further research [4]. For individuals seeking to learn more about dietary choices and their health, licensed dietitians, primary care providers, and physical therapists are all good sources of information.
References
[1] J. Brand-Miller et al., “The glycemic index and cardiovascular disease risk,” Current Atherosclerosis Reports, vol. 9, no. 6, p. 479-485, March 2008. [Online]. Available: https://doi.org/10.1007/s11883-007-0064-x.
[2] S. Brandhorst and V. D. Longo, “Dietary Restrictions and Nutrition in the Prevention and Treatment of Cardiovascular Disease,” Circulation Research, vol. 124, no. 6, p. 952-965, March 2019. [Online]. Available: https://doi.org/10.1161/CIRCRESAHA.118.313352.
[3] D. J. A. Jenkins et al., “Glycemic Index, Glycemic Load, and Cardiovascular Disease and Mortality,” The New England Journal of Medicine, vol. 384, no. 14, p. 1312-1322, April 2021. [Online]. Available: https://doi.org/10.1056/NEJMoa2007123.
[4] A. Mirrahimi et al., “The Role of Glycemic Index and Glycemic Load In Cardiovascular Disease and Its Risk Factors: A Review of the Recent Literature,” Current Atherosclerosis Reports, vol. 16, no. 1, p. 1-10, January 2014. [Online]. Available: https://doi.org/10.1007/s11883-013-0381-1.
[5] F. M. Sacks et al., “Effects of High vs Low Glycemic Index of Dietary Carbohydrate on Cardiovascular Disease Risk Factors and Insulin Sensitivity,” JAMA, vol. 312, no. 23, p. 2531-2541, December 2014. [Online]. Available: https://doi.org/10.1001/jama.2014.16658.
[6] S. Vega-López, B. J. Benn, and J. L. Slavin, “Relevance of the Glycemic Index and Glycemic Load for Body Weight, Diabetes, and Cardiovascular Disease,” Nutrients, vol. 10, no. 10, p. 1-27, September 2018. [Online]. Available: https://doi.org/10.3390/nu10101361.