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Glycaemic index, load & low-carb

A meta-analysis of prospective cohort studies understanding impact of glycaemic index and glycaemic load...

Glycaemic index, load & low-carb

Low-glycaemic index sources of food is now recommended by NICE (NICE, 2022).

A meta-analysis of prospective cohort studies understanding impact of glycaemic index and glycaemic load in the risk of type 2 diabetes (Dong, Zhang, Zhang, & Qin, 2011) was undertaken.

Thirteen studies of dietary GI or GL related to diabetes risk were included. “The summary RR of type 2 diabetes for the highest category of the GI compared with the lowest was 1.16. For the GL, the summary RR was 1.20” The study came to conclusions that reducing the intake of high GI foods may bring benefits for diabetes prevention,

A second meta-analysis (Brand-Miller, Hayne, Petocz, & Colagiuri, 2003) comprised 14 studies and 356 subjects; 203 with T1DM and 153 with T2DM. The average GI of the high GI diet was 83 and the average GI of the low diet was 65. The mean difference in units was -0.33% (DCCT) and after 12 weeks the average was -0.4% (c.5 mmol/mol).

A third meta-analysis observed impact on GI and also identified impact on blood lipids; - total cholesterol average reductions of 6.4mg/dL and LDL 5.5 mg/dL with a dose dependent effect identified. The low GI diets had a statistically significant impact in reducing weight for obese individuals, but not for those of normal weight or overweight category (Zafar, et al., 2019).

Although NICE supports low glycaemic index in its statements for dietary recommendations (NICE, 2022) it explicitly states it does not endorse a low-carbohydrate diet.

In review of resources that it had previously endorsed from Dr David Unwin and retracting them, it states, “our diabetes guideline clearly recommends that people should follow a healthy balanced diet that contains, but is not limited to, eating low glycaemic index sources of carbohydrates.

We have therefore taken the decision to revoke our endorsement of Dr Unwin’s resource and have removed the link to it from NICE’s website”.

Dr David Unwin has studied glycaemic-related interventions in NHS General Practice interventions. Average body weight fell by 9kg, waist circumference by 15cm, reduction in hba1c by 10mmol/L (19%) and 5% reduction in total cholesterol and Dr Unwin has estimated a saving of £45,000 of prescribing costs in a single practice (Unwin, Livesey, & Haslam, It is the glycaemic response to, not the carbohydrate content of food that matters in diabetes and obesity: The glycaemic index revisited, 2016).

A meta-analysis of studies by Meng et al (2017) confirms a significant effect of the low carb diet on Hba1c levels and in the short-term; weight loss but not in the long-term.

They identified an improvement in cardiovascular risks of lower triglyceride levels, raised HDL, but no overall change in LDL or Total Cholesterol levels (Meng, et al., 2017). The authors wrote the beneficial impacts including on weight could be related to improvements in glucose metabolism and insulin sensitivity.

They noted reduced insulin requirements for patients and that the diet might directly improve liver glucose output [via glycogen stores] and also glucose utilisation through production of ketone antibodies and made reference to two papers in-view of this conclusion (Henry, Brechtel, & Lim, 1990; Muller, Paschen, & Seitz, 1984).

Position statements as identified by Kelly et al (2020) include: Diabetes UK (2011) – “Diabetes UK support the view that low-carbohydrate diets may be considered an option for weight loss in T2DM when supported by a registered healthcare professional (Dyson, et al., 2011).

The Scientific Advisory Committee on Nutrition (2015) recommends that carbohydrate intake should be approximately 50% of dietary energy (SACN, 2015).

SIGN guidelines suggest a low glycaemic index is an option as well as temporarily very low consumption of carbohydrates (<50g) up to 6 months (SIGN, 2017). The American Diabetes Association and European Association for the Study of Diabetes (USA and Europe) have put out consensus reports in 2018 which include low carb, low gi, high protein and DASH approaches, although they identify the Mediterranean diet may be the most effective (Davies, et al., 2018). Consensus reports by the ADA lower carbohydrate diets is a viable approach (Evert, et al., 2019).

Potential negative impacts

Low-carbohydrate diets have been associated with increased all-cause mortality risk including cancer and cardiovascular risk (Noto, A, Tsujimoto, & al, 2013; Fung, van Dam, Hankinson, & al, 2010; Sjogren, Becker, Warensjo, & al, 2010).

Sjogren et al noticed a reduction in cardiovascular risk with a Mediterranean dietary approach whereas carbohydrate restriction appeared to increase mortality (Sjogren, Becker, Warensjo, & al, 2010). Schulze et al identified when carbs were switched to protein, an increased incidence of type 2 diabetes, and when fat was substituted for carbohydrate, no significant change in incidence (Schulze, et al., 2008). Noto identifies the potential changed risk depending on the overall diet (i.e. plant-based inferred a lower risk with lower-carbohydrate method).

It is unclear whether it is the replacement with higher protein or other fats from the analyses led to increased risk, or whether it was related directly to limiting carbohydrates.

A key drawback to these studies is the understanding of ultra-processed foods in these studies is limited, and the impact of the level of processing.

Glycaemic diets - Impact on function, blood pressure and cholesterol

The focus of the program is Hba1c improvement for prediabetes and type 2 diabetes patients. The program should not lead to other negative impact on individuals’ health do not occur as a result, especially cardiovascular risk.

Diabetes management is important largely to do with its cardiovascular implications.

As identified above in meta-analyses and studies there are other benefits that are realised from taking on glycaemic related approaches. This includes positive impacts on cholesterol (Brand-Miller, Hayne, Petocz, & Colagiuri, 2003; Zafar, et al., 2019).

Low carbohydrate diets have been associated with improved renal risk factors. Unwin (2021) studied the impact on 143 patients’ renal function (those with normal renal function or mild CKD) and noted an improvement of serum creatinine by mean 4.7 micromol/L (Unwin D. , Unwin, Delon, Guess, & Wong, 2021)

The DASH diet (Dietary Approaches to Stop Hypertension), specifically created for improving hypertension outcomes, is advocated as a diet that can help with diabetes outcomes and recommended by ADA (Davies, et al., 2018). Dr Unwin has studied the impact of a low carb approach on blood pressure.

154 patients studied showed reductions in blood pressure (mean reduction of systolic BP 10.9 and diastolic 6.3, alongside a mean weight reduction of 9.5kg and improved lipid profiles. These readings occurred alongside a 20% reduction in anti-hypertensive medications (Unwin, Tobin, Murray, & Delon, 2019)

References

Brand-Miller, J., Hayne, S., Petocz, P., & Colagiuri, S. (2003). Low–glycemic index diets in the management of diabetes: a meta-analysis of randomized controlled trials. Diabetes care, 26(8), 2261-2267

Dong, J. Y., Zhang, L., Zhang, Y. H., & Qin, L. Q. (2011). Dietary glycaemic index and glycaemic load in relation to the risk of type 2 diabetes: a meta-analysis of prospective cohort studies. . British Journal of Nutrition, 106(11), 1649-1654.

Meng, Y., Bai, H., Wang, S., Li, Z., Wang, Q., & Chen, L. (2017). Efficacy of low carbohydrate diet for type 2 diabetes mellitus management: A systematic review and meta-analysis of randomized controlled trials. Diabetes research and clinical practice, 131, 124-131

NICE. (2022). National Insitute for Clinical Excellence - Type 2 Diabetes in adults: management. Retrieved June 2022, from https://www.nice.org.uk/guidance/ng28/ifp/chapter/diet-and-lifestyle

Unwin, D., Livesey, G., & Haslam, D. (2016). It is the glycaemic response to, not the carbohydrate content of food that matters in diabetes and obesity: The glycaemic index revisited. . Journal of Insulin Resistance, 1(1), 1-9

Zafar, M. I., Mills, K. E., Zheng, J., Regmi, A., Hu, S. Q., Gou, L., & L, a. C. (2019). Low-glycemic index diets as an intervention for diabetes: a systematic review and meta-analysis. The American journal of clinical nutrition, 110(4), 891-902

Henry, R. R., Brechtel, G., & Lim, K. H. (1990). Effects of ketone bodies on carbohydrate metabolism in non-inuslin-dependent (type II) diabetes mellitus. Metabolism - Clinical and Experimental, 39, 853-858.

Kelly, T., Unwin, D., & Finucane, F. (2020). Low-Carbohydrate diets in the management of obesity and type 2 diabetes: a review from clinicians using the approach in practice. International journal of environmental research and public health, 17(7), 2557

Dyson, P. A., Kelly, T., Deakin, T., Duncan, A., Frost, G., Harrison, Z., . . . al, e. (2011). Diabetes UK Position Statements and Care Recommendations Diabetes UK evidence-based nutrition guidelines for the prevention and management of diabetes. Diabetic Medicine Journal, 28 , 1282–1288.

SACN. (2015). Carbohydrates and Health; Available online: https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/ 445503/SACN_Carbohydrates_and_Health.pdf (accessed on 29 Decembe. Edinburgh, UK: SACN (UK).

Noto, H., A, G., Tsujimoto, T., & al, e. (2013). Low-carbohydrate diets and all-cause mortality: a systematic review and meta-analysis of observational studies. . PLoS One, 8, e55030

Fung, T. T., van Dam, R. M., Hankinson, S. E., & al, e. (2010). Low-carbohydrate diets and all-cause and cause-specific mortality: two cohort studies . Annals of Internal Medicine, 153, 289-298

Davies, M. J., D'Alessio, D. A., Fradkin, J., Kernan, W. N., Mathieu, C., Mingrone, G., . . . Buse, J. B. (2018). Management of hyperglycaemia in type 2 diabetes, 2018. A consensus report by the American Diabetes Association (ADA) and the European Association for the Study of Diabetes (EASD). Diabetes Care, 41, 2669-2701.

Schulze, M. B., Schulz, M., Heidemann, C., Schienkiewitz, A., Hoffman, K., & Boeing, H. (2008). Carbohydrate intake and incidence of type 2 diabetes in the European Prospective Investigation into Cancer and Nutrition (EPIC)-Potsdam Study. British Journal of Nutrition, 99(5), 1107-1116

Sjogren, P., Becker, W., Warensjo, E., & al, e. (2010). Mediterranean and carbohydrate-restricted diets and mortality among elderly men: a cohort study in Sweden. American Journal of Clinical Nutrition , 92, 967-974.

Unwin, D., Tobin, S. D., Murray, S. W., & Delon, C. (2019). Substantial and sustained improvements in blood pressure, weight and lipid profiles from a carbohydrate restricted diet: an observational study of insulin resistant patients in primary care. International Journal of Environmental Research and Public Health, 16(15), 2680.

Unwin, D., Unwin, J. C., Delon, C., Guess, N., & Wong, C. (2021). Renal function in patients following a low carbohydrate diet for type 2 diabetes: a review of the literature and analysis of routine clinical data from a primary care service over 7 years. Current Opinion in Endocrinology & Diabetes and Obesity, 28(5), 469-479.

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