Expert advice on recommended carbohydrate intake for type 2 diabetes remains controversial making it particularly confusing to know how much to have. This article summarises research on the impact of a low carb diet on type 2 diabetes.
Why low carb for type 2 diabetes?
Carbohydrates (carbs) are the macronutrient that raise both sugar (glucose) and insulin levels most potently. Type 2 diabetes, insufficient insulin secretion and insulin resistance, is characterised by high blood glucose levels and high insulin levels. It is logical that restricting carbs may reduce spikes of blood glucose levels, improve the management of blood glucose levels and reduce the requirements for insulin.
A low carb diet is considered to be approximately <130 g/day of total carbohydrate or <26% of total kcals, although there is no strict definition. A very low carbohydrate ketogenic diet is considered to be 20-50g/day or <10% of total kcal.
Current recommendations for type 2 diabetes carb intake
The National Institute for Clinical Excellence (NICE) recommends approximately 50% of the diet to be starchy carbs. Other institutions, (Scottish Intercollegiate Guidelines Network (SIGN), Diabetes UK and American Diabetes Association (ADA)) recommend an ‘individualised’ carbohydrate approach, which may involve a low carb diet.
To understand more about the carbohydrate content and energy value of food, check out calorie and macronutrient breakdown of common foods, and the downloadable PDF.
Low carb benefits
All benefits stated utilise research from clinical studies (randomised and non-randomised trials) on individuals with type 2 diabetes.
Improved blood glucose control
Managing blood glucose levels (glycaemic control) is the primary target of treatment in type 2 diabetes (1). Multiple reviews of large clinical trials (+1300 participants) show low carb to be better than high carb for glycaemic control (2,3). HbA1c levels, a biomarker for glycaemic control are improved with a low carb diet, with greater glucose lowering effects associated with a greater reduction in carbs (4,5,2).
Experimental evidence shows low carb to benefit blood glucose levels independent of weight loss and improve other diabetes related symptoms (1), beneficial for type 2 diabetes individuals who are not overweight – which research suggests to be approximately one third of individuals with type 2 diabetes (6).
Reduced insulin demands and improved insulin sensitivity
Carb restricted diets considerably reduce fasting insulin levels, may improve insulin sensitivity and reduce insulin resistance (7,8,9).
Weight loss
Low carb is frequently shown to beat low fat for weight loss (10,11,12). Low carb diets may also be better adhered to (10,1). However, this will obviously come down to the individual.
Reduced hunger to facilitate weight maintenance
Following weight loss, levels of hunger hormones increase, making weight maintenance challenging. People with type 2 diabetes on a very low carb diet (ketogenic diet < 50 g carbs), report significant reduced hunger despite significant weight loss (13). This may be due to increases in the more satiating protein and fat content (1).
Beneficial for inflammatory levels
Low carb diets may reduce inflammatory levels significantly more than low fat diets (14) with one and two years showing significant reductions in inflammatory biomarkers for people going low carb (15).
Improved cardiovascular disease (CVD) risk profile
Individuals with type 2 diabetes have 2-4 times greater risk of CVD (e.g. heart attack, stroke). Studies for up to a 3-year duration, show low carb diets to significantly improve CVD risk factors: waist circumference, blood pressure, triglycerides, HbA1c and insulin levels, inflammatory biomarkers, high density lipoprotein cholesterol and weight loss (10,11,16).
Reductions and / or elimination in diabetes medication use
Over >50% of individuals following a very low carb diet (20-50g) reduced or eliminated type 2 diabetes medications within 12 weeks (excluding metformin) (13). Over 2 years, 53.5% of patients on a very low carb diet reversed diabetes and 17.6% were in remission (glycaemic control without medication) (15). Low carb versus moderate carb may be superior for patients reducing or discontinuing their medication, reducing the number and severity of hyperglycaemic and hypoglycaemic episodes (1).
Concerns of going low carb
Insufficient evidence
Some authorities state that there is insufficient evidence to support going low carb. However, a growing body of evidence indicates the benefits and safety of low carb diets for type 2 diabetes. It is also argued that all available evidence should be considered for evaluation (instead of select studies that meet specific criteria). A group of leading experts (26 doctors/researchers) in the field critically evaluated the current literature on low carb diets to treat type 2 diabetes. They concluded that the evidence represents “the best-documented, least controversial results” (1).
Historical fat phobia
Historically fats have been regarded as ‘unhealthy’ – a study in the 1970s associated dietary total/saturated fat with Cardiovascular (CVD) risk (17). However, since this study, there have been several large clinical studies showing that this is not the case – that dietary total/saturated fat and CVD risk are not correlated (18,19,1). Studies have evaluated how macronutrients affect CVD risk, and have found that replacing saturated fats with carbohydrate has no effect (20).
Kidney function
A high protein diet was historically indicated to impair kidney function, but this is now indicated to be the case only for those individuals with pre-existing kidney issues; with no adverse effects on kidney function shown from low carb diets (21,15). Low carb diets have also been shown to be equally safe as low-fat and Mediterranean diets in preserving and improving renal function (22). Additionally, most low carb diets for type 2 diabetes use a higher fat content, rather than a higher protein content!
Safety
Insufficient evidence may always be associated with long-term safety concerns. However, effects of carb restriction are not comparable to the effects of intensive pharmacological treatment. The halt of the ACCORD (Action to Control Cardiovascular Disease in Diabetes) trial may have added to concerns for high risk patients with type 2 diabetes, however these concerns may be attributed to the effect of a pharmacological agent. Additionally, there is a growing body of substantial evidence showing the benefits of a low carb diet for type 2 diabetes.
Evolving recommendations
The Scientific Advisory Committee recently reviewed the effects of a low carb diet for type 2 diabetes and found consistent evidence to support its benefits in: HbA1c (glycaemic control), fasting plasma glucose levels and levels of triglycerides (fats). They also found that a low carb diet may improve high density lipoprotein cholesterol levels and reduce reliance on medications to control blood glucose. They did not measure the effect of a low carb diet on diabetes related symptoms (23).
Low carb meals
For meal ideas, check out our range of low carb recipes.
Take away messages… a nutritionist’s thoughts
Evidence-based, whilst open-minded
There is a growing body of robust evidence showing the benefits of a low carb diet as part of comprehensive treatment plan for type 2 diabetes. Whilst evidence-based research is critical to consider, any recommendation must be centred upon the needs of that individual.
Low carb does not equal no carbs: carbs can still be eaten on a low carb diet and low carb is significantly different to keto! Individuals have different amounts of carbs that work for them and it’s about finding that right amount that works for them and their health. This is one of the key challenges of dietary labels!
Personalisation
Generalised recommendations may not account for the individual’s needs. Diets have to be individualised to accommodate genetic make-up, biochemical individuality, lifestyle and preferences. The diet needs to fit the individual, not the other way around! This is by far the best diet!
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References
- Feinman et al. (2015). Dietary carbohydrate restriction as the first approach in diabetes management: critical review and evidence base.
- Snorgaard et al. (2017). Systematic review and meta-analysis of dietary carbohydrate restriction in patients with type 2 diabetes
- Meng et al. (2017). Efficacy of low carbohydrate diet for type 2 diabetes mellitus management: a systematic review and meta-analysis of randomised clinical trials.
- Saslow et al. (2017). Twelve-month outcomes of a randomised trial of moderate carbohydrate versus very low carbohydrate diet in overweight adults with type 2 diabetes mellitus or prediabetes.
- Westman et al. (2008). The effect of a low-carbohydrate, ketogenic diet versus a low-glycaemic index diet on glycaemic control in type 2 diabetes.
- Taylor et al. (2015). Normal weight individuals who develop type 2 diabetes: the personal fat threshold.
- Noakes et al. (2006). Comparison of isocaloric very low carbohydrate/low saturated fat diets on body composition and cardiovascular risk.
- Volek et al. (2005). Carbohydrate restriction improves the features of metabolic syndrome. Metabolic syndrome may be defined by the response to carbohydrate restriction
- Volek et al. (2008). Dietary carbohydrate restriction induces a unique metabolic state positively affecting atherogenic dyslipidaemia fatty acid partitioning and metabolic syndrome.
- Hession et al. (2009). Systematic review of randomised controlled trials of very low carbohydrate vs very low fat/low calorie diets in the management of obesity and its comorbidities
- Sackner-Bernstein et al. (2015). Dietary intervention for overweight and obese adults: comparison of low-carbohydrate and low-fat diets. A meta-analysis.
- Bueno et al. (2013). Very low carbohydrate ketogenic diet vs low fat diet for long-term weight loss: a meta-analysis of randomised controlled trials.
- McKenzie et al. (2017). A novel intervention including individualised nutritional recommendations reduces haemoglobin A1c level, medication use, and weight type 2 diabetes
- Forsythe et al. (2008). Comparison of low fat and low carbohydrate diets on circulating fatty acid composition and markers of inflammation
- Athinarayanan S.J, Adams R.N, Hallberg S.J, McKenzie A.L, Bhanpuri N.H, Campbell W.W, Volek J.S, Phinney S.D and McCarter J.P (2019). Long-term effects of a novel continuous remote care intervention including nutritional ketosis for the management of type 2 diabetes: a 2-year non-randomised clinical trial.
- Santos et al. (2012). Systematic review and meta-analysis of clinical trials of the effects of low carbohydrate diets on cardiovascular risk factors.
- Keys (1970). Coronary heart disease in seven countries.
- Anderson et al. (1987). Cholesterol and mortality. 30 y of follow-up from the Framingham study.
- Howard et al. (2006). Low-fat dietary pattern and risk of cardiovascular disease: the Women’s Health initiative randomised controlled dietary modification trial.
- Jakobsen et al. (2009). Major types of dietary fat and risk of coronary heart disease: a pooled analysis of 11 cohort studies
- Tay et al. (2015). Long-term effects of a very low carbohydrate compared with a high carbohydrate diet on renal function in individuals with type 2 diabetes: a randomised trial.
- Triosh et al. (2013). Renal function following three distinct weight loss dietary strategies during 2 years of randomised controlled trials.
- Scientific Advisory Committee on Nutrition (2020). Lower carbohydrate diets for adults with type 2 diabetes. (Draft for consultation).
