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Lower carbohydrate diets in type 2 diabetes

Updated: Nov 19, 2020

Providing clarity on key messages, considerations for clinical practice and limitations of the research.

Written by Shane McAuliffe RD


Insights from a general practice service evaluation supporting a lower carbohydrate diet in patients with type 2 diabetes mellitus and prediabetes: A secondary analysis of routine clinic data including HbA1c, weight and prescribing over 6 years

D Unwin, A Khalid, J Unwin, D Crocombe, C Delon, K Martyn, R Golubic, S Ray

A new publication in BMJ Nutrition, Prevention and Health has shown that advice based on lower carbohydrate diets (LCDs) can be successfully incorporated into routine primary care practice, while demonstrating benefits for patients with type 2 diabetes mellitus (T2D) helping to better manage glucose control, reduce weight, cholesterol and significantly reduce medication prescribing costs. In this blog piece, we will untangle what the results of this audit tell us, and some important considerations for future practice and research.

The global prevalence of T2D is growing rapidly and there is demand from both patients and healthcare professionals for effective and sustainable lifestyle approaches to manage the condition. There is already some evidence for the benefits of providing LCD advice to patients with T2D, particularly for blood sugar control and reducing body weight. For this reason, LCD’s have become a significant source of attention and discussion for those living and working with diabetes.

This service evaluation from Dr David Unwin and colleagues measured the effects of introducing LCD advice to a group of willing patients with T2D from his Norwood general practice in Southport (UK), over a six year period. The audit included 27% of the total T2D population for the practice, and average adherence to a LCD was reported to be 23 months. The approach comprised on average 3 one-to-one appointments (conventional GP consultations) per year alongside optional group sessions every 6 weeks, which the authors acknowledge was likely a significant contributing factor to the patients’ success. This is an important point, given that we know this level of sustained support is a key ingredient for success in any long-term dietary intervention. It is also important to acknowledge that more than two-thirds of the practice T2D population did not follow the LCD advice, meaning a large proportion remain to be considered and catered for, requiring a focus on alternative dietary approaches to meet their needs.

The approach taken at the Norwood practice is an interesting one, because patients were advised on healthy eating patterns, with a focus on food-based targets rather than quantifying specific amounts. Particular attention was paid to reducing sugar, refined and starchy carbohydrates and high glycaemic index (GI) foods, but amounts or percentages of carbohydrates or other nutrients were not advised or prescribed (Fig 1). Replacement of these foods largely centred around green leafy vegetables, berries, eggs, full fat dairy, meat, oily fish, nuts and sugar free beverages, all of which are features consistent across a number of dietary approaches, not just LCD’s. It is possible that providing this practical advice around ‘simple swaps’ in a manner that was easily accessible and understandable could also have contributed significantly to the success of the Norwood approach. Ultimately, this was largely focussed on overall diet quality.

Figure 1 from the paper shows the diet sheet provided to patients undertaking the LCD at the Norwood GP practice.

The Norwood approach demonstrated some impressive results, especially for blood sugar control, with an average reduction in HbA1c (a marker of blood sugar control over a three-month period) of 17.5mmol/mol. In those who followed LCD advice, 46% achieved drug free remission, meaning that they maintained their blood sugar levels within a healthy range (HbA1c less than 48mmol/mol) without the use of diabetes medications. In patients with prediabetes (HbA1c 42 to 48mmol/mol), LCD advice contributed to improving HbA1c back to below the prediabetes threshold in 93% of patients.

Other markers of good health also significantly improved, with an average reduction in body weight loss of 8.1kg. Significant improvements in blood cholesterol, triglycerides and blood pressure were also seen.

Interestingly, older patients (over 65 years) and those with long-standing T2D (for over 6 years), in whom it is often thought more difficult to achieve remission, were helped to achieve significant improvements in blood sugar control with LCD advice. For this reason, the authors suggest that LCD advice can be effective for these patients and that they should not be excluded from future clinical trials of dietary approaches to T2D, as they have been previously.

In terms of cost, there was a £50,885 annual saving on the Norwood GP practice NHS T2D drug budget compared with the average for the other 17 GP practices in the Southport and Form by region. If every GP practice in England were to make savings on T2D medications in a similar way to Norwood, the NHS could save up to £277,000,000 per year.

It is important to acknowledge the limitations of the data presented in the audit too. The provision of LCD advice was self-selected by patients, which may mean that they were more motivated to achieve positive results in the first place. In this group, adherence to advice was self-reported, meaning we have no objective evidence as to how closely it was followed. We also cannot account for additional lifestyle or behavioural factors that may have influenced the results further. As alluded to, this group was only 29% of the total practice T2D population, meaning that a significant portion were not catered for by this approach. The audit was a service evaluation and not a formal, interventional clinical trial and so there was no control group for direct comparison with regular practice - although for context, the authors point towards very low rates of remission in control groups from clinical studies of patients with T2D. It is however likely that the level of regular and sustained support mentioned above would not have been present in regular practice. In order to improve the quality of future research, we must aim to assess the effectiveness of LCD’s in more robust clinical trials, whether this is compared with regular practice or alternative dietary approaches. This will require controlled conditions, randomisation and ensuring that both groups receive the same level of support and attention that we are understanding to play a crucial role in success.

Despite these limitations, the results of this real-world service evaluation from the Norwood practice suggest that with adequate support and supervision, LCD advice in primary care can be an effective means of improving blood sugar control and other important health markers. It may even be presented as an opportunity to achieve drug-free T2D remission in those who choose to pursue it. These benefits are likely to be an important motivating factor for patients and have the potential to confer significant cost savings for primary care practices.

In summary, we should celebrate any intervention that improves an individuals’ health and happiness - and we are increasingly seeing the provision of LCD advice as a means of this being achieved. This audit has shown us that LCD advice can be a means of achieving this goal for patients with T2D in primary care, but this does not mean it is the answer for everyone. As individuals, our preferences, culture and environment will shape the dietary approach that is most likely to be sustainable and achievable for us in the long term. It is important to recognise this and be willing to facilitate these needs, through whatever dietary approach that may be. After all, it is this individualisation that is so often the key to success. So let us acknowledge the success of those who have followed LCD advice in Norwood, while also considering those who have not. Let us move forward with an openness to consider a variety of dietary approaches, in a way that puts the individual first, then applies the fundamentals of good nutrition to best meet their needs and values.

Further references:

Given NNEdPro’s involved in writing and data analysis, we have prepared a position statement to convey our interpretation of the findings

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