Authors: Dr Dominic Crocombe & Dr Rajna Golubic
Reviewers and Editors: Ramya Rajaram, Sumantra Ray
Copyediting: Veronica Funk
Diet is a key factor in the development, progression, and outcomes of many chronic diseases. Since its inception, NNEdPro Global Institute for Food, Nutrition and Health (NNEdPro Global Institute) has supported the research, development, and implementation of safe, effective and sustainable dietary interventions, including for type 2 diabetes mellitus (T2D). There is particularly good clinical evidence to support energy restricted diets to induce weight loss and subsequent remission of T2D (1,2), especially for low and/or very low calorie diets following the success of the DiRECT trial in the UK (3).
In recent years, the body of evidence for low carbohydrate diets (LCDs) to achieve the same goals has also grown. NNEdPro Global Institute is proud to have contributed research on this topic and has published a number of scientific papers, including in our journal, BMJ Nutrition, Prevention and Health (4–7). In 2020, we published the clinical outcomes of an innovative NHS primary care service in which a LCD approach was offered to patients with T2D under the clinical supervision of Dr David Unwin at the Norwood Surgery (4). This initial paper reported the outcomes of 128 patients with T2D (27% of the total practice population who had T2D) who had been counselled and supported to follow a LCD over an average of 23 months. Significant improvements in body weight, glycaemic control, other cardiometabolic markers, and reduced the need for T2D medications were demonstrated. Remarkably, the rate of drug-free T2D remission, which is of utmost importance to long-term health outcomes (8), was 46%. Encouragingly, positive results were seen across a wide range of patients, including those of older age (>65 years), those with long-standing T2D (>6 years since diagnosis), and those with high baseline HbA1c.
We also observed a significant improvement in lipid profile in this cohort, which predominantly comprised overweight or obese adults. However, we are aware of the emerging evidence of differential lipid responses to LCD according to adiposity. This phenomenon is termed the “lean mass hyper-responder phenotype” whereby consumption of LCD is associated with an elevated low density lipoprotein cholesterol in those with normal body weight but not in those with elevated body weight (9). Further studies from the Norwood Surgery cohort have suggested an improvement in renal function with a LCD, despite some concerns that a LCD may be detrimental to kidney health (10), and that patients in their first year of T2D diagnosis were particularly likely to achieve remission (5).
It is worth noting that all results from the Norwood Surgery to date have come from retrospective clinical service evaluation/audit, and all patients had opted for the LCD intervention without randomisation or a formal control group. There are limitations to this research, especially in comparison to formal interventional trials, but the results are insightful, remarkable in their impact (both clinically and financially), and they make a compelling case for the potential of LCD interventions in routine clinical practice. Furthermore, the mechanisms that make clinical trials superior in the hierarchy of evidence, namely control groups, randomisation, and blinding, are notoriously difficult to implement in dietary intervention trials. We have commented further on the utility of both clinical audit and science-led research for dietary interventions elsewhere (6).
In recent years, several more studies have reported in favour of LCDs in T2D. These include population-level studies (11), clinical trials (12–14), and systematic reviews and meta-analyses of existing evidence, amongst which is evidence of a dose-response relationship between reducing carbohydrate intake and positive outcomes (15–18). Others have highlighted how the quality of carbohydrates eaten, and indeed the quality of the overall diet, are also important considerations (11,19).
Other points worth noting include a recent clinical trial of vegetarian and vegan LCDs in patients with T2D, which demonstrated effectiveness in clinical parameters, and a potentially favourable impact on greenhouse gas emissions for vegan LCDs (13). Finally, the LCD approach for T2D and other metabolic conditions has been demonstrated to be beneficial when provided via novel care models, including large scale telemedicine services (20,21). Important issues still open to debate include the definition of low (and/or very low) carbohydrate diets or ketogenic diets, the physiological effects of LCDs independent of weight loss, and the best strategies for implementation and long-term maintenance.
In summary, we at NNEdPro Global Institute celebrate the growing acceptance that T2D remission is possible through dietary modification. Low and very low-calorie diets have a robust evidence base for this indication. The evidence base for LCDs is growing and this should be considered another valid option that is offered to patients with T2D. Modern healthcare systems would be of greater benefit to patients with T2D for expanding their nutrition and dietetics workforces. This, in addition to better nutrition education and training for all healthcare professionals providing care to patients with T2D is strongly recommended.
References
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