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The Scientific Advisory Committee on Nutrition (SACN) recently published a report on lower carbohydrate diets for adults with type 2 diabetes (T2D) ¹. The report reviewed the evidence available on low carbohydrate diets and compared this with current UK government advice on carbohydrate intake for adults with T2D.
SACN advises Public Health England on nutrition and public health related matters, and does not typically make recommendations about clinical conditions ². As such, a joint working group was established to create the report, consisting of members from SACN, Diabetes UK, the British Dietetic Association, the Royal College of Physicians, and the Royal College of General Practitioners.
The working group reviewed evidence published up to September 2018 which compared the impact of lower versus high carbohydrate diets on markers and clinical outcomes of T2D. Eight systematic reviews and one network meta-analysis were identified as suitable and were therefore included in the report. This article summarises the report, its findings, and the recommendations made by SACN.
In 2018, it was estimated that 4.7 million people in the UK were living with diabetes ³. By 2019, this figure rose to 4.9 million, with T2D accounting for 90% of cases ⁴. Complications of T2D can include ⁵:
Management of T2D may include medication, but will usually involve behavioural and lifestyle interventions, including diet, exercise, reducing alcohol use, and smoking cessation.
SACN’s report came about as a result of a request from Public Health England for a systematic assessment of the scientific evidence on low carbohydrate diets, following recognition that such diets are becoming increasingly popular.
Since there is no agreed and widely used definition of a ‘low’ carbohydrate diet, comparisons in this report were between lower and higher carbohydrate diets. For the purposes of this report, in order to enable comparisons of carbohydrate intakes across the studies, the classification proposed by Feinman et al (2015) was used to categorise carbohydrate intake. ⁶ (see table 1).
Table 1: Definitions proposed by Feinman et al (2015) used in the SACN repor
| Carbohydrate category | Amount of carbohydrate | |
| gram/day | % total energy (based on 2000kcal/day) | |
| Very low | 20 to 50 | ≤10 |
| Low | >50 to <130 | >10 to <26 |
| Moderate | 130 to 230 | 26 to 45 |
| High | >230 | >45 |
In the UK, it is recommended that adults with T2D reduce their saturated fat intake, and reduce their energy intake with a goal of weight loss if they are also living with overweight or obesity (⁷, ⁸).
However, there are no specific recommendations for people with T2D relating to the amount of carbohydrate intake. Current government advice for the general population is to follow a balanced dietary pattern with around half of the recommended total daily energy (calorie) intake coming from carbohydrate foods. This advice for the general UK population also applies to those with T2D.
The primary outcomes of interest were changes in body weight (≥12 months) and HbA1c (≥3 months). Secondary outcomes of interest were changes in body weight (≥3 to <12 months), fasting plasma glucose (≥3 months), blood lipids (≥3 months), and medication use.
The SACN working group found that due to limitations with the evidence base, it was not possible to assess the impact of a ‘low’ compared to a ‘high’ carbohydrate diet on these outcomes. For example, prescribed carbohydrate intakes in lower carbohydrate groups ranged from 14 to 50% total energy intake. Instead, comparisons were made between ‘lower’ and ‘higher’ carbohydrate diets.
The evidence suggested beneficial effects of lower carbohydrate diets for HbA1c, fasting plasma glucose, and serum triacylglycerol in the short term, but it was unclear if these benefits were maintained beyond six months. No differences were observed between higher or lower carbohydrate diets for any other outcomes.
The SACN report recognises limitations in their findings. For example, it is not known if the reported effects of lower carbohydrate diets apply to individuals of different ethnicities since many of the studies analysed were conducted in predominantly White populations. Additionally, the report did not look at the impact of lower carbohydrate diets in the general population without T2D.
There was insufficient evidence to make recommendations for adults who have T2D without overweight or obesity. Therefore, the following recommendations are applicable only to adults living with T2D and overweight or obesity.
Overall, the SACN report found that although a lower carbohydrate diet may have short-term beneficial effects on glycaemic control and serum triacylglycerol concentrations, there is little evidence to support the recommendation of lower carbohydrate diets for the long-term management of adults with T2D.
Patients who choose a lower carbohydrate diet, should aim to maintain a healthy body weight, include wholegrain or higher fibre foods, a variety of fruits and vegetables and limit intakes of saturated fats, reflecting current dietary advice for the general population.
The report also highlights the need for more high-quality research into the role of low and high carbohydrate diets in the management of T2D in adults with and without overweight and obesity.
