Reduced carbs help type 2 diabetics regulate blood sugar levels

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Patients with type 2 diabetes improve their ability to regulate blood sugar levels if they eat food with a reduced carbohydrate content and an increased share of protein and fat. This is shown by a small recent study conducted at Bispebjerg Hospital in collaboration with, among other partners, Aarhus University and the department of nutrition, exercise and sports at the University of Copenhagen. The findings are contrary to the conventional dietary recommendations for type 2 diabetics.

Nutritional therapy is important to treat the type 2 diabetes optimally, but the recommendations are unclear. According to the Danish Health Authority, up to 85% of newly diagnosed patients with type 2 diabetes are overweight, and they are typically advised to follow a diet focused on weight loss: containing less calories than they burn, low fat content and a high content of carbohydrates with a low ‘glycaemic index’ (which indicates how quickly a food affects blood sugar levels).

A central aspect in the treatment of type 2 diabetes is the patient’s ability to regulate their blood sugar levels, and new research now indicates that a diet with a reduced carbohydrate content and an increased share of protein and fat improves the patient’s ability to regulate his or her blood sugar levels compared with the conventional dietary recommendations. In addition, it reduces liver fat content and also has a beneficial effect on fat metabolism in type 2 diabetics.

“The purpose of our study was to investigate the effects of the diet without ‘interference’ from a weight loss. For that reason, the patients were asked to maintain their weight. Our study confirms the assumption that a diet with a reduced carbohydrate content can improve patients’ ability to regulate their blood sugar levels – without the patients concurrently losing weight,” explains senior consultant, Dr Thure Krarup, from the department of endocrinology at Bispebjerg Hospital. He continues: “Our findings are important, because we’ve removed weight loss from the equation. Previous studies have provided contradictory conclusions, and weight loss has complicated interpretations in a number of these studies.”

Based on the growing body of evidence, we might rethink the dietary recommendations for patients with type 2 diabetes, stresses Thure Krarup: “The study shows that by reducing the share of carbohydrates in the diet and increasing the share of protein and fat, you can both treat high blood sugar and reduce liver fat content. Further intensive research is needed in order to optimise our dietary recommendations for patients with type 2 diabetes,” says Thure Krarup, stressing that the findings should be confirmed in large-scale, long-term controlled trials.

A diet with a reduced carbohydrate content, high protein content and moderately increased fat content improves glycaemic control (the ability to regulate blood sugar) by reducing blood sugar after meals and ‘long-term blood sugar’ (measured by ‘HbA1c’, which is a blood test used to measure the average blood sugar level over approximately the past two months).

A diet with a reduced carbohydrate content, a high protein content and a moderately increased fat content reduces liver fat content. A diet with a reduced carbohydrate content may be beneficial to patients with type 2 diabetes – even if it does not lead to weight loss.

The study forms part of CutDM, which – supported by a grant of DKK 4m from Arla Food for Health – examines whether a diet with reduced carbohydrate content and increased protein and fat content improves type 2 patients’ blood sugar regulation.

28 patients with type 2 diabetes participated in the study over a total period of 12 weeks. For six weeks, the patients were given a conventional diabetes diet with a high carbohydrate content, and, for the other six weeks, they were given a diet with a reduced carbohydrate content, high protein content and moderately increased fat content. The patients were given the diet types in random order.

Aims/hypothesis: Dietary recommendations for treating type 2 diabetes are unclear but a trend towards recommending a diet reduced in carbohydrate content is acknowledged. We compared a carbohydrate-reduced high-protein (CRHP) diet with an iso-energetic conventional diabetes (CD) diet to elucidate the effects on glycaemic control and selected cardiovascular risk markers during 6 weeks of full food provision of each diet.
Methods: The primary outcome of the study was change in HbA1c. Secondary outcomes reported in the present paper include glycaemic variables, ectopic fat content and 24 h blood pressure. Eligibility criteria were: men and women with type 2 diabetes, HbA1c 48–97 mmol/mol (6.5–11%), age >18 years, haemoglobin >6/>7 mmol/l (women/men) and eGFR >30 ml min−1(1.73 m)−2. Participants were randomised by drawing blinded ballots to 6 + 6 weeks of an iso-energetic CRHP vs CD diet in an open label, crossover design aiming at body weight stability. The CRHP/CD diets contained carbohydrate 30/50 energy per cent (E%), protein 30/17E% and fat 40/33E%, respectively. Participants underwent a meal test at the end of each diet period and glycaemic variables, lipid profiles, 24 h blood pressure and ectopic fat including liver and pancreatic fat content were assessed at baseline and at the end of each diet period. Data were collected at Copenhagen University Hospital, Bispebjerg and Copenhagen University Hospital, Herlev.
Results: Twenty-eight participants completed the study. Fourteen participants carried out 6 weeks of the CRHP intervention followed by 6 weeks of the CD intervention, and 14 participants received the dietary interventions in the reverse order. Compared with a CD diet, a CRHP diet reduced the primary outcome of HbA1c (mean ± SEM: −6.2 ± 0.8 mmol/mol (−0.6 ± 0.1%) vs −0.75 ± 1.0 mmol/mol (−0.1 ± 0.1%); p < 0.001). Nine (out of 37) pre-specified secondary outcomes are reported in the present paper, of which five were significantly different between the diets, (p < 0.05); compared with a CD diet, a CRHP diet reduced the secondary outcomes (mean ± SEM or medians [interquartile range]) of fasting plasma glucose (−0.71 ± 0.20 mmol/l vs 0.03 ± 0.23 mmol/l; p < 0.05), postprandial plasma glucose AUC (9.58 ± 0.29 mmol/l × 240 min vs 11.89 ± 0.43 mmol/l × 240 min; p < 0.001) and net AUC (1.25 ± 0.20 mmol/l × 240 min vs 3.10 ± 0.25 mmol/l × 240 min; p < 0.001), hepatic fat content (−2.4% [−7.8% to −1.0%] vs 0.2% [−2.3% to 0.9%]; p < 0.01) and pancreatic fat content (−1.7% [−3.5% to 0.6%] vs 0.5% [−1.0% to 2.0%]; p < 0.05). Changes in other secondary outcomes, i.e. 24 h blood pressure and muscle-, visceral- or subcutaneous adipose tissue, did not differ between diets.
Conclusions/interpretation: A moderate macronutrient shift by substituting carbohydrates with protein and fat for 6 weeks reduced HbA1c and hepatic fat content in weight stable individuals with type 2 diabetes.

Mads J Skytte, Amirsalar Samkani, Amy D Petersen, Mads N Thomsen, Arne Astrup, Elizaveta Chabanova, Jan Frystyk, Jens J Holst, Henrik S Thomsen, Sten Madsbad, Thomas M Larsen, Steen B Haugaard, Thure Krarup

Faculty of Science – University of Copenhagen material
Diabetologia abstract

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