Food with reduced carbohydrate content and more protein and fat improves type 2 diabetics’ ability to regulate blood sugar

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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 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 percent of newly diagnosed patients with type 2 diabetes are overweight, and they are typically advised to follow a diet focused on weight loss containing fewer calories than they burn, low fat content and a high content of carbohydrates with a low glycemic index (a measure of how quickly a food affects blood sugar levels).

Reduced carbohydrate content – increase in protein and fat

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,” says Thure Krarup, MD, from the Department of Endocrinology at Bispebjerg Hospital.

“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.”

New dietary recommendations for type 2 diabetics in future

Reduced carbohydrate intake improves type 2 diabetics' ability to regulate blood sugar
An example of one of the trial meals with a reduced carbohydrate content and an increased protein and fat content. Credit: University of Copenhagen

Based on the growing body of evidence, clinicians might rethink the dietary recommendations for patients with type 2 diabetes.

Thure Krarup says, “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 optimize our dietary recommendations for patients with type 2 diabetes.” Krarup says that the findings should be confirmed in large-scale, long-term controlled trials.

The findings of the study have been published in Diabetologia in an article titled “A carbohydrate-reduced high-protein diet improves HbA1c and liver fat content in weight stable subjects with type 2 diabetes: a randomized controlled trial.”

Summary: What did the study show?

  • A diet with a reduced carbohydrate content, high protein content and moderately increased fat content improves glycemic 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 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.


One of the issues with the term “low carbohydrate” is uncertainty about what this means in terms of carbohydrate intake.

Ketosis readily occurs at carbohydrate intakes below 50 g/day [11], and these very low carbohydrate, ketogenic diets (VLCKD) appear to have more pronounced effects than other, less restricted carbohydrate diets [12].

The taxonomy for diets containing various amounts of dietary carbohydrate has been suggested in a recent paper [4], see Table 1.

In practice, most Atkins-style diets are designed to be very low in carbohydrate (less than 20 g/day initially) and high in protein and fat [13], and other diets, e.g., the Zone [14] and the South Beach Diet [15], promote a moderate carbohydrate restriction together with high protein and low fat intakes.

Table 1

Taxonomy of diets containing differing amounts of carbohydrate

DescriptionAmount of carbohydrate
g/day% total energy intake
Very low carbohydrate ketogenic diet20–50≤10
Low carbohydrate<130<26
Moderate carbohydrate130–23026–45
High carbohydrate>230>45

Adapted from Feinman et al. [4]

The Role of Low Carbohydrate Diets in Treating Type 2 Diabetes

Treating type 2 diabetes is challenging, encompassing as it does management of glycemia, cardiovascular disease (CVD) risk factors, obesity, and other co-morbidities by a combination of lifestyle strategies (diet and physical activity), behavioral and psychological interventions, pharmaceutical treatment, and bariatric surgery.

Medical management of type 2 diabetes has led to cynicism about the efficacy of lifestyle management, particularly dietary strategies, and at present the components of the most effective diet remain unknown.

A recent systematic review and meta-analysis suggested that low carbohydrate, low glycemic index (GI), Mediterranean, and high protein diets all showed greater improvements in glycemic control than control diets [16].

Despite criticism of the statistical analysis due to heterogeneity of the studies included [17], this review supports the premise that improvements in glycemic control, CVD risk, and weight loss are achievable with different diets with varying amounts of carbohydrate, and that low carbohydrate diets are not necessarily superior in effect.

Weight Loss

All eight studies reported weight loss in the group receiving the reduced carbohydrate intervention, with mean weight losses ranging from 1.7 kg [18] to 12.0 kg [25].

The greatest weight loss was reported in the shortest study lasting 6 months [25].

There appeared to be no relationship between degree of carbohydrate restriction and weight loss.

However, these studies all included a control group receiving dietary interventions that provided higher carbohydrate intakes but were designed for weight loss, consequently those in the control groups also lost weight during the course of the studies.

Mean weight losses in the control group were similar to those in the reduced carbohydrate group and ranged from 0.2 kg [18] to 11.5 kg [25], with the result that none of the eight studies reported significantly greater weight loss in the group receiving the reduced carbohydrate intervention.

Glycemic Control

Despite no significant differences in weight losses, three of the studies reported significantly greater reductions in HbA1c in the reduced carbohydrate intervention group [192324].

One of the studies did not report HbA1c [25] despite the fact that this measurement was defined as the primary outcome, leading to the speculation that there were no differences in glycemic control between the two groups [26].

This has now been confirmed, with recent publication of a follow-up at 12 months reporting no difference in HbA1c reductions between the low and high carbohydrate intakes [27]. Changes in HbA1c in the reduced carbohydrate intervention groups were variable between studies, ranging from +0.1% [22] to −2.0% [19], with the greatest reduction seen in studies of shorter duration.

There appeared to be little correlation between the degree of carbohydrate restriction and changes in glycemic control. HbA1c levels were also reduced in five of the seven control groups, with changes ranging from +0.1% [22] to −0.3% [20]. In summary, one study failed to report HbA1c [25], three studies showed significant reductions in HbA1c in the reduced carbohydrate group [192324], and four studies showed no significant differences between the two groups [182022].

Cardiovascular Risk

Cardiovascular risk was assessed by changes in lipid concentrations and blood pressure. All eight studies measured lipid concentrations, and seven studies measured blood pressure [182025].

Most studies reported reductions in lipid concentrations in both the reduced carbohydrate intervention and higher carbohydrate control group, with no significant differences between the two groups.

However, significantly greater reductions in the reduced carbohydrate group were reported for total cholesterol concentrations in one study [22], low density lipoprotein (LDL) and high density lipoprotein (HDL) concentrations in one study [19], and triglycerides in three studies [192225].

Changes in blood pressure were variable and showed no significant differences in six of the seven studies reporting outcomes; four studies reported reductions in systolic blood pressure (SBP) in the reduced carbohydrate group compared to the higher carbohydrate group [18202325], and three reported increases [212224]; for diastolic blood pressure four reported decreases in the reduced carbohydrate intervention group [18202325] and three reported increases [212224].

In summary, although there was no evidence of a deleterious effect of a reduced carbohydrate diet on CVD risk, equally, there was no evidence of superiority over a higher carbohydrate intake.

Adherence and Attrition

Adherence to the prescribed intervention was assessed by self-reported dietary intake using a variety of methods including 24-hour diet histories and 3-, 4-, and 7-day food diaries. In the majority of the studies, mean intake of carbohydrate in the reduced carbohydrate intervention group was higher than that prescribed; in only two studies did the participants achieve target intakes [2425].

Attrition rates were reported for seven studies, and ranged from no dropouts [24] to 60% [18]. There were no differences in attrition rates between the intervention and control groups in any of the studies.

In general, lower attrition rates were reported for shorter studies, and for those with fewer participants.


More information: Mads J. Skytte et al, A carbohydrate-reduced high-protein diet improves HbA1c and liver fat content in weight stable participants with type 2 diabetes: a randomised controlled trial, Diabetologia (2019). DOI: 10.1007/s00125-019-4956-4

Journal information:Diabetologia

Provided by University of Copenhagen

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