Low-Carb, Low-Saturated-Fat Diet Benefits Type 2 Diabetes

Miriam E. Tucker

July 30, 2014

A diet low in both carbohydrates and saturated fat may be an ideal recipe for treating type 2 diabetes, a new study suggests.

The findings were published online July 28, 2014 in Diabetes Care by Jeannie Tay, of the Commonwealth Scientific and Industrial Research Organisation (CSIRO) and the University of Adelaide, Australia, and colleagues.

In the 24-week outpatient clinical trial of 93 adults randomized to either a low-carb, low–saturated-fat (LC) diet or a high-carb, low-fat diet (HC) — both containing the same amount of calories — the LC diet performed better in improving glycemic control and reducing cardiovascular risk factors.

"The findings from this study suggest that a novel eating pattern that markedly limits carbohydrates and increases protein and unsaturated fat may have more favorable therapeutic potential for optimizing the management of type 2 diabetes and reducing cardiovascular disease risk as part of a holistic lifestyle-modification program," principal investigator Grant D. Brinkworth, PhD, associate professor and senior research scientist at CSIRO, told Medscape Medical News in an email.

This study differs from previous studies of low-carb diets in several ways. Saturated fat was not increased with the low-carb diet, but rather both diets limited saturated fat to less than 10% of total energy. Also, the investigators measured glycemic variability in addition to HbA1c and included a physical-activity intervention in both groups, neither of which had been done in previous studies.

"Lifestyle modification for diabetes treatment recommends both diet and exercise, and therefore, to understand the role of the dietary patterns being tested as a diabetes-management therapy, they need to be evaluated in combination with physical activity," Dr. Brinkworth told Medscape Medical News.

Low Carb, Low Saturated Fat Wins Out

The study population included 115 overweight or obese adults with type 2 diabetes and HbA1c levels of 7% or higher. They were randomized to either the LC diet (14% carbohydrate with the aim of less than 50g/day, 28% protein, and 58% total fat, including 35% monounsaturated fat and 13% polyunsaturated fat) or the HC diet (53% carbohydrate with emphasis on low–glycemic-index foods, 17% protein, and less than 30% total fat, including 15% monounsaturated and 9% polyunsaturated fat). Saturated fat was limited to less than 10% of total calories in both groups.

Both groups attended 60-minute structured exercise classes on 3 nonconsecutive days per week. A total of 93 patients completed the 24-week study.

Reduction in HbA1c was greater in the LC diet group, dropping by 2.6 percentage points vs 1.9 in the HC group. The effect was significant only among those with baseline HbA1c levels greater than 7.8% (P = .002).

Mean blood glucose levels were also reduced to a greater extent with the LC diet, by 3.4 mmol/L (61 mg/dL) vs 2.5 (45 mg/dL) with the HC (P = .01) diet, seen among those with baseline mean blood glucose levels above 8.6 mmol/L (155 mg/dL). The difference among those with lower mean blood glucose levels was not significant.

The LC diet was also associated with lower glycemic variability by several measures. In regression analysis, those following the LC diet were 85% more likely to spend time in euglycemic range and 56% less likely to spend time with hyperglycemia (P < .03).

Dr. Brinkworth told Medscape Medical News that emerging evidence suggests that glycemic variability — which is not reflected in the HbA1c value — may be an independent predictor of diabetes-related complications. "Further research is required to establish and demonstrate the role of glycemic variability in type 2 diabetes control that will lead to greater usage in clinical practice."

Triglycerides were reduced by a 5-fold greater margin with the LC compared with the HC diet (P = .001). But the effect on HDL cholesterol also depended on baseline levels, with a significant increase seen only among those with baseline levels below 1.3 mmol/L (50.3 mg/dL).

Weight loss was significant in both groups, but not different between them (by 12 kg with LC vs 11.5 kg for HC). Similarly, roughly equal reductions were seen in both groups in other cardiometabolic parameters, including waist circumference, LDL cholesterol, total cholesterol, blood pressure, and insulin levels.

There was a diet effect on medication usage, however. At 24 weeks the LC-diet group was able to reduce their glucose-lowering medication potency and dosage 2-fold compared with the HC group (P = .003) and were 3 times more likely to be able to reduce their medication potency/dosage by 20% or more ( P < .005).

Is It Realistic?

In their discussion, the authors acknowledge that long-term adherence to nutritional therapy is "notoriously difficult."

Dr. Brinkworth told Medscape Medical News that the 2 study groups were equally adherent, although it took effort in both cases. To facilitate compliance to the dietary patterns in the study, participants were provided with regular professional counseling by a registered dietician and were provided with prescriptive diet plans and appropriate food-exchange options.

The physical-activity program may have also contributed to the program's success in the study, the authors note in the paper.

"Future initiatives need to integrate these lifestyle program components within cost-effective community-based delivery models. Whether the observed effects are sustained beyond 24 weeks also requires further investigation," they conclude.

This study was supported by a National Health and Medical Research Council project grant. The authors have reported no relevant financial relationships.

Diabetes Care. Published online July 28, 2014. Abstract

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