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Greater weight loss, HbA1c reduction with very low-carb vs. moderate-carb diet

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January 5, 2018

Adults with overweight and type 2 diabetes or prediabetes experienced greater weight loss and a greater reduction in HbA1c when randomly assigned to a very low-carbohydrate, ketogenic diet vs. those assigned to a moderate-carbohydrate, low-fat diet, according to findings published in Nutrition & Diabetes.

Laura R. Saslow, PhD, assistant professor in the department of health behavior and biological sciences at the University of Michigan in Ann Arbor, and colleagues analyzed data from 34 adults with an HbA1c of at least 6% and a BMI of at least 25 kg/m² who were not using insulin or taking more than three glucose-lowering medications. Participants were assigned to an ad libitum very low-carbohydrate, likely ketogenic diet, reducing their carbohydrate intake to between 20 g and 50 g daily (n = 16), or to a moderate-carbohydrate, calorie-restricted, low-fat diet (n = 18). Participants attended 19 classes over 12 months on calorie reduction, the importance of sleep and exercise, supportive behavioral adherence exercises and mindful eating strategies. Researchers measured HbA1c, lipid profile, fasting glucose, fasting insulin and C-reactive protein at baseline and at 3, 6 and 12 months, as well as insulin resistance using homeostatic model assessment (HOMA2).

At 6 and 12 months, the very low-carbohydrate group reported consuming fewer non-fiber grams of carbohydrates, more grams of fat and more grams of protein vs. those in the moderate-carbohydrate group. There were no between-group differences for daily calorie consumption.

Between baseline and 12 months, participants in the very low-carbohydrate group saw a greater HbA1c reduction (mean, 6.6% to 6.1%) vs. the moderate-carbohydrate group (mean, 6.9% to 6.7%). Participants in the very low-carbohydrate group also lost more weight and experienced a greater reduction in BMI over 12 months (mean, 35.9 kg/m² to 33.3 kg/m²) vs. those in the moderate-carbohydrate group (mean, 36.9 kg/m² to 36 kg/m²). Those in the very low-carbohydrate group lost a mean of 8.3% body weight, whereas those in the moderate-carbohydrate group lost a mean of 3.8% body weight.

Additionally, among 10 participants who reported taking sulfonylureas or DPP-IV inhibitors at baseline, all six participants in the very low-carbohydrate group had discontinued these medications by 12 months, whereas the four patients in the moderate-carbohydrate group had not. Three in 10 participants in the very low-carbohydrate group who reported taking metformin at baseline had also discontinued the medication by 12 months, whereas none of the 12 patients taking metformin in the moderate-carbohydrate group had discontinued the medication.

The researchers also found that LDL cholesterol increased more in the very low-carbohydrate group at 6 months vs. the moderate-carbohydrate group; however, this difference did not persist at 12 months.

“This may raise some concerns about the long-term effects of such a diet on cardiovascular disease,” the researchers wrote. “Recent research suggests that the correlation of LDL to cardiovascular risk varies based on particle size, and that low-carbohydrate, ketogenic diets tend to increase LDL particle size, which suggests that the increase in total LDL may not be accompanied by increased cardiovascular risk. However, we did find that the ratio of triglycerides to HDL, which predicts coronary disease, decreased in the [very low-carbohydrate] group compared to the [moderate-carbohydrate] group, suggesting that the very low-carbohydrate, ketogenic diet may have certain benefits on lipid profiles.” – by Regina Schaffer

Disclosures: One of the study authors reports he is a paid member of the Atkins scientific advisory board, a founder of Virta Health and has authored three books on low-carbohydrate, high-fat diets. Another author reports he is on the scientific advisory board for Virta Health.

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