It’s an ongoing debate in the diabetes world: Is it ideal to consume a very-low-carbohydrate diet, or is it better to go with moderate amounts of healthful carbs?
At the annual scientific sessions of the American Diabetes Association, Carol F. Kirkpatrick, PhD, RDN, spoke first, arguing in favor of diets consisting of moderate, high-quality carbohydrates.
Dina Hafez Griauzde, MD, countered that very-low-carbohydrate diets are more beneficial for people with diabetes, primarily type 2 diabetes.
Both speakers based their arguments on published evidence but agreed in the end that discussion with patients about individual dietary preferences should play a major role in the ultimate decision.
Moderate-carbohydrate eating is best
Dr. Kirkpatrick began by explaining that definitions of “low carb” vary in the literature, which makes comparisons between studies difficult. On the basis of a 2019 review that she coauthored, “moderate” carbohydrate consumption was defined as a diet in which 26%-44% of total daily calories are from carbohydrates. “Low” carbohydrate consumption was defined as a diet in which 10%-25% of calories were from carbohydrates. Consuming less than 10% was defined as a very-low-carbohydrate diet (i.e., a ketogenic diet).
Across studies, she noted, the literature shows that within the first 6 months weight loss is typically greater with carbohydrate-restricted diets than with higher-carbohydrate diets, but that by 1 year and beyond weight loss is similar.
“That can be partly due to the difficulty in people maintaining that very severe dietary restriction, although ... we can all acknowledge that it’s difficult for patients to adhere to any dietary pattern, so for sure by 12 months, the difference in the weight loss is gone between the two,” said Dr. Kirkpatrick, of Midwest Biomedical Research, Pocatello, Idaho.
In a recent meta-analysis of 35 trials that examined the dose-dependent effects of carbohydrate restriction for patients with type 2 diabetes, there was a significant decrease in weight as carbohydrates were reduced. But by 12 months (17 trials), the greatest weight reduction was seen at 35% carbohydrate intake.
“It may just be that people were able to adhere to that moderate intake better,” she explained.
Regarding lipids, in her 2019 review and in several meta-analyses since, the effects on low-density lipoprotein cholesterol (LDL-C) varied. For some patients, adhering to a low-carb diet led to reductions in LDL-C, especially if the participants also lost weight, whereas in other patients, a low-carb diet led to an increase in LDL-C.
Either way, a high intake of saturated fatty acids is key to an increase in LDL-C, Dr. Kirkpatrick noted. “So, it’s important that, if a patient chooses to follow a very low carbohydrate diet or any kind of dietary pattern that restricts carbohydrate, that they replace the carbohydrate with unsaturated fat and not saturated fatty acid foods to avoid that increase in LDL-C.”
Generally, the evidence also shows that carbohydrate restriction typically leads to lower triglyceride levels and higher high-density lipoprotein (HDL) cholesterol levels. However, the same meta-analysis showed that the greatest reduction in LDL-C occurred at about 40% carbohydrate consumption.
Another recent meta-analysis showed that LDL-C rose significantly by an average 12.4 mg/dL with very-low-carb (3%-30%) diets, but only slightly, by 0.4 mg/dL, with moderate carb (40%-45%) intake.
Consuming very-low-carb diets did lead to greater reductions in triglycerides, compared with consuming moderate carb diets (23.9 mg/dL vs. 8.9 mg/dL).
“However, in terms of cardiovascular health, we are not entirely sure what that means. ... We have to look at the overall results in the presence of both triglyceride lowering as well as LDL cholesterol,” Dr. Kirkpatrick noted.
Carbohydrate restriction did consistently lead to lower hemoglobin A1c levels by an average of 0.4, 0.6, and 1.0 percentage points at 6 months for diets of 40%, 30%, and 15% carbohydrate, respectively. However, by 12 months, the effect had waned to 0.15, 0.2, and 0.4 A1c percentage points.
“Again, carbohydrate restriction, especially severe, is difficult for people to adhere to, and moderate carbohydrate intake would allow our patients to consume an appropriate amount of carbohydrate and still achieve improved glycemic control,” Dr. Kirkpatrick said.
Two large randomized controlled trials – PREDIMED and CORDIOPREV – examined the effects of the Mediterranean diet on cardiovascular disease prevention. Both showed a decrease in cardiovascular events with the Mediterranean diet, which involves consuming moderate amounts of carbohydrates.
“The Mediterranean dietary pattern has the strongest evidence for benefit, and it’s moderate in carbohydrates,” she concluded.