The link between carbs and type 2 diabetes (T2D) is well-established, but new research suggests that cutting carbs could help minimize the risk for those who may be susceptible to developing the condition.
The study, a random clinical trial (RCT) recently published in JAMA Network Open Diabetes and Endocrinology, found that a low-carbohydrate diet promoted weight loss and improved fasting glucose levels in subjects at risk for developing T2D.
Lead author and epidemiologist Kirsten S. Dorans of Tulane University in New Orleans, LA, told Medical News Today: “While low-carb diets are often recommended for those with type 2 diabetes, little evidence has existed for whether eating fewer carbs can impact the blood sugar of those with mild diabetes or prediabetes who aren’t treated by medications. This study was conducted on people with blood sugar levels that ranged from prediabetes to mild diabetes levels who were not on diabetes medications.”
Lowering blood sugar with a low-carb diet
Hemoglobin A1C is a widely used clinical term to measure long-term blood sugar levels.
According to the American Diabetes Foundation, a person who has prediabetes has A1C levels between 5.7 and less than 6.5%. Higher A1C levels may signify diabetes.
Dr Dorans explained that subjects enrolled in the study had a haemoglobin A1C range of 6.0 to 6.9%.
“This range chosen as the lower bound aligns with the World Health Organization’s lower cutoff point for prediabetes and the upper bound with less than the 7.0% American Diabetes Association haemoglobin A1C target,” she said.
For the study, 150 adults were recruited at a New Orleans academic centre. The six-month trial ran from September 2018 to June 2021. Participants ranged in age from 40 to 70 and were divided into two groups.
The first group was tasked with reducing their daily carbohydrate intake to less than 40 grams for the first 3 months and less than 60 grams from month 3 to the end of the trial.
“We found that nutritional counselling promoting a low-carbohydrate diet lowered haemoglobin A1C over 6 months,” Dr Dorans said.
“In line with prior work, the low-carbohydrate diet group also lost substantial weight compared with those who stayed with their usual diet.”
At the end of 6 months, Dr Dorans and her research team found that A1C levels were reduced by 0.23% more in the low-carb group than in the usual diet group.
Low-carb diets and ketosis
Very low-carb diets, such as the ketogenic diet, may trigger a metabolic process known as ketosis, which is when the body burns stored fats for energy instead of glucose.
But ketosis does not typically occur with a low-carb diet.
According to the study authors, “few participants had detectable urinary ketones, suggesting ketosis was unlikely to account for the findings.”
Still, Dr Samuel Klein, a professor of cell biology and physiology at the Washington University School of Medicine in St. Louis, not involved in the study, expressed concerns about the study’s participants meeting their carbohydrate targets.
He told MNT the data “shows that there is poor compliance with the diet.”
Possible limitations and biases of the research
The authors note a limitation of the study: “There were significant decreases in caloric intake in the low-carbohydrate diet intervention group during follow-up, aligning with large observed weight loss. With this study design, we cannot conduct an isocaloric comparison between the low-carbohydrate and usual diet groups or to determine effects on HbA1c [haemoglobin A1C] independently of weight loss,” the authors wrote.
Dr. Klein pointed out that the carb-reduction group had greater contact with study interventionists offering guidance than the usual diet group.
Both groups were supplied with a handbook containing dietary guidelines and recipes at the start of the trial.
To help hit the goal of fewer than 40 grams of carbs, the carb-reduction group received individual sessions, four group sessions on alternate weeks, and four telephone follow-ups. For the 60-gram goal, there were three monthly group meetings and three telephone calls.
The usual-diet group was offered optional monthly sessions but did not receive guidance beyond the initial handouts.
“There was a lot more contact in the treatment group than in the control group,” said Dr Klein.
Long-term low-carb diets: What are the risks?
Dr Jason Ng, clinical associate professor of medicine at the University of Pittsburgh Medical Center, not involved in the study, told MNT:
“Improving sugar levels via less carb intake can be an effective type 2 diabetes lifestyle treatment. This may or may not influence weight loss, as weight loss has many variables to consider. However, if you have prediabetes or mild type 2 diabetes, this intervention can lower your sugar levels even if one does not experience accompanying weight loss.”
Dr Klein added that when you reduce carbohydrate intake and increase your fat intake, “you tend to increase LDL cholesterol, which was not the case here, but you do decrease triglycerides and increase HDL cholesterol, which is good.”
However, whether a low-carb diet is hazardous to health may depend on the individual.
“We don’t have good evidence of long-term adverse effects. We know that many people are on the Atkins diet, and we don’t see any real reports of problems,” he said.
