- Researchers recently examined the effects of a low-carbohydrate diet in people with prediabetes and people who have mild, untreated type 2 diabetes (T2D).
- In the randomized clinical trial, participants who lowered their carbs saw a moderate reduction in their blood sugar, an indicator of diabetes.
- The study’s findings are somewhat tempered by a range of variables beyond the researchers’ control.
The link between carbs and type 2 diabetes (T2D) is well-established, but new research suggests that cutting carbs could help minimize 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 who were 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 in people with blood sugar 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 hemoglobin 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 hemoglobin A1C target,” she said.
For the study, 150 adults were recruited at a New Orleans academic center. The 6-month trial ran from September 2018 to June 2021. Participants ranged in age from 40 to 70 years old 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 counseling promoting a low-carbohydrate diet lowered hemoglobin A1C over 6 months,” Dr. Dorans said.
“In line with prior work, the low-carbohydrate diet group also lost substantial weight compared with the group of people who stayed with their usual diet.”
At the end of 6 months, Dr. Dorans and her research team found that A1C levels reduced by 0.23% more in the low carb group than the usual diet group.
Low carb diets and ketosis
Very low carb diets, such as the ketogenic diet, may triggers 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 study’s participants meeting their carbohydrate targets.
He told MNT the data “shows that there is poor compliance with the diet.”
“It doesn’t mean [study participants] didn’t reduce their carbohydrate intake, but they didn’t achieve the goals set out. If they were more compliant, [there] might have been a greater change. They must have changed their carbohydrate intake, which reduced their calorie intake. It doesn’t look like they were very ketogenic.”
– Dr. Samuel Klein, professor of cell biology and physiology
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 are unable to conduct an isocaloric comparison between the low-carbohydrate and usual diet groups or to determine effects on HbA1c [hemoglobin A1C] independently of weight loss,” the authors wrote.
Dr. Klein pointed out the amount of contact the carb-reduction group had with study interventionists offering guidance versus 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, along with 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 otherwise 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 take into consideration. 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 intake of fat, “you tend to increase LDL cholesterol, which was not the case here, but you do decrease triglyceride and increase HDL cholesterol, which is a good thing.”
But whether a low carb diet is hazardous to health may really be dependent on the individual.
“I would say we don’t have good evidence of long-term adverse effects. We know that a lot of people are on the Atkins diet, and we don’t see any real reports of problems,” he said.
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