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Home » Low-carb diet helps reduce HbA1c in prediabetes

Low-carb diet helps reduce HbA1c in prediabetes

In my ongoing series of articles on diets, I ran across some good research about low-carb (low-carbohydrate) diets and prediabetes. A new study published in a peer-reviewed journal indicates that the diet reduces blood glucose levels in prediabetics. More than that, it might be a valid treatment strategy to prevent type 2 diabetes.

As I do with other primary research like this, I’ll present what they published and then give my take on the quality of the study.

glucometer lying among scattered sugar cubes
Photo by Polina Tankilevitch on

Prediabetes and type 2 diabetes

Just for background, prediabetes is a condition where an individual’s blood sugar is elevated but is not high enough to qualify as diabetes. Many individuals with prediabetes eventually develop type 2 diabetes.

Type 2 diabetes mellitus (or type 2 diabetes, T2DM) is a metabolic disorder that is characterized by high blood glucose with insulin resistance and relative insulin deficiency. In general, someone with T2DM produces low (or maybe even adequate) insulin levels, but various cells and organs become resistant to insulin, so cells don’t remove or store blood glucose.

Although the cause of T2DM is not entirely understood, it results from a complex interaction between diet, obesity, genetics, age, and gender. Some of the causes of T2DM are under a person’s control, like diet and obesity, but many of the causal factors are not.

Because they are often confused, it’s important to note that T2DM has a completely different etiology and pathophysiology compared to type 1 diabetes mellitus (T1DM, once called juvenile diabetes). Type 1 diabetes results from the inability of the beta cells of the pancreas to produce insulin, as a result of an autoimmune disease. Diet and lifestyle are not related to T1DM.

There are numerous medical treatments and lifestyle changes that can moderate, or even reverse, the course of T2DM. On the other hand, there are no cures (at this time) for T1DM, and it can be a death sentence for the patient without regular daily insulin injections. Over 90-95% of diabetes in the USA is Type 2.

The consequences of both types of diabetes are almost the same. Complications of poorly managed diabetes mellitus may include cardiovascular diseasediabetic neuropathy, and diabetic retinopathy, among many other chronic conditions. 

Although most diabetics test their blood sugar with easy-to-use glucose monitors, a blood test for HbA1c (or glycated hemoglobin) is a more accurate method of determining the blood glucose average over the past 110 days. The values for HbA1c are interpreted as follows:

Most diet and diabetes studies use HbA1c levels, like the study that we’re going to discuss. However, there are formulas to convert the HbA1c levels to average blood glucose levels, if you are so interested.

The low-carb diet and prediabetes study

In a paper published on 26 October 2022 in JAMA Network Open, Dr. Kirsten S. Dorans, ScD, of Tulane University School of Public Health and Tropical Medicine in New Orleans, and colleagues set up a randomized clinical trial to ascertain the effect on prediabetes by a low carb diet.

The six-month clinical trial included 150 participants who were randomized into two groups — a low-carbohydrate diet intervention (target <40 net grams of carbohydrates during the first 3 months; <60 net grams for months 3 to 6) or a usual diet. The low-carbohydrate diet group received dietary counseling during the clinical trial.

Here are the key results:

  • Compared with those eating their typical diet, people with an untreated, elevated HbA1c who ate a low-carb diet saw a significantly greater improvement (-10.3 mg/dL) in fasting plasma glucose at month 6.
  • Those on the low-carb diet, which also included dietary counseling, also saw a 0.23% greater drop in HbA1c. Although this HbA1c reduction was “modest,” the researchers stated that it was still a little greater than the 0.17% reduction seen in the lifestyle intervention arm of the DPP trial. Even then, the study showed a 58% reduced risk for type 2 diabetes progression over 2.8 years, so the 0.23% drop in the low-carb diet study could mean an even larger drop in risk for type 2 diabetes.
  • The low-carb diet group also lost an average of 5.9 kg (13 lb for those barbarians who hate the metric system) in body weight over the six-month study.
  • The low-carb diet group also spent longer in the target glucose range (70-120 mg/dL) according to readings from their continuous glucose monitors.
  • Other positive indicators for the low-carb diet study group were:
    • Waist circumference — -4.7 cm
    • HOMA-IR (which measures insulin resistance, one of the signs of type 2 diabetes) — -2.4
    • Fasting insulin — -6.2 μIU/L
Photo by James Kern on Unsplash

Skeptical Raptor Rating™

This was a small randomized clinical trial that showed some impressive results. I mostly dismiss diet studies that rely upon the memory of the participants, which can make the study a bit fuzzy to interpret. Even though this study was small, it was a clinical trial where the researchers were able to compare key indicators of prediabetes and type 2 diabetes between low-carb and normal diet groups.

I’m going to give this study a 4 out of 5 stars. I continue to be bothered by the small size of these types of clinical trials, but I’m used to vaccine clinical trials which have thousands (if not tens of thousands of participants). However, the results of this study were striking, and I think a low-carb diet for those with prediabetes may be something that diabetic nutritionists should consider.

I know what you’re thinking — bacon 24/7. It might get boring after a while. Or maybe not.


Michael Simpson

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