What is a low carb diet? Many Americans are Obscure

Interest in low-carbohydrate diets (or “low-carbohydrate” diets) continues to grow. In fact, low-carb diets have doubled among US consumers in the past decade.¹ But, despite the popularity of the eating pattern, there is still confusion about what exactly qualifies as a low-carb lifestyle. Now, a scoping review published in Critical Reviews in Food Science and Nutrition sheds new light on the subject and suggests that a scientific consensus is emerging on the term. Of the more than 500 clinical trials reviewed, the majority defined a low-carb diet as limiting carbohydrate intake to 30% or less of total calories or eating less than 100 grams of carbohydrates daily. The review included results from a total of 508 clinical studies published between 2002 and 2022, over half of which were randomized controlled trials and almost one third of which were government funded.

“The sheer number of clinical trials on low-carb diets published over the past two decades has been staggering,” notes principal investigator Dr. Taylor Wallace. “The data clearly do not support any view that there is a lack of scientific evidence on low-carbohydrate eating patterns, or even a lack of government-funded evidence on the subject.”

The review also found that 152 of the studies included in the analysis were designed to assess the effect of a low-carbohydrate diet on weight or body composition. In particular, these studies are often excluded from consideration in some federal nutrition evidence review processes, such as updates to the Dietary Reference Intake (DRI) guidelines for carbohydrates and the Dietary Guidelines for Americans assessment of low-carbohydrate dietary patterns. These guidelines serve as the basis for numerous public health and nutrition activities, including food and nutrition labeling, federal nutrition programs, patient counseling and public health education initiatives.²

“While it is not surprising to find that so many studies evaluating the impact of low-carb dietary interventions have focused on weight-related outcomes, it is important to understand that this translates into a wealth of clinical data that shows no impact part of it. the most basic tools in the US nutrition guide,” says Wallace. “It leaves a lot of the scientific evidence on the table – given the high rates of overweight and obesity in this country.”

In addition, the investigators noted important gaps in the published literature. Although most studies classified most low-carbohydrate diets as consuming 30% or less of total calories from carbohydrates or limiting carb intake to less than 100 grams per day, the results showed discrepancies too. Of the studies that used percent of total calories as their parameter to define a low-carb diet, the percentages ranged from zero to 50% of total calories from carbohydrates. And, of the studies that define “low-carb” according to the number of grams of carbohydrates consumed daily, many used thresholds that fell well below 100 grams per day.

“With both consumers and public health officials interested in understanding the potential benefits of low-carbohydrate eating patterns, an agreed-upon standard definition is elusive and urgently needed,” says Wallace. The researchers note that systematic reviews and dose-response meta-regressions using patient-level data on carbohydrate intake, status and health markers are the next steps to inform a clear, consistent definition and wide acceptance of the term “low-carbohydrate.”

This research was funded by an unrestricted educational grant from Simply Good Foods USA, Inc. to Think Healthy Group, LLC. Simply Good Foods had no influence on the study design, conduct, execution or writing of the manuscript. Think Healthy Group, LLC strictly adheres to the American Nutrition Association’s guidelines for funding food science and nutrition research.

The article, “Defining “low-carb” in the scientific literature: A scoping review of clinical studies,” is published in Critical Reviews in Food Science and Nutrition. (doi: https://doi.org/10.1080/10408398.2023.2300705)

References:

1. Basile A. The Demand for Commercial and Non-Commercial Diets from 2010-2020: A Google Trends Analysis. Current Developments in Nutrition. doi:10.1093/cdn/nzab038_003
2. US Department of Health and Human Services. Office for Disease Prevention and Health Promotion. Dietary Reference Intake. Available at: https://health.gov/our-work/nutrition-physical-activity/dietary-guidelines/dietary-reference-intakes