What Makes Up a Low Carb Diet? Many Americans Are Uncertain

Interest in low-carb (or “low-carb”) diets continues to grow. In fact, low-carb diets have doubled in popularity among U.S. consumers in the last decade.^one But despite the eating pattern’s popularity, confusion remains about what exactly qualifies as a low-carb lifestyle. Now, a scoping review published in Critical Reviews on Food Science and Nutrition sheds new light on the topic and suggests that scientific consensus is forming around the term. The majority of the more than 500 clinical studies reviewed defined a low-carb diet as limiting carbohydrate intake to 30% or less of total calories or consuming less than 100 grams of carbohydrates per day. The review included results from a total of 508 clinical trials published between 2002 and 2022, more than half of which were randomized controlled trials and almost a third of which were publicly funded.

Chief investigator Dr. “The abundance of clinical studies on low-carb diets published in the last two decades has been remarkable,” says Taylor Wallace. “Any perception that there is a lack of scientific evidence for low-carb eating habits, or even government-funded evidence on the subject, is clearly not supported by the data.”

The review also found that 152 of the studies included in the analysis were designed to evaluate the effect of a low-carb diet on weight or body composition. Notably, these studies are often disregarded in various federal nutrition evidence review processes, such as updates to the Dietary Reference Intake (DRI) guidelines for carbohydrates and updates to the Dietary Guidelines for Americans to evaluate low-carbohydrate dietary patterns. These guidelines form 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 learn that many studies evaluating the impact of low-carbohydrate nutritional interventions focus on weight-related outcomes, it is important to understand that this translates into a wealth of clinical data that has nothing to do with some of the most essential tools in US dietary guidance,” adds Wallace. “Given the high rates of overweight and obesity in this country, a lot of scientific evidence remains on the table.”

Additionally, researchers noted significant gaps in the published literature. Although most studies classify low-carb diets as consuming 30% or less of total calories from carbohydrates or limiting carbohydrate intake to less than 100 grams per day, the findings also revealed inconsistencies. In studies that used percentage of total calories as a parameter to define a low-carb diet, the percentages ranged from zero to 50% of total calories coming from carbohydrates. And most studies that define “low carb” by the number of grams of carbohydrates consumed per day have used thresholds that fall well below 100 grams per day.

“With both consumers and public health officials interested in understanding the potential benefits of low-carb eating habits, achieving a standard consensus is non-negotiable and urgently needed,” says Wallace. The researchers note that systematic reviews and dose-response meta-regressions using patient-level data on carbohydrate intake, status markers, and health are important next steps in establishing a clear, consistent, and widely adopted definition of the term “low carbohydrate.”

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

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

References:

1. Basile A. Popularity of Commercial and Non-Commercial Diets Between 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 of Disease Prevention and Health Promotion. Dietary Reference Intakes. Available at: https://health.gov/our-work/nutrition-physical-activity/dietary-guidelines/dietary-reference-intakes