USDA Excluding Virtually all Low-Carb Studies

Blog: USDA Excluding Virtually all Low-Carb Studies

USDA Continues to Exclude Low-Carb Studies

By Jessica Wharton

In an astonishing development, the U.S. Dept. of Agriculture (USDA) was recently found to have excluded nearly every study on low-carb diets from the scientific reviews that will inform the 2020 Dietary Guidelines for Americans (DGA). The only exception was a single low-carb study, by a member of the Dietary Guidelines Advisory Committee (DGAC), the expert group overseeing these reviews. It appears, in fact, that the exclusion criteria created by USDA officials together with this committee may have been designed with the specific intent of excluding these studies.

This is shocking and unacceptable.

The scientific reviews demonstrate extreme bias against low carbohydrate diets. The facts supporting this statement are:

  1. Of the 52 low-carb studies that the Low-Carb Action Network formally submitted to the Committee via public comment, 11 could not be found on either the inclusion or exclusion lists. These studies were simply ignored, despite the fact that their titles, which included the terms “low-carbohydrate” and carbohydrate restriction clearly should have been picked up by the search terms spelled out in the USDA protocol.
  2. The USDA’s exclusion criteria appear to have be written with the specific intent of excluding the entire scientific literature on low-carb diets. The exclusion was: “Does not describe the entire macronutrient distribution of the diet (i.e., studies that only examine a single macronutrient in relation to outcomes).” This is, in fact, the exact definition of a low-carbohydrate diet: the examination of what occurs when carbohydrates are reduced. Even with none of the other issues found, this alone ensures that ZERO low carbohydrate diet trials would be included in the review. This must be explained.
  3. “Weight loss” was part of the exclusion criteria for all diets.1 How can this exclusion be possible when obesity is such an enormous problem in America, and one of the Guidelines’ stated aims is to help people achieve a healthy weight?
  4. The DGAC’s Subcommittee on Dietary Patterns, which oversaw the reviews of low-carb studies, excluded any that were of less than 12 weeks duration. This 12-week standard was uniquely strict and inconsistent with the more lax standards applied by other Subcommittees. For instance:

    1. A study period of only 4-weeks duration was employed as the exclusion criteria by both the Subcommittee on Sugar and Sweetened Beverages and the Subcommittee on Dietary Fat and Seafood.
    2. In many other Subcommittees, there was not even a mention of study-duration requirements.
  5. The Subcommittee on Dietary Patterns used inconsistent standards even within its own reviews. For example: The one low-carb study included, by the DGAC member, as mentioned above, was only included for the review on heart disease; it was excluded from the review on obesity, even though the study was designed to look at both outcomes.

The egregious lack of rigor and apparent outright bias leave this Committee and its conclusions open to scientific ridicule. There is an obvious need for an additional meeting of the DGAC at which the public could ask questions regarding these issues. A delay of the expert report is also warranted so that the Committee can fix the serious issues cited above.


1. A non-official yet professional transcript of the public meeting of the Dietary Guidelines Advisory Committee, March 23, 2020, https://static1.squarespace.com/static/5a4d5666bff20053c65b7ff2/t/5e73d18616772f0fd8940644/1584648584430/March+12%2C+2020+-+Afternoon+Session+-+2020+Dietary+Guidelines+Advisory+Committee+Public+Meeting.pdf @ Minute 29:16

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