Spot the missing nutrition trials


You would imagine from its title that the US Department of Agriculture’s Nutrition Evidence Library would be a comprehensive database of all scientific research on nutrition.

Unfortunately, it isn’t. Here is its methodology:

  • Step 1: Develop systematic review questions and analytic frameworks
  • Step 2: Search, screen, and select studies to review
  • Step 3: Extract data and assess the risk of bias of the research
  • Step 4: Describe and synthesize the evidence
  • Step 5: Develop conclusion statements and grade the evidence
  • Step 6: Identify research recommendations.

All this seems very thorough doesn’t it? Well, when our friend Nina Teicholz, author of The Big Fat Surprise started looking for some of the recent nutrition trials, she noticed something strange.

“What I’ve found is that the Nutrition Evidence Library omits all the major Randomised Controlled Trials (RCTs) on saturated fats, nearly all the major RCTs testing the diet-heart hypothesis and its offspring, the low-fat diet, and nearly all the low-carb studies. That would be, in sum, pretty much all the research on nutrition, most of it NIH funded, since the birth of the diet-heart hypothesis.”

Or in other words, the selective inclusion of studies in steps 1 and 2 just happens to exclude the major trials and focuses instead on epidemiological studies, which are a weaker kind of evidence that cannot demonstrate cause and effect.

Why does this matter? Well, the US Dietary Guidelines for Americans are the most influential nutrition policy in the world. They are followed by governments all over the world.

These guidelines are underpinned by an expert report, which draws its evidence from the (incomplete) Nutrition Evidence Library. Can it be a surprise that the dietary guidance hasn’t changed for decades?

Nina is giving testimony on Friday (19 February) to the US Department of Agriculture, which publishes the US Dietary Guidelines. It is holding “listening sessions” because the US Congress mandated a review of the Guidelines by the National Academy of Medicine to find out what’s gone wrong.

She has started to compile a list of the nutrition research missing from the Nutrition Evidence Library which she would like to present on Friday. Could you help to complete the list? … in the next 24 hours!?

What to do to help complete the list:

  • find a nutrition study (clinical trial, observational study or review paper) on the low-fat diet, saturated fats or the low carbohydrate diet
  • check that it isn’t already in the list
  • enter the surname of the first author in the search on the top right of the Nutrition Evidence Library home page
  • if the study does not appear in the search results, add it to the list in the appropriate group in chronological order


Thanks to everyone who has helped to expand the list considerably so far. Here is the list as it stands now.

As you may realise from the list, most of the recent trials are missing from it. Of course, it could be a complete coincidence that the missing trials seem to be the ones which concluded positively about a low carbohydrate diet.

On the other hand, … take a look at the pages on Carbohydrates on the NEL website:

– Systematic review questions listed under the 2015 Methodology: (all questions and answers appear to be from the 2010 dietary guidelines)

– the Carbohydrates section from the DGAC 2010 methodology:

All study designs were originally included in the searches, but cross-sectional studies were later excluded from the review if there was sufficient evidence from studies with stronger study designs. The Committee excluded studies that only included participants diagnosed with chronic disease, hyperlipidemia, hypertension (HTN) and related health conditions.”

“… The Committee only considered studies that directly assessed the relationship between the intake of food groups and health outcomes; studies examining the intake of food groups as a part of a larger dietary pattern were not considered in the review. “

For the topics considered by the 2005 DGAC, the Conclusions expressed in the 2010 DGAC report are informed by the evidence compiled for the 2005 DGAC report, but are based primarily on the NEL evidence gathered and reviewed since 2004. As discussed in the associated review, for some questions, the search was extended back further to capture a larger body of evidence. Studies of carbohydrates and health outcomes on a macronutrient level are often inconsistent or ambiguous due to inaccurate measures and varying food categorizations and definitions. The science cannot progress without further advances in both methodology and theory.”

Perhaps that last sentence should have said that the dietary guidelines cannot progress without further advances in both methodology and theory of reading the available scientific research?

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