Updated 24th April 2024

Why are women not equally represented in nutrition research?

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Nutrition plays a fundamental role in everyone’s life, whatever their age, race, ethnicity, or sex. But much of the research that informs nutrition guidelines is missing a key ingredient — diverse representation. 

At ZOE, we run the largest nutrition science research program in the world. And we want everyone to be represented in our studies because nutrition and health are personal. 

We harness the latest technologies in the form of apps and in-home test kits to bring our research into our study participants’ homes, and women make up half or more of the participants in each of our trials. 

But across the broad field of medical and nutrition research, there is a long way to go before trial participants truly look like the diverse populations that we all live in. 

The long road to gender balance

There is plenty of evidence that a person’s sex and racial or ethnic background can impact how they respond to medicines and what nutritional needs they have.  

Yet, researchers have a history of favoring white males over female study participants or those from racial and ethnic minority groups. 

In 1977, the U.S. Food and Drug Administration (FDA) recommended that women of childbearing age be excluded from clinical trials to avoid a repeat of the thalidomide tragedy

It took until 1994 for the tide to change. Finally, a new law required that biomedical research funded by the National Institutes of Health (NIH) must include women. But it was another 20 years until the NIH called for the inclusion of female animals or cells derived from female donors in preclinical research. 

There are signs of progress. A recent analysis of nearly 20,000 clinical trials conducted between 2000 and 2020 in the U.S. found that on average, across all of the trials, around 50% of participants were female. 

When the researchers dug into the data, they found that around 50% of study participants were female in trials funded by the pharmaceutical industry or academic institutions, but this percentage stood at 46.7% for trials funded by the U.S. government. 

Crucially, they also saw that females were still underrepresented in many trials, particularly in the fields of oncology, cardiology, pediatrics, and infectious diseases.

It’s clear to see there has been progress and that clinical trials are more representative. But many of the drugs used to treat health conditions today stem from studies that were done in the last century, when female participation was far from equal.  

And efforts to include people from marginalized communities and minority ethnic and racial backgrounds remain, for the most part, woefully inadequate

Nutrition studies and guidelines lag behind

While clinical trials to develop drugs are increasingly achieving gender parity, the same isn’t true for nutrition research. 

A team of scientists recently reported that nutrition guidelines for people living in the U.S. and Canada are based on evidence skewed toward male study participants. 

They reviewed 704 studies, of which 16.5% included only male participants, and less than one-third reported the race or ethnicity of the study volunteers. Females made up just under a third of study participants in those trials that included female volunteers. 

Over 80% of studies didn’t include participants who were pregnant or lactating, but the studies can still be used as the basis for recommendations during this life stage. 

Dr. Sarah Berry, a reader in nutritional sciences at King's College London and Lead Nutritional Scientist at ZOE, explains the challenges of including female participants in nutrition research: 

“Until I worked on ZOE’s PREDICT trial, I had only recruited men in most of my preceding 30 randomized controlled trials. Why? Funding! Because women are challenging to study, as you have to consider the phase of their menstrual cycle and menopause status.” — Dr. Sarah Berry

“So if I was to do a postprandial study including women, I would need to spend around three times the budget as doing the same study in men. And given that it's near impossible to get funding for nutrition research, we have to budget as competitively as possible,” Dr. Berry continued. 

Revolutionizing study representation

Advances in technology have changed the way that we do nutrition research at ZOE. Apps and home testing kits have, over time, replaced in-person visits to clinical trial units. 

“Previously, we were able to do large scale studies with lower precision, and smaller scale studies with higher precision. With the modern advancements, we can get the best of both worlds,” Dr. Berry said in a recent interview

Our PREDICT research program has over 15,000 participants so far, with tens of thousands of blood fat test results, millions of blood sugar measurements, and a staggering amount of data on the gut microbiome.

Females make up between 67–80% of the study participants in each of the trials included in this research program. 

“We are able to study women separately to men in our research and have the numbers to do this in a meaningful way,” Dr. Berry explains. 

For example, we’ve found that women’s cholesterol levels and blood sugar responses to food are very different to men’s, and that this changes a lot with age. Meaningful nutrition guidelines should take this into consideration. 

We also run the ZOE COVID study, with over 4 million participants since the start of the COVID-19 pandemic. 

Self-reported data from nearly 600,000 of these study participants allowed us to show that following a healthy diet can decrease the risk of severe COVID-19. Just over two-thirds of participants who took part in the study were female. 

There is clearly still a long way to go before medical and nutrition research is representative of our society. The way we do our research at ZOE allows us to reach an unprecedented number of participants, and we are proud that a great number of them are female. 

You can find out more about our research and join our studies here. 


Analysis of female enrollment and participant sex by burden of disease in US clinical trials between 2000 and 2020. JAMA Network Open. (2021). https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2781192 

Gender differences in drug responses. Pharmacological Research. (2007).  https://pubmed.ncbi.nlm.nih.gov/17129734/

Limited data exist to inform our basic understanding of micronutrient requirements in pregnancy. Science Advances. (2021). https://www.science.org/doi/10.1126/sciadv.abj8016 

Racial/ethnic differences in drug disposition and response: Review of recently approved drugs. Clinical Pharmacology & Therapeutics. (2014). https://ascpt.onlinelibrary.wiley.com/doi/10.1002/cpt.61

Sarah Berry – Science is my favorite hobby. (2021). https://blog.frontiersin.org/2021/11/11/science-is-my-favorite-hobby/

The thalidomide disaster, lessons from the past. Methods in Molecular Biology. (2013). https://pubmed.ncbi.nlm.nih.gov/23138926/

Twenty years and still counting: including women as participants and studying sex and gender in biomedical research. BMC Women’s Health. (2015). https://bmcwomenshealth.biomedcentral.com/articles/10.1186/s12905-015-0251-9 

When will clinical trials finally reflect diversity? Nature. (2018). https://www.nature.com/articles/d41586-018-05049-5

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