Every Body’s Different: 2 Landmark Nutrition Studies Prove One-Size-Fits-All Diet Advice Is Wrong

5 Mins Read

Over the years, diet trends and wellness fads have come and gone. You might have heard a few of your friends hailing intermittent fasting as “super effective” or the ketogenic diet as the “best thing they’ve done all year” for their health. And you may have wondered, why didn’t it work for me? Turns out, two landmark pieces of nutrition research suggest that one size fits all health/diet advice is a myth. While certain basic health and wellbeing guidelines can by and large apply to many of us (we could all use more and better sleep, for example), most of us have individualised responses to food and require a personalised dietary approach.

Story Highlights

•  The Personalised Nutrition Project overturned most of what we know about diets and eating, illustrating that every single individual’s response to the same food is different.

• The Predict Study shows that every person contains a unique microbiome makeup, which affects the way they respond to food.

• Universal medical advice needs to be questioned, as most research has been based upon white, middle class male samples.

The Personalised Nutrition Project: The Study That Overturned Everything We Thought We Knew About Food

A groundbreaking study in 2015 revealed that we ought to question everything we thought we knew about dieting and health. Conducted in Israel, the Personalised Nutrition Project found that every single one of our bodily responses to food is different. 

Researchers at the Weizmann Institute of Science, who worked on the project, monitored the blood sugar levels of 800 participants for one week. Surprisingly, they found that the body’s response to all foods is highly individualised. While some saw their blood glucose rise sharply after ingesting white bread, others didn’t. The same went for ice cream!

Individual responses to food varied depending on lifestyle, medical history, gut microbiome, time of exercise and sleep patterns.

Using their initial set of data, researchers generated an algorithm to predict individualised responses to food based on one’s lifestyle, medical history and the composition of the gut microbiome. The algorithm worked – it was able to successfully predict the variance in blood sugar level response among different individuals when exposed to the same food. Responses also varied significantly depending on whether food was consumed before exercise and sleep. 

“Personalised eating choices are more likely to help people stay healthy than universal dietary advice,” said Professor Erin Segal who worked on the project. 

The Predict Study: Every Person Responds Differently To Food Because Of Microbiome Variability

A collaborative research effort between King’s College London and the medical schools at Harvard and Stanford, the Predict Study’s aim is to find out why different diets suit different people. So far they have measured thousands of people’s reactions to a wide range of foods and hope to use this data to develop an individualised preventative medical tool – Zoe, – an app that predicts food choices for each person. 

Diet advice cannot be applied universally, every person responds differently to food.

The idea behind the Predict study is that eating what is optimised for each individuals’ unique physiology could prevent specific diseases that person is genetically susceptible to. 

Leading scientist of the study Tim Spector said: “It’s a real paradigm shift of how people are going to give advice in the future. We were stuck in this time warp of: ‘Fasting blood test for cholesterol, step on the scales and everyone’s the same.’ It’s clearly much more complicated than that. That’s why diets…don’t suit everybody. Despite all the advice, we’re all getting fatter.” 

Macro-nutrients are only one part of the bigger picture.

After collecting blood samples and stool samples from thousands of patients on a carefully lab-controlled diet, Spector said that the results showed huge variability between different individuals. Analysis of the data demonstrated that macronutrient breakdown accounts for only 40% of how people respond to meals – that means that other factors loom significantly larger. 

“The range of responses to the same foods is huge,” commented Spector. Interestingly, genetics aren’t behind the difference either. Spector’s previous research on food responses in 250 pairs of identical twins also found huge variation. 

It’s not down to genes either.

The study appears to suggest that it is our very behaviour that can modify responses to food. For example, one can improve their blood sugar levels by selecting foods that result in smaller peaks and altering meal times to harmonise with your circadian rhythm, which can improve gut microbiome diversity.

Other behavioural mechanisms that can alter the way we respond to food is the time and amount we exercise and sleep. One of the key reasons why these behavioural changes have an impact is because it affects our gut microbiomes. To put into perspective the importance of gut bacteria in causing variation, humans share 99% of our genetic makeup, compared to only 25% of our gut microbiomes. 

Our gut microbiome has a big impact on dietary response because humans share only 25% of them, meaning one person’s microbiome makeup can be extraordinarily different from the next.

“It’s related to your weight, your propensity to diabetes, it controls how you metabolise fat,” explains Spector. Other scientific studies have also shown how the gut microbiome affects mood, appetite, vitamins and food response. 

We Need To Question Universal Medical Advice

Most medical research has been conducted using unrepresentative samples, predominantly made up of white, middle-class men.

Just as universal dietary advice needs to be taken with caution, so should one-size-fits-all medical nutritional recommendations. This is because clinical research often fails to fully capture diversity in populations. Despite the fact that governing bodies, such as the Food and Drug Administration (FDA), require pharmaceutical companies to prove that drugs are safe for the market through stringent testing, these trials often fail to involve a diverse sample of participants.

According to a study conducted at the University of California, Davis, Hispanic and black patients represent as little as 1.3% of participants in cancer clinical studies. When it comes to the % of women involved in clinical, to say nothing of LGBTQ populations, it’s difficult to find any data at all.

This lack of diversity in research can lead to health risks and real consequences.

With research suggesting that different ethnicities have distinct genes that make certain groups more vulnerable to some diseases and respond differently to medicines, this gap in medical research can produce real life-and-death consequences. 

One thing’s for sure: the one-size-fits-all mentality needs to go. Personalised nutrition matched to an individual’s microbiome makeup and lifestyle habits are the way forward.

Lead image courtesy of Pexels.


  • Sally Ho

    Sally Ho is Green Queen's former resident writer and lead reporter. Passionate about the environment, social issues and health, she is always looking into the latest climate stories in Hong Kong and beyond. A long-time vegan, she also hopes to promote healthy and plant-based lifestyle choices in Asia. Sally has a background in Politics and International Relations from her studies at the London School of Economics and Political Science.

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