Until now we thought that everyone reacts the same to food. But how is it possible that one person feels energized after eating an oatmeal breakfast, while the other doesn’t? Or how is it possible that someone who eats pasta every day doesn’t gain any weight, while the other does? To understand why everyone reacts differently to nutrition, we share 3 groundbreaking insights that have been revolutionary in science. These studies showed, for example, that in addition to meal choice, there are a number of other factors that influence your response to food. In this blog, we share what these factors are and how Clear can help you make better food choices.

Study 1

The first study to show that people react differently to food came from two researchers at the Weizmann Institute of Science in Israel in 2015. The researchers asked 800 people to participate in their study of the individual blood glucose response to food for a week. 

💡 When you eat something that contains carbohydrates, these carbohydrates are directly converted into glucose in your stomach and intestines. Glucose is sugar. The glucose is absorbed into your blood. Blood glucose is fuel for your body. The glucose is transported through your blood to your muscles and organs that need it. By “blood glucose response” we mean the response of your blood glucose after eating a meal. This is measured by looking at your blood glucose levels. The blood glucose value is the amount of sugar or glucose in your blood.

The participants were allowed to maintain their own diet, apart from breakfast: they only had to eat bread, or bread with butter. The researchers saw that when a person ate exactly the same breakfast again a day later, the response was 77% similar. We can deduce 2 important things from this:

  • There are more factors that influence the blood glucose response than just the content of the meal
  • The content of the meal is the most important factor for the blood glucose response, namely 77%

The differences in blood glucose levels were even greater between the participants then for an individual participant. In other words, the researchers saw that 2 people who ate exactly the same breakfast reacted differently.

This study also attempted to predict a response that included 137 different variables. Variables included activity, blood count, microbiome, nutritional value of the meal, age and weight. The researchers were able to predict the response to food up to 68% accuracy. They saw that carbohydrates cause a worse response, and fats for a better response. It also indicates that there was a bad reaction directly after eating nutrition with fibers, but these meals resulted in better reactions in the longer term. With a better response we mean a less high and / or less long high peak in the blood sugar level. 

Study 2

In 2019,  study 1 was repeated with the question whether the results could be reproduced on a new group of people, in this case on 327 Americans. Here, too, the researchers asked to participate in their study of the individual blood glucose response to food for a week. In the study, the participants were allowed to maintain their own diet, apart from breakfast, where they had to eat a bagel with cheese. It was noticeable that:

  • The blood glucose response when a person ate the same breakfast again a day later, in this case a bagel with cheese, was 66% similar. This is slightly lower than the 77% of the first study. The theory is that the more complex a meal, the more different the responses can be. And this difference also applies per person.
  • The researchers were able to predict the response to food up to 62%, which is slightly lower than the 68% of the first study.
  • If you only looked at the calorie content or the carbohydrate content of a meal, you would get 34% and 40% accuracy.

The accuracy of the model of these researchers is higher than just using calorie or carbohydrate content. This again means that more factors are important that can predict the response to food than just the carbohydrate intake and that the response to food is personal.

Study 3

The latest recent study from 2020 on this is published in the medical journal Nature Medicine. A model was developed for this study and tested on, amongst others, 1002 twins. The model shows that the blood glucose response to food is determined by three major components:

  • for the most part through the meal itself
  • through DNA
  • through the microbiome

The researchers also showed that when someone has a bad reaction to a certain meal, it is almost certain that that person also reacts badly to a meal that is comparable in macronutrients. They also showed that the same breakfast consumed before lunch can give twice as bad a reaction.

💡The microbiome is the collective name for the bacteria in and on our body. The microbiome is made up of tiny bugs, mostly bacteria, but also fungi, yeasts, viruses and other unicellular creatures. Humans carry about 1.5 kilos of microbes. Important functions of the microbiome are the protection against pathogens and the digestion of fibers.

The latest insight from this research looks at the order of the meals. Does the jam sandwich cause a peak in glucose for everyone, despite personal differences? They showed that this generally applies, but that there are also exceptions for certain meals. These may be the best meal for one person and the worst for another.


All three studies conclude the same: the response of your blood glucose level to food is personal and depends largely on the complexity of the meal itself, but also on your DNA and your microbiome. It is important to mention that there are other factors that have not yet been measured, or that we cannot (easily) measure that can also influence the response to food. For example, how fast someone eats, stress from the days before, hormonal cycle, an annoying phone call, or a broken night. Also, the microbiome changes based on what you eat in 2-3 months, thus changing your response to food. It is therefore a myth to say that everyone reacts the same to food. It also fully explains to us why there has not yet been a one-size-fits-all diet and why the effectiveness of diets contradict each other.

How can you make the best nutritional choice?

With these insights you can take matters into your own hands and start measuring your personal blood glucose response to food. At Clear we measure the effect of your blood glucose response to nutrition over a minimum period of 2 weeks. This allows you to make insightful choices for the nutrition that works for you. Want to learn more? Find out how Clear can help you.

Do you want to know more about these studies? The two scientists of the first study have written an accessible book explaining this research and many other experiments.

Are you a scientist? You may want to read these articles:

Zeevi D, Korem T, Zmora N, Israeli D, Rothschild D, Weinberger A, Ben-Yacov O, Lador D, Avnit-Sagi T, Lotan-Pompan M, Suez J, Mahdi JA, Matot E, Malka G, Kosower N , Rein M, Zilberman-Schapira G, Dohnalová L, Pevsner-Fischer M, Bikovsky R, Halpern Z, Elinav E, Segal E. Personalized Nutrition by Prediction of Glycemic Responses. Cell. 2015 Nov 19; 163 (5): 1079-1094. doi: 10.1016 / j.cell.2015.11.001. PMID: 26590418.

Mendes-Soares H, Raveh-Sadka T, Azulay S, Edens K, Ben-Shlomo Y, Cohen Y, Ofek T, Bachrach D, Stevens J, Colibaseanu D, Segal L, Kashyap P, Nelson H. Assessment of a Personalized Approach to Predicting Postprandial Glycemic Responses to Food Among Individuals Without Diabetes. JAMA Netw Open. 2019 Feb 1; 2 (2): e188102. doi: 10.1001 / jamanetworkopen.2018.8102. PMID: 30735238; PMCID: PMC6484621.

Berry, S.E., Valdes, A.M., Drew, D.A. et al. Human postprandial responses to food and potential for precision nutrition. Nat Med 26, 964–973 (2020). https://doi.org/10.1038/s41591-020-0934-0