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Why everyone reacts differently to food

For a long time it was thought that everyone reacts the same to food. But how is it possible that one person feels energized after eating an oatmeal breakfast and the other doesn’t? Or how is it possible that someone who eats a large plate of pasta every night keeps on weight and the other does not?

To understand why everyone reacts differently to food, we share three insights that have been revolutionary in science. For example, these studies showed that in addition to the meal, a number of other factors also influence your response to food. What factors are these and how can Clear.bio help you make better food choices? .

Research 1

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

💡 When you eat something that contains carbohydrates, these carbohydrates are converted directly into glucose in your stomach and intestines. Glucose is sugar. The glucose is absorbed into your blood. Blood glucose is fuel for your body. Due to the transport through your blood, the glucose ends up with 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 in the study were allowed to maintain their own eating pattern, except for breakfast, where they only had to eat bread or bread with butter.

The researchers saw that when a person ate the same breakfast again the next day, their blood sugar response was 77% the same. It was long thought that the reaction of a person after the same meal would be exactly the same, but that is not the case. We can deduce two important things from this:

The content of the meal largely determines the blood sugar response.
But there are more factors that influence blood glucose response than just the content of the meal. For example sleep, sports, stress and hormones.

There were also differences between the participants. For example, two people after exactly the same breakfast had a clearly different response of their blood sugar.

Finally, this study attempted to predict the response of blood sugar to food based on the data collected from the participants. For example, activity, blood values, nutritional value of the meal, age, weight and microbiome.

Using this ‘predictor’, they then put together healthy meals and unhealthy foods for everyone. This predictor turned out to be correct in 68% of the cases: the unhealthy meals led to a strong increase in the sugar level, while the healthy meals remained more stable.

Research 2

In 2019, the research from study 1 was repeated with the question whether the results could be demonstrated again in a new group of people, in this case on 327 Americans.

Here, too, the researchers asked to participate in their research into the individual blood glucose response to food for a week. The participants in the study were allowed to maintain their own eating pattern, except for breakfast: they had to eat a bagel with cheese. It was noticed that:

  • The blood glucose response a day later after the same breakfast – in this case a bagel with cheese – is 66% the same. This is therefore slightly lower than the 77% of the first study. The theory is that the more complex a meal is, the more the response differs. And this difference also applies per person.
  • The researchers were able to predict the response of blood sugar to food by up to 62%. This is slightly lower than the 68% of the first study.
  • If you only looked at the amount of calories or carbohydrates in a meal, you can predict the response of the sugar by up to 34% and 40%.

The predictability of these researchers’ model is therefore higher than when only looking at calories or carbohydrates. Again, this means that more factors influence blood sugar response and its prediction than carbohydrate intake alone.

Research 3

The last study we discuss is a recent 2020 study published in the medical journal Nature Medicine. For this study they worked with 1002 twins. The study showed that the response of the sugar level to food is determined by three major components:

  • The composition of the meal
    Your DNA
    The microbiome

💡 The microbiome is the collective name for the bacteria in and on our body. The microbiome is made up of tiny critters that are mostly bacteria, but also include fungi, yeasts, viruses, and other single-celled creatures. Humans carry about 1.5 kilograms of microbes, most of which are in our gut. Important functions of the microbiome are the protection against pathogens and the digestion of fiber.

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 similar in composition in terms of proteins, fats and carbohydrates.

Furthermore, this study showed that when a certain breakfast is eaten as lunch, the reaction can be twice as bad. The order of the meals therefore also influences the response of the blood sugar.

Conclusion: no one reacts the same to food

All three studies conclude the same thing: 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 many other factors that have not been measured or that we cannot (easily) measure, but that can influence the response to food.

Consider, for example, how fast someone eats, stress from the previous days, the hormonal cycle, an annoying telephone conversation or a broken night.

Also, the microbiome changes based on what you eat in 2 to 3 months and so your response to food can change again.

It is therefore a myth to say that everyone reacts the same to food. It explains to us why there has not been a “one-size-fits-all” diet until now and why the effectiveness of diets contradict each other.

How do you make the best food choice?

With these insights you can start measuring your personal response of your blood sugar to food.

At Clear.bio we measure the effect of your blood sugar on food. This allows you to make insightful choices in the diet that works for you. Knowing more? Find out how Clear.bio can help you.

Want to know more about the studies?

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

For scientists

Are you a scientist? You might 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 Network 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).