There is no such thing as a diet that suits everyone, researchers find
The Israeli research tracked the blood sugar levels of 800 people over a week and found that the glycemic index (GI) of any given food is not a set value, but depends on the individual.
The finding is important as the GI is currently used to rank foods based on how they affect blood sugar level and is a factor used by doctors and nutritionists to develop healthy diets.
The new study, led by Eran Segal and Eran Elinav of the Weizmann Institute of Science in Israel and published in Cell, found that the individual gut bacteria determined whether blood sugar was delivered as a slow rise or a sharp spike.
"If my and your response to the same food are opposite then by definition a similar diet cannot be effective for both of us," Elinav told reporters.
The researchers collected data through health questionnaires, body measurements, blood tests, glucose monitoring, stool samples, and a mobile-app used to report lifestyle and food intake. Several meals were standardised across all participants.
Over the study, a total of 46,898 meals were measured.
As expected, age and body mass index (BMI) were found to be associated with blood glucose levels after meals. However, the data also revealed that different people show vastly different responses to the same food, even though their individual responses did not change from one day to another.
"We would expect that in average people, their blood sugar would spike more on ice cream than rice," Elinav told the ABC. "What we found in this really large cohort is that some people did exactly that but others did exactly the opposite.
"They were not responsive to ice cream at all, and actually close to 70% of the study population did not even spike on ice cream."
The researchers even developed an algorithm to predict an individual's glycaemic response to a food, based on factors such as their microbiome, daily activity, blood parameters such as cholesterol, and food content.
"Measuring such a large cohort without any prejudice really enlightened us on how inaccurate we all were about one of the most basic concepts of our existence, which is what we eat and how we integrate nutrition into our daily life", says Elinav.
"In contrast to our current practices, tailoring diets to the individual may allow us to utilise nutrition as means of controlling elevated blood sugar levels and its associated medical conditions."