Two people eat the same healthy diet: one loses weight, the other does not. Why?
Researchers from the Weizmann Institute of Science in Israel have shown that even if everyone ate the same meals, the effect would differ from one person to another because of metabolism.
Blood sugar is closely related to diabetes and obesity and is measured using a continuous glucose monitor. The standard glycemic index (GI) enables ranking of foods based on how they affect blood sugar level, and it is a factor used to develop healthy diets.
However, that system was based on studies averaging how small groups of people respond to various foods.
The new study was led by Eran Segal of Weizmann's Department of Computer Science and Applied Math and Eran Elinav of the Department of Immunology. It tracked the blood sugar levels of 800 people over a week and found that found that the GI of any given food is not a set value, but it depends on the individual.
Participants ate a standardized breakfast such as bread or glucose each morning, items of which were provided; they also recorded all food intake in a mobile app food diary.
Additional data were collected through health questionnaires, body measurements, blood tests, glucose monitoring and stool samples.
A motivational factor was that the researchers provided an analysis of the participants' personalized responses to food, which relied on strict adherence to the protocol.
Individual differences evident
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.
One middle-aged woman with obesity and pre-diabetes, who had tried a range of diets unsuccessfully, learned that her "healthy" eating habits may have been contributing to the problem. Her blood sugar levels spiked after eating tomatoes, which she ate multiple times over the course of the week of the study.
For this person, an individualized tailored diet would exclude tomatoes but include other ingredients not generally considered healthy that are in fact healthy for her. Such information could substantially impact the progress of her condition.
Segal points out that most dietary recommendations are based on standardized grading systems, but it is not often appreciated that individuals display profound differences; some people may have the opposite response to others, and this needs addressing.
Microbiome studies show why differences exist
To understand such differences, microbiome analyses on stool samples were carried out.
Growing evidence links gut bacteria to obesity, glucose intolerance and diabetes; this study confirms that specific microbes correlate with how much blood sugar rises post-meal.
In personalized dietary interventions among 26 additional study participants, the researchers were able to reduce post-meal blood sugar levels and alter gut microbiota.
Interestingly, despite the diets being personalized and thus differing greatly across participants, several of the gut microbiota alterations were consistent across participants.
"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, In contrast to our current practices, tailoring diets to the individual may allow us to utilize nutrition as means of controlling elevated blood sugar levels and its associated medical conditions."
There is sometimes a sense that we know what needs to be done in terms of diet, but that people are not listening and are eating out of control. This study suggests that people may be complying, but the advice is not right for them.
Limitations of the study include relying on participants to rigidly following a diet and honestly record their food intake. Nevertheless, the results suggest that we may need a new way of looking at diabetes and obesity.
The researchers would like to simplify the method used so that it could be applied to a wider audience, who could then be provided with personalized nutritional reports.
Last month, Medical News Today reported that differences in gut microbiota may impact people with anorexia.