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Diets should be personally tailored to your gut microbiome, study says


Rather diets should be tailored to an individual's gut microbiome, or combination of gut bacteria, Israeli scientists said.

The glycaemic index is used by doctors and nutritionists to develop healthy diets based on how different foods affect glucose levels in the blood.

But the study, published today in Cell, shows different people can have a very different glycaemic response to a food.

"If my and your response to the same food are opposite then by definition a similar diet cannot be effective for both of us," said co-author Dr Elan Elinav, from the Immunology Department at the Weizmann Institute of Science.

What is the glycaemic index

What is the glycaemic index (GI)?

  • The glycaemic index scale ranks carbohydrate foods based on their effect on glucose levels in the blood over a period of two hours.
  • Carbohydrate foods are compared gram for gram against glucose or white bread, which have a GI score of 100.
  • High-GI foods such as baked potato with a score more than 70 break down quickly, causing a spike in blood glucose levels.
  • Low GI foods such as oats, lentils, beans and nuts release with a score of 55 or less release glucose gradually into the blood.

The team found that an individual's gut bacteria was a key factor influencing whether a food delivers a long, slow rise in blood sugar, or a short, sharp spike.

In the first part of the study, 800 volunteers — some healthy, some with pre-diabetes — were hooked up with devices that continually monitored their blood sugar levels, and equipped with an app to record their every move and meal.

Over one week, this revealed dramatic differences in each person's blood sugar response to different foods.

"We would expect that in average people, their blood sugar would spike more on ice-cream than rice," Dr Elinav said.

"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 per cent of the study population did not even spike on ice-cream."

At the same time, researchers took blood and sampled each individual's gut bacteria, looking not only at the makeup of their gut bacteria but also the functional profile of the microbiome.

Algorithm predicts individual's glycaemic response

Using all this data, the group 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.

When they applied this algorithm to a separate group of 100 people who had participated in the week-long monitoring, they found the algorithm accurately predicted what each individual's blood glucose response would be to each meal.

Some of the food ingredients that were included in some of these people's good diets were included in other people's bad diets, so it was completely individualised.

Dr Elan Elinav

"This told us that we had a very useful tool that could utilise this huge amount of data to do something predictive at the individual level, but the third phase of our study was an interventional study in which we put ourselves to the test," Dr Elinav said.

When they pitted the algorithm against the tailored advice of experienced dieticians, in a group of people with pre-diabetes, the algorithm proved better at devising a diet that would improve these at-risk people's blood sugar profile.

"What was interesting was that some of the food ingredients that were included in some of these people's good diets were included in other people's bad diets, so it was completely individualised," he said.

Variation averages out over time

Commenting on the study, Professor Jennie Brand-Miller, director of the Sydney University Glycemic Index Research Service, said it was well known that individuals would respond differently to different foods, because the response was influenced by factors such as exercise and sleep and stress.

Related links for personalised diet

However, she said, this day-to-day variation within an individual did average out over time to the established glycaemia index values for foods, and pointed out that the study only followed individuals for one week.

Dr Elinav said there are now plans to extend the study and see if the algorithm-tailored diet held up against gold standard diabetes diets over longer periods of time.

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