One-size-fits-all diets don't work

Study shows big differences in how people respond to same food

Many diets recommend more fruit, vegetables and complex carbohydrates, while avoiding refined sugars and carbs, and too much fat, such as this cheese and pork rib combination.
Many diets recommend more fruit, vegetables and complex carbohydrates, while avoiding refined sugars and carbs, and too much fat, such as this cheese and pork rib combination.PHOTO: REUTERS

MIAMI • A healthy food for one person may lead another to gain weight, according to a new study that suggests a one-size-fits-all approach to dieting is fundamentally wrong.

For instance, one woman in the study repeatedly experienced a spike in blood sugar after eating tomatoes, which would generally be considered a low-fat, nutritious food. The findings are based on a study of 800 people in Israel and are published in the journal Cell Press.

"The first very big surprise and striking finding we had was the very vast variability we saw in people's response to identical meals," said researcher Eran Segal of the Weizmann Institute of Science in Israel. Participants wore blood sugar monitors that took measurements every five minutes for an entire week.

They also provided stool samples so that their gut microbiome could be analysed and kept a careful log of everything they consumed. None of the participants had diabetes, but some were obese and had a condition known as pre-diabetes.

Researchers were stunned to see the difference in people's metabolic responses to the exact same foods. For instance, some people's blood sugar rose higher after eating sushi than after having ice cream. And for one middle-aged woman, the act of eating tomatoes actually caused her blood sugar to rise significantly.

"There are profound differences between individuals - in some cases, individuals have opposite responses to one another - and this is really a big hole in the literature," said Professor Segal.

High blood sugar is dangerous because it can lead to diabetes, obesity, heart problems and complications, including eye, kidney and nerve disease. Many diets aim to keep blood sugar low by incorporating fruit, vegetables and complex carbohydrates like brown rice and whole grains, while avoiding refined sugars and goods made with white flour.

But those recommendations do not work for everyone, and often, overweight people are blamed for eating too much or not stic-king to a healthy lifestyle.

Co-author Eran Elinav said the study "really enlightened us on how inaccurate we were about... what we eat and how we integrate nutrition into our daily life."

Instead of urging people to eat low-fat diets, a more personalised approach - one that puts an individual at the centre of the plan, rather than the diet - could be useful to help people control high blood sugar and improve their health, he said.

The researchers also used their findings to forge an algorithm that could predict how different people would react to certain foods, based on a host of personal characteristics and their gut microbes.

Prof Segal said he and colleagues are now working on a system that could bring better nutritional analysis to the individual consumer.

The process would involve mailing stool samples for analysis of the bacteria in the digestive system, because researchers found that specific microbes correlated with blood sugar levels after eating.

Mount Sinai Beth Israel clinical nutrition senior director Rebecca Blake said the role of the gut microflora contributing to obesity and metabolism "is certainly an evolving discipline... However, we need to consider whether this is the chicken or the egg: Does our diet affect our gut microbiota and our obesity, or is the microbiota somehow causal when it comes to weight status?" added Ms Blake.


A version of this article appeared in the print edition of The Straits Times on November 21, 2015, with the headline 'One-size-fits-all diets don't work'. Subscribe