Personalised diets challenge one-size-fits-all approach to rice and bread

Emerging research suggests that individual responses to staple foods like rice and bread vary widely, prompting a shift towards personalised dietary advice based on gut microbiome and personal factors rather than universal rules.

Cutting out white rice altogether may be a far cruder blood-sugar strategy than many people assume. Research cited by the Taiwanese nutritionist Zhang Xinfang points to a more complicated picture: identical meals can produce sharply different post-meal glucose rises in different people, and part of that variation appears to be linked to the gut microbiome as well as to activity, body composition and other personal factors.

That is why Zhang argued that rice does not need to be treated as a universal forbidden food. Writing on Facebook, she said the size of the portion, what is eaten alongside it, the order in which a meal is eaten and differences in age, muscle mass, insulin sensitivity and gut bacteria can all change what happens after the same bowl of rice. Her practical advice was modest rather than extreme: pair rice with vegetables and protein, try eating those foods first, and add a short walk after meals instead of relying on blanket bans.

The broader science behind that view came from a 2015 Weizmann Institute study that tracked 800 people for a week with continuous glucose monitors. According to the Cell paper behind the work, the team measured responses to 46,898 meals and found “high variability” in blood-glucose responses even when people ate identical foods. ABC News reported that the volunteers included both healthy people and some with pre-diabetes, and that they logged meals, sleep and exercise through a phone app while also providing blood and stool samples.

Those findings challenged one of the most common assumptions in dietary advice: that a food can be neatly ranked for everyone in the same way. Nature reported that meals with the same glycaemic index still produced widely different glucose responses from one person to another. The researchers then combined blood results, dietary habits, body measurements, physical activity and microbiome data in a machine-learning model, and tested personalised diets in 26 people. Nature said those tailored diets brought lower after-meal glucose levels than non-personalised plans. As co-author Dr Elan Elinav put it in comments reported by ABC News: “If my and your response to the same food are opposite then by definition a similar diet cannot be effective for both of us.”

A later bread experiment from the same Israeli research group pushed that argument further. In a randomised crossover trial reported by Cell Metabolism and described by the Weizmann Institute, participants spent one week eating industrial white bread and another eating artisanal sourdough wholegrain bread. The average result was strikingly unsensational: there was no significant overall clinical advantage for one bread over the other. The Washington Post reported that the study involved 20 participants, while the institute said about half had higher blood sugar after white bread and the other half after the sourdough loaf.

That split is important because it undercuts the tidy idea that brown or wholegrain versions of a staple are always better for every individual. “The body’s response to bread is a highly personal matter,” Elinav said, according to the Weizmann Institute’s summary of the study. The Washington Post reported that researchers examined genes and stool samples and could predict a participant’s response from microbiome data alone, particularly the balance of two kinds of bacteria, although they did not yet know exactly how those microbes were influencing blood sugar. The Cell Metabolism paper also said the microbiome itself stayed broadly stable during the short bread intervention, suggesting the differences were not simply caused by a week of switching loaves.

That does not mean white rice gets a scientific free pass. The underlying studies did not test white rice on its own; they looked at mixed meals in everyday life and, in the later experiment, at bread. They do, however, support Zhang’s wider point that staple carbohydrates should not be judged in isolation. Quantity still matters, and so does context. A large portion of refined carbohydrate eaten quickly and alone is not the same as a smaller serving eaten with fibre, protein and movement built into the day.

Time, in a broader feature on why diets work so unevenly from person to person, described the Weizmann work as part of a shift away from generic meal plans and towards highly specific nutrition advice. In that study, participants wore devices that measured blood sugar every five minutes, completed questionnaires, and had their microbiomes sequenced. The idea emerging from that research is not that science has already produced a perfect personalised diet for everyone, but that average food rules can miss biologically important differences between individuals.

For readers wondering what to do with a bowl of rice tonight, the most defensible message is therefore neither “rice is harmless” nor “rice must go”. It is that blood-sugar control depends on the whole meal and the person eating it. Zhang’s everyday suggestions – watch the amount, add vegetables and protein, consider eating them first, and move after eating – sit comfortably with the best-supported evidence from the Israeli studies: the same food can behave very differently in different bodies, so the most useful diet is often the one adjusted to individual response rather than to fear of a single staple.