Dr Saleyha Ahsan travelled to Israel to take part in a study, being carried out by the Weizmann Institute in Rehovot and led by Prof Eran Segal and Dr Eran Elinav.

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They have recruited nearly 1000 people so far to take part. Each has filled in detailed data about their health and medical background, and then taken part in a week-long close examination of how their blood sugar levels react to different foods.

During the week, their blood sugar levels are measured constantly by a glucometer placed under the skin, their sleep and activity levels monitored by a wrist-band, and they are given an app to record their mood, feelings, sleep and exercise regimes and what they eat. Throughout the week, their meals are planned – some are given to them as standard foods that everyone tries. Others they are allowed to choose, but they have to weigh it all accurately, and record it in precise detail.

Each person in the study has also given a stool – poo – sample. From this, the researchers analyse the gut bacteria living inside each person. Our gut bacteria are unique to us – it is almost like a ‘fingerprint’ of a person – but, crucially, they can change.