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The croissant test
Tim Spector had spare testing kits left over from the start of the research, so his wife wore one too. She loves croissants, and they sat down with one each.
His own meals
His own testing had already turned up surprises. A breakfast of muesli with low-fat milk, orange juice, and tea gave him a massive sugar spike and a dip at 11 o'clock. He switched to full-fat yogurt with nuts, seeds, and a few berries, plus lots of black coffee.
A healthy-looking hospital-canteen lunch, a sandwich on brown bread with sweet corn and tuna plus a smoothie in a little bottle, also gave a massive spike. His wife's result on the croissant made the point that everyone reacts differently.
Why do people react differently to the same food?
The PREDICT study, led by Sarah Berry and colleagues and published in Nature Medicine in 2020, fed standardized meals to about 1,100 adults in the UK and US, including twins. Blood sugar and fat responses to the same meal varied widely, and even identical twins responded differently. Genes explained only a small share of the variation, and the gut microbiome explained more.
Why does a croissant raise blood sugar?
A croissant is made largely of refined wheat flour, whose starch is quickly broken down by the enzyme amylase into glucose. The butter in the dough slows stomach emptying, which delays and flattens the peak. Gastric emptying speed varies from person to person, which is one reason responses to the same pastry differ.
How do fat and protein change blood sugar rises?
Fat and protein slow gastric emptying, so food reaches the small intestine more gradually. They also prompt the gut hormones GLP-1 and GIP, which influence insulin release. In a 2015 study in Diabetes Care, Alpana Shukla and colleagues at Weill Cornell Medicine found that eating vegetables and protein before carbohydrates lowered the glucose rise after a meal in people with type 2 diabetes.
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