When two people follow the same weight-loss diet to the letter, but one fails to lose weight, the problem might be their bodies' different responses to the same foods, a recent Israeli study suggests.
That's because when two people eat the same meal, one may experience a spike in blood sugar levels when the other person doesn't, the study found. Over time, elevated blood sugar can lead to health problems like obesity and diabetes.
Many popular diets such as Atkins, The Zone and South Beach center on a component known as the glycemic index (GI), a fixed ranking of foods based on how fast and how high they raise blood sugar after meals. The index was originally developed to help people with diabetes choose foods that wouldn't cause blood sugar to rise too high.
The logic behind the weight-loss diets is that consuming foods with a lower GI like fish, lean meat and vegetables can help keep blood sugar low and promote weight loss.
"The idea behind the low-GI diet is that the glycemic response to a certain food is an intrinsic property of the food which means that we should be able to predict how a certain individual would respond to some food by looking at the average response of a small group of other people to that food," senior study authors Eran Segal and Eran Elinav of the Weizmann Institute of Science in Rehovot said by email. "Our study demonstrates that this cannot be done."
To see how foods are digested, Segal, Elinav and colleagues recruited 800 adult volunteers and collected data through health questionnaires, body measurements, blood tests, glucose monitoring, stool samples and a mobile app used to report lifestyle and food intake for a total of 46,898 meals.
In addition, they asked participants to eat similar meals for breakfast each day.
As expected, age and body weight appeared to impact blood sugar levels after meals.
But the study also found that different people show vastly different responses to the same food, even though their individual responses remained the same from day to day.