By Lisa Rapaport (Reuters Health) – 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. 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.