"High-glycaemic" foods - rapidly digested by the body - could be causing "fatty liver", increasing the risk of serious illness.
Boston-based researchers, writing in the journal Obesity, found mice fed starchy foods developed the disease.
Those those fed a similar quantity of other foods did not.
Fatty liver is exactly as it sounds - a build-up over time of fat deposits around the organ.
At the time, no ill-effects are felt, but it has been linked with a higher risk of potentially fatal liver failure later in life.
The study, carried out at Boston Children's Hospital, looked at the effect of diets with precisely the same calorific content, but very different ingredients when measured using the glycaemic index (GI).
This is a measure of how quickly the energy in the food is absorbed by the body, producing a rise in blood sugar levels - high GI foods lead to sharper rises in blood sugar, and similar rises in insulin levels, as the body releases the chemical in response.
High GI foods include many breakfast cereals and processed foods such as white bread and white rice.
Low GI foods include unprocessed fruit, nuts, pulses and grains, including rye or granary bread, spaghetti, apples and oranges.