BEIJING, July 16 (Xinhua) -- Researchers from Chinese Academy of Sciences claim that eating too much fat is the only cause of obesity in mice, after extensive experiments on the animal.

People's diet is comprised of fat, protein, and carbohydrates. Since the 1980s, global research has focused on finding out which ingredients are the key factors for gaining weight.

Some argued that carbohydrates, especially sugar, was the leading cause, while others thought of protein, saying the purpose of eating food is to obtain protein rather than energy. A low protein diet may lead people to eat more, resulting in more energy and weight.

There was also a popular view that dietary fat could help people lose, not gain weight.

In this study, researchers exposed mice to 29 different diets varying from 8.3 percent to 80 percent fat, 10 percent to 80 percent carbohydrates, 5 percent to 30 percent protein, and 5 percent to 30 percent sucrose.

The experiment, involving five groups of 100,000 mice, lasted for three months, equivalent to nine years of human life.

They found that only increased dietary fat led to high energy intake and weight gains. Furthermore, food with high sugar content did not cause an increase in body weight, and low protein did not result in excessive energy intake, either.

The research, led by the academy's Institute of Genetics and Developmental Biology, was recently published in the international journal Cell Metabolism.

"The shortcoming of the research is that the experiment only used mice rather than humans. However, they have many similarities in physiology and metabolism, and it seems impossible to do such a long-term diet control study in humans," said John Speakman, leading researcher in the study.

"The research will help us better understand the human diet," said Speakman.