Researchers have found that among the three major food groups, fat is the only cause of weight gain in the long run.

In the most comprehensive study yet of its kind, researchers at the University of Aberdeen in Scotland and the Chinese Academy of Sciences in Beijing, China concluded that only fat causes mice to gain excessive weight over a long period of time.

The findings of the study could potentially put a nail in the coffin on the long-standing controversial debate on which among the several diets in the world is the best for avoiding excessive weight gain.

Studying The 3 Major Food Groups

Food is made up of the three macronutrients, such as carbohydrates, protein, and fat. The goal of the study was to see which among these macronutrients caused weight gain in mice.

The research published in the journal Cell Metabolism examined a total of 30 different diets, each one having different proportions of carbohydrates, protein, and fat.

The scientists conducted the study on laboratory mice. Each of the mice was made to eat a single diet for three months. This is equivalent to nine years for humans.

Over the course of the study, the researchers made more than 100,000 measurements of changes in both body weight and body fat in the mice using micro MRI machines.

Only Fat Causes Weight Gain

The researchers concluded that among the food groups, only fat caused weight gain in mice. Lead author John Speakman, chair of zoology at the University of Aberdeen, says that the amount of carbohydrates and protein in the diet did not induce weight gain in the subjects.

"The result of this enormous study was unequivocal - the only thing that made the mice get fat was eating more fat in their diets," Speakman says.

The researchers also found that even carbohydrates that contain 30 percent of calories from sugar, which is widely believed to induce weight gain, did not have an effect. Sugar and fat, a combination found commonly in baked goods and pastries, were also found to not have any impact more than fat alone.

They also found that diets with very low amounts of protein (5 percent or less) did not cause the mice to eat more. This suggests that there is no such thing as a protein target.

The researchers believe that dietary fat has this impact on weight gain because it stimulates the reward centers in the brain, causing the mice to eat more when they eat fat.

The Right Direction

The study was conducted on mice, which is its biggest limitation. However, mice are often used in laboratory experiments in instances where human studies pose a challenge because mice and humans have similar physiologies and metabolism patterns.

Speakman says it is unlikely that a study of this scope and kind will be done on humans because it is difficult to subject humans to such a controlled diet for extremely long periods of time. Research done on mice may be the best scientific evidence humans may have for now.

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