A team of American researchers is now proposing a unifying theory that brings together these seemingly contradictory ideas under a single common mechanism.

Scientists believe they have discovered the potential culprit for the obesity epidemic: fructose.

According to the team led by Dr. Richard Johnson, a researcher at the Anschutz Medical Campus of the University of Colorado, fructose, found in table sugar and high-fructose corn syrup, is at the heart of the obesity problem.

Fructose can also be produced in the body from carbohydrates, especially from glucose.

When the body metabolizes fructose, it reduces active energy, known as ATP (adenosine triphosphate), which subsequently triggers hunger and increased food consumption.

This concept, which researchers call the "fructose survival hypothesis", integrates various dietary theories related to obesity, including two that were previously contradictory: the energy balance theory, which suggests that excessive food intake, especially fats, leads to obesity, and the carbohydrate-insulin model, which emphasizes the role of carbohydrates in weight gain.

These theories, which previously seemed incompatible, can now be seen as pieces of a larger puzzle, united by a crucial component: fructose.

"In essence, these theories, which place a series of metabolic and dietary factors at the center of the obesity epidemic, are all pieces of a unified puzzle with one last piece: fructose", Dr. Johnson writes in a university statement.

Fructose is what triggers the metabolism to switch to low power mode and to lose control of appetite, but fatty foods become the main source of calories that cause weight gain, he writes.

To illustrate this unifying theory, researchers point to hibernating animals.

When people are hungry and no longer have enough active energy, the body enters the survival mode, just like animals preparing for winter by searching for food.

Fruits, known for being rich in fructose, can significantly decrease active energy. Meanwhile, fats serve as stored energy.

Consuming foods high in fructose prevents the replenishment of active energy from fat storage, leaving active energy at a low level, similar to a bear preparing for a long winter hibernation.

"This theory sees obesity as a state of low energy", notes Dr. Johnson.

Identifying fructose as the conduit that redirects the replacement of active energy to fat storage shows that fructose is what leads to energy imbalance, uniting existing theories about obesity, he concludes.

The study was published on Tuesday, October 17th, in the journal Obesity.