Nutritional experts have for years debated the primary culprit for increasing obesity. While diets that are high in fat and carbohydrates contribute to the condition, it turns out, fructose may be one true driver of obesity, according to a study.

According to Richard Johnson, from the University of Colorado Anschutz Medical Campus, the primary problem in obesity is fructose which is present in table sugar and high fructose corn syrup.

Fructose can also be made in the body from carbohydrates (particularly glucose).

When fructose is metabolised, it lowers the active energy in the body (known as ATP, or adenosine triphosphate) which causes hunger and food intake.

What Johnson calls the “fructose survival hypothesis” brings together most of the dietary hypotheses of obesity, including the two that have been most incompatible with each other -- the energy balance theory, which proposes too much food (and primarily fat) drives obesity, and the carbohydrate-insulin model, which puts carbohydrates at the centre of weight gain.

“Fructose is what triggers our metabolism to go into low power mode and lose our control of appetite, but fatty foods become the major source of calories that drive weight gain,” Johnson said.

Obesity is a known risk factor for various diseases including heart disease, diabetes, cancer and dementia.

Data from the World Health Organisation (WHO) shows that worldwide, more than 1 billion people are obese 650 million adults, 340 million adolescents, and 39 million children.

The World Obesity Federation predicts that by 2030, one in five women and one in seven men will have obesity.

The new study published in the research journal Obesity suggests various obesity-causing theories are not incompatible with each other, and that they can all be brought together in one unified pathway that centres around one true driver: fructose.

Fruits are high-fructose foods, and fructose significantly stifles active energy. Fat acts as stored energy, but eating high-fructose foods blocks the replacement of active energy from fat storage, keeping active energy low like a bear preparing for a long winter’s nap.

"This theory views obesity as a low-energy state," Johnson said. "Identifying fructose as the conduit that redirects active energy replacement to fat storage shows that fructose is what drives energy imbalance, which unites theories.

"While more work is needed to fully validate this unifying hypothesis, this is a hopeful first step in potentially identifying more targeted preventions for obesity and related metabolic imbalance management."