Fructose appears to be the main cause of obesity

 In the continuing search for what causes the self-inflicted wounds of obesity, it seems that the main culprit has been identified: fructose.

According to a new study, fructose, while not the main source of calories, triggers the need to eat more fatty foods in larger amounts, resulting in overeating.

One important analysis, led by Richard Johnson, MD, of the Anschutz Medical Campus at the University of Colorado, suggests that you can lose weight most effectively by reducing sugar and carbs at the same time. "Although virtually all studies recognize the importance of reducing ultra-processed and 'junk' foods, it is unclear whether the focus should be on reducing sugar intake, or high glycemic index carbohydrate intake, or fat intake, or polyunsaturated fat intake, or simply increasing protein intake," the researchers explain in the article published in the journal Obesity.

"Here, we review the various dietary hypotheses for obesity," the article continues. "We propose that all the various hypotheses are largely correct and that, although they appear to be incompatible, they can all be unified on the basis of another hypothesis known as the fructose survival hypothesis."

The cause of obesity

Fructose is a type of sugar found in fruit, where it is offset by the vitamins and fiber it contains. The problem is that it is also found in sweeteners, such as table sugar, at much higher levels. Our bodies can also make fructose from carbohydrates such as glucose and salty foods.

Johnson and his colleagues conducted an exhaustive study of all known factors that contribute to obesity and found that fructose metabolism in the body causes a decrease in a compound called adenosine triphosphate (ATP). ATP is the compound that provides the energy needed for the body's cellular processes; when ATP levels drop to a sufficiently low level, a signal (hunger) is triggered in the body, alerting it that the body needs more fuel. The natural response to hunger is to eat something to quickly replenish the body's energy stores.

Diagram showing how the fructose survival theory ties together other theories of obesity. ( Johnson et al, Obesity, 2023 )

This is what the researchers call the "fructose survival hypothesis," and it links different theories about what causes obesity, even those that seem completely incompatible, such as fat intake versus carbohydrate intake.