Fructose and Obesity: Are They Connected?

A new hypothesis suggests that the consumption of fructose may explain the cause of obesity.

Nutrition scientists agree that Western diets rich in fats and sugar may be behind the cause of obesity, but there is a lack of consensus over the primary culprit. Some suggest too high caloric intake or high-fat diets combined with less energy expenditure is to blame, while others point to specific foods such as carbohydrates or fat.

A new hypothesis laid out in the journal Obesity proposes that many theories about the cause of obesity are compatible with each other, while the primary problem could be fructose.

What are the effects of fructose?

Found in table sugar and high fructose corn syrup, fructose can also be made from carbohydrates, particularly glucose.

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

Richard Johnson, M.D., University of Colorado Anschutz Medical Campus researcher, says that the "fructose survival hypothesis" brings together most of the dietary hypotheses of obesity.

Among them are the two that have been most incompatible with each other — the energy balance theory, which suggests too much food (and primarily fat) drives obesity, and the carbohydrate-insulin model, which considers carbohydrates the main cause of obesity.

"Essentially, these theories, which put a litany of metabolic and dietary drivers at the center of the obesity epidemic, are all pieces of a puzzle unified by one last piece: fructose," says Johnson.

"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."

- Richard Johnson, M.D.

Researchers note that animals know to forage for food when energy levels begin to fall. That’s why bears prepare for hibernation by eating fruits. These are foods have high fructose content and fructose significantly stifles active energy.

Fat acts as stored energy, but eating a high-fructose diet blocks the replacement of active energy from fat storage, keeping active energy low like a bear preparing for hibernation.

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

However, most previous studies investigating how fructose works have been animal studies, and the findings may not be applicable to humans. The authors also recognize that there are likely multiple other mechanisms involved in the development of obesity.

The prevalence of obesity impacts one in four Americans, and the rate is expected to reach 47% by 2023. Obesity is often accompanied by other conditions, including type 2 diabetes, heart disease, stroke, hypertension, and certain cancers.

Further research is needed to validate the hypothesis on the link between fructose consumption and the incidence of obesity. However, if confirmed, the findings could lead to more targeted approaches for the prevention and management of obesity.