Is Fructose to Blame for Obesity?

A recent article hypothesized that fructose causes more metabolic disease than does sucrose when overfed in the human diet. Fructose intake as high-fructose corn syrup (HFCS) has risen since its use in soft drinks in the United States and parallels the increase in the prevalence of obesity.

The newest hypothesis regarding fructose invokes a genetic survival of the fittest rationale for how fructose enhanced fat deposition exacerbates the increased caloric consumption from the Western diet to promote metabolic disease especially in our adolescent and young adult population. This theory suggests that fructose consumption causes low adenosine triphosphate, which stimulates energy intake causing an imbalance of energy regulation.

Caroline Apovian, MD

Ongoing interest in the association between the increased use of HFCS and the prevalence of obesity in the United States continues. The use of HFCS in sugary sweetened beverages (SSBs) has reduced the cost of these beverages because of technology in preparing HFCS from corn and the substitution of the cheaper HFCS for sugar in SSBs. Although SSBs haven't been proven to cause obesity, there has been an increase in the risk for type 2 diabetes, cardiovascular disease (CVD), nonalcoholic fatty liver disease (NAFLD), and even cancer. Research in HFCS, weight gain, and metabolic disease continues despite little definitive evidence of causation.

The relationship between SSBs consumption and obesity has been attributed to the increase in overall total caloric intake of the diet. These liquid calories do not suppress the intake of other foods to equalize the total amount of calories ingested. This knowledge has been gleaned from work performed by R. Mattes and B. Rolls in the 1990s through the early 2000s.

This research and the current work on HFCS and metabolic disease is important because there are adolescents and young adults in the United States and globally that ingest a large amount of SSBs and therefore are at risk for metabolic disease, type 2 diabetes, NAFLD, and CVD at an early age.

The concern over fructose stems from the association between the advent of increasing HFCS in SSBs and the increase in prevalence of obesity occurring at similar time periods in the United States, around 1970-1980.

Researchers noted the association and began to focus on potential reasons to pinpoint HFCS or fructose itself so we have a mechanism of action specific to fructose. Therefore, the public could be warned about the risk of drinking SSBs due to the HFCS and fructose ingested and the possibility of metabolic disease. Perhaps, there is a method to remove harmful HFCS from the food supply much like what has happened with industrially produced trans fatty acids. In 2018, the World Health Organization called for a total ban on trans fats due to causation of 500 million early deaths per year globally.

Similar to the process of making HFCS, most trans fats are formed through an industrial process that alters vegetable oil and creates a shelf stable inexpensive partially hydrogenated oil. Trans fats have been shown to increase low-density lipoprotein (LDL) cholesterol and decrease high-density lipoprotein (HDL) increasing the risk for myocardial infarction and stroke.

What was the pivotal moment for the ban on trans fats? It was tough convincing the scientific community and certainly the industry that trans fats were especially harmful. This is because of the dogma that margarine and Crisco oils were somehow better for you than were lard and butter. The evidence kept coming in from epidemiological studies showing that people who ate more trans fats had increased levels of LDL and decreased levels of HDL, and the dogma that saturated fat was the villain in heart disease was reinforced. Maybe that pivotal moment was when a researcher with experience testing trans fat deposition in cadavers and pigs sued the US Food and Drug Administration (FDA) for not acting on cumulative evidence sooner.

Do we have this kind of evidence to make a claim for the FDA to ban HFCS? What we have is the time course of HFCS entry into the food supply which occurred in 1970. This coincided with the growing prevalence of obesity between 1960 and 2000.

The excess energy in SSBs can provide a hedonic stimulus that overcomes the natural energy balance regulatory mechanism because SSBs excess energy comes in liquid form and may bypass the satiety signal in the hypothalamus.

We still have to prove this.

Blaming fructose in HFCS as the sole cause for the increase obesity will be much tougher than blaming trans fats for an increase in LDL cholesterol and a decrease in HDL cholesterol. The prevalence of obesity has increased worldwide, even in countries where SSBs do not contain HFCS.

Still, the proof that HFCS can override the satiety pathway and cause excess calorie intake is intriguing and may have teeth if we can pinpoint the increase in prevalence of obesity in children and adolescents on increased ingestion of HFCS in SSBs. There is no reason nutritionally to add sugar or HFCS to liquids. Plus, if HFCS has a metabolic disadvantage then all the more reason to ban it. Then, it becomes like trans fats: a toxin in the food supply.

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Cite this: Is Fructose to Blame for Obesity? - Medscape - Dec 01, 2023.