How Does Fructose Cause Metabolic Syndrome?

Heather Campbell
 min read

This article discusses how fructose causes metabolic syndrome, which affects many people in the Western world.

How Does Fructose Cause Metabolic SyndromeIn the United States, around 96 million people aged 18 or older (about 38% of the US adult population) have prediabetes.

Prediabetes is a combination of excess body fat and insulin resistance. It is considered an underlying cause of metabolic syndrome.

This means that more than a third of the American adult population is at risk of suffering from metabolic syndrome.


How does fructose cause metabolic syndrome? Introduction

Fructose, also known as fruit sugar, is found in honey, ripe fruits, berries, root vegetables, flowers, etc. It is also artificially produced as a taste enhancer in the food industry.

The issue with fructose is that excessive consumption of food and drinks containing fructose may contribute to developing metabolic syndrome.

Metabolic syndrome is diagnosed when you have at least 3 of the following 5 symptoms:

Is sugar guilty or innocent?

One camp of scientists sees sugar as the big culprit! Sugar causes all the diseases associated with metabolic syndrome, such as elevated cholesterol, overweight, obesity, high blood pressure, elevated blood sugar, etc.

Also, metabolic syndrome is a significant risk factor for heart disease and diabetes.

However, it is not widely accepted that metabolic syndrome results from consuming too much sugar.

Syndrome X, as metabolic syndrome is also called, is primarily associated with an unhealthy lifestyle. So there is no one specific cause.

There is also a camp of scientists who argue that metabolic syndrome is caused by overeating, a sedentary lifestyle, and too little exercise.

They say sugar plays no significant role in the prevailing view of the causes of metabolic syndrome.

According to this camp of researchers, the best prevention against metabolic syndrome is a healthy lifestyle characterized by a healthy weight with adequate exercise and a responsible diet.

They say a responsible diet is one with plenty of vegetables, fruits, whole grain products, and limited salt consumption.

Consumption of products containing sugar is not necessarily excluded from this lifestyle, according to this camp of scientists.

But the question remains whether sugar really is so harmless…

According to Professor Robert Lustig, who belongs to the other camp, this is absolutely not the case. He says sugar really is dangerous and causes metabolic syndrome.

Source: R.H. Lustig, et al., Isocaloric fructose restriction and metabolic improvement in children with obesity and metabolic syndrome, Obesity, 2015

Metabolic syndrome, fructose, and why we overeat

Typically, patients suffering from metabolic syndrome exhibit resistance to insulin, a hormone that regulates blood sugar levels.

One of the possible causes of metabolic syndrome that is increasingly being investigated is fructose (fruit sugar).

In fact, fructose triggers insulin resistance, which causes leptin resistance, making us overeat and more likely to become obese or overweight.

Domino effect due to fructose | How does fructose cause metabolic syndrome?

Scientific research on fructose frequently uses laboratory animals such as rats.

Researchers then work with rats resistant to insulin, the hallmark symptom of metabolic syndrome.

Fructose leads to insulin resistance

Making rats insulin-resistant to use for research is something the late Stanford University professor and researcher Gerald Reaven knew better than anyone.

He simply put the rats on a fructose diet to make them insulin-resistant.

The process of making the rats resistant to insulin is faster on a diet high in fructose. On the other hand, it is slightly slower on a diet more similar to what we humans eat.

Another research team (M. Baena et al.) from the International University of Catalonia discovered the same findings.

Moreover, this Spanish team of researchers discovered something else!

A group of other rats eating the same amount of calories and the same diet but replacing fructose with glucose did not develop metabolic syndrome.

In other words, fructose – and not glucose – causes metabolic syndrome.

Insulin resistance leads to leptin resistance

It is well known that insulin resistance can lead to type 2 diabetes. In addition, it can also lead to leptin resistance.

The late Professor Reaven noted that the fructose-fed rats became obese because they had become leptin-resistant.

Leptin is a hormone that makes you feel satiated and thus makes you stop eating (because you are no longer hungry).

However, fructose made the rats resistant to leptin, so they kept experiencing continuous hunger and thus continued eating. This is a phenomenon that can occur in humans as well.

Leptin resistance leads to overeating

During a presentation at the University of California, Professor Robert Lustig gave an update in 2013 on his popular video “Sugar: The Bitter Truth.”

This interesting presentation and talk on sugar as a cause of the obesity epidemic can be viewed below:

This presentation explains that the effects of fructose in rats, as discovered by several scientists, also apply to humans.

In other words, insulin resistance in humans also leads to leptin resistance, leading to overeating and, eventually, obesity.

He says sugar is a tremendously destructive force in our daily lives. In fact, sugar causes our insulin levels to be 2 to 3 times higher today compared to several decades ago.

The following domino effect occurs: Our high sugar consumption (including the intake of fructose) topples the domino blocks of insulin, then leptin, and then topples the obesity block.

In other words, our increased sugar consumption causes us to become obese because we are no longer inhibited by leptin. So the substance that is supposed to make us feel satiated no longer affects us.


How does fructose cause metabolic syndrome and other adverse effects? Conclusion

In the domino effect described above, about 90 percent of fructose is processed by the liver (in both rats and humans).

In practice, the liver responds to fructose by producing different types of fat. Moreover, the liver cannot extract much energy from fructose.

Even worse, sugar and fructose damage mitochondria (the cells’ power plants).

The net result of consuming fructose is not very positive, with the following consequences:

Fructose is alcohol without the intoxication

Fructose also promotes the formation of reactive oxygen types, leading to cell dysfunction and aging.

And fructose stimulates changes in the brain’s reward system, prompting excessive sugar consumption.

Thus, in addition to its calories, fructose can have adverse health effects in ways similar to those of ethanol, its metabolic cousin.

The only difference is that fructose is not metabolized in the central nervous system. Thus, it does not cause acute neuronal depression experienced by people who drink ethanol.

These analogies argue that we should simply start considering fructose as alcohol without the intoxication and without the kick.

Source: Robert H. Lustig, Fructose: It’s “Alcohol Without the Buzz,” Advances in Nutrition, 2013

Insulin is the warehouse hormone

When discussing sugar and its effects on your body, we quickly turn to the subject of insulin.

This substance causes nutrients to be stored in the body, mainly in the form of fat.

In other words, we can only store fat if a lot of the insulin hormone is circulating in our blood.

In small amounts, we definitely need insulin. Unfortunately, large amounts of insulin in our bodies give rise to problems.

For example, if we constantly eat sugary foods or drink sugary drinks (soda or soft drinks), our pancreas is always pumping insulin into our bloodstream.

As a result, insulin opens a one-way street to fat cells to regulate fat storage. The fat can get in but cannot get out since we continuously consume fructose and sugar.

That is why you should learn how to eat smarter.

About Heather Campbell

As a nutritionist, my field of specialization is science-based nutritional advice but more importantly, it is my goal to share capturing and inspiring stories, examples and solutions which can help plus-size individuals overcome their specific difficulties. Read More