Fructose: Low on the Glycemic Index But Still May Trigger Weight Gain

Fructose converts to fat in the liver, and may cause overeating

Young People Drinking Soft Drinks
Most of the fructose we consume comes from sweetened drinks. Image Source/Getty Images

Fructose is a monosaccharide (simple sugar), which the body can use for energy. Because it has a low glycemic index, meaning it does not cause blood sugar to rise very high,  it was once thought that fructose was a good substitute for sucrose (table sugar). However, the American Diabetes Association and nutritional experts have changed their minds about fructose.

In fact, since high-fructose corn syrup began being added to many beverages and processed foods in the American food supply, there has been a rise in obesity and diabetes in this country—and many experts believe it is playing a role in the growing obesity epidemic.

Is All Fructose Bad for Me?

A small amount of fructose, such as the amount found in most vegetables and fruits, is not bad at all; in fact, a diet rich in these foods is essential for disease prevention. However, consuming too much fructose at once, such as in processed foods, seems to overwhelm the body's capacity to process it. The diets of our ancestors contained only very small amounts of fructose. These days, estimates are that about 10 percent of the modern diet comes from fructose.

What Happens If I Consume Too Much Fructose?

Most of the carbohydrates we eat are made up of chains of glucose. When glucose enters the bloodstream, the body releases insulin to help regulate it. Fructose, on the other hand, is processed in the liver. To simplify the situation: When too much fructose enters the liver, the liver can't process it all fast enough for the body to use as sugar. Instead, it starts making fats from the fructose and sending them off into the bloodstream as triglycerides.

Worse, the type of fat generated from excess fructose may be the worst kind for us.

A Fructose-heavy Diet May Lead to Diabetes, Obesity, Heart Disease, and More

Excess fructose in your diet does more than just raise your triglycerides, which is a risk factor for heart disease. Consuming lots of fructose also raises bad cholesterol, also known as LDL, and may facilitate insulin resistance, and eventually type 2  diabetes.

In addition, a 2013 study published in the Journal of the American Medical Association found that when compared with glucose, fructose may cause you to eat more. Researchers at Yale discovered that hormones associated with feeling full were released in lesser amounts when participants consumed fructose as opposed to glucose.

In essence, fructose ends up circumventing the normal appetite signaling system, so appetite-regulating hormones aren't triggered—and you're left feeling unsatisfied. This is probably at least part of the reason why excess fructose consumption is associated with weight gain.

What Are the Top Sources of Fructose?

Fruits and vegetables have relatively small, healthy amounts of fructose that most bodies can handle quite well, and medical experts and nutritionists encourage the consumption of these foods. The problem comes with added sugars in the modern diet, the volume of which has grown rapidly in recent decades. The blame has often been attributed to high fructose corn syrup (HFCS), which manufacturers say is made up of 55% fructose and 45% glucose. In truth, the exact proportions have been revealed in testing to be somewhat variable. For example, this study revealed an average of 59% fructose in HFCS, with some major brands of soda containing 65% fructose.

Still, sucrose (granulated sugar) is half fructose and half glucose. So HFCS supposedly doesn't have a whole lot more fructose than "regular" sugar, gram for gram.

High fructose corn syrup, which is derived from corn starch, has become incredibly inexpensive and abundant, partially due to corn subsidies in the United States. So many argue that the problem is that it has become so cheap that it has crept its way into a great number of the foods we eat every day, such as:

  • Salad dressings
  • Frozen foods and dinners
  • Condiments

Is High Fructose Corn Syrup The Same As Regular Fructose?

Yes, all fructose works the same in the body, whether it comes from corn syrup, cane sugar, beet sugar, strawberries, honey, or tomatoes. Only the amounts are different. For example, a cup of chopped tomatoes has 2.5 grams of fructose, a can of regular (non-diet) soda supplies 23 grams, and a super-size soda has about 62 grams (using the "55% fructose" standard).

Today, almost all packaged foods have sugar added in some form, and that usually always consists of a lot of fructose. Honey has about the same fructose/glucose ratio as high fructose corn syrup. Fruit juice concentrates, sometimes used as "healthy sweeteners," usually have quite a lot of fructose (never mind that the processing of these concentrates strips away most of their nutritional value). Agave syrup is up to 90% fructose. 

Sources

Page, A. Kathleen, MD; Chan, Owen; Arora, Jagriti, MS; et al. Effects of Fructose vs Glucose on Regional Cerebral Blood Flow in Brain Regions Involved With Appetite and Reward Pathways. Journal of the American Medical Association. 2013;309(1):63-70.

American Diabetes Association. "Nutrition Recommendations and Interventions for Diabetes–2006." Diabetes Care 29 (2006): 2140-2157.

Harvard Health Publications. Abundance of fructose not good for the liver, heart. September 2011. 

U.S. Food and Drug Administration. High Fructose Corn Syrup: Questions & Answers

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