Fructose, especially high fructose corn syrup, is a controversial sweetener. According to some experts, fructose fuels obesity and insulin resistance because it’s rapidly absorbed and goes immediately to the liver. Once there, it’s processed differently than glucose and is more readily converted into triglycerides, some of which enter your bloodstream while others are stored as liver fat.
Opponents of high-fructose corn syrup support their argument by the fact that the obesity epidemic started to take off around the time high-fructose corn syrup was introduced. Others argue that fructose is no different than other forms of sugar and doesn’t make a significant contribution to the obesity epidemic. Who’s right? A recent study sheds new light on how sugars, including fructose, behave in your body.
The Tale of Two Sugars: Fructose and Sucrose (Table Sugar)
Sucrose, or table sugar, is made up of equal parts of glucose and fructose. High-fructose corn syrup in many processed foods is typically 55% fructose and 45% glucose. Doesn’t sound like an enormous difference, does it? Despite this, they seem to be handled differently by your body. The problem is the fructose and glucose aren’t bound together as they are in table sugar so they’re rapidly absorbed and quickly make their way to the liver whereas table sugar takes more time to be broken down.
Now there’s a new wrinkle in the fructose-sucrose argument and more evidence that fructose drives insulin resistance. In a new study, researchers at the University of Colorado School of Medicine discovered that mice are able to convert glucose to fructose in their liver and it’s this conversion that seems to drive insulin resistance. Based on this, they believe when we eat table sugar or high-glycemic carbs, a portion of the glucose is converted to fructose. This conversion may explain why obesity and insulin resistance is such a problem in countries that eat lots of foods with added sugar. So high-glycemic foods and table sugar may be a problem because the glucose in these foods is converted to fructose.
Combine the fructose your body potentially makes from glucose with high-fructose corn syrup in processed foods and your liver gets hit with a double dose of fructose. Another condition called non-alcoholic fatty liver is on the rise and research suggests fructose directly contributes to its development.
How Might Fructose Cause Insulin Resistance?
When excessive amounts of fructose make their way to the liver, it disrupts normal glucose metabolism and increases production of fats that circulate in the blood called triglycerides. It also increases the synthesis of fat. This fat ends up being stored by the liver, leading to fatty liver. It’s this disruption of glucose metabolism that triggers insulin resistance. Insulin resistance is one of the most common health problems in countries that eat a processed food diet and it’s a direct contributor to obesity and type 2 diabetes.
What Does This Mean?
If this study holds true in humans, both arguments about high-fructose corn syrup are correct. High-fructose corn syrup contributes to obesity, insulin resistance, and fatty liver because of the way it’s metabolized BUT all sugars, and high-glycemic carbs are bad because they’re broken down to glucose and glucose can be converted to fructose.
Here’s the deal. Sugar in any form is a contributor to obesity. Plus, it’s devoid of nutritional value. Yes, there’s varying amounts of glucose and fructose in fruit, but when you eat a piece of fruit you benefit from the antioxidants and fiber. Plus fiber slows down the absorption of the sugars. Probably the worst offender is sweetened sodas and sports drinks that have up to 16 teaspoons of sugar per serving. Even fruit juice isn’t a good choice because you get natural sugars WITHOUT the fiber.
Fructose doesn’t seem to be as effective at satiating appetite because it doesn’t stimulate leptin production. Leptin is a hormone produced by fat cells that signals your brain you’re full. Without this signal, you tend to keep on eating. Fructose seems to blunt the satiety response.
The Bottom Line?
The safest option? Cut back on all sugars in your diet and avoid processed foods. High-fructose corn syrup is found in most processed and packaged foods that are sweetened. It’s hard to avoid and even a product sweetened with pure cane sugar like foods in some natural food markets, you’re still getting fructose from conversion of glucose to fructose as well as the fructose that’s already part of the sucrose. Once you begin cutting back on sweeteners and sweetened foods consistently and begin eating more whole foods – you’ll gradually lose your taste for sweetness. It may take a few weeks or even a few months but you’ll learn to enjoy the taste of foods in their natural state – without added sweeteners.
Hepatology. 2013 Jun;57(6):2525-31.
EurekAlert. “Researchers Link Obesity and the Body’s Production of Fructose”
Am J Clin Nutr April 2004 vol. 79 no. 4 537-543.