Fructose Stimulates Fat Production

Fructose is a type of sugar found naturally in fruits, and unnaturally in processed foods to which sweeteners such as high fructose corn syrup have been added.

A very small study out of Texas, published in The Journal of Nutrition in June, found that intake of fructose can stimulate lipogenesis (fat production) more than intake of glucose. ¹

Four men and two women were given a beverage containing 85g of either: 100% glucose, 50% each glucose and fructose, or 25% and 75% each glucose and fructose as a morning meal. Blood was analyzed immediately after consumption, and after a standard lunch 4 hours later.

"When fructose was consumed, absolute lipogenesis was 2-fold greater than when it was absent."

That triglyceride production was enhanced both after the morning beverage was consumed and again after lunch, revealing a carry-over effect.

The 85g morning beverage contained one of the following:

• 85g glucose and 0g fructose
  
• 42.5g glucose and 42.5g fructose
  
• 21g glucose and 64g fructose

For comparison (quantities are approximate): ²

• 1 medium peach contains 3g glucose and 2g fructose
  
• 1/2 cup blueberries contains 4g glucose and 4g fructose
  
  
• 1 tablespoon pure corn syrup (100% glucose) contains 0g fructose
  
• 1 tablespoon high fructose corn syrup (45% glucose and 55% fructose) contains about 6g sugar, 2.7g glucose and 3.3g fructose
  
• 1 teaspoon sugar (sucrose, 50% glucose and 50% fructose) contains about 4g sugar, 2.0g glucose and 2.0g fructose ³
  
  
• 1 medium (21 ounce) cola beverage that contains about 58g of sugar, if it was sweetened with high fructose corn syrup, might contain about 26g glucose and 32g fructose.
  
• 1 medium (21 ounce) cola beverage that contains about 58g of sugar, if it was sweetened with sugar, might contain about 29g glucose and 29g fructose.

It is likely not the fructose in fruit, nor even in sugar or high fructose corn syrup alone, that may be problematic. It is the sheer quantity of these isolated sweeteners added to foods that's the issue.

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¹ Dietary Sugars Stimulate Fatty Acid Synthesis In Adults, Journal of Nutrition, 2008

² NutritionData.com is a great site for looking up nutrients in foods. It's the site I used for these figures.

³ The fructose bound in the disaccharide sucrose may not be as readily available for absorption as free fructose in high fructose corn syrup.

Two active discussions about this study:
Does Fructose Make You Fatter? (New York Times, Well Blog)
What's Making Us Fat? Maybe It's All That High-Fructose Corn Syrup (Los Angeles Times)