Tuesday, July 21, 2009

Can You Believe that Fructose Causes Obesity?

I have been listening to my wife, daughter and coworkers bemoaning fructose in the diet, and how it is another agribusiness evil. Fructose is the sugar found in corn syrup, which is used to sweeten nearly every processed food. Fructose is the natural product from degrading starches.

I was skeptical about anti-fructose talk, because I thought that fructose was metabolized like other sugars. It seems that actually fructose is subtly different, and the difference can make ME fat.

It all started in July 2005 when Hella Jurgens and 15 coauthors wrote that a fructose based diet made mice 90% fatter than the same calories in regular mouse chow. Furthermore sucrose based soda and diet soda were not a problem.

This is interesting because sugar-based pop or Kool-aid was OK. Fructose-based pop was not.

The graph at right shows the weight of the 39 gram mice, and how they increased during the 65 day study. These were skinny mice, and they all gained weight, even the ones on water or diet soda. Anyway, the ones on fructose-water are the open squares with the highest weight gain.

Jurgens speculates on two reasons for this.

First is that fructose is primarily metabolized to fat unlike sucrose. Fructose is transported to the liver, and phosphorylated. It is converted to adipose fat at a greater rate than glucose, because the metabolism of glucose to fat is inhibited at high levels of energy; this mechanism does not work for fructose, and adipose fat formation is favored. It should be noted that the sucrose in sugar-sweetened foods is quickly converted to glucose, and acts like glucose in the body. The classical biochemistry of fructose is on Wikipedia; Jurgens argues that the regulation of fructose metabolism favors adipose fat formation compared to glucose.

Second, is that fructose does not stimulate insulin production, which directly effects energy level, the central nervous system, the activity of fat cells, and stimulates ghrelin production that decreases appetite.

It turns out that faster fat formation from fructose over glucose was seen as early as 1974 by Aoyama at Nagoya University. So even when I took biochemistry, it was old news that fructose was different than glucose.

Last year, EJ Parks and friends at U of Texas - Dallas showed that the fructose fattened people as well as rats & mice.

Body-builders, who want really lean bodies, are talking about cutting out fruit before competitions. Some think that this is just counter intuitive -- that fruit is too wholesome to be a junk food, and others -- disagree. The argument seems to be about whether a small amount of food would make you fat -- well it might make you a little fat.

I tend to think that starchy fruit like bananas or apples are not really that healthy. Strangely eating Jolly Rancher's might be better!

Although, my wife and daughter were right, I don't think this is an agribusiness conspiracy, though. Instead it is another screw-up of dieticians, like the low-fat, diet fad in the 1990s.

In summary, Kool-Aid made from sugar is healthier than apple juice, which has mostly fructose.