Fructose is a simple sugar (a monosaccharide, in technical terms) that has been the subject of a great deal of recent nutritional controversy. Alarmist websites, Youtube videos, and even some peer-reviewed research papers have railed against the consumption of fructose, linking it with obesity and the onset of disease. A popular “health guru” has gone as far to call it the “worst of the worst,” and has suggested that fruit intake be severely curtailed (fructose is found in fruit). Are these claims warranted?
To help clear up the confusion, I consulted with nutrition expert James Krieger. I’ve known James for about a decade, and have found him to be one of the most astute fitness pros around (you might remember that I wrote a post overviewing his meta-analysis about Single vs. Multiple Sets). Here he sets the record straight on what is often a misunderstood topic. I’m sure you’ll find his comments of great interest.
BJS: Thanks for agreeing to do this interview, James. Let’s first start off by telling us about your background.
JK: I am the founder of Weightology, LLC, a website dedicated to providing honest, accurate, evidence-based information on weight management. I have a Master’s degree in nutrition from the University of Florida, and a second Master’s degree in Exercise Science from Washington State University. I am the former research director for a corporate weight management program that treated over 400 people per year, with an average weight loss of 40 pounds in 3 months. My research papers have been published in journals such as the American Journal of Clinical Nutrition and the Journal of Applied Physiology. I am also the editor of Journal of Pure Power, an online magazine that delivers scientific information on training and nutrition to athletes and coaches.
BJS: Fructose consumption is a controversial subject these days. How does fructose differ from other simple sugars?
JK: Fructose is much sweeter than other sugars. There are also differences in the way your body metabolizes fructose compared to other sugars. Fructose doesn’t go straight to your bloodstream; instead, it is metabolized by the liver first. The liver can take the fructose, convert it to glucose, and then release that glucose into the blood. It can also take that fructose and store it as glycogen. Finally, it can convert the fructose to fat. It is this conversion to fat that causes a lot of confusion and alarmism.
BJS: There are studies showing that fructose can have a detrimental effect on various markers of health. What’s your take on this?
JK: There certainly are studies showing that fructose can have this detrimental effect. However, these studies have used extremely high doses of fructose. Unfortunately, people have taken this information to the extreme and have concluded that, since high amounts of fructose can be a problem, then any fructose must be a problem. This is simply not the case.
Do we consume too much fructose in our society? Certainly, but we consume too much of everything else too. It is a mistake to try to point the finger at one thing. Anything consumed in excess can be problematic.
BJS: What about the theory that fructose has a greater propensity to be converted into body fat?
JK: This theory unfortunately takes fructose metabolism out of context, and fails to address the bigger picture. People think this because fructose bypasses an important enzyme in the liver, and thus think it is easier to convert the fructose to fat. The problem with this line of thinking is that it fails to address the fact that fructose metabolism changes depending upon the energy state of the body. If you are in an energy deficit, the fructose will not have a greater propensity to be converted to body fat. Rather, it will be directed towards storage as glycogen, or conversion to glucose for energy.
The other problem with this line of thinking is people confuse triglycerides with body fat. If fructose is converted to fat in the liver, it doesn’t mean the fat ends up as body fat. In fact, there is some evidence that fructose is less likely to be converted to body fat. We also have to remember that any fat formed from fructose in the liver can be burned and used for energy. Again, we have to look at the big picture.
BJS: Fruits contain fructose. Should people limit their intake of fruits if they want to lose weight?
JK: As long as you are in an energy deficit, you will lose weight. It doesn’t matter how much fructose you consume. There is no valid scientific reason to limit intake of fruit. Fruit can actually be very beneficial for weight loss because of its fiber content, which makes you feel fuller. It is also low in energy density, and there is a lot of research showing that eating foods that are low in energy density helps promote weight loss.
In the weight management program that I did research for, our clients started the program on high protein shakes sweetened with fructose, and mixed with berries. Our clients were getting a lot of fructose in the diet from the combination of shakes and berries. Yet, they lost tremendous amounts of weight.
BJS: High fructose corn syrup (HFCS) is used in many food products. Is HFCS worse for you than sugar?
JK: There is little difference in the composition of sugar and high fructose corn syrup. Both contain similar amounts of fructose. The only reason manufacturers choose HFCS over regular sugar is because HFCS is cheaper.
When you look at all of the studies that compare sucrose (table sugar) metabolism to HFCS metabolism, they are identical as far as your body is concerned.
BJS: How do you explain the studies showing that obesity rates skyrocketed after the introduction of HFCS?
JK: This research suffers from a fallacy known as post hoc, ergo propter hoc (after this, therefore because of this). Just because event B happens after event A, doesn’t mean event A caused event B. Obesity also skyrocketed after the introduction of microwave ovens and VCR’s, but that doesn’t mean microwave ovens and VCR’s cause obesity!
BJS: What about the fact that HFCS isn’t “natural.” Should this matter?
JK: There is no evidence that products that are “natural” are any healthier or safer than products that are not “natural.” For example, there are many natural substances out there that are poisonous or carcinogenic to the human body. Calamus oil, which was a natural food additive before it was banned in 1968, is a carcinogen.
In fact, I often ask people to define what they mean by “natural” and they struggle to do so. If you think about it, there is really no clear cut way to determine what is natural or artificial. For example, aspartame is actually made up of natural ingredients (aspartic acid, phenylalanine, and methanol). So why would we call aspartame artificial? Also, we call Stevia natural, but that doesn’t make sense because it requires human intervention to extract it from the stevia herb.
BJS: Anything else you’d like to add on the topic?
JK: I would say that people do not need to worry about moderate fructose consumption. Basically, the idea of “everything in moderation” applies to fructose just like anything else. Thanks for the opportunity to interview!
Check out James’ website at: weightology.net
Check out the Journal of Pure Power at: Journal of Pure Power