Fructose: Public Enemy #1?
Stan Reents, PharmD
11/18/2008 09:55 AM
Last Revision: 01/15/2016 08:10 AM
A dietician once said: "There are no bad foods, only bad diets." I always thought that was a good, common-sense perspective.
However, research published during the past 5-10 years suggests that fructose may be one of the worst "nutrients" you can consume. In fact, the Center for Science in the Public Interest (CSPI) feels so strongly about the health risks of fructose that, in July 2005, they petitioned the FDA to require warning labels on sodas.
But how can this be? After all, fructose occurs naturally in honey and many fruits such as bananas, nectarines, and peaches. Apple juice is 65% fructose. Also, many sports drinks contain fructose.
In this review, I will summarize some of the research on fructose and its health effects.
BIOCHEMISTRY OF FRUCTOSE
I don't want to make this review overly scientific, however, there are several biochemistry details that need to be pointed out:
First, simple sugars are grouped as either "monosaccharides" or "disaccharides." Fructose is considered a monosaccharide:
| MONOSACCHARIDES|| DISACCHARIDES|
This is important because fructose is found as "free" fructose (ie., as the monosaccharide), and, it is also a component of sucrose, which we know by the common name "table sugar."
Fructose is the sweetest of all the sugars. Sucrose (ordinary table sugar) is arbitrarily given a sweetness rating of "100." The sweetness rating of fructose is 170. This explains why honey is so sweet and why even small amounts of "high-fructose corn syrup" (HFCS) in a food product can make that item taste sweet. Food manufacturers have been increasing the amount of fructose in corn syrup in ever higher concentrations. Today, when you see "high fructose corn syrup" on a food label, you are consuming corn syrup that has 42-55% fructose (see table below).
Sucrose (table sugar) is a
combination of [glucose] + [fructose] in a 50:50 ratio. So, both HFCS and sucrose contain roughly the same amount of fructose. What's the difference? The distinction here is that the fructose in HFCS is "free" (ie., unbound), whereas the fructose in sugar is bound to glucose. There is currently a debate in the nutrition community as to whether "free" fructose (as found in HFCS) is worse for your health than the fructose that is found in sugar (Bray G, et al. 2004a) (Tan D, et al. 2008). More on this below....From a chemical perspective, fructose truly is unique....even among the 3 monosaccharides listed above: glucose and galactose are one type ("aldoses") whereas fructose is different (a "ketose"). This minor, but significant, chemical distinction may explain why fructose's actions on the body are so unique.
SOURCES OF FRUCTOSE
Some dietary sources of fructose are listed below:
| FOOD SOURCE|| FRUCTOSE|
HFCS in soda pop
table sugar (sucrose)
HFCS in baked goods
In the table above, the fructose that is found in "table sugar" is bound to glucose, whereas the other 4 examples represent free (unbound) fructose. Does this matter? Nutrition researchers at Rutgers University in New Jersey have reported that a single can of carbonated soda pop contains 5 times the concentration of a specific damaging chemical ("methylglyoxal") than is found in the blood stream of the typical diabetic person (Tan D, et al. 2008). They believe these molecules are related to the free fructose found in HFCS.
However, in May 2008, Havel and colleagues showed that free fructose (eg., HFCS) and bound fructose (eg., sucrose) increased triglycerides to the same degree (Stanhope KL, et al. 2008). So, deciding whether free fructose is worse than bound fructose depends on which health complication you choose to look at.
METABOLIC EFFECTS OF FRUCTOSE
The human body responds to fructose differently than other mono- or disaccharides. In fact, it can be said that fructose actually disrupts several metabolic pathways (Havel PJ. 2005):
Increased Lipogenesis (fat synthesis)
Diets that are high in carbohydrates (defined as >55% of energy
intake coming from carbs) tend to increase triglyceride levels in the
blood (Parks EJ. 2001). Note that this action occurs regardless of the type of carbohydrate ingested, but the process of lipogenesis (ie., the synthesis of fat cells) can be as much as 2-fold greater after consuming fructose than after consuming glucose (Krilanovich NJ. 2004) (Parks EJ, et al. 2008) (Stanhope KL, et al. 2008).
Nicholas Krilanovich, writing in the November 2004 issue (p. 1447) of the American Journal of Clinical Nutrition, summarizes the effects of fructose as follows:
"...ingestion of large quantities of fructose has profound metabolic consequences because it bypasses the regulatory step catalyzed by phosphofructokinase. This allows fructose to flood the pathways in the liver, leading to enhanced fatty acid synthesis, increased esterification of fatty acids, and increased VLDL secretion, which may raise serum triacylglycerols and ultimately raise LDL cholesterol concentrations."
Translation?: Fructose stimulates fat synthesis in the liver and worsens the lipid profile in the bloodstream. Both actions are not good for your health.
Impaired Hormonal Response
For some unknown reason, the hormonal response to dietary fructose differs from the response to other simple sugars.
The normal response works like this: When blood glucose goes up, a signal is sent to the pancreas to release insulin. Insulin, in turn, stimulates the release of another hormone known as
leptin. And leptin suppresses a 3rd hormone known as ghrelin. It is thought that this hormonal domino effect is one
ways the sensation of hunger is suppressed in the brain.
But, when different types of simple sugars were studied, it was found that the hormonal response differed: Researchers gave healthy adults an equivalent dose of 3 sugar solutions: (a) 100% glucose, (b) a 50:50 mixture of glucose and fructose, and (c) a 25:75 mixture of glucose and fructose. Insulin output was lower after the glucose:fructose mixtures compared to the 100% glucose solution (Parks EJ, et al. 2008). Fructose did not stimulate insulin output as strongly as glucose did.
Translation?: If fructose does not stimulate the "stop eating" signal as readily as other carbs, then, it's possible that people will consume more calories before they feel full.
Elevated Uric Acid
Starting in late 2005, nephrologists at the University of Florida began reporting that fructose led to elevations in uric acid (Nakagawa T, et al. 2005) (Nakagawa T, et al. 2006). Elevations in uric acid can lead to kidney stones. But, these researchers found that high uric acid levels reduced nitric oxide levels, and this, in turn, contributes to insulin resistance and a serious medical condition known as "metabolic syndrome."
Then, in 2007, the Florida nephrologists reported that fructose -- but not glucose -- accelerated the progression of kidney disease (Gersch MS, et al. 2007). However, up to this point, all of this research was conducted in rats.
In January 2008, researchers from Harvard reported that the incidence of kidney stones in both men and women was related to fructose consumption (Taylor EN, et al. 2008).
Translation?: Fructose has detrimental effects on kidney function, which, in turn, can lead to other health problems.
MEDICAL CONDITIONS RELATED TO FRUCTOSE
So what are the health consequences of consuming fructose on a regular basis?
Fructose and Obesity
Keep in mind, the research discussed above showing that fructose
stimulates fat synthesis is not proof that fructose causes obesity.
Weight gain, ultimately, comes down to consuming more calories than you
If fructose doesn't activate the body's hormonal response in the normal way, isn't it possible that people might eat more than they should? That certainly seems possible. The late Robert Atkins, MD, ("The Atkins Diet") claimed that the rapid increase in obesity we have witnessed in our society is due to the adoption of a carbohydrate-based diet. He advocated a high-protein, low-carbohydrate diet. Unfortunately, there are serious health risks associated with a high-protein diet, too (Fleming RM. 2000), but that's a topic for another review....
So, is weight gain and obesity due to eating too many carbs in general, or, is it due to the specific types of carbohydrates in the diet? Andy Briscoe, president of the Sugar Association in
Washington, DC, states: "Over the last 30 years, the per capita
consumption of sugar — sucrose — has gone down from 72 pounds per
person to 45 pounds per person a year. If sugar intake has gone down,
then it's not as a significant contributing factor to the obesity issue
as some people have made it out to be."
The statement from Briscoe above needs to be kept in perspective. Some researchers point the finger at high-fructose corn syrup (HFCS) as one of the
main causes of the obesity epidemic in the US (Bray GA, et al. 2004b). Over the past 15-20 years, a large percent of the sugar (sucrose) used as a sweetener in food products has been replaced with high-fructose corn syrup (HFCS).
Most brands of soda-pop are sweetened with HFCS. Consumption of soft drinks, though it has leveled-off and even declined recently, is still in the range of 50 gallons per person per year. Yet, even if consumers switch to fruit drinks, often the sweetener in these beverages is also HFCS. Some brands of fruit-flavored iced tea are also sweetened with HFCS!
When the incidence of obesity and the consumption of HFCS in the US are plotted together on a graph, a very troubling pattern emerges. The use of HFCS containing 42% fructose began in 1970; the use of HFCS containing 55% fructose began around 1980. Between 1970 and 2000 there has been a gradual decrease in the use of HFCS-42 and a gradual increase in the consumption of HFCS-55. Concomitantly, there is a noticeable increase in the incidence of obesity in the US starting in the early 1980s (Bray GA, et al. 2004-b).The problem, I feel, is that so many food products contain HFCS. Even if you don't drink soda pop, you are still ingesting HFCS in small amounts from a variety of foods, perhaps every single day. Look closely at food labels: you will see HFCS listed in tomato sauces, chocolate milk, and even multi-grain breads.
Considering that fructose can (a) suppress the signal in the brain to stop eating, and (b) induce fat synthesis, I believe people struggling to lose weight should carefully evaluate the foods they are eating and look not only for the total calorie count, but, also, if it contains HFCS.
Fructose and Metabolic Syndrome
Fructose increases triglyceride levels (Havel PJ. 2005). And there is evidence that this process is worse in people with insulin resistance (Abraha A, et al. 1998). Insulin resistance means that the actions of insulin are less effective, and this occurs in people who are obese or who have a condition known as "metabolic syndrome."
Currently, 27% of adults in the US have metabolic syndrome. These people should be especially diligent about reducing their consumption of foods sweetened with HFCS and/or sugar, and foods naturally high in fructose such as apple juice.
The "Nutrition Facts" panel on packaged foods in the US provides some very helpful information. But, it doesn't clarify how much fructose a specific product contains.
In the top half of the Nutrition Facts panel (as seen in the image to the right), "Total Carbohydrates" are listed. However, this is the total amount of all carbohydrates; i.e., this number (in grams) does not allow you to calculate the amount of a specific carbohydrate. There is also a specific amount listed for "Sugars" (in this case, "8 g"), however, again, this represents all types of sugars in the food item.
At the bottom of the panel (not shown here), there is a section called "Ingredients." Here is where HFCS would be listed, however specific amounts are not provided in this section of the label.
Thus, it is not possible to calculate the exact amount of HFCS in a specific food product from the information that currently appears on food labels.
Here is an example where this would be helpful for consumers: "Maple" syrup and
"pancake" syrup are not the same. Maple syrup is 90-95% sucrose,
whereas imitation maple syrup is sweetened with HFCS. (In that case,
in the US, manufacturers are prohibited from calling it maple syrup,
and use names such as "pancake" syrup.) Most consumers probably assume that "maple" syrup and "pancake" syrup are similar. Knowing the amount of HFCS in each would help differentiate them.
Q: Sports drinks such as Gatorade® and Powerade® contain fructose. Should I stop drinking them?
ANSWER: It is my opinion that not exercising regularly is a LOT worse than consuming the relatively small amounts of fructose from sports drinks.
Consider this research:
When laboratory rats were fed a high-fructose diet and not allowed to
run, in as little as 2 weeks their blood pressure increased and
metabolic changes were seen. However, in rats that were allowed to
run, the effects of the high-fructose diet were minimized (Reaven GM,
et al. 1988).
Keep in mind that the amount of fructose from sports drinks is a lot less than from soda-pop or apple juice. Also, note that the use of simple sugars (such as glucose and fructose) in combination has been found to be the optimum formula for fueling your body during exercise. "Simple" carbohydrates are absorbed more readily from the GI tract than complex carbs, and, using several simple carbs together (in a sports drink) also allows for more efficient absorption as compared to a solution containing only a single carbohydrate.
So, even if you exercise regularly, yes it is smart to minimize the amount of HFCS-containing products you consume. But, until they come up with something better, don't worry about sports drinks that contain "glucose-fructose syrup"....just get out there and exercise 5-7 days per week!
The late Robert Atkins, MD, woke everyone up to the problems of a high-carbohydrate diet. However, it is important to make a distinction between "good" carbs and "bad" carbs.
Fructose, it seems, is the worst carbohydrate of all. It causes very unique and puzzling metabolic effects, and these actions, in turn, contribute to obesity, lipid disorders, and metabolic syndrome.
Consumers should be judicious about reading food labels, and avoid products containing high-fructose corn syrup. In addition, it would also be worthwhile to keep a nutrition resource handy so that they can look up nutritional information on foods (eg., produce) that don't come with nutrition labels.
FOR MORE INFORMATION
The best web site for information on glycemic index and glycemic load is www.GlycemicIndex.com,
maintained by the University of Sydney. Unfortunately, the glycemic
index value for most manufactured food products has not yet been determined.
Readers may also be interested in the following related Articles: Although it is intended to be an academic text, "Perspectives In Nutrition"
(by Wardlaw, Hampl, and DiSilvestro) is a nutrition book that most
consumers could use. The information is written in easy to understand
language, and, the multitude of colorful diagrams, tables, and pictures
help to explain the concepts. The Appendix alone is 203 pages! Read our review.
EXPERT HEALTH and FITNESS COACHING
Stan Reents, PharmD, is available to speak on this and many other exercise-related topics. (Here is a downloadable recording of one of his Health Talks.) He also provides a one-on-one Health Coaching Service. Contact him through the Contact Us page.
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Fleming RM. The effect of high-protein diets on coronary blood flow. Angiology 2000;51:817-826. Abstract
Gersch MS, Mu W, Cirillo P, et al. Fructose, but not dextrose, accelerates the progression of chronic kidney disease. Am J Physiol Renal Physiol 2007; 293:F1256-F1261. Abstract
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Parks EJ, Skokan LE, Timlin MT, et al. Dietary sugars stimulate fatty acid synthesis in adults. J Nutr 2008;138:1039-1046. Abstract
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Stanhope KL, Griffen SC, Bair BR, et al. Twenty-four endocrine and metabolic profiles following consumption of high-fructose corn syrup-, sucrose-, fructose-, and glucose-sweetened beverages with meals. Am J Clin Nutr 2008;87:1194-1203. Abstract
Swarbrick MM, Stanhope KL, Elliott SS, et al. Consumption of fructose-sweetened beverages for 10 weeks increases postprandial triacylglycerol and apolipoprotein-B concentrations in overweight and obese women. Br J Nutr 2008;100:947-952. Abstract
Tan D, Wang Y, Lo CY, et al. Methylglyoxal: its presence and potential scavengers. Asia Pac J Clin Nutr 2008;17 suppl.1:261-264. Abstract
Taylor EN, Curhan GC. Fructose consumption and the risk of kidney stones. Kidney Int 2008;73:207-212. Abstract
ABOUT THE AUTHOR
Stan Reents, PharmD, is a former healthcare professional. He is a member of the American College of Sports Medicine (ACSM) and holds current certifications from ACSM (Health & Fitness Specialist), ACE (Health Coach) and has been certified as a tennis coach by USTA. He is the author of Sport and Exercise Pharmacology (published by Human Kinetics) and has written for Runner's World magazine, Training and Conditioning, Club Solutions, and other fitness publications.
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