Chemistry Project: "When Sugar Isn't So Sweet"

A Cheaper Sweetener than Fructose?

2005-11-09T04:02:00.000-05:00

One of the main attractions of high fructose corn syrup is that it is significantly cheaper than sucrose. As a liquid, it is easier and therefore cheaper to handle than powdered sucrose, for example, and it is manufactured from very cheap and "natural" cornstarch. In contrast, other sucrose alternatives such as saccharin require multiple reactions and begin as toluene, which is not a palatable material.

However, there exist two related, entirely "natural" glycosides stevioside and rebaudioside that are extracted from the South American herb Stevia rebaudiana that are each some 250 to 300 times sweeter than sucrose. Stevia has been cultivated in Paraguay and in Brazil for centuries as a sweetener, and Stevia-derived sweeteners have been used in Japan since the 1970s, when the artificial sweeteners cyclamate and saccharin were being investigated as carcinogens. Although both are now considered reasonably safe, the use of Stevia extracts and their derivatives as sweeteners continued and at one point offered serious competition to what would become NutraSweet, the maker of aspartame.

Unfortunately, although Stevia is now common in much of Asia, it is illegal in the United States as a food additive. In 1991 the FDA concluded that there was insufficient toxicological data to prove its safety, initially restricting its import for all purposes before relaxing its stand in 1995 to the current ruling. Stevia sweeteners sold in America must be labeled as food supplements and no advertisements may be made of their use in conventional foods. This restriction is enforced with some vigor, as this FDA warning letter demonstrates. There are conspiracy theories which conclude that the FDA ruling resulted from NutraSweet payoffs to officials, some of whom received high-paying jobs as NutraSweet employees afterwards.

"Fructose Bad"

2005-11-09T03:16:00.000-05:00

It is usually the case that any controversial scientific topic inevitably spawns a number of false claims. Some are deliberate fabrications, some are honest mistakes, and some simply defy classification. Here are a few of the most notable ones, returned by a Google search for the exact phrase "fructose bad."

Laura Lee Transcript: Laura Lee hosts a talk show that invites researchers from an "eclectic range of fields." Of the six examples of such fields, two are not fields and the other four are consciousness studies, wisdom traditions, ancient mysteries, and the unexplained. One of these researchers is Dr. Nancy Appleton of a previous article, who returns to speak of sugar as though it were heroin, to claim that sugar causes autoimmune reactions, and "logically" conclude that if sugar (or, more accurately, byproducts of anaerobic fructose metabolism) can dissolve enamel, then it must also wreak havoc upon the softer tissues of the body. There are times when even Laura Lee seems to be mocking her guest, such as when she exclaims, "And the good news is, you can do something about it," and "And you can't trust what your government says!"

The South Beach Diet Online: This is an advertisement for a variant of the high-protein, low-carbohydrate diet such as that prescribed by Dr. Atkins. There appears to be no relationship to fructose, but nonetheless it is listed, along with 635 equally unrelated words including the phrases "hysterectomy tummy tuck" and "inhibitor kinase tyrosine" in a search-engine trap at the top of the page. The link goes to Google's cache of the page because the actual page has disappeared.

Honey = Fructose = Bad Post-Workout?: Hope springs eternal indeed. Today's bodybuilders, if the visitors of this forum are any indication, are surprisingly scientific, once they realize that levulose is only another name for fructose. MS implies that fructose goes preferentially to the liver, which is correct according to these two sites: wikipedia and biomedical hypertexts. According to the first, fructose is transported first by GLUT-5 and then GLUT-2, and according to the second GLUT-5 is located primarily in the small intestine and used to absorb dietary fructose, and GLUT-2 is located in the liver, among other things, and acts in times of high concentration, such as immediately after a meal or a "postworkout carbs."

Don't Drink So Much Soda

2005-11-09T02:03:00.000-05:00

According to this article from the Pak Tribune website, an American teenager’s main source of calories comes from sugary soft drinks. Teenagers will consume fifteen teaspoons of sugar daily because of soft drinks. Medical researchers say this is unhealthy because these calories are empty calories which means that they have no nutritional value and only help people put on more weight. This also means that sugary soft drinks may be one of the major factors behind the climbing obesity rates in America and may also be helping cause diabetes. This amount of sugar definitely leads to tooth decay. Dr. Barry Ponkin, an obesity researcher at the University of North Caroline at Chapel Hill, and his colleagues conducted several studies, one of them the effect of soda on school children. Their study found “that each additional daily serving of any sugar-sweetened beverage, including fruit drinks, increased the likelihood of obesity in a child by 60 percent.” So kids need to be informed to cut back on their intake of soft drinks and sugary drinks.

Even though soft drinks and obesity rates climbing cannot be directly related, it probably does cause children to become obese. In the 1970s, children choose milk over sugary drinks almost 4 to 1. In the 1990s it was around even, and now sugary drinks have likely surpassed milk as the preferred beverage by children. Kids do not even realize the amount of soft drinks they are drinking because liquids do not fill up the body as easily as food, and excess amounts of sugar are detrimental to health.

Just how sweet is too sweet?

2005-11-08T21:03:00.000-05:00

The World Health Organization has even acknowledged the problem of the dietary prevalence of such added sweeteners as HFCS. According to this Washington Post article, in 2003 they decreed that one should not consume more than 10% of one's daily caloric intake in the form of these sugar additives. This recommendation is much stricter than those posed by American groups. According to the Houston Chronicle, the FDA suggests a limit of eight teaspoons of added sugars per day. The article lists the high added sugar contents of several beverage varieties (all of which are labeled as containing 2.5 servings despite the fact that most people simply drink the entire bottle) including Arizona Raspberry Iced Tea, Pepsi and Hawaiian Punch. Although it is clear that the exact amounts of sugar to consume will always be squabbled over, one should be sure to reasonably restrict one’s added sugar intake.

A CEO's contrary opinion

2005-11-08T12:46:00.000-05:00

The American Sugar Association recently met in Sun Valley, Idaho. Here Andrew Briscoe, CEO of the association, stated in his address to the convention that sugar was not to blame for the nationwide obesity epidemic, but rather, the poor exercise habits and high caloric intake of Americans. The following is an excerpt from his remarks:

"Every major, comprehensive review of the total body of scientific literature continues to exonerate sugars intake as the causative factor in any lifestyle disease, including obesity. We believe in calories in and calories out. Sugar is not a part of obesity issues."

As previously mentioned in this weblog, there exists substantial evidence indicating a link between the addition of HFCS to the American diet and the rapid rise in obesity rates. Perhaps Briscoe is trying to fight the decline in sugar consumption that has occurred in the last thirty years as the country has become more concerned about issues of health. Hopefully the CEO can well support his remarks. If not, he can expect quite a violent backlash from informed consumers.

Honey Could Make Sweets Healthier

2005-11-04T01:41:00.000-05:00

According to this article from Science Daily, scientists and researchers from the University of Illinois at Urbana-Champaign believe that honey may be a healthy alternative to high fructose corn syrup (HFCS) in food products. They believe this because honey has more antioxidants than HFCS, and some studies show that honey may have the same amount of antioxidants as some common fruits.

The purpose of antioxidants is to stop free radicals from damaging important cellular components like DNA by neutralizing them. Free radicals are atoms or molecules that contain an odd number of electrons, and they form when oxygen combines with certain molecules. Since honey contains more antioxidants than HFCS, it will help prevent cancer, heart disease, and varies other diseases better than HFCS. Also darker honey like buckwheat honey is believed to have more antioxidants than lighter colored honey. Replacing HFCS with honey in food products could also help the obesity epidemic in America because it would take a lot of unnecessary fructose out of people’s diets.

And Now the Other Side's Story

2005-11-03T20:38:00.000-05:00

Fructose, especially in the form of high fructose corn syrup (HFCS), has been so vilified recently that the Corn Refiners' Association (CRA) felt that it needed to publish its own website on the benefits of HFCS. Like Dr. Appleton's article, it is undoubtedly biased, but its numerous citations from sources such as the Journal of the American Dietetic Association prove that this bias is at least better controlled than in Dr. Appleton's article. The CRA website explains how consumers benefit from the use of HFCS, and also presents counterarguments to claims made by HFCS's detractors.

In addition to sweetening foods, HFCS is used to improve freshness, texture, browning, stability, viscosity, and fermentation. It inhibits microbial growth, and prevents freezer burn. Texture is improved because high fructose corn syrup maintains moistness, enabling goods such as cookies to remain soft and chewy longer than with other sweeteners; in general, products containing HFCS remain stable despite unfavorable temperatures or acidity. HFCS also improves the viscosity of liquids that would otherwise be difficult to pour, such as ketchup and "frozen" concentrates, which remain liquid in the freezer due to HFCS's low freezing point. Finally, baked goods containing HFCS brown better and (for reasons that the CRA says are often overlooked) taste sweeter. High fructose corn syrup is about half fructose and half glucose, but because yeast prefer glucose to fructose most of the sugar that remain after baking is fructose, which makes the finished product sweeter.

The CRA's website also responds to some of the criticism HFCS has received. It refutes, for example, the alleged link between HFCS and obesity by pointing out that although HFCS is purified to 90% fructose, the version that reaches consumers has been diluted with unrefined corn syrup to produce a fructose-to-glucose ratio comparable to that of the table sugar HFCS replaces—about 1:1. For this reason, although HFCS consumption has indeed risen, the consumption of the basic monosaccharides into which all sugars are broken before absorption has remained about the same. It supports this defense of HFCS with an article on a Virginia Tech University study that connected the rising American obesity rate not with any specific food but with a sedentary lifestyle and demographic factors.

One of the very few failings of this website, which otherwise provides a well-written and very much needed reply to an otherwise lopsided discussion of high fructose corn syrup, is its statement that HFCS is a "natural" sweetener. The "natural" dialogue is a classic example of what a programmer would call "garbage in, garbage out," but the CRA manages to keep its response garbage-free until the very last sentence. It reads, "By contrast, products that […] are chemically modified are not considered natural." (link)

Corn refiners apparently operate under a different understanding of chemical modification. To produce HFCS, starch, a very large polymer of glucose, is first cleaved into short glucose oligomers and then into individual glucose molecules by the enzymes alpha-amylase and glucoamylase, respectively. The glucose solution is then passed over columns of glucose-isomerase, which converts about half of the glucose into fructose. Here are two chemical modifications already: the cleavage of starch into individual glucoses, and the conversion of glucose into fructose. Furthermore, tracing the ingredients back into the corn plant, the starch was assembled from glucose monomers, which were in turn pieced together one carbon at a time from carbon dioxide within the plant's chloroplasts. All of these are chemical modifications.

Well, why fructose?

2005-11-03T19:19:00.000-05:00

With all of the problems with fructose that have been discovered in recent years, one finds it difficult to imagine how fructose could have ever seemed a wise choice for a sweetener in the first place. From agonizing sufferers of hereditary fructose intolerance, raising obesity levels and increasing triglyceride counts, it seems that high fructose corn syrup is a pesky substance.

It is important to consider the reasons behind the choice of high fructose corn syrup, and they are undeniably well founded. In a Washington Post article, “Sweet but Not So Innocent,” the logic behind using high fructose corn syrup is discussed. The piece quotes George A. Bray, former director of Louisiana State University's Pennington Biomedical Research Center, as saying “[fructose] tastes sweeter than refined sugar,” making it usable in smaller amounts. Additionally, it was not known that fructose was metabolized differently from glucose. Also important were the economic reasons for the switch:

“In the 1980s, manufacturing methods improved, prompting a boost in production of high-fructose corn syrup and a drop in price to just pennies below that of refined sugar. ‘While that may not sound like much to the average consumer, when you consider how many pounds [the soft drink industry buys], it was millions of dollars if not hundreds of millions of dollars in savings,’ says Drew Davis, NSDA's vice president for federal affairs.”

One must always keep in mind that hindsight is always 20/20 and that the decisions of the past were not made without reasonable justification.

Scare Tactics

2005-10-28T10:26:00.000-04:00

Fructose definitely has a number of disadvantages compared to sucrose, but Dr. Nancy Appleton takes it to an extreme. She lists sixteen reasons to avoid fructose. Some of them are questionable, such as the statement that some “advanced Maillard products,” which fructose forms much faster than sucrose, cause mutation or cancer, and that the Maillard reactions play a role in aging and sometimes diabetes. Although this may seem extremely harmful, the information that Dr. Appleton gives about Maillard products’ effects could also fit water. It is the solvent in which all the chemical reactions of the human body takes place, so one might also state that the presence of water is associated with and required for cancer, mutation, aging, and diabetes. Until Dr. Appleton expands upon precisely what role fructose-derived Maillard products play in these disorders, her claims should not be seriously considered. Dr. Appleton’s other claims are no better. Another one states that we should avoid fructose because it contains no enzymes, vitamins, or minerals. Again, this is absolutely true, but because fructose is pure sugar. For that reason, if a sample of fructose were to have enzymes, vitamins, or minerals, it would be considered contaminated. Dr. Appleton does not explain that this is entirely benign, possibly because she publishes her article on a commercial website.

Fructose and Triglycerides

2005-10-28T09:31:00.000-04:00

Fructose and similar sugars have been shown to increase triglyceride levels in the blood. This can lead to not only obesity but also clotting and other complications. A triglyceride is the basic storage form of fat, consisting of three fatty acid tails and a glycerol head. Hypertriglyceridemia is the technical term for an excess of triglycerides in the blood plasma, a condition that can result in heart disease.

The International Food Information Council published an FAQ in which the question of fructose’s effect on triglyceride levels was addressed. Essentially, the consumption of fructose (as with many other sugars) greatly increases the presence of triglycerides in the plasma.

However, a University of Minnesota study was performed in which certain subjects were administered high-fructose diets, others high-glucose diets. The results were as follows:

The responses to the study diets differed by sex. In men, the fructose diet produced significantly higher fasting, postprandial, and daylong plasma triacylglycerol concentrations than did the glucose diet. The daylong plasma triacylglycerol concentration after 6 wk of the fructose diet was 32% greater in men than the corresponding concentration during the glucose diet. The fructose diet had no significant effect on fasting or postprandial plasma triacylglycerol concentrations in women. The fructose diet also had no persistent effect on fasting plasma cholesterol, HDL cholesterol, or LDL cholesterol in either men or women.

It is important to remember that fructose itself might not be a particularly evil purveyor of triglycerides – in general, one should avoid the overconsumption of sugar. However, it remains apparent that fructose accounts for a disproportionate percentage of the American diet and thus no doubt accounts for much of Americans' inflated triglyceride levels.

Kids Need to Eat Healthier

2005-10-28T02:44:00.000-04:00

According to the National Center for Health Statistics, around 15 percent of kids from the ages of 6 to 11 and 15 percent of teenagers from the ages 12 to 19 in the U.S. are overweight or obese. These statistics were from 1999 to 2002, and these percentages have increased since that time. Kids have to start eating healthier or else kids will start getting diseases like diabetes and heart disease at a young age greatly shortening their life span.

Kids developing healthy eating habits at a young age starts at their home. Families should eat some of their meals together everyday because kids that live in families that eat together are more likely to eat healthier foods like fruits and vegetables rather than snack on unhealthy foods. Also parents should buy healthy foods so that their family can eat well when they eat together. Parents should get their kids into the routine of eating five servings of fruits or vegetables daily. Some good ideas for snacks would be yogurt and whole grain crackers, and good sources of protein are lean meats, eggs, and nuts. For fiber children should eat whole-grain bread and cereal. Fast food and fatty foods should be limited, and for beverages milk and water are healthy and good for the body while soft drinks should be avoided. This Baylor College of Medicine Children’s Nutrition Center website and this website from netrition.com gives the amounts a child should have of fat, protein, calories, cholesterol, vitamins, and other nutrients daily.

Another interesting fact for parents is that they should never force their kids to eat more than they want. Many parents train their kids at a young age to eat all the food on their plate. This can actually be harmful because as kids get older the serving sizes of food usually get bigger than what is necessary for someone their age. Also fatty and sugary foods should not be completely banned becuase once they can get them, they will binge on them.

Type 2 Diabetes

2005-10-21T11:53:00.000-04:00

More than 18 million people in America, or about 6.3 percent of the population, have diabetes with 90 to 95 percent of these people having type 2 Diabetes. Type 2 diabetes is a disease that causes a person’s blood to have high glucose levels or hyperglycemia. Two main reasons for high blood glucose are insulin resistance and the pancreas’s inability to secrete the necessary amount of insulin. Insulin is a hormone secreted by the beta cells of the pancreas to help move glucose from the blood into body cells for energy and to decrease the amount of glucose produced by the liver. Insulin resistance causes the cells ignore the insulin and can lead to either the liver producing too much glucose or the body does not take glucose from the blood effectively. Too much glucose in the blood can damage a person’s eyes, kidneys, nerves, or heart.

Symptoms of diabetes include blurry vision, unusual thirst, a need to urinate frequently, unexplainable weight loss, and exhaustion. Treatments of Type 2 diabetes include taking oral medicines that decrease insulin resistance and increase the amount of insulin the pancreas produces. The person can also just take insulin. Exercising and having a healthy diet are also important. Exercising will help weight loss, which may reverse insulin resistance and lower blood glucose if a person is overweight. More information about Type 2 diabetes can be found at this diabetes self-management site and at the American Diabetes Association site.

Even though eating a healthy diet would prevent or help people with diabetes, people in America have ignored this. Now more youth in America are being diagnosed with diabetes because of obesity and lack of exercise. According to this article at the Yale Medical Group site, "Every 25 seconds someone in the United States is diagnosed with diabetes," says Vice Admiral Richard H. Carmona, the US Surgeon General. It's the sixth-leading cause of death in the United States, costing thousands of lives and billions of dollars every year.”

Fructose and Hormone Stimulation

2005-10-21T11:35:00.000-04:00

"[…] unlike glucose, fructose does not stimulate insulin secretion or enhance leptin production. Because insulin and leptin act as key afferent signals in the regulation of food intake and body weight, this suggests that dietary fructose may contribute to increased energy intake and weight gain."

In their paper investigating the contribution of high fructose corn syrup to recent increase in American obesity, Bray et al wrote that fructose is a possible promoter of obesity because it is processed for energy but does not decrease appetite afterwards as glucose does. Glucose and fructose are taken up from the blood by different receptors. Glucose enters cells by the receptor GLUT4 that is present in the brain, whereas fructose enters by the receptor GLUT5 that is absent in brain tissue. Because fructose cannot enter the brain, it does not provide the feeling of fullness that glucose does, even though each gram of it provides a comparable number of calories.

This could be compensated for by the use of intermediate hormones that can enter the brain, such as insulin and leptin. These have been proven to decrease food intake. Peter Havel in his paper cites an experiment in which insulin was infused into the cerebral ventricles of baboons. Although the baboons were allowed to eat at will, they fasted voluntarily for twenty days, showing that insulin can inhibit food intake even, as in the case of the baboons, in the face of starvation. In diabetic rats, a similar intraventricular insulin infusion reduced their excessive feeding by 50%. Leptin's role has illustrated by the obesity of completely leptin deficient humans, whose inability to produce leptin leads to severe overeating and obesity. Small doses of leptin cause weight loss entirely due to the reduction of body fat, although similar doses of leptin has more moderate effects in non-leptin deficient people.

Unfortunately, fructose does not stimulate production of these hormones, as shown by the experiments reviewed in Peter Havel's paper. For example, rats, like humans, that are allowed free access to food eat if their blood glucose concentration drops briefly; intravenously administered glucose can stop this, but not intravenously administered fructose. More directly, intravenously administered fructose does not increase insulin secretion or circulating leptin concentration in rhesus monkeys, but glucose does. For humans, subjects who drank a fructose-sweetened beverage with each meal had insulin and leptin levels lower that those of subjects who drank a glucose-sweetened beverage of equal caloric value. Havel concludes,"Because insulin and leptin function as long-term regulators of energy balance, consumption of diets with a high percentage of energy derived from fructose could lead to increased energy intake and obesity."

High Fructose Corn Syrup and Obesity

2005-10-21T11:16:00.000-04:00

In addition to being problematic for sufferers of hereditary fructose intolerance, high fructose corn syrup (HFCS) is widely believed to be a significant cause of the current American obesity epidemic. This 2004 study from the American Journal of Clinical Nutrition explores this problem. Through the analysis of 33 years’ worth of Department of Agriculture food consumption data, the authors of the study found that there exists a relationship between the increases in HFCS consumption and American obesity. HFCS is the only caloric sweetener used in the US, and its prevalence increased 1000% from 1970 to 1990. Americans consume an average of 136 Calories from HFCS daily, with the top 20% of consumers up to 316 Calories.
The study postulates that the obesity link is due to the specifics of the digestion of fructose:

The digestion, absorption, and metabolism of fructose differ from those of glucose. Hepatic metabolism of fructose favors de novo lipogenesis. In addition, unlike glucose, fructose does not stimulate insulin secretion or enhance leptin production. Because insulin and leptin act as key afferent signals in the regulation of food intake and body weight, this suggests that dietary fructose may contribute to increased energy intake and weight gain. Furthermore, calorically sweetened beverages may enhance caloric overconsumption.

Clearly, HFCS is not only a problem for those afflicted with hereditary fructose intolerance but perhaps for the population as a whole.

A Liver Biopsy

2005-10-14T00:20:00.000-04:00

Hereditary Fructose Intolerance is a hard disorder to diagnosis, but one way to check for it is a liver biopsy. A liver biopsy is when a doctor removes some liver tissue to see if it is damaged or diseased. In the case of HFI, a liver biopsy would be used to check the liver for a lack of the aldolase B enzyme. The operation itself has minor risk, but if complications do occur they could be fatal.

Before the operation, a doctor has to take blood samples to make sure the patient’s blood clots properly. If the patient has blood clotting abnormalities or fluid in the abdomen, an alternative method called transvenous biopsy will have to be used. This will be discussed later on. Once the blood tests are completed, the operation can be carried out. A person getting the operation done should not eat or drink anything eight hours before the operation.

At the start of the operation, the patient will lie on a hospital bed on their back and put their right arm above their head. The doctor then makes an outline of the liver and he numbs the area in which the operation will take place using a local anesthetic. After the patient's side has been numbed, the doctor makes a small opening in the right side of the patient and inserts a biopsy needle. There are three types of biopsy needles, and they are suction needles, cutting needles, and spring-loaded needles. The doctor uses one of these needles to retrieve a sample of liver tissue, and it is important that the patient lies still during this time or else the doctor might cut the lungs or the gallbladder. The whole operation usually takes around twenty minutes. For more detailed information on the procedure of a liver biopsy, visit the National Digestive Diseases Information Clearinghouse’s webpage or e-Medicine’s article on liver biopsy by Kenneth D Flora, MD.

As mentioned early an alternative method of doing a biopsy is called a transvenous biopsy. Since the person has blood-clotting problems, a tube called a catheter is put into a vein in the neck and lowered down to the liver. The doctor puts a biopsy needle through the catheter and into the liver to remove the liver tissue. After either type of operation, the patient must remain in bed for eight to twelve hours and avoid strenuous activity.

The Lesser of Two Evils

2005-10-13T23:33:00.000-04:00

You've probably heard that brushing for two minutes after each meal with a good brush and fluoridated toothpaste, or some equivalent of this process, is the only way to prevent cavities. This myth is reinforced by the television commercials for products that make this easier, quicker, or more thorough, all the while backhandedly implying that it really is necessary. As anybody with DFI or HFI can tell you, this is absolutely wrong: there is indeed an alternative.

An integral part of tooth enamel is calcium phosphate, which does not dissolve at the pH usually found inside your mouth. However, there is also in your mouth a bacterium Streptococcus mutans. Because it lacks the mitochondria needed to process pyruvate and NADH, it uses lactic acid fermentation (more information on that at a Biology Century wepage and a diagram here) to recover the NAD+, producing as a waste product the eponymous lactic acid. The lactic acid lowers the pH enough that the calcium phosphate dissolves, starting cavities. (The link between fructose and cavities is more thoroughly explained by the Virtual Chembook webpage.) To quote the Virtual Chembook, "[…] only the S. mutans is able to cause cavities. […] The lactic acid creates extra acidity to decrease the pH to the extent of dissolving the calcium phosphate in the tooth enamel leading to the start of a cavity."

Fortunately, S. mutans feeds only on fructose. So if you want to be sure that you don't get cavities, you need only avoid all fructose. The University of Iowa has compiled a brief list of these products here: <http://www.uihc.uiowa.edu/FRUCTOSE/DietBasics.htm>. It includes table sugar; honey; most fruits, fruit and vegetable juices and "juice drinks;" many cookies, breads, cakes, and cereals; beer, chocolate milk, and wine; all nuts other than pistachios; yogurt; vinegar and soy sauce; ketchup and other tomato-containing products such as pizza, spaghetti sauce, salsa…maybe we are better off brushing.

High Fructose Corn Syrup

2005-10-13T21:33:00.000-04:00

Besides, of course, avoiding the consumption of fruit, high fructose corn syrup (HFCS) is probably the most common problem sufferers of hereditary fructose intolerance will encounter. One might imagine that with a name like “high fructose corn syrup” it would be a pretty easy substance to eliminate from one’s diet. However, HFCS is included in many processed foods. The Weston A. Price Foundation maintains a webpage that offers a great description of the production of high fructose corn syrup and its prevalence in the American food supply:

The process for making the sweetener high fructose corn syrup (HFCS) out of corn was developed in the 1970s. Use of HFCS grew rapidly, from less than three million short tons in 1980 to almost 8 million short tons in 1995. During the late 1990s, use of sugar actually declined as it was eclipsed by HFCS. Today Americans consume more HFCS than sugar.

High fructose corn syrup typically contains 55 percent fructose and is found in many unexpected places. HFCSfacts.com lists many uses of high fructose corn syrup, which include everything from breakfast cereals to hotdogs to mustard. Clearly, those afflicted with HFI must pay close attention to their diets.

Dietary Fructose Intolerance

2005-10-07T00:35:00.000-04:00

It is important to differentiate between hereditary fructose intolerance, the primary subject of "When Sugar Isn't So Sweet," and dietary fructose intolerance, or fructose malabsorption. Hereditary fructose intolerance (HFI), as the name suggests, is an inborn trait that remains with a person for life. People afflicted with HFI lack a specific enzyme that digests fructose, called aldolase B or fructose-1-phosphate aldolase. This leads to fructose buildup in the liver, kidneys and intestines, causing such further complications as hypoglycemia after fructose consumption.
However, individuals suffering from dietary fructose intolerance (DFI) experience less severe symptoms including diarrhea and intestinal discomfort. Despite the obvious differences between the disorders, the treatments are the same – staying clear of fructose. An excellent source for more information on DFI is The University of Iowa’s DFI page.

Sugar Metabolism: Glycolysis

2005-10-07T00:30:00.000-04:00

The principal monosaccharide in humans is glucose, and the principal monosaccharide-metabolizing pathway-glycolysis-deals with glucose. We deal with other sugars, such as galactose, and fructose, and various oligomers and polymers of these three, by converting them into forms that can be processed using the pathways and enzymes in use for glucose. So to understand fructose metabolism one must find understand glucose metabolism.

Glucose monosaccharide is, suprisingly, quite uncommon in our diets; we get it in oligosaccharides and polysaccharides such as starch, glycogen, sucrose, and lactose and break these down with enzymes in the mouth and the small intestine and absorbed to produce the three major monosaccharides in body cells: glucose, fructose, and galactose (this explanation omits many intermediate steps that are well explained here: http://www.med.unibs.it/~marchesi/glycolys.html#intro).

Glucose is passed through glycolysis, then the Krebs cycle, and then finally electron transport and oxidative phosphorylation to produce the energy unit of the cell, ATP. This article is not meant to teach these pathways, so only summaries and links to the more detailed pages are provided.

Glucose is converted to two pyruvate, two ATP, and two NADH through glycolysis. A diagram and animation of glycolysis may be found here: http://www.people.virginia.edu/~rjh9u/glycol.html. Of the intermediate molecules of glycolysis, only two-fructose-6-phosphate (F6P), and glyceraldehydes-3-phosphate (G3P)- are important to this article becuase fructose will be converted into these molecules.

Each pyruvate enters the Krebs cycle, which produces four NADH, one ATP, and one FADH2 per glucose. A diagram and animation of the Krebs cycle, which shows each step, may be found at http://www.people.virginia.edu/~rjh9u/krebs.html, but for the purpose of understnading fructose metabolism the Krebs cycle might as well be considered single reaction.

The NADH and FADH2 enter the electron transport chain and power oxidative phosphorylation. This completes the conversion of glucose to ATP- thirty-eight of them. An animation of this process is provided at http://www.science.smith.edu/departments/ Biology/Bio231/ect.html, but like Krebs cycle the details are unimportant to fructose metabolism. It is enough to know that after the fructose products enter glycolysis they are treated as though they were derived from glucose.

So how does fructose enter glycolysis? The answer depends on what type of cell the fructose is in. Muscle cells have hexokinases (a type of enzyme) that will work as readily with glucose as with fructose. They add a phosphate group to fructose to produce fructose-6-phosphate (F6P), the product of the second reaction of glycolysis, and then the same enzymes and pathways used for glucose-derived F6P also handle the fructose-derived F6P.

In liver cells, the entry is more complicated. Fructose is phosphorylated to produce fructose-1-phosphate, then cleaved into two trioses: glyceraldehyde and dihydroxyacetone phosphate (DHAP). Both can be immediately converted to glyceraldehyde-3-phosphate and handed over to the glycolytic enzymes, but glyceraldehyde can also take a more roundabout and energy-consuming path. If it follows this path, it becomes glycerol, glycerol-3-phosphate, and then DHAP.

This complexity comes from the type of hexokinase present in liver cells. Unlike muscle cells, liver cells use a type of hexokinase called glucokinase, which accepts only glucose. Therefore liver cells need extra enzymes to metabolize fructose. Fructose intolerance occurs when one of these enzymes is defective.

What is Hereditary Fructose Intolerance?

2005-10-06T22:12:00.000-04:00

According to Dr. Joe Schwarz's The Fly in the Ointment, Hereditary Fructose Intolerance (HFI) is a genetic disorder where a person lacks the enzyme aldolase B. The BC Health Guide and FDA, state that other names for the disorder include Fructose-1-Phosphate Adolase Deficiency and fructosemia, and it is an autosomal recessive trait. This enzyme metabolizes fructose-1-phospate, and the lack of it causes fructose to build up in the kidney and liver. If left untreated this buildup can lead to organ failure and death, and fructose can also build up in the intestine causing severe pain. Symptoms of HFI include vomiting, dehyrdration, liver problems, excessive sleepiness, intolerance for fruits and sweets, poor eating habits as a baby, and low blood sugar and hypoglycemia. Low blood sugar occurs becuase buildup of fructose in the liver prevents the breakdown of glycogen which when broken down turns into glucose. This lack of glucose causes low blood sugar and hypoglycemia.
Research from the HFI laboratory at Boston University shows that 1 in 22,000 people get ths disorder worldwide. However it is hard to diagnosis, so it may range from 1 in 12,000 to 1 in 58,000 people. If its close to 1 in 10,000 births than that means 1 in 50 people carry the recesssive trait. The only treatment for HFI is to have a diet completely free of fructose. Examples of food that may be eaten are rhubarb, asparagus, cauliflower, and spinach.

Welcome

2005-09-28T11:27:00.000-04:00

This blog is dedicated to discussing the essay "When Sugar Isn't So Sweet" from Dr. Schwarcz's The Flt in the Ointment. This essay focuses on the genetic disorder hereditary fructose intolerance (HFI). Our group consists of Christopher Witrak, Damon Wang, and Molly Fitzpatrick, and we hope you enjoy our research on this genetic disorder and on other relevant topics.