Fructose

One of the greatest sources of Fructose is soft drinks.

Fructose can be good or bad for an athlete depending on when it's consumed. Fructose can help athletic performance when taken as a fuel source during exercise, but at other times excessive fructose can create health issues. Fructose is found in sugar (sucrose), High Fructose Corn Syrup, Honey and Agave. Excessive fructose intake has been described as "an environmental toxin with major health implications". High Fructose Corn Syrup may be slightly worse for health than sugar, and may be a source of toxic mercury.

1 What is Fructose?

Fructose is a common simple sugar that along with glucose makes up ordinary table sugar (sucrose), and High Fructose Corn Syrup (HFCS). In table sugar, one molecule of fructose is combined with one molecule of glucose. In High Fructose Corn Syrup the fructose and glucose are not linked together, but mixed in various ratios, generally close to 50:50 (55% and 42% is common, with 55% being used in drinks and 42% being used in foods). Fructose is sometimes called "fruit sugar" because it is commonly found in fruit. Some fruit, such as apples and pears contain twice as much fructose as glucose.

2 Health risks of Fructose

The effect of fructose is very different from glucose, with different pathways in the body being used. Fructose tends to result in the production of fat, influences hormones that control appetite, energy balance, and the storage of body fat, as well as tending to create insulin resistance. It has been proposed that intakes of >50g per day of fructose may be a cause of type II diabetes. Fructose is also believed to be a risk factor for hypertension, elevated triglycerides, obesity, preeclampsia, chronic kidney disease, stroke, cardiovascular disease, and mortality, as well as causing liver disease similar to that seen in alcoholics. Also, there may be a link between fructose and dementia and reduced aerobic capacity. Both Fructose and Glucose tend to result in increased body fat, Fructose can produce a greater increase in visceral (internal) fat, which is a risk factor for heart disease and diabetes. Between 1977 and 2001 Americans increased the percentage of their daily calories from soft drinks from 2.8% to 7.0% and from fruit juice from 1.1% to 2.2%.

2.1 Fructose and Fruit

The health risks of high fructose consumption and not generally seen with high intakes of whole fruit. While fruit does contain fructose, it's not easy to consume significant quantities of fructose from whole fruit. For instance, an Apple contains about 10g of fructose, and a 16 ounce soft drink contains about 26g of fructose. The Apple is generally much slower to consume than a soft drink, and in addition, the Apple contains fiber couple slow absorption. However, the health benefits of whole fruit do not seem to apply to fruit juice. There does not appear to be any evidence that fruit juice has a lower health risk than soft drinks.

2.2 Sugar and High Fructose Corn Syrup

Corn syrup does not naturally contain any fructose, but it can be processed so that some of the glucose is converted to fructose, hence the term High Fructose Corn Syrup. Typically high fructose corn syrup has a similar amount of fructose as ordinary table sugar (sucrose) which is 50:50 fructose and glucose. With table sugar, the fructose and glucose are linked together, but they are separate in High Fructose Corn Syrup, as well as honey, and cooking sugar with and an acid (such as jam making) separates the fructose and glucose. The consensus of research indicates that High Fructose Corn Syrup has a similar effect to ordinary table sugar. There are a few studies which indicate differences between the separate fructose/glucose which is found in High Fructose Corn Syrup or honey and table sugar. Rats fed 40% of calories from fructose/glucose had impaired fasting glucose and were less active than with equivalent amounts of sugar, and higher triglycerides (60% of calories). Fructose metabolism is different for different species so animal studies, especially concerning triglycerides, may not be applicable to humans. I found two studies that showed a difference in humans. Carbohydrate sensitive men had a greater insulin response to a large dose of separate fructose/glucose after a 9 hour fast compared with table sugar, though not a greater blood sugar level. Another study showed higher triglyceride levels from separate fructose/glucose than table sugar in 8 healthy men. A more significant concern is mercury contamination of HFCS which a study found in half of the samples analyzed. Overall, I would conclude that high fructose corn syrup is slightly worse than sugar, which combined with the risk of mercury contamination indicates it may be worth avoiding.

3 Fructose and Obesity

Studies have shown that drinking soft drinks results in an increase in energy intake and body weight in both overweight and normal weight subjects. This weight gain has also been shown in animal studies, and a study of diabetics. One mechanism may be that fructose does not stimulate the hormone leptin that reduces appetite. One study showed that drinking artificially sweetened (aspartame) soda actually caused a reduction in energy intake compared with no soda and some also lost body weight.

4 Fructose for Athletes

As noted in Nutrient Timing, the human body responds to nutrition differently when exercising. This is also true for fructose, which can be a beneficial addition to a sports drink. Combined carbohydrate types, such as fructose, glucose or Maltodextrin are absorbed more easily than when taken in isolation, and the combination of fructose and glucose provides more carbohydrate fuel than glucose alone. While fructose alone does not improve performance in the way that glucose does, the combination of fructose and glucose improves performance more than glucose alone. The combination of fructose and glucose also results in better fluid absorption than either alone. Also, some of the health issues of fructose are mitigated by exercise. Fructose on its own can cause digestive upsets, but the combining glucose with fructose either as sugar (sucrose) or separately dramatically improves fructose absorption. Therefore a good sports drink should contain some fructose along with glucose and/or Maltodextrin. See Fellrnr's Go Juice.