Fructose is a natural sweetener found in honey, fruits, berries, and vegetables. Fructose is among the most commonly consumed simple sugars-along with glucose (found in candy, gum, jams) and sucrose (table sugar). For example, an apple contains an average of 15 to 20 grams of sugar, the majority of which is fructose.¹  With regard to taste, fructose is approximately 1.7 times sweeter than sucrose and 2.3 times sweeter than glucose. Because fructose is sweeter than sucrose or glucose, less fructose is required for the same sweetness effect.

Although fructose is a simple sugar, like glucose, and is part of the sucrose molecule (sucrose is composed of glucose and fructose bonded together), its glycemic index (01) is much lower than those of glucose or sucrose. In fact, fructose is known to have the lowest 01 of any of the sugars, and little or no increase in blood sugar is noted after ingestion of large amounts of fructose.² This fact has led to the promotion of fructose as the preferred sugar source for diabetics.³

Fructose is primarily absorbed in the gastrointestinal tract through a facilitated transport process, which results in a slower and less effective absorption than glucose.² However, fructose absorption is increased in the presence of glucose, possibly due to the ability of glucose to influence or alter intestinal permeability.⁴ And sucrose is broken down to glucose and fructose during digestion. Less fructose, therefore, may be absorbed when it is used as the primary or exclusive sweetener than when it is used in the form of sucrose. Furthermore, in humans fructose is converted into glycogen--a process that requires energy and prevents fructose from reaching direct circulation.^2,4  This is another reason consumption of fructose does not significantly increase blood sugar levels.

A recent trial demonstrated that no increase is seen in blood glucose after ingestion of fructose at 15 grams or less.⁵  This lowered glycemic response with fructose ingestion appeared to be most effective in those individuals who had the poorest glucose tolerance profiles. ^5,6 In non-diabetic individuals, fructose consumption results in little to no discernable rise in blood insulin levels.³ Research suggests that fructose is approximately 30% less potent than glucose at promoting insulin secretion in individuals with insulin dysregulation.

Consumption of fructose along with glucose has been shown in several studies to beneficially influence the level of blood glucose as well. For example, ingestion of a high dose of fructose (50 grams) led to only a modest increase in blood fructose, glucose, and insulin levels after a bolus glucose dose in one study.⁵ Another study demonstrated that 7.5 grams of fructose significantly lessened the glucose peak after a 75-gram glucose load in both healthy and type 2 diabetic adults and researchers determined that this effect was not a result of stimulation of insulin secretion.⁷ Furthermore, in a human clinical trial, 13 patients with type 2 diabetes were instructed to consume either the standard American Dietetic Association (ADA) diet or the standard ADA diet plus 60 grams of fructose per day for 6 months. Consumption of fructose was associated with a significant decrease in both serum glycosylated hemoglobin and fasting blood sugar levels.⁸

Although fructose has been shown to have many benefits in comparison to glucose or sucrose, it is nevertheless a sugar and people with sensitivities to sugars, such as insulin-deficient individuals, should carefully monitor their total sugar intake. As one scientific review points out, most human studies have shown conflicting results-partly because of heterogeneity of design and/or high intakes of dietary sucrose or fructose.⁹  For instance, some human studies have shown an increase in serum triglyceride levels after fructose consumption. It is important to keep in mind, however, that participants in these studies are commonly instructed to consume one-serving doses of 50 grams of fructose or more in addition to a high-fat intake. ¹⁰ Therefore, the ability of fructose to promote insulin deficiency has not been clearly shown, and most recent clinical trials performed to clarify the role of fructose have shown that it improves both glucose and insulin peaks induced by other sugars. In addition, fructose alone appears to result in little or no increase in blood sugar and insulin levels.

Since many factors can influence the blood sugar and insulin responses, the best course of action for individuals that are sensitive to sugars, such as patients with insulin resistance, is to choose products that have been tested and shown to have a low GI response. This is especially important since the GI of a food tests the effects of the entire food, not just one component. Therefore, GI of a food is a direct and more reliable marker for glycemic response of the food in an individual than are theoretical calculations based on content of various sugars.

• Fructose is the main sweetener found in honey, fruits, berries, and vegetables.

• Fructose is a natural, low glycemic index (GI) simple sugar with a high sweetness profile.

• Fructose is absorbed by the body through a facilitated transport process, which leads to a slower and decreased level of absorption than that observed for glucose.

• Fructose does not increase blood sugar after normal levels of consumption, and only modestly increases it after a large bolus dose (approximately 50 grams). 

• Fructose is not transported directly into the bloodstream after digestion and absorption, but is converted into glycogen in the liver where it is stored and used for energy at a later time.

REFERENCES

• Ensminger AH, Ensminger ME, Konlande JE, et al. Foods and Nutrition Encyclopedia. Clovis , CA : Pegas Press; 1983.

• Mann JI. Simple sugars and diabetes. Diabet Med 1987;4(2):135-39.

• Uusitupa MIJ. Fructose in the diabetic diet. Am J Clin Nutr 1994;59(3 Suppl):S753-S57. 4. 

•  Shi X, Schedl HP, Summers RM, et at. Fructose transport mechanisms in humans. Gastroenterology 1997;113(4):1171-79.

• Moore MC, Cherrington AD, Mann SL, et at. Acute & fructose administration decreases the glycemic response to an oral glucose tolerance test in normal adults. J Clm Endocrinol Metab 2000;85(12):4515-19.

• Nuttall FQ, Khan MA, Gannon MC. Peripheral glucose appearance rate following fructose ingestion in normal subjects. Metabolism 2000;49(12):1565-71.

• Moore MC, Mann SL, Davis SN, et at. Acute fructose administration improves oral glucose tolerance in adults with type 2 diabetes. Diabetes Care 2001;24(11):1882-87.

• Osei K, Bossetti B. Dietary fructose as a natural sweetener in poorly controlled type 2 diabetes: a 12-month crossover study of effects on glucose, lipoprotein and apolipoprotein metabolism. Diabet Med 1989;6(6):506-11. 

• Daly ME, Vale C, Walker M, et al. Dietary carbohydrates and insulin sensitivity: a review ofthe evidence and clinical implications. Am J Clin Nutr 1997;66(5):1072-85.

• Jeppesen J, Chen YI, Zhou MY, et at. Postprandial triglyceride and retinyl ester responses to oral fat: