Is High-Fructose Corn Syrup making us fat?

Maybe. A 1990 study found that after three weeks of drinking three-and-a-half cans of high-fructose corn syrup-sweetened soda daily women gained an average of +2.1 pounds while men gained +1.1 pounds.1 The reason for the weight gain was simple ? they consumed 13 percent more calories per day. Men consumed 374 calories and women 247 calories more each day. When the same subjects were given sodas sweetened with NutraSweet? (aspartame) for three weeks calorie intake was 7 percent lower than normal. Women gained an average of +0.6 pounds, which was not statistically significant, while men lost -1 pound.

Sugar consumed in the rest of the diet decreased by one-third during both study periods. I would like to see a longer-term study compared sodas sweetened with high-fructose corn syrup compared to sodas sweetened with sucrose. Here is an explanation as to why high-fructose corn syrup may be making us fat.

Most carbohydrates are not converted to fat despite a popular belief otherwise. According to Harper?s Biochemistry (p. 217) ?There is little conversion of dietary carbohydrates to fat… when [the diet contains] more than 10% fat.?(2) Animal studies have shown that levels of body fat decrease as dietary fat decreases until fat intake falls below 10 percent of calories.(3) Below this amount body fat levels increase.

Fructose, however, is more easily converted to fat than other carbohydrates. This is because it is able to skip a step in its conversion to fat.(2) As Harper?s Biochemistry (p. 217) states ?[fructose] floods the lipogenic pathway.?(2) For this reason sucrose, which is half glucose and half fructose, is more lipogenic than glucose even though glucose raises levels of blood sugar and insulin more than sucrose.(2)

High-fructose corn syrup more lipogenic than fructose. Not only is fructose more lipogenic than other carbohydrates, high-fructose corn syrup is probably more lipogenic than fructose. Peter A. Mayes, Ph.D, D.Sc., retired Professor of Biochemistry at the Royal Veterinary College at the University of London and the author of several chapters on carbohydrate metabolism in Harper?s Biochemistry wrote in another paper that ?If fructose were administered with an equal amount of glucose there might well be increased lipogenesis, particularly if this was accompanied by a rise in insulin.?(4) Well, this is exactly what happens with high-fructose corn syrup. Most high-fructose corn syrup being used is either 42 or 55 percent fructose and the rest glucose and other sugars and raises insulin levels.

High-fructose corn syrup raises insulin. High-fructose corn syrup raises levels of blood sugar and insulin more than fructose. According to one study of six older male non-obese type II diabetics blood sugar levels increased 43-46 percent more after a meal containing high-fructose corn syrup than after a meal containing fructose; while insulin levels were 36-37 percent higher.(5) Moreover, the difference is probably greater than this because the high-fructose corn syrup used in this study contained a much lower percentage of glucose and a much higher percentage fructose (90 percent) and than most high-fructose syrups being used.

Fructose is not the same as High-fructose corn syrup. One point to be taken from this study is that fructose should not be equated with high-fructose corn syrup. Pure fructose is probably less fattening than high-fructose corn syrup because it does not cause the same rise in insulin levels. In fact, some studies suggest that fructose, when given alone without other carbohydrates, may suppress appetite.(6)

One study found that an hour-and-a-half after consuming fifty grams of fructose mixed in sixteen ounces of water subjects ate 26 fewer calories including the calories from fructose than those who just drank water.(7) However, subjects given the same amount of glucose consumed 450 calories more than those given water.(7) This study needs to be repeated with obese patients and for a longer period of time.

Fructose increases insulin in the presence of glucose. Fructose can potentiate insulin release in the presence of glucose.(8) And elevated insulin levels have been shown to increase calorie intake and the preference for sweets.(9)

Insulin stimulates lipogenesis. The reason that it is important to realize that high-fructose corn syrup increases insulin levels is that insulin stimulates the conversion of carbohydrates to fat.(2) It does this in two ways. Insulin increases the transport of glucose into cells, including fat cells.(2) And secondly, insulin inhibits the lipolysis, the release of fat from fat cells.(2)

High-fructose corn syrup increases absorption of fructose. Another reason that high-fructose corn syrup may cause more weight gain that fructose is that it increases fructose absorption. Large doses of fructose of 50 grams or more are not completely absorbed because the carrier necessary for fructose absorption becomes saturated. However, combining fructose with glucose increases the absorption of fructose.

Intake of free fructose has increased. The total amount of fructose consumed, both free and bound, has remained relatively constant over the past 20 years.(10) However, the amount of free fructose in food has increased considerably.(10) Based on the 1977-78 USDA Nationwide Food Consumption Survey the average male aged 15- to 18-years-old consumed 54 grams of fructose daily, with an average intake of 37 grams for the entire population.(10) Fructose accounts for 8 percent of calories consumed by the average American.(10)

Introduced in 1967. High-fructose corn syrup was introduced in 1967 and is found in nearly all sweetened sodas, sweetened fruit juices, cookies and baked goods. Crystalline fructose was introduced in 1986.(11) High-fructose corn syrup is consumed in amounts equal to sucrose.(10)

Conclusion. The dramatic increase in the consumption of high-fructose corn syrup may be one of the reasons that people are getting fatter but longer-term studies comparing high-fructose corn syrup to sucrose need to be done.

REFERENCES

1. Tordoff MG; Alleva AM. Effect of drinking soda sweetened with aspartame or high-fructose corn syrup on food intake and body weight. American Journal of Clinical Nutrition, 1990 Jun, 51(6):963-9.

2. Mayes PA. Biosynthesis of Fatty Acids. In Harper?s Biochemistry: 23rd Edition. Murray RK, Granner DK, Mayes, Rodwell VW (editors). Appleton and Lange, Norwalk, 1993b.

3. Flatt JP. Body composition, respiratory quotient, and weight maintenance. American Journal of Clinical Nutrition, 1995 Nov, 62(5 Suppl):1107S-1117S.

4. Mayes PA. Intermediary metabolism of fructose. American Journal of Clinical Nutrition, 1993a Nov, 58(5 Suppl):754S-765S.

5. Akgun S; Ertel NH. Plasma glucose and insulin after fructose an high-fructose corn syrup meals in subjects with non-insulin-dependent diabetes mellitus. Diabetes Care, 1981 Jul-Aug, 4(4):464-7.

6. Moyer AE; Rodin J. Fructose and behavior: does fructose influence food intake and macronutrient selection? American Journal of Clinical Nutrition, 1993 Nov, 58(5 Suppl):810S-814S.

7. Spitzer L; Rodin J. Effects of fructose and glucose preloads on subsequent food intake. Appetite, 1987 Apr, 8(2):135-45.

8. Curry DL; Curry KP; Gomez M. Fructose potentiation of insulin secretion. Endocrinology, 1972 Dec, 91(6):1493-8.

9. Rodin J; Wack J; Ferrannini E; DeFronzo RA. Effect of insulin and glucose on feeding behavior. Metabolism: Clinical and Experimental, 1985 Sep, 34(9):826-31.

10. Park YK; Yetley EA. Intakes and food sources of fructose in the United States. American Journal of Clinical Nutrition, 1993 Nov, 58(5 Suppl):737S-747S.

11. Hanover LM; White JS. Manufacturing, composition, and applications of fructose. American Journal of Clinical Nutrition, 1993 Nov, 58(5 Suppl):724S-732S.

Articles on the same subject can be found here:

• High-Fructose Corn Syrup