Fructose, which constitutes one-half of cane sugar and high fructose corn syrup, raises blood sugar and metabolic risks in clinical trialby Craig Weatherby
Last month, the American Heart Association (AHA) recommended that people cut back on sugar and foods high in added sugars.
This warning was prompted by ample evidence showing that an excess of dietary sugars and starches harms heart health.
The AHA’s new scientific statement targeted “sugars and syrups added to foods during processing or preparation and sugars and syrups added at the table.”
- Men given added fructose suffered rises in uric acid blood levels.
- This uric acid spike raised their blood pressure and worsened other risk factors for diabetes and cardiovascular disease.
- Fructose hinders the body’s food-satiety (fullness) signals leading to overeating, diabetes, and more.
- Cane sugar is no healthier than high-fructose corn syrup… both sweeteners are one-half fructose and one-half glucose.
As the AHA noted in their press release, “High intake of added sugars, as opposed to [the] naturally occurring sugars [in plant foods and juices], is implicated in the rise in obesity. It’s also associated with increased risks for high blood pressure, high triglyceride levels, other risk factors for heart disease, stroke, and inflammation...” (AHA 8/2009).
(The warning should have included refined starches such as white flour in their advice, since resemble sugars in terms of their effects in the body.)
Last week, researchers from the University of Colorado-Denver reported the results of a clinical study with alarming implications for people who consume the sugary/starchy diets typical in America.
Study links excess fructose to high blood pressure
The new findings—presented at American Heart Association’s 63rd High Blood Pressure Research Conference—suggest that excessive fructose consumption may raise blood pressure and promote the pre-diabetic condition called metabolic syndrome (Johnson R et al. 2009).
The researchers recruited 74 adult men (average age 51) for a two-month clinical trial with these conditions:
After only two weeks on the diet, the results were striking:
- All the men consumed 200 grams (seven ounces) of fructose per day in addition to their regular diet. This is about three times more fructose than the estimated amount of fructose—60 grams or 2.1 ounces—consumed by the average adult American.
- Half of the men got the anti-gout drug allopurinol and half got placebo pills.
These findings are pretty big news, since, as study co-author Richard Johnson, M.D., said in a press release from the AHA, “This is the first evidence of a role of fructose in raising blood pressure...” (AHA 9/2009).
- The fructose+placebo group experienced significant average blood pressure increases (6 mm Hg systolic and 3 mm Hg diastolic).
- The fructose+gout-drug group had virtually no increase in blood pressure, and showed significantly lower uric acid levels.
The blood pressure levels of most of the men returned to normal within two months of the study’s conclusion when the participants returned to their normal dietary intake.
The participants given a gout drug that lower blood levels of uric acid did not suffer any blood pressure increase... which pretty well proves that the uric acid rise caused the blood pressure rise.
Uric acid is a normal bodily chemical that can exert antioxidant effects... but it is also known to affect blood pressure.
|About Metabolic syndrome|
Metabolic syndrome—also called MetS—is a cluster of risk factors associated with the development of cardiovascular disease and type 2 diabetes.
MetS is usually defined as having three or more of these six risk factors:
- Abdominal obesity (excessive fat tissue in and around the abdomen).
- High blood triglycerides, low HDL cholesterol and high LDL cholesterol: a state that fosters plaque buildups in artery walls.
- Elevated blood pressure.
- High fasting blood sugar (i.e., the body can’t properly use insulin or blood sugar, resulting in insulin resistance and/or glucose intolerance).
- Sticky blood that promotes dangerous clots (e.g., a “pro-thrombotic” state with high blood levels of fibrinogen and/or plasminogen activator inhibitor–1).
- Pro-inflammatory state in the blood (e.g., elevated C-reactive protein levels).
Fructose also raised diabetes risk
In addition to raising blood pressure, fructose seems to worsen risk factors for metabolic syndrome... called MetS for short.
Within just two weeks after the two-month study began, the incidence of MetS more than doubled in the men who ate fructose without the counteracting drug.
To be exact, the men who ate fructose without the counteracting drug were 130 percent more likely to have developed MetS.
And the researchers tied this increased MetS risk directly the rise in blood uric acid levels caused by eating extra fructose.
But there was virtually no change in the rate of metabolic syndrome among the men given anti-gout allopurinol.
This was because the gout medicine prevented any rise in uric acid levels, which in turn prevented the blood pressure rises and other problems seen in the placebo group.
Thus, by taking allopurinol, the men in that group reduced two of the six risk factors that define MetS.
(It would be foolish to take allopurinol to counteract some of the ill effects of sugary/starchy diets instead of simply cutting back on sugars and starches... the drug has limited benefits and can induce rare but serious side effects.)
Men in both groups had an increase in fasting triglyceride levels and insulin resistance while on the added-fructose diet.
As Dr. Johnson said, “These results suggest that fructose may be a cause of metabolic syndrome. They also suggest that excessive fructose intake may have a role in the worldwide epidemic of obesity and diabetes” (AHA 9/2009).
While that statement is accurate, it is misleading because excessive glucose intake also promotes obesity and diabetes (See the sidebar titled “Cane sugar vs. corn syrup”).
In truth, it is most accurate—and of more practical use in educating consumers—to say that excessive sugar intake promotes obesity and diabetes.
Fructose and glucose: A pair with diabetes blame to share
Fructose makes up half of all the sugar molecules in table sugar (cane sugar) and from 45% to 55% of the sugar molecules in high-fructose corn syrup (HFCS).
|Cane sugar vs. corn syrup… is either sugar better for health?|
There’s been relatively little research comparing the metabolic effects of HFCS to those of cane sugar (sucrose) and other caloric sweeteners.
But cane sugar (sucrose) and high-fructose corn syrup (HFCS) contain equivalent amounts of fructose and glucose… and as you’d expect, the available evidence suggests that HFCS and cane sugar have similar metabolic effects (Angelopoulos TJ et al. 2009).
In short-term animal feeding studies, dietary fructose significantly increases blood triglyceride levels and has little effect on blood glucose levels, whereas dietary glucose has the opposite effects (Schaefer EJ et al. 2009).
Dietary glucose largely escapes removal from blood by the liver, whereas fructose does not… a difference that helps explain some of the two sugars’ differing metabolic effects (Schaefer EJ et al. 2009).
When dietary glucose and fructose have been directly compared in studies where they constituted 20-25 percent of calories, dietary fructose caused significant increases in fasting blood triglyceride and LDL cholesterol levels, but dietary glucose did not (Schaefer EJ et al. 2009).
However, dietary glucose increases blood glucose and insulin levels whereas dietary fructose does not (Schaefer EJ et al. 2009).
In studies where fructose constituted only 4-12 percent of calories, researchers saw no significant adverse effects on blood levels of fat or glucose (Schaefer EJ et al. 2009).
Glucose—also called “blood sugar”—is the kind of sugar the body uses to fuel its cells. Glucose makes up the other half of cane sugar and HFCS.
HFCS is increasingly used to sweeten packaged products because it’s cheaper than cane sugar.
Fructose is the only common sugar known to increase uric acid levels... an effect that would explain the results seen in the new study.
When researchers give fructose to animals, they develop key features of metabolic syndrome: abdominal fat, high triglycerides, low HDL cholesterol levels, high blood pressure, and insulin resistance.
However, it takes massive amounts of fructose to raise rats’ uric acid levels, because they and most other animals have an enzyme that breaks down uric acid.
Humans lack that enzyme and therefore can develop gout—which is caused in part by high uric acid levels—but other animals don’t.
Thus, it’s no surprise that patients with high blood pressure, diabetes and kidney disease often have high uric acid levels.
There is no evidence that cane sugar (white table sugar) is any healthier than high-fructose corn syrup, because both sweeteners are about one-half fructose.
Instead, heart and diabetes risks stem from excessive consumption of any kind of sugar, including HFCS, cane sugar, beet sugar, and honey.
Both glucose and fructose have distinct drawbacks when eaten in excess.
All of the commonly used sugars are about 50/50 glucose and fructose, and either will promote disease when eaten in excess … especially when these combined sugars are used (in the form of cane sugar or HFCS) to sweeten almost every packaged and prepared food in sight.
America's sugar habit worsens, and drives disease
According to the National Cancer Institute, the average American’s intake of added sugars totaled a whopping 22 teaspoons per day in 2004… two to four times the maximum recommended by the AHA (NCI 2008).
And Louisiana State University researchers estimated that, from 1977 to 1995, the average American’s intake of added sugars increased by more than one-third (35 percent), from 235 calories to 318 calories (Bray GA et al. 2004).
During this 18-year period, they estimated that average American’s intake of high-fructose corn syrup (HFCS) intake increased from 80 to 132 calories per person. This means that HFCS accounted for more than half (62 percent) of the increase in added sugars.
Rates of overweight and obesity have been on a steady rise for decades, and a very compelling case can be made that excess sugar consumption has played a significant role.
Fructose is seen as particularly to blame for obesity because it bypasses many of the body’s satiation signals, which makes it easier to over-consume calories, gain weight, and develop insulin resistance.
And as we've seen, fructose increases uric acid levels, which in turn promotes many of the components of metabolic syndrome, including high triglyceride levels.
But as explained in the sidebar titled “Cane sugar vs. corn syrup”, glucose has plenty to answer for, too.
Fructose: “Fruit sugar” in name only
Marketers have misleadingly labeled fructose “fruit sugar” to make it sound friendly, even though most of the sugar in most fruits is sucrose, only half of which is fructose.
You could just as accurately call glucose “fruit sugar.”
Fruits only contain from four to 10 grams (1/7 to 1/3 of an ounce) of fructose per serving, and they also provide antioxidants, vitamin C, potassium, and fiber, which help counter the ill effects of fructose.
In fact, a recent clinical study from Pennsylvania State University indicates that eating fruit at the start of a meal can reduce the total amount of calories that diners consume (Flood-Obbagy JE et al. 2009).
Interestingly, consumption of fruit juice is not linked to increased obesity risk, even though juices contain just as much sugar (glucose and fructose) per serving, compared with sodas sweetened with either cane sugar or HFCS.
Instead of fruit or juice, the main risk for excessive fructose consumption in the Western diet comes from sweetened drinks and foods rich in cane sugar or high fructose corn syrup (HFCS).
Sugar-sweetened drinks are the leading source of added sugars in Americans’ diet, with one 12-ounce can of regular soda averaging about 130 calories, derived from the full ounce (28 grams) of corn syrup or cane sugar most such beverages contain per 8 fluid ounce serving.
That fact seems like further affirmation of the superiority of real, whole food… and moderate amounts of naturally sweet fruit or vegetable juice.
America’s public health efforts should focus on persuading people to cut back on dietary calories, sucrose, and HFCS… and to increase their exercise and their intake of vegetables, fish, fruit, whole grains, and fiber.
- American Heart Association (AHA). Association recommends reduced intake of added sugars. August 24, 2009. Accessed at http://americanheart.mediaroom.com/index.php?s=43&item=800
- American Heart Association (AHA). High-sugar diet increases men’s blood pressure; gout drug protective. September 23, 2009. Accessed at http://americanheart.mediaroom.com/index.php?s=43&item=829
- Angelopoulos TJ, Lowndes J, Zukley L, Melanson KJ, Nguyen V, Huffman A, Rippe JM. The effect of high-fructose corn syrup consumption on triglycerides and uric acid. J Nutr. 2009 Jun;139(6):1242S-1245S. Epub 2009 Apr 29. Review.
- Bray GA, Nielsen SJ, Popkin BM. Consumption of high-fructose corn syrup in beverages may play a role in the epidemic of obesity [published correction appears in Am J Clin Nutr. 2004;80:1090]. Am J Clin Nutr. 2004;79:537–543.
- Flood-Obbagy JE, Rolls BJ. The effect of fruit in different forms on energy intake and satiety at a meal. Appetite. 2009 Apr;52(2):416-22. Epub 2008 Dec 6.
- Johnson R et al. Abstract P127. American Heart Association 63rd High Blood Pressure Research Conference, Chicago, Il September 23, 2009.
- National Cancer Institute (NCI). Usual intake of added sugars. In: Usual Dietary Intakes: Food Intakes, US Population 2001–04. November 2008. Available at: http://riskfactor.cancer.gov/diet/usualintakes/pop/t35.html.
- Schaefer EJ, Gleason JA, Dansinger ML. Dietary fructose and glucose differentially affect lipid and glucose homeostasis. J Nutr. 2009 Jun;139(6):1257S-1262S. Epub 2009 Apr 29. Review.