October 22, 2009

Fructose and Blood Pressure

Large quantities of fructose, the sugar sweetening most foods (don't worry about fruit), raises blood pressure and the risk of metabolic syndrome. The waste product uric acid is the culprit.

It's hardly a secret that a diet high in sugar is unhealthy. A recent study found that it can also raise blood pressure. This increase is caused by the sugar, fructose.

Fructose makes up about half the sugar content of nearly all sweet foods, no matter how they were sweetened. People with a sweet tooth can't avoid it by switching the type of sweets they eat. Changing from foods sweetened with high fructose corn syrup to foods sweetened with table sugar won't help.

The diet also more than doubled the number of men who were classed as having metabolic syndrome.

The study looked at 74 men, average age 51, who were given 200 grams (about seven ounces) of fructose daily, on top of their normal diet. After two weeks on this diet, their average Systolic pressure rose by about six points and their average Diastolic pressure rose by about three points. The diet also more than doubled the number of men who were classed as having metabolic syndrome. A person is classed as having metabolic syndrome if they have at least three of these five attributes: high fasting blood sugar, high blood triglycerides, high blood pressure, above average waist size, low HDL−cholesterol. Metabolic syndrome is an indicator that a person is at risk for several unpleasant health complications in the not so distant future.

The increase in blood pressure from fructose was due to a buildup of the waste product uric acid. Of all the dietary sugars, only fructose is known to cause a rise in uric acid.

The drug allopurinol minimized these effects. Half of the men in the study were given allopurinol in addition to the fructose. Not only did these men have significantly lower uric acid levels than the other group; they also showed only a one point rise in systolic blood pressure and virtually no increase in the incidence of metabolic syndrome. Allopurinol is commonly given to gout patients and works by lowering their uric acid level.

After the study's end, the blood pressure of most of the affected men returned to normal within two months.

To put some of these findings into context, you should realize that 200 grams of extra sugar per day is a lot of sugar. To add that much sugar, you'd have to drink five cans of soda daily, on top of your normal diet (though only half of the sugar in soda is fructose). Estimates are that the average U.S. adult consumes only 50−70 grams of total fructose per day. So it's not clear how these findings apply to people who eat an occasional cookie or piece of cake. The study does suggest that if you eat enough sugar, your blood pressure will rise.

One lesson not to take home from this study is to lower your fruit consumption. Fructose is sometimes called fruit sugar. This is because the sugar in certain fruits, notably apples and pears, is largely fructose. But a serving of fruit contains only about 4−10 grams of fructose, while a can of soda contains about 20 grams (plus 20 grams of the sugar glucose). Fruit is a food, containing vitamins, minerals, antioxidants and fiber; soda is manufactured sugar water with flavoring. Current dietary recommendations say that people should be eating more fruit, not less of it.

The results of the study were presented at the American Heart Association's 63rd High Blood Pressure Research Conference on September 23, 2009. The conference was held in Chicago.

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