Experts question study linking potatoes to high blood pressure

A new study about the possible health impact of one of America's most popular foods is stirring controversy.

Research published by The BMJ finds that eating more potatoes -- boiled, baked, mashed, or in French fry form -- is associated with an increased risk of developing high blood pressure in adults.

However, experts not involved with the research argue that the study has several important shortcomings, and that looking at overall dietary patterns may be a better predictor of health than single foods or nutrients.

For the study, researchers from Brigham and Women's Hospital and Harvard Medical School followed over 187,000 men and women from three large U.S. health studies for more than 20 years. Participants self-reported their dietary habits, including how frequently they ate potatoes. They also reported whether or not they had been diagnosed with hypertension, or high blood pressure, by a health professional.

"In our observational study participants who did not have high blood pressure at baseline, and consumed four or more servings a week of potatoes (boiled, baked or mashed) later had a higher risk of developing hypertension compared to those who consumed one or less than one serving a month," lead author Dr. Lea Borgi, a physician in the Renal Division at Brigham and Women's Hospital, said in a statement.

Furthermore, the researchers found that replacing one serving a day of boiled, baked, or mashed potatoes with one serving of a non-starchy vegetable was associated with a lower risk of developing hypertension.

The authors say a possible explanation for the findings is that since potatoes have a high glycemic index compared with other vegetables, they can trigger a sharp rise in blood sugar levels.

They note the study has important limitations, including that it just shows an association -- it does not prove that consuming high levels of potatoes actually causes high blood pressure.

In an accompanying editorial, a group of researchers from Australia note several other important caveats. First, they point out that glycemic index of potatoes varies depending on the type of potato and the cooking method.

Additionally, while the study authors did their best to control for other dietary factors, including overall calorie consumption, the nature of self-reported data makes this very difficult. Eating French fries, the editorial points out, may be characteristic of a diet "higher in sodium and saturated fat not fully captured in the food frequency questionnaire and therefore not adequately controlled for in the analysis."

Finally, the Australian doctors note that there is a "broader problem" looking at the associations between disease risk and consumption of single foods or nutrients rather than considering overall dietary patterns.

In the U.S., the National Institutes of Health recommend the DASH diet (which stands for "Dietary Approaches to Stop Hypertension") as a strategy to reduce high blood pressure. The diet is rich in fruit, vegetables, and whole grains and includes low-fat dairy foods, meat, poultry, fish, nuts, and beans -- while at the same time limiting sugar-sweetened foods and drinks, red meat, and added fats.

"The DASH diet includes potatoes because they are high in potassium and low in sodium and fat," the editorial authors write. "Evidence from the DASH trials suggests that potatoes can be included as part of this overall dietary pattern and that this is effective in preventing and controlling hypertension."

Of course, some methods of cooking potatoes are healthier than others and experts recommend focusing on those.

"You can make mashed potatoes with olive oil, nonfat milk or soy milk and add mixed herbs and spices," Samantha Heller, a senior clinical nutritionist at New York University Medical Center in New York City, told HealthDay. "I do not peel the potatoes and I mix in vegetables, such as sauteed spinach and garlic."

However, she warns to watch portion sizes. "For example, today's russet potatoes can be the size of a city bus," she said. "Alternate potatoes with other whole grain starches like brown rice or pasta. And remember, only about a quarter of your plate should be taken up with starchy foods."