First, the nutritional pyramid turns into a platter. Now the humble potato is responsible for a health-care epidemic.

It’s enough to cause a severe case of nutritional whiplash.

Researchers at Harvard University reported Wednesday that an extra serving of potatoes is more likely to cause weight gain than an extra can of soda pop.

Over the past year, potatoes have gone from the near-perfect vegetable — cheap, convenient, easy to prepare — to the nutritional no-no list.

What a turn of events.

Three years ago the United Nations celebrated the “Year of the Potato,” praising tubers as an excellent source of vitamins and minerals. For years, the American Heart Association declared the white potato a “heart-healthy” food.

Human beings have been eating potatoes without apparent ill effect for at least 7,000 years. The ancient Incas even worshiped a potato god.

Now the potato, a mainstay of the American diet, is under attack.

According to a large, three-part study that followed 120,000 health-care professionals over 12 years, researchers concluded that potato eaters were the most likely to gain weight over time.

The researchers found the average study participant gained .8 pounds per year, which added up to 16 pounds over 20 years.

Researchers detected, however, that people who ate one extra serving of potatoes per day gained even more.

The experts theorize that potatoes cause a quick spike in blood sugar. As blood sugar levels then drop, people get hungry, leading them to snack.

Which is very confusing. Is it the potato that causes the weight gain or the Snickers bar eaten an hour later in response to the insulin spike?

And how do researchers separate potato consumption from other eating habits, like drizzling cheese or butter on those spuds?

The potato debate has serious economic consequences for Maine and other potato-growing states.

Recent government efforts to reduce the use of potatoes in school lunches and other federal feeding programs set off alarms in Congress.

According to the Bangor Daily News, Maine’s two U.S. senators, as well as U.S. Rep. Mike Michaud, are fighting efforts to change federal potato-consumption recommendations.

Sen. Olympia Snowe pointed out that limiting potato consumption would “drive up the cost of healthy meals for students” and argued that the limits were not based upon sound science.

Giving Americans the latest and best nutritional information is critical. We are suffering from a very real obesity health crisis in the U.S.

Adult life expectancy is declining for the first time in a century in some communities, and experts blame poor dietary habits.

At the same time, we should not allow ourselves to be whipsawed by every study that appears in a medical journal.

We can all think of scary studies that have been superseded by later research. The truth often takes time to emerge. When it does, it’s often not as frightening as originally reported.

In the meantime, the best advice is likely the oldest — all things in moderation.

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The opinions expressed in this column reflect the views of the ownership and editorial board.