Ask a Dietitian: In Defense of Potatoes, Other Starchy Vegetables

Published online: Jun 08, 2018 Articles Mary Agnew
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Source: Austin American-Statesman

“Corn doesn’t count as a vegetable! It’s all starch,” I heard a father say recently when his son told me that corn was his favorite vegetable.

According to the United States Department of Agriculture, corn is a vegetable, a grain and a fruit. Growing up, we were told to eat plenty of vegetables, so why does corn (and other starchy vegetables) get such a bad rap?

Vegetables are generally separated into two categories: starchy (corn, potatoes peas, carrots, beets and other tubers) and non-starchy (leafy greens, broccoli, cauliflower, peppers and mushrooms). Starchy vegetables contain more carbohydrates than non-starchy vegetables, so they increase your blood sugar at a quicker rate.

Carbohydrates often get blamed for weight gain. But most people have a fairly vague understanding of the different types of carbohydrates, so let’s review.

Carbohydrates are compounds that contain carbon, hydrogen and oxygen. They are the primary source of energy for our body and are divided into two groups: simple carbohydrates (sugars) and complex carbohydrates (dietary fiber and starches). The difference between a simple and a complex carbohydrate is how quickly it is digested and absorbed.

Simple carbohydrates, or sugars, include table sugar, honey, corn syrup and the natural sugars found in fruit (fructose) and milk (lactose). Wait, what? Fruit is a simple sugar? Aren’t simple sugars bad for us? Relax. Fruit also contains fiber, which slows down digestion, slowing the spike in blood sugar. That’s why it’s recommended to eat fruit more than you drink it.

Milk and other dairy products also contain protein, which slows digestion as well. Unfortunately, most of the sugar Americans eat is not from whole fruit and dairy products, but instead is the processed variety that’s added to foods such as candy, cake, ice cream, many breakfast cereals and bars, and soft drinks.

Complex carbohydrates, which are found in potatoes, corn, beans, rice and pasta, are starch or dietary fiber. Dietary fiber is not like other carbohydrates. Although the bacteria living naturally in your intestines convert very small amounts of dietary fiber to fatty acids, dietary fiber is not considered a source of energy because the bonds that hold its sugar units together cannot be broken by human digestive enzymes. Dietary fiber, does, however, aid the movement of food through our bodies.

Starches, on the other hand, are excellent sources of energy. They are long chains of glucose molecules that our bodies break down into individual glucose molecules, which we can, in turn, use for energy. Complex carbohydrates have anywhere from three to a billion units of sugars, and your body takes longer to digest them than it takes to digest simple carbohydrates. As a result, digesting complex carbohydrates releases glucose into your bloodstream more slowly and evenly than digesting simple carbs.

That brings us back to our starchy vegetables. If starch is a complex carbohydrate, therefore better for us than simple carbohydrates, and corn and potatoes are mostly starch and a good source of complex carbohydrates, then why are they often looked down upon?

It’s because starchy vegetables generally contain more carbohydrates than non-starchy vegetables, and we currently live in a carb-fearing world. One cup of broccoli florets contains about 4 grams of carbohydrates, while 1 cup of corn kernels and 1 cup of boiled potatoes contain 39 grams and 31 grams of carbohydrates, respectively.

So, what to do? If you eat 2,000 calories a day, you should consume about 250 grams of carbohydrates a day (50 percent of calories coming from carbohydrates). A good starting place for meals is roughly 45 to 60 grams of carbohydrates and for snacks, 15 to 30 grams. If you pair that 1 cup of corn or potatoes with a lean protein and maybe a non-starchy vegetable, you’ll have a complete, nutritious meal.

Like non-starchy vegetables, starchy vegetables also contain fiber, vitamins and minerals, including potassium, which the 2015 Dietary Guidelines Advisory Committee declared as “an under-consumed nutrient of public health concern.” One cup of boiled potatoes contains 591 milligrams of potassium, which is 13 percent of your daily needs, while 1 cup of broccoli contains only 5 percent of your daily needs. Potassium-rich foods can help reduce blood pressure, but less than 3 percent of the population gets the recommended amount of it each day. (As the new nutrition facts label rolls out over the next couple of years, you will start seeing potassium listed.)

Most Americans eat less than half the fiber they need. Adults need about 25 to 38 grams of fiber a day. This is where all vegetables, both starchy and non-starchy, shine. A cup of corn contains 5 grams of fiber, which is 13 percent of our daily needs, while 1 cup of broccoli and 1 cup of potatoes contain 5 percent and 8 percent, respectively.

So when it comes down to it, what matters is the type of carbohydrates you eat. A serving of regular M&M’s contains 34 grams of carbohydrates, which is about the same as 1 cup of boiled potatoes. Which is going to give you more nutrition? The potatoes, of course. Which will make you happier? That’s up for debate. I firmly believe that all foods can fit into a healthy diet, but it’s all about balance.

The bottom line? Starchy vegetables don’t have to be off-limits, even for people with diabetes. A better way to approach it is by learning how to identify them and portion-control them. Eating a variety of foods will ensure that you are meeting your daily needs for energy, vitamins and minerals.