This time of year, markets are full to the brim with pumpkins, squash and carrots. These vegetables are classified as the orange-yellow family and their vibrant colors carry not only nostalgia of the autumnal season, but also a clue as to what nutrients they contain.

Dieticians classify fruits and vegetables by their color because it often points to what the produce really contains. The chemicals in a plant are called phytochemicals, which give the plant color and perform defense mechanisms for the plant, said Becky Roach, a nutrition professor at the University of Illinois at Urbana-Champaign.

“You can get a fairly good idea of what nutritive substances are in food by its color,” Roach said.

Although research has still not determined how, it is believed the defense mechanisms “ultimately become defense mechanisms in our bodies,” Roach said.

Registered dietician Megan Campbell said the phytochemicals in the orange-yellow family are believed to slow the aging process in human bodies,  reduce the risk of chronic disease and also strengthen immunity and vision.

When considering squash, Campbell pointed out that acorn squash, which has green skin but orange meat, is eaten in the fall and is more nutritious than summer squash. Winter squash is extremely nutritious with fiber, potassium and vitamin C. The potassium and folate in winter squash are also good for the heart.

Due to the popularity of orange-yellow vegetables this season, consumers get an “extra dose” of all these nutrients and benefits, said Karen Chapman-Novakofski, nutrition professor at U of I.

As people eat autumn vegetables in a plethora of ways, namely in desserts like pumpkin bread and pie,  Roach said cooking the vegetables is OK and should not diminish any of the health benefits.

“The issue is what we add, not what we take away from them by cooking them,” Roach said of the additional sugar and fat most desserts contain. When made with less sugar and fat, orange-yellow vegetables will maintain most of their unique nutrients.

Carotenoid is one of the phytochemicals abundant in orange-yellow fruits and vegetables. Chapman-Novakofski said more than 500 carotenoids have been discovered, beta-carotene being the most well-known.

Carotenoids are what the body turns into vitamin A, Roach said.

“Very similar to what lemon juice would do to a cut apple … carotenoids prevent oxidation of things,” Chapman-Novakofski said. She also said it is believed that carotenoids fight cancer and heart disease this way, because otherwise, oxidation leads to mutated cells and to more fat in arteries.

“Fall is a great time for a bunch of cruciferous vegetables,” Roach said. “Cruciferous are particularly beneficial when it comes to protection against cancer.”

Cruciferous vegetables such as broccoli and turnips are not in the orange and yellow family, but they are also fall-time food.

Still, many people do not get a variety in the produce they eat, and in order to get her clients to try vegetables of many colors, Campbell said she encourages them to purchase vibrant produce that are intriguing to them.

“Different colors are more prominent from season to season, but as long as you keep all the colors of the rainbow on your plate, you’ll be alright,” Chapman-Novakofski said.

This is the battle for most dieticians, getting people out of a “food rut,” as Campbell calls it. She said other harvest vegetables include leafy greens, kale, spinach and collard greens.

Chapman-Novakofski said white vegetables are also prominent fall foods and they contain anthocyanins, which help lower cholesterol and blood pressure like carotenoids.

Chapman-Novakofski listed some examples like cauliflower and garlic. “In soups and stews, you’re always going to put in potatoes or parsnips,” Chapman-Novakofski said.

Within the same color families, produce can vary by season. Similar to how acorn squash is more nutritious than its summer cousin, Campbell said sweet potatoes have more fiber than white potatoes.

So fully indulge in the season and reap its

healthy benefits by eating plenty of pumpkin and other orange-yellow vegetables.

tgleason@chroniclemail.com