What's that in your grocery cart?James Caldwell It's a bird, it's a plane, it's... a superfood?

A superfood certainly sounds like something you want to eat more of. But what does it mean?

For starters, the term "superfood" isn't one that real experts in the field typically use. Registered dietitian Caroline Thomason tells USA TODAY that superfoods are "more of a descriptor word than a scientific term."

But it's a buzzy term that often gets thrown around in nutrition circles online anyway — so let's break down what "superfoods" actually are, and how experts say they should fit into your daily eating habits.

What are superfoods? 

Superfoods are "nutrient-dense foods that either have a lot of one nutrient or are a good source of several (nutrients)," Thomason says. "For example, a food that is a superior source of Omega-3’s might be dubbed a superfood if it’s hard to find that source in other foods."

Which foods are superfoods? 

There's no definitive list of superfoods, but Harvard Health breaks down 10 notable ones and the nutrients that make them good for you:

• Berries: Fiber and antioxidants
• Fish: Contain protein and omega-3 fatty acids
• Leafy greens: Vitamin A, vitamin C, calcium and fiber
• Nuts: Protein and monounsaturated fats
• Olive oil: Vitamin E and monounsaturated fatty acids
• Whole grains: Fiber, B vitamins and minerals
• Yogurt: calcium, protein and probiotics
• Cruciferous vegetables, like broccoli and kale: Fiber and vitamins
• Legumes, like black beans and chickpeas: Fiber and protein
• Tomatoes: Vitamin C and lycopene

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How often should you eat superfoods?

There's no one answer for how much of or how often you should consume a superfood — the best diet plan for you depends on a whole slew of factors. As a whole, Thomason recommends just aiming to add more of these types of foods into your daily meals.

"If you think of your nutrition choices as a bank account, where you make daily deposits and withdrawals, choosing nutrient dense options the majority of the time will ultimately compound on itself for your health," she says. "A healthy diet is made up of our collective choices over time. One single diet choice cannot worsen your health and similarly one nutrition choice cannot improve your health. Using language like 'the healthiest' doesn’t help us understand the complexities of nutrition and choosing balanced choices the majority of the time."

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