A calorie is a calorie, right? Wrong.

Nutritionists increasingly urge people to evaluate foods holistically, rather than based on individual nutrients or calorie counts.

Take avocados, for example. A cup has 234 calories and 14 grams of monounsaturated fat, along with smaller doses of polyunsaturated (2.7 g) and saturated fat (3.1 g). But an avocado also provides good doses of fiber, protein, and potassium,which can help maintain healthy blood-pressure levels. No one would suggest you'd get the same health benefits or stay as full after eating 234 calories' worth of potato chips (that'd be about 25 chips).

Recent studies have shown that plants are the best choice for our health, and consuming more processed foods — even with the exact same amount of calories on offer — can lead to weight gain.