If you want to gain weight, eat smaller, more frequent meals throughout the day and use toppings (gravies, chopped nuts, ranch dressing) to add calories without bulk.

Top your bagel with some nut butter (about 190 calories) and fruit spread (about 50 calories) and you'll have yourself a tasty, energy-packed mid-morning snack that totals 420–540 calories.

Pasta is another calorie-dense source of carbs that provides an ideal base for any number of meals. Simply add the sauce and you're ready to go.

Give yourself a quick calorie boost by eating a handful or two of dried fruit. They have less volume than their fresh counterparts, so you can eat more in one go without feeling stuffed.

Olive oil is rich in healthy monounsaturated fats and can add calories and flavor to pasta, bread, or vegetables. Canola oil is a great source of omega-3 (alpha-linolenic acid or ALA) and monounsaturated fats, making it a terrific, all-purpose cooking oil.

You might also want to try adding avocado to your favorite smoothie recipe. The mild flavor mixes well with ingredients like berries or chocolate.