If you've fallen into a groggy pre-lunch slump, this is the time to eat a small protein snack, advises Wurtman. To heighten alertness she recommends low-fat yogurt, cottage cheese, string-cheese sticks or milk (perhaps in your industrial-strength latte). Avoid fat, she says, or you'll feel even fuzzier.
How much: One serving size
Extra perk: The extra calcium helps to prevent osteoporosis, reduce PMS symptoms and improve heart health. The calcium in just one 8-ounce serving of plain low-fat yogurt (about 415 mg) takes you almost halfway to the recommended daily allowance of 1,000 milligrams.