Carbohydrates make the brain produce more serotonin, the same relaxing brain chemical released when you eat dark chocolate. The more slowly your body absorbs carbs, the more steadily serotonin flows, according to Judith Wurtman, co-author of The Serotonin Power Diet. The result: a less-likely-to-snap you. Because thick, hearty oats are high in fibre, few things take longer for your stomach to digest, says Elizabeth Somer, author of Food & Mood. Wurtman also recommends topping it with a swirl of jam for a quicker release of serotonin. When you know it’s going to be a bastard of a day, avoid heavily processed varieties (eg, the sugary kind that come in packets meant for the microwave), which are digested more quickly, and take the time to cook old-fashioned oats, like Lotus Steel Cut Oats. But if two minutes for breakfast is all you have, you can still do your mood a favour by opting for instant oats over Coco Pops.
(source : http://nz.lifestyle.yahoo.com/womens-health/nutrition/galleries/g/-/10445428/3/7-foods-you-should-eat-every-day/)