We all have them at times-days when life really tests us. Your car gets a flat on the way to work, you flub an important report, you can't help your child with his math homework, and to top it all off, you burn dinner. Your mood? Lower than this week's stock market, and understandably so. But what about days when things are okay on the surface, and yet you just can't seem to shake off your irritability? There may be a connection between your low spirits and what and how you've been eating.

Our brains and bodies need regular, nourishing food to fuel our daily activities, and if they're not getting what they need, crankiness can result. Think about your dietary habits. Do you feel particularly bad after a certain meal or at a certain time of day? Sometimes, simple tweaks are all it takes to boost your mood from foul to fair. Some of the most common bad-mood food habits include:

  • Eating too many carbohydrates. Carbohydrates have a calming effect on us because they affect our levels of serotonin, a brain chemical that regulates our mood, appetite, pain sensitivity, and sleep habits. But there can be too much of a good thing when it comes to carbs-particularly refined carbs-and it can be tough to stop eating them once you start. The result? I-can't-believe-I-ate-the-whole-bag-of-chips fatigue.
  • Not eating enough carbohydrates. Conversely, people who shun carbs, such as followers of the Atkins diet, are not getting enough serotonin to boost their mood. Eating protein when you really crave pasta can lead to irritability.
  • Relying too heavily on caffeine. The energy boost you get from your morning java may morph into afternoon jitters, making you tense and jumpy.
  • Skimping on foods with mood-boosting properties. Studies show that eating plenty of foods with folate may help ward off depression. Opt for dark green leafy vegetables, lentils, kidney beans, orange juice, and folic acid-enriched cereals and breads. The mineral selenium is also important for mental health and is found in wheat germ, garlic, fish, shellfish, whole grains, sunflower seeds, and Brazil nuts.
  • Skipping or going too long between meals. This is a common reason for blood-sugar crashes, which can leave you weak, shaky, and unable to concentrate. Experts advocate eating something every three to four hours to keep your system on an even keel.