In addition to what you eat affecting your brain chemistry, mood, alertness, energy level, and performance, we’re now learning that how much and when you eat also has an impact. You may know this intuitively from the post-Thanksgiving dinner crash you experience, but not think about how food affects you every day of the year.

High-fat/high-calorie meals slow down absorption of food needed for energy, hence that logy feeling that hits us mid-afternoon or after a heavy meal when blood is re-directed away from the brain to the stomach to aid digestion. It makes sense that a dearth of blood to the brain would cause fatigue. So if you’re tired a lot, could be that your stomach is getting more blood than your brain is and you might consider whether your food intake, timing, and meal size could be the cause.

Our circadian rhythms (changes in physical and mental characteristics over the course of 24 hours) are influenced by food. Experts recommend that if you’re a “morning person” who finds their energy dropping mid-afternoon, you eat a large chunk of protein to promote alertness beyond the afternoon into the evening, especially if you want to be alert and at peak performance. Alternately, if you’re a night owl or someone who tends to have more energy later in the day, you would do best eating lots of protein-rich foods for breakfast and enjoying a mid-morning snack.

Want to know why many of us crave a nosh mid-afternoon? Because serotonin levels drop around that time, making us feeling tired and a little fuzzy in the thinking department. An informative book on the subject is MIT researcher Judith Wurtman’s MANAGING YOUR MIND AND MOOD THROUGH FOOD. In it, she points out that certain people really are carb cravers and experience a strong irritable, fidgety feeling late in the afternoon due to a depletion of serotonin. If you’re one of these people, you should try snacking on healthy carbs with very little or no protein in order to generate the production of serotonin which will reduce grumpiness and lethargy.

I’m not trying to make scientists out of you. I’m trying to help you think through how food affects you so that you can make wiser choices. Primitive humans didn’t have the good fortune to spend a lot of time needing to consider food preferences: they ate what they killed or what grew around them. We have options (maybe too many!) and will benefit from using information about energy level and how nutrients affect us to help us decide what foods serve us best.