Lunch is a productivity ball-and-chain. After a hearty meal, I’m an afternoon work zombie, struggling through mental fog in search of a place to nap. To free myself from this fate, I replaced my 30-minute lunch with a 3-mile run. It was a resounding success: I was far (far) more alert.
I measured my hunch on a Stanford-designed test of mental focus, specifically designed for quantified health nuts like myself. Indeed, my afternoon mental focus after a run was about 11% higher, compared to a healthy lunch that tanked my mind by about 9%.
The popular academic way to test cognitive focus is with a series of reaction-time tests. For example, one test measures how fast you can pair nonsense symbols with numbers (picture below). A circle with a dot may be “3” on the keypad, while an arrow could be “9.” As soon as the symbol flashes on the screen, you’re supposed to press the associated number. After 20 seconds, you’re only going to maintain my speed if you’re alert.
The Experiment: Workout vs. Lunch
Last Friday, I took a sweaty 3-mile run through the hills and valleys of San Francisco’s historic Mission District. It wasn’t just any run—it’s a protocol designed to increase endurance by maintaining a heart rate that is just shy of a sprint (a so-called “tempo run”). Because I know that high-intensity exercise has a greater impact on cognitive focus, I needed to push myself. My coaches at Breakaway Performance Labs found that I needed to maintain a heart rate of 168-178 beats/min. So, for 25 minutes (or exactly as long as it takes me to run to Whole Foods), I ran like the dickens.
Other than a coconut water to replenish my blood sugar, I was food-free from 11 a.m. to 4 p.m. I tested myself at quantified-mind before and after my run, because I needed to baseline my mental focus for that specific day (sleep and other factors can influence overall focus day-to-day).
On lunch day, I took a pleasant stroll to the famous Ferry Building farmer’s market—not just because I needed to do my grocery shopping, but also because I needed to control variables (sunlight, for example) and simulate the effect of leaving work to pick up some grub. The blue spectrum of light—especially sunlight—increases cognitive focus. It’s possible that any positive effect from my run was mostly due to sunlight. (If so, I would just need to take my laptop outside and avoid the nasty workout!)
To pre-empt naysayers who think that a healthy lunch boosts productivity, I selected the most nutritious foods I could: 12 ounces of fresh- caught pacific tuna, a local avocado, and a “raw” parfait, which consisted of buckwheat, strawberries, and a ripe banana. I was a vitamin-munching machine.
Compared to this day at the farmer’s market, my post-run high felt like a sweet injection of coffee—I was filled with a surge of energy. After lunch, I literally had to take a nap before I could write this article.
The results line up with my intuition. Compared to lunch, exercise boosted my reaction time test 13% and my short-term working memory by 7%. After lunch, I entered a mental haze: reaction times dropped 12% and short-term memory 11%.
I am not convinced that eating throughout the day is the best for health or productivity, and there’s a fierce debate within the medical community about if and when time of consumption matters. (Note: I did not eat fewer calories per day. I just changed when I ate them.) As with all self-experiments, readers will need to judge what works best for themselves—and with a licensed physician. (Both my exercise and diet come with the oversight of professionals.)
So, the prince in the old saying “eat breakfast like a king, lunch like a prince, and dinner like a pauper” might need to retire.