Why when we eat matters

Written by: Harry Booth



Time to read 3 min

When it comes to maintaining a healthy diet, the old adage "calories in, calories out" doesn't tell the whole story. Sure, the types of foods we eat play a crucial role in our overall health and wellness. But the timing of our meals and snacks can have just as much of an impact on our bodies and overall health as the contents of our plates. From regulating metabolism to improving sleep and digestion, the when of eating is worthy of our attention. In this article, we delve into the science behind meal timing and offer tips for building a healthy eating schedule that works for you. 

Your metabolism speed depends on the time of day

We’ve all met someone with a fast metabolism. No matter how much they eat, they magically burn it right off. For others of us, metabolism feels less like a raging inferno and more like smoldering embers. When even a modest amount of fuel is added, it can take hours to burn through. Fire isn’t just a metaphor for metabolism. The modern calorie—a unit of nutritional energy—was devised in the 19th century by French chemist Nicholas Clément, by burning substances and measuring how many degrees they heated a liter of water. And while it’s true that the rate of burn varies from person to person, it also changes constantly throughout the day.

The reason our metabolism’s speed is constantly changing makes perfect sense when you consider how our ancestors lived. Food either had to be foraged for or hunted. Calories were scarce. Keeping our metabolism running at a blazing pace continually was downright wasteful. Instead, our bodies evolved to speed up the metabolism during the day when we were likely to eat and slow burn through the night while we slept.

Our eating window has widened, but it has come at a cost

The timing of these shifts is set by the circadian rhythm. Today our world looks nothing like that of our ancestors. Our food-stuffed refrigerators conveniently light up when opened. It’s almost like they were purposely designed for late-night snacking. But our underlying biology hasn’t changed. Night-time calories are converted to energy slowly because they’re being chucked on glowing embers. As our eating window has widened, creeping into the night, so have our waistlines.

In several pilot studies, participants lost weight and reduced markers for pre-diabetes simply by changing their eating times, with or without an explicit reduction in calories. Results like these have contributed to the meteoric rise in popularity of intermittent fasting. The most enthusiastic practitioners take it to the extreme, eating only once per day, which is impractical for most. Yet sticking to the general principle of eating while the sun is up and fasting three hours before bed is a good idea. That means avoiding heavy meals before bed, but it also rules out lighter snacks and beverages. Anything other than water and prescription medication will technically break the fast. The benefits of timed eating extend far beyond weight loss—think improved digestion, appetite regulation, sleep, energy, and more.

"Yet sticking to the general principle of eating while the sun is up and fasting three hours before bed is a good idea."

Eating at the right time reinforces your body clock

The circadian rhythm— the roughly twenty-four-hour biological clock that keeps all our body’s systems synchronized with one another —is the common thread that ties all these benefits together. Think of the circadian rhythm like the conductor of an orchestra, ensuring that all our systems are playing in unison.

The timing of the circadian rhythm is set primarily by blue light, to synchronise with Earth’s day-night cycle. But it also takes cues from the systems under its regulation. So, when you eat during your circadian night, it pushes your circadian rhythm out of alignment, which has cascading effects on other aspects of your health. On the other hand, eating at the right time reinforces the circadian rhythm with far-reaching benefits.

In the fast-paced world, we live in, it's easy to get caught up in the hustle and bustle and forget about the importance of meal timing. But as it turns out, when we eat can be just as crucial as what we eat when it comes to maintaining a healthy diet and overall wellness. From regulating metabolism to controlling appetite, the timing of our meals can have a significant impact on our bodies. So the next time you reach for a snack, consider not just what you're eating but when you're eating it.


  • The time we eat has a big impact on the way our body processes that food.
  • Avoid consuming calories three hours before bedtime.
  • Aim to consume all your calories within a ten-hour window.

You might also like