You’ve probably heard about nutrient timing — the idea that when you eat, and not just what you eat, can play a key role in health.
One approach to nutrient timing is the circadian rhythm diet, a type of intermittent fasting based on following your body’s natural internal clock. But does the circadian rhythm diet work? Before you start shifting your meal times, here’s the science behind this diet.
What Is the Circadian Rhythm?
The circadian rhythm — also known as the sleep/wake cycle — is a 24-hour cycle in our metabolism, physiology, and behavior.
The rising and setting of the sun plays the biggest role in regulating your circadian system, but research suggests meal timing can also affect your circadian rhythm.
What’s Wrong with Disrupted Circadian Rhythms?
Your circadian rhythm regulates when you’re tired and when you’re alert — but it can also influence other aspects of your health, like hormone release, eating patterns, and digestion.
So when something messes with your circadian rhythm — like working a night shift, eating a high-calorie late-night snack, or staring at a screen before bedtime — it can affect more than just your sleep habits.
“We often go through our days without putting much thought to how the repetitive 24-hour cycle of the rising and setting of the sun impacts our health, especially our metabolic health,” says nutritionist Mike Roussell, Ph.D., of the The Dr. Mike Show. “Our body clock is the master regulator of our health.”
What Is the Circadian Rhythm Diet?
As we learn more about the connection between circadian rhythm and eating habits, it was only a matter of time before someone developed a diet around it.
Two recent books have helped build hype around the circadian rhythm diet: The Circadian Code by Satchin Panda, Ph.D., and What To Eat When by Michael Roizen, M.D., and Michael Crupain, M.D.
The circadian rhythm diet offers two key rules for eating in line with your internal clock:
1. Eat during daylight hours.
“The circadian rhythm diet is based around eating when it is light out and then having your last meal as close to sunset as possible,” Roussell explains. It’s a form of time-restricted eating, or intermittent fasting, since you eat during the window of time when the sun is up. In theory, this means you’re eating when your body is primed to take that food and use it efficiently.
2. Make breakfast your biggest meal.
The other key tenet of the circadian rhythm diet is eating your largest meal for breakfast and then eating progressively smaller meals as the day goes on. The belief is that our bodies are better at digesting and metabolizing food earlier in the day than later in the day (though more research is still needed to support this theory).
Can Timed Eating Help You Lose Weight?
Beyond the potential health benefits of supporting your circadian rhythm, you may be wondering if the circadian rhythm diet can help with weight loss. Short answer: it might.
Time-restricted eating can help with weight loss because it limits how many calories you can consume in a day — as long as you do not overeat during your eating window. This can be especially helpful for those who mindlessly nibble after dinner.
“For most people, the snacks they eat at night are lower quality and higher calorie,” Roussell says. “So stopping eat[ing] at 6 p.m. can be a simple way to cut out calories.”
Eating when the sun is up may also benefit your metabolism. In a small study published in The Journal of Nutrition, four women ate 70 percent of their daily calories in the morning, while the other six women ate 70 percent of their daily calories at night. After six weeks, the groups changed their eating patterns to the other timing. The researchers found that eating the majority of your calories in the morning — 35 percent at breakfast and 35 percent at lunch — led to greater reductions in body weight.
Does Science Support the Circadian Rhythm Diet?
It’s too soon to say. While some research suggests that intermittent fasting may help with weight loss, there’s not much research specifically focusing on how meal timing impacts circadian rhythms. And some researchers note that any study results may turn out differently in real life, which is much less regulated than a trial in a lab.
Still, given what we know about circadian rhythms and intermittent fasting, the circadian rhythm diet could be worth trying.
Just keep in mind that this eating pattern will likely take some adjustment. Many of us eat in windows of 12 to 15 hours (or more!), and we tend to skimp at breakfast and consume the most at dinner. The circadian diet “is the opposite of how most function — dinner is usually the largest, not smallest, meal of the day,” Roussell says.
He recommends getting the basics of healthy eating down first — and once that’s second nature, decide whether you want to try timing your meals with the cycles of the sun.