The types of food you eat can make a massive difference to your sleep and energy levels, with certain nutrients making it easier to fall (and stay) asleep or get us moving. We also know that there might be some gut health and blood sugar benefits to the order in which we eat our foods. But have you ever stopped to think about how the timing of your meals affects you?

This brings us to the circadian diet – an approach to eating designed to follow the fluctuations of our natural body clock. Known as your ‘circadian rhythm’, this internal timer is responsible for everything from your sleep hormones to your body temperature. Our metabolism and gut microbiome are also linked to this rhythm, which is where the circadian diet comes in.  

Fans of the circadian diet claim that keeping the circadian-related fluctuations in our metabolism and gut microbiome in mind while we’re eating can help to improve digestion, reduce insulin resistance and optimise metabolic function – all of which can have implications for our short- and long-term health. But what actually is the circadian diet? And is it something we should follow? 

There are several different interpretations of the circadian diet, but most typically involve eating within a set ‘window’ and fasting overnight. This usually involves a 12 hours on/12 hours off approach. That might mean, for example, eating between 7am and 7pm and then fasting until the morning.

“Some research also suggests that the ideal eating hours for a circadian rhythm fast might be between 8am-6pm,” explains Hannah Alderson, a BANT-registered nutritionist and hormone specialist. “This is a kind of early time-restricted eating pattern, where you break your fast in the morning and enter into another fast later in the afternoon.” 

This varies from most forms of intermittent fasting because it involves eating first thing when you wake up in the morning, as opposed to holding off until later in the day. This is because fluctuations in your circadian rhythm lead to an increase in insulin sensitivity in the morning, which allows the cells of the body to use glucose more effectively, keeping blood sugar stable. 

Staying away from midnight snacks and heavy late-night meals is also a key aspect of the circadian diet, as this is when insulin sensitivity is at its lowest. The gut microbiome also follows a circadian rhythm and tends to be least active at night, so you’re more likely to experience digestive discomfort by eating your last meal long before you go to bed.  

The circadian diet is not only designed to support digestive health and reduce potential discomfort; by eating in a way that mimics a healthy circadian rhythm, studies have shown that we may be able to avoid circadian rhythm disruption and keep things running as they’re supposed to.

“Your circadian rhythms, metabolism, hormone health and nutrition are all intimately linked, so promoting an eating window to support this intricate bond can support optimal health,” Alderson says. 

“In studies, timed meals have been shown to play a role in synchronising peripheral circadian rhythms [the part of the circadian rhythm which exists in our organs and tissues] in humans and may have particular relevance for patients with circadian rhythm disorders or hormonal dysfunction.”

In this way, following a circadian diet could potentially be beneficial for people who struggle with disrupted sleep or other symptoms of circadian disruption.  

While following a circadian diet may be good news for your body’s ability to function, Alderson warns against being too restrictive when it comes to eating. There’s a difference between trying to do what’s best for your body and getting stuck in a pattern of restriction, so it’s best to take things slow.

“Focusing on an early time-restricted eating pattern can lead to you cutting out vital nutrients in the evening and seeing a negative impact on social patterns, like going out for dinner with friends in the evening,” she explains. Being overly restrictive about when you can and can’t eat can also be a trigger for binge eating, she adds.

She also recommends avoiding a fasting-based circadian diet (like the 8am-6pm pattern) if you are pregnant, breastfeeding or trying to conceive. This is because “you could be missing out on windows of opportunities to maximise important nutrients that are essential for hormone health, fertility and reproductive functions,” says Alderson. 

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