The circadian rhythm: how it impacts our weight, sleep and hormones

Your circadian rhythm, which, in short, dictates your sleep-wake cycle, is heavily influenced by your lifestyle choices; from what you eat and drink to how much you move during the day.

For women in midlife, hormone fluctuations can make a big difference to our sleep and energy levels. But, there’s evidence to suggest that becoming better acquainted with your circadian rhythm can help you to get a good night’s sleep and feel more energised.

Here we explain how to become better acquainted with your circadian rhythm and reap the benefits for our weight, sleep and hormones.

What is our circadian rhythm?

“Our circadian rhythm is our internal 24-hour clock and it tells our body what to do at certain times of the day,” says Dr Lindsay Browning a sleep expert at Trouble Sleeping and on social media @DrBrowningSleep. “It influences many aspects of our health and wellbeing, including core body temperature, when we feel sleepy or awake, food digestion, our immune system and stress hormones (such as cortisol).”

How does our sleep impact our hormones?

“Hormones are internal messengers and are used by the body clock, cells and organs to communicate,” says Dr Kat Lederle, sleep and body-clock scientist.

The two main hormones that dictate your sleep cycle are melatonin and cortisol. Cortisol, aka the stress hormone, starts to rise as morning approaches, helping you to wake.

“Cortisol affects the liver and insulin sensitivity of the body, which has a knock-on effect on our metabolism,” explains Dr Lederle. “Melatonin is also suppressed by the morning light, which, at the same time, increases serotonin levels and improves our mood.”

Does bedtime impact weight gain?

“One cause of weight gain that is often overlooked is circadian misalignment, for example, eating at night when the body is not used to it,” says Dr Lederle. “It’s not just our body and mind that feels different throughout the day, the microbiome inside the gut changes too. Daytime gut bacteria help us to digest food, but night-time gut bacteria are not usually involved in digestion. When you eat late and the ‘wrong’ type of bacteria are present, it will take longer to digest the food.”

In a study conducted by researchers from Kings College London and ZOE, irregular sleep patterns were found to be associated with harmful bacteria in your gut. And, as Kat explains, it’s not just digestion that’s affected by changing your mealtimes.

“If you eat later,  the nutrients that are extracted and enter the bloodstream won’t be taken up by the destination cells/organs as easily as during the day,” she explains. “Weight gain might be another side-effect of irregular eating, particularly late or night-time eating. Eating at the wrong time of day means we tend to go for calorie-dense, palatable unhealthy food to keep our energy levels up.

“Finally, our appetite hormones, including leptin and ghrelin are under circadian control. If their rhythms are disrupted by irregular eating and/or irregular sleep times, this can negatively affect our weight.”

4 ways we can help our circadian rhythm

If you want to sleep through the night, then it’s a good idea to make sure you’re nailing the basics. Working with your body’s natural rhythm will give you more energy during the day and help you drift off quicker come bedtime.

Keep to regular mealtimes

“If you can, stick to regular mealtimes and have your last meal in the late afternoon or early evening so your body, particularly your gut, can prepare for bedtime,” advises Kat. “Limiting your eating window to 11 hours or less seems to be beneficial for metabolic health and sleep.”

Get your morning sunlight

“Making sure that you have regular exposure to light and dark can help your circadian rhythm,” says Kat. “Morning light is a strong waking signal as it tells the body clock that the day is starting. Make your environment bright in the morning and then lower the light intensities in the evening.”

Ditch the midnight snacks

“If you wake up in the night hungry, it is a good idea to try not to eat food when your body thinks you should still be asleep,” says Lindsay. “This is because your circadian rhythm controls your digestive system, which slows down overnight. Eating food when your body thinks you should be asleep can lead to gut health issues.”

Avoid checking emails before bed

“Electronic devices such as smartphones and tablets produce bright light,” says Lindsay. “To fall asleep quickly and to avoid disrupting our circadian rhythm, we should ditch these devices near bedtime. The bright light they emit can confuse our circadian rhythm into thinking that it’s still daytime. Instead, wind down with a book or a piece of relaxing music.”

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