+ Our Circadian Clocks
Research shows that time-restricted eating, a type of intermittent fasting, may provide potential health benefits. But when you fast may be the key. Find out what the research says about when and how long your “eating window” should be to reap health benefits.
On today’s episode of The Sitch, we’re talking time-restricted eating. Or “time-restricted feeding,” if we’re talking about mice.
WHAT IS TIME-RESTRICTED EATING/FEEDING?
TRF for short refers to a type of intermittent fasting where all of the day’s calories are consumed during a specified time window – usually an 8-12 hour period. I talked about TRF in my previous video on Intermittent Fasting and shared the emerging research on its benefits.
To recap, TRF has been shown to improve metabolic markers like insulin sensitivity, beta-cell functioning, and hemoglobin A1C. It’s also been shown to lower blood pressure, decrease appetite in subjects, and potentially reduce the risk of breast cancer.
EARLY TIME-RESTRICTED EATING + OUR CIRCADIAN CLOCKS
However, these benefits may be limited to TRF regimens where the majority of food intake occurs during daylight hours, which aligns with our body’s natural circadian rhythm. Circadian rhythm refers to the 24-hour cycle in which our body’s physiological processes revolve.
It is internally regulated by “clocks” or genes that are turned on and off at different times of the day based on input from both internal and external stimuli. Light, temperature, and food are all external stimuli that tell our clocks it’s time to reset.
For example, in the morning, in response to light and food, our clocks increase insulin sensitivity and decrease melatonin. In the evening, insulin sensitivity decreases and melatonin increases, preparing the body for rest and processes related to cell repair.
EFFECTS OF LATE TIME-RESTRICTED EATING
If we are constantly eating late at night, when our body should be switching into repair mode, it throws off our circadian rhythm and may lead to metabolic problems and sleep disturbance. And that’s exactly what the research shows.
Studies of time-restricted eating show that people with longer eating windows, whose food consumption spills into the night, have worse health outcomes than those with shorter windows. For example, women with early breast cancer who eat for more than 13 hours a day have a 36% higher risk of breast cancer reoccurrence than those who eat for less than 13 hours a day.
Studies of nurses who work rotating overnight shifts have also shown increased rates of breast cancer in the range of 36-79%. In fact, the international agency for research on cancer has classified “night shift work” as a “probable carcinogen to humans” based on studies showing a link between night shift work and breast, prostate and colorectal cancer.
They believe the mechanism, at least in breast cancer, may be alterations in estrogen homeostasis. An increased concentration of circulating estrogen is strongly associated with a higher risk of breast cancer.
This goes back to what we were talking about with our circadian clocks. These genes, found in every cell and organ of our body, control various physiological processes – like the production of hormones – and they are turned on or off at certain times of the day based on internal and external feedback.
If genes in breast tissue that control estrogen production – that are supposed to be off at night – are constantly on due to light and food intake at odd hours, you can see how this could easily disrupt the delicate hormonal balance.
- We should aim to align our food intake with our sleep cycle as much as possible. Eating during daytime and fasting at night.
- We should aim to keep food intake within a 12-hour window or less. For most people that just means ending eating after dinner and beginning again at breakfast – or what I call “Common Sense Fasting.”
WHAT ABOUT SHIFT WORKERS?
What if you’re someone who does night shift work? Are you doomed? Not at all! These studies simply show a link between circadian disruption and poor health outcomes. They do not prove causation and they are certainly not a sentence.
Also, they didn’t take into account dietary pattern or duration of food intake – it’s possible that a healthy diet or time-restricted feeding could help to mitigate the negative effects of night shift work. My advice would be to attain as much normalcy with your diet/shift schedule as possible.
If you need to be awake for extended periods of time for work, still aim to limit food intake to a 12 hour or less window and try to stop eating 2-3 hours before you go to sleep, to avoid interfering with your body’s melatonin production.
Eating a plant-based diet is also a good bet as research shows that vegans and vegetarians have lower rates of hormone-dependent cancers like breast and prostate cancer.
And that’s The Sitch!
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Do you practice time-restricted eating? When do you typically start and stop eating each day?