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In recent years, a type of intermittent fasting called Time-Restricted Eating/Feeding (TRE/TRF) has received unprecedented attention in the wellness world. This diet involves only eating during a defined window of time in the day, usually spanning eight to twelve hours. Studies have suggested that this type of structured eating may have a wide range of benefits, including promoting weight loss, supporting cognitive health and even reducing cancer risk. How can one simple practice have so many diverse effects on health?
The answer comes down to our body’s circadian rhythm regulation system, which functions similar to an orchestra. In the same way an orchestra has many different musicians working together to produce a beautiful song, your body has biological clocks ticking away in every cell. And similar to the conductor, there is a master clock in your brain that keeps all of the biological clocks in the body synchronized through physiological and hormonal signals. Just as a conductor can respond to the way the orchestra is playing, the master clock can receive signals back from the players about their performance. This feedback creates a cycle of information that allows all the clocks to adapt to changes and remain in synch. In a perfect world, this biological symphony functions without error.
However, modern society has produced many challenges for this system. Due to the advent of electricity and electronics, we are increasingly exposed to light at night. The conductor clock in our head responds primarily to light cues, and exposure to artificial light when it should be dark can throw it off. An imperfect conductor leaves the rest of the system to fend for itself, causing the body’s clocks to become desynchronized. And because of the built-in feedback loop within the system, these disorganized time cues can reach the brain, making it even more difficult to restore synchrony among all the body’s clocks. This desynchrony is referred to as circadian misalignment. You don’t have to look too far to see the consequences of this misalignment – it’s what is occurring when you experience jet lag, when you are adjusting to daylight savings time, and even why Mondays can feel so terrible after an irregular weekend sleep schedule. In all these situations, the different clocks within your body are receiving disorganized time cues and are struggling to readjust.
When it happens occasionally, circadian misalignment is not a fun experience but does no real lasting harm. However, when this misalignment happens chronically (as in the case of shift work), it can have significant effects on health. Between 15-20% of the workforce in the United States is comprised of shift workers (1), who work out of sync with the light-dark cycle. There are strong correlations between shift work, cancer, and obesity, particularly in women. One study showed that five years of night shift work in women slightly increased breast cancer risk (2). Additionally, in experiments where participants were subjected to just 10 days of simulated shift work, subjects exhibited markers of a pre-diabetic state (3). These stark health consequences are likely related to the role of the ‘conductor’ clock as a key regulator of genes involved in metabolism, clearance of old, damaged, or abnormal proteins, and DNA repair processes (4). Shift work is a dramatic demonstration of the concept of circadian misalignment, but this chronic desynchrony is becoming a reality even for those who work standard 9-5 jobs but are not in sync with the environmental light-dark cycle.
So how can we get this system back on track in spite of modern society’s interference? Research points to the timing of one potent time cue: food. In a perfectly functioning system, the central clock tells our bodies when we should eat, priming the pancreas, liver and gut to break down and absorb the nutrients from food. However, the feedback-based desynchronization of the central clock means we rarely adhere to the ideal eating schedule. One team of researchers investigated this relationship through a smartphone app that tracks feeding behavior. They discovered that participants ate erratically during waking hours, stopping food intake for extended periods of time only during sleep (5). This constant food intake means the body is unable to predict when to prime the metabolic system to most efficiently process these calories, throwing off the body’s circadian clocks – and, in turn, the master clock in the brain.
Time-Restricted Feeding (TRF) solves this problem by giving our body a predictable time window for calorie intake, helping to realign our metabolic clocks. Several studies have demonstrated the metabolic benefits of this practice. One study in mice showed that mice fed during a restricted window lose weight despite ingesting the same calories as free-fed mice, and when fed a high fat diet (similar to the average Western diet), TRF mice were protected from obesity. In humans, when obese and overweight participants shrank their food intake window to 8-12h, they lost weight, improved their sleep, and reported increased energy levels (6-8).
The metabolic alarm clock generated by time-restricted feeding also serves as an important feedback signal to align the multitude of clocks around your body. TRF may have benefits for cognitive health, as it has been shown to improve symptoms of depression and anxiety in response to shift work in rodents (9). In other mouse studies, TRF has been shown to reduce symptoms of the neurodegenerative diseases Huntington’s and Alzheimer’s (10,11) and decrease cancer incidence (12).
In a world full of erratic circadian signals, the timing of food is a simple and accessible intervention to combat misalignment and provide a wide range of health benefits.