circadian rhythm and time-restricted eating
Our personal sense of health changes throughout the day with our circadian rhythm. In the morning we hope to feel well-rested and fully digested, while during the day, healthy is more about not being hungry and being productive. By the time we go to bed, being able to fall asleep quickly and easily is important. This 24 hour circadian system drives rhythms of rest and activity. Our circadian rhythm both impacts and is impacted by our health.
The rhythms of the core clocks change over our lifespan. Over time becoming increasingly disregulated, which is associated with aging and disease.
Light is the primary signal that guides the master clock. In addition, our body temperature, oxygen delivery to tissues, and food intake also can change the circadian system. All of these cues can alter the expression of key metabolism genes.
WHEN we eat, in part, determines our physiological response to food, and it’s impact on our health. For example, Dr Rhonda Patrick describes a trial that analyzed the glycemic response to the same meal at different times of the day. She states, "(the study) demonstrated that the postprandial (after a meal) glucose increase was lowest in the morning and highest in the evening. Time-restricted eating (TRE) has emerged as a key intervention to maintain synchronized circadian rhythms between the master and peripheral clocks as a means to improve health." When we eat within a smaller window of time we can greatly benefit our health and wellbeing through influencing our circadian rhythm and the associated processes.
“Our modern lifestyles see us eating throughout the day and the night, causing insulin resistance and inflammation, removing the satiety effect of leptin, which leads to further feeding, usually as snacks containing simple sugars, which further increase fat storage and tissue inflammation.”
key benefits of time-restricted eating
According to recent research, time-restricted eating (TRE) improves health and longevity outside of calories or diet composition (Yes. You read that right! If you aren’t ready to change what you are eating, start with when you are eating).
Obesity and Metabolic Syndrome: Pour sleep impacts our health in many ways including our weight and our tendency toward metabolic syndrome! A recent study showed that TRE may have important applications for people with impacted circadian rhythms (shift workers, elderly etc.), and could result in weight loss and a reduction in metabolic issues, such as increased blood pressure, high blood sugar, excess body fat around the waist, and abnormal cholesterol or triglyceride levels. Even when there wasn’t weight loss, studies have shown TRE positively impacts blood pressure, insulin sensitivity, blood biomarkers, and oxidative stress. Other studies have confirmed these benefits and have shown eating within a 6-hour window reduces evening appetite.
For an added impact, this study suggests we train in a fasted state. “While training of any kind promotes better insulin sensitivity, training in the fasted state enhances this effect. This study found that relatively high-intensity “cardio” performed while fasted increased subjects’ insulin sensitivity beyond the group who did the same training after a carb meal, even in the context of a normally obesogenic high-fat, high-carb diet,” states Mark Sisson, from Mark’s Daily Apple.
Gut Health and Inflammation: Multiple sclerosis (MS) is an autoimmune disease that is believed to have a person's diet as a potential contributing factor. In a pilot clinical trial on MS patients, TRE protectively altered the gut flora and decreased inflammation. Time-restricted eating has been shown to increase gut bacteria richness in species that have previously been shown to promote health in the colon.
Cardiovascular Health: An American Heart Association meta-analysis concluded limiting the number of hours of eating during the day or maintaining overnight fasting (e.g.TRE) was beneficial for maintaining cardiovascular health.
Autophagy and Neurodegenerative Diseases: Autophagy, recycling damaged cells (autophagy blog here), is reduced in the presence of insulin, so those with insulin resistance, pre-diabetes, and diabetes have suppressed autophagy and age faster. TRE, on the other hand, enables us to achieve the rates of autophagy of a younger individual by impacting our insulin sensitivity.
Research has focused specifically on the way fasting promotes autophagy in the brain, suggesting that it could be an effective way to lower the risk of neurodegenerative diseases like Alzheimer’s and Parkinson’s! Studies have shown that TRE can protect neurons against oxidative and metabolic stress of these neurodegenerative disorders (these effects are accentuated by physical exercise and intellectual activity). TRE (and exercise), also induces mitochondrial biogenesis, which is critical for the formation of synapses in developing hippocampal neurons and the maintenance of synapses in the hippocampus of adult mice...another plus for neurodegenerative disorders.
Tumor Growth: An important 2016 study with a large cohort of breast cancer patients, demonstrated a night-time fast of 13 hours or more was associated with a 36% reduction in breast cancer recurrence!
As we've stated, positive metabolic changes associated with TRE includes improved blood sugar regulation. An analysis of patients with breast cancer found that, compared with women whose HbA1c (3 month blood sugar average) was less than 6.5%, the risk of all-cause mortality was twice as high in women whose HbA1c was 7.0% or more. As blood sugar is lowered, mortality in those with breast cancer went down.
Notably, circadian rhythm misalignment has been linked to increased risk of many cancers, as evidenced by the well-documented association between shift work and increased risk of breast cancer, therefore, we can theorize that “when we eat” could likely impact the chance of a number of types of cancers through its connection to our circadian rhythm.
Photo by Don Ross III on Unsplash
Can I Drink My Coffee When Fasting?
Nutrients can activate peripheral clocks such as those in the liver, but it is unclear whether caffeine acts in the same way. We do know that caffeine disrupts circadian rhythms (i.e. inability to fall asleep) through its stimulating effects, so some argue that it could activate these systems too. Additionally, caffeine metabolized in the liver initiates metabolic processes that could potentially start the circadian clocks.
HOWEVER, some time-restricted eating (TRE) studies included black coffee, while demonstrating notable health benefits. For example, the study that showed a 36% reduction in breast cancer recurrence when compared to those that didn't use TRE allowed black coffee during the fasting period!
In another study in which people with diabetes practiced TRE +black coffee/tea the participants showed improvements in glucose regulation and weight loss.
Finally, polyphenols in caffeinated or decaffeinated coffee induce autophagy in the liver, muscle, and heart in mice four hours after consumption. Autophagy or "self-eating" is our bodies way of removing damaged cells (It is a very good thing!).
Since caffeine may hinder some of the benefits of TRE and I don't want to artificially activate my cortisol levels too early in the morning, I start my day with Trader Joe's Fair Trade Organic Decaf French Roach, and get my caffeinated coffee when I "break my fast". Thankfully, caffeine between 11 and noon does not impact my sleep, but for some it will. In addition, the lower the caffeine, the smaller the impact on metabolism and digestion.
More on exercise…
Those who use resistance training and time-restricted eating (TRE), are likely to have a decrease in blood glucose, blood insulin, and fat mass, while maintaining muscle mass. When weight lifting in a fasted state you are using more fatty acids as fuel rather than carbohydrates. So lifting in a fasted state can result in more fat loss and a better body composition.
With endurance workouts, such as running, there are a lot of benefits to a fasted state, the two key ones include: our body becomes better at burning fat and we have increased glucose sensitivity. So during a workout where performance is not as important to you as health benefits, participating in an aerobic workout in a fasted state is best, especially when your body is used to burning fat (i.e. you are fat adapted b/c you generally eat low carb).
I run at the end of my TRE 16:8 fast so that I can "feed my workout". If I were to do a longer fast, I would likely avoid endurance training since I am at a higher risk of an electrolyte imbalance and fluid loss in that state. Resistance training during longer fasts, on the other hand, does not present with those same issues.
In the end, follow your fasted workout with some kind of protein, and you will mobilize your amino acids and help with the "repair and rebuild" state.
Final tips:
First, whether you are not ready to give up your favorite vice or are happy with what you are eating, but want an added boost to your health…time-restrict eating could be an easy-to-implement next step!! We don't have to follow TRE every day to get its benefits. Recent animal studies have revealed that TRE's improvement of metabolic health is maintained even when there is a temporarily disruption by unrestricted eating on the weekends!
According to Dr. Mark Mattson, Neuroscientist from Johns Hopkins (who researches the impact of TRE), the key is to not have any carbs during the fasting time, but there seems to still be benefits if you have a little bit of fat (i.e. MTC oil). So, if you are struggling to get by without cream in your coffee, there are still benefits.
According to Dr. Panda, Ideally the window of eating ends by 5, 6, or 7 PM. Fasting for 10-14 hours allows us to give our gut a break from processing food. When the fasting is timed so there are 3-4 hours of no eating before bed, our sleep may even be benefited.
Finally, keep in mind that it usually takes about 30 days to adapt to this eating strategy, so don’t become discouraged if it feels hard at the beginning. As with any positive change, finding others who are interested in the same strategy can build positive momentum, encouragement and accountability.
“There are benefits with time-restricted eating even when not following the above plan, so find a window you think you can embrace, and give it a try. This doesn’t need to be an everyday deal either, so you may want to start with just weekdays or every-other-day etc.”
be part of a study by taking pictures
If you are thinking of giving time-restricted eating a try, there is an app that can both help you and help research! Dr. Panda's mobile app-based study of time-restricted eating is available for those that are at least 18 years of age. Just go to myCircadianClock.org.
Just a reminder that you can take all kinds of rabbit trails to learn more about this topic by clicking on the blue words.
This is an update on a past TRE blog.
Amazing sighting on my most resent fasted run!
Wendy Dellis is a certified wellness coach. She joins years of training and work in the area of behavior change, experience as a fitness instructor and run club coordinator with a passion for adventure and people. She lives in Minnesota with her husband, Jay, and two sons.
The information contained on this page is for general information purposes only. Nothing here should be construed as medical or healthcare advice, but only topics for discussion. No physician-patient relationship exists; please consult your physician before making changes in diet or lifestyle.