We often hear what is healthy to eat, but when was the last time you saw recommendations on your local food guide about when is the best time to eat? There is an emerging topic in nutritional research called Time-Restricted Eating, also referred to as TRE.
The basis of TRE is very straight forward and just as it sounds: you limit the amount of time you are consuming food during the day. As simple as this may sound, TRE is one of the most powerful strategies you can implement to improve your health without changing what you eat.
What is Time-Restricted Eating?
As mentioned previously, time-restricted eating is simply the act of reducing your eating window during the day. There is no change in what you eat or how much you eat. TRE protocols range from a 12 hour feeding period down to just eating one meal per day in a 1-2 hour window.
Restricting food for MORE than 24 hours is considered to be intermittent fasting and is a separate practice with different physiological outcomes and benefits than TRE.
In most TRE studies, participants consume an isocaloric diet (meaning the same number of calories just in a smaller window). For example, instead of eating 3 meals between the hours of 7am-9pm for a total of 2000 daily calories, participants eat the same 3 meals/ 2000 calories between 8am-4pm (shifting from a 14 hour to 8 hour eating window).
Time-Restricted Eating Benefits
The benefits of TRE are nearly endless because of its impact on two key health fundamentals:
1. Circadian Rhythm
Your circadian rhythm is the natural sleep-wake cycle that occurs approximately every 24 hours in all living things. It is your master clock that regulates your cellular function and gene expression. Circadian disruption is now recognized as a major causative factor in disease development and cancer, especially in shift workers.
Light is the most important input to regulate our natural circadian rhythms, but food also plays a crucial role. Eating at the wrong time (late at night) instead of during the day when our body is optimized for food digestion and utilization can significantly disrupt our circadian rhythm.
Since TRE usually limits the eating window to a period during the day, this supports a healthy circadian rhythm and mimics an ancestral way of eating (no uber eats or fridges to grab a late night snack!).
To play devil’s advocate, you could still technically do TRE with an eating window late at night but this has proven to be inferior to “early TRE” where the feeding window occurs earlier in the day.
Learn more about optimizing circadian rhythm in our Circadian Rhythm Academy section in our blog.
2. Metabolic Flexibility
Metabolic flexibility is your body's ability to efficiently shift between different fuel sources. The 2 main sources of fuel are fat and sugar (glucose). A healthy metabolism will shift between glucose and fat each day, primarily utilizing fat as the primary fuel source between meals and while sleeping.
In westernized cultures, not only do we eat too much, but we also eat too often, rarely allowing our body to shift into fat burning mode. Circadian researcher Sachin Panda estimates that 90% of people eat for more than 12 hours per day.
TRE forces the body into using its own stores of fat for energy. This is the key to weight loss and good overall metabolic health. When you are constantly eating (especially high carbohydrate/sugar foods) your body never has the opportunity to shift from glucose to fat metabolism. Several studies have demonstrated the metabolic benefits of TRE including weight loss, decreased blood glucose, improvements in body composition and much more.
How to Implement Time-Restricted Eating?
- Always eat within a 12 hour eating window, minimum! This is a good place to start if you have never experimented with TRE.
- NO calories should be consumed within your fasting period. Black coffee, tea and other non-caloric beverages are fine.
- Ensure your eating window ends no later than 3 hours before you go to bed to avoid circadian disruption (8PM latest if you’re a night owl).
- As a general rule of thumb, aim to limit your eating window to only while the sun is up. This is extra difficult in the winter months when the sun sets earlier. Naturally your eating window should be shorter during the winter months due to shorter days, so use this knowledge to apply to your life & just do the best you can.
- Once you become comfortable with a 12 hour eating window, slowly reduce it 1 hour at a time until you find your optimal feeding window (for most people it is fasting between 14-18 hours, with a feeding window somewhere between 6-10 hours). Every body is different. Speak to a health professional to find your optimal feeding window!
- Choose 1 day per week where you commit to a longer fast with the goal of increasing your metabolic flexibility. If you are just starting out this may be a 12-16 hour fast. If you are more experienced this may be up to 24 hours. I recommend Metabolic Mondays (thanks Mike Mutzel)!
*Always speak with a medical professional before attempting a fast.