Written by: Peyton Lessard
Reviewed by: Emily J., MSc RD
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Time-restricted eating (TRE), a form of intermittent fasting that focuses on meal time frames rather than food quality or quantity, has been gaining popularity in recent years — but is it right for you? Learn the ins and outs of TRE and its impact on your health.
From keto to high-protein, there are a lot of ways to eat. Some show promising health outcomes, while others haven’t yet reached scientific consensus.
Time-restricted eating is a relatively new form of eating that focuses on the hours that you eat in the day rather than following a specific diet. Time-restricted eating research has shown promising health benefits — and implementing this eating pattern into your routine is pretty simple.
Time-restricted eating (TRE) involves consolidating your eating window to less than 12 hours of the day . The importance here is the time frame of your meals rather than the quality or quantity of the foods you eat.
Put simply, you have fewer hours in the day to eat your calories, but the source of the calories can be whatever you want.
Another term commonly used in place of TRE is intermittent fasting (IF).
In a fasting diet, your calories are severely limited during specific times of the day, week, or month . Calorie restriction, or counting calories, is commonly understood as sticking to a certain number of calories each day.
In other words, calorie restriction refers to reducing your daily caloric intake below normal, without malnutrition or loss of essential nutrients, often with the goal of losing weight. TRE is just one type of fasting diet. Alternate-day fasting, a 5:2 eating pattern, and periodic fasting are also common .
While these are all different names for eating patterns, they all have the same endpoint: fewer calories consumed in a day.
TRE has gained popularity, specifically in its role as a weight loss strategy. Most time-restricted eating studies suggest that while it is effective, it’s actually not too different from calorie restriction .
IF or TRE may be easier for you to sustain because you’re not actively counting calories at every meal and don’t have to restrict the types of food you eat. Instead, you can eat what you like, as long as it’s within a designated window of time.
This shift in thinking may provide psychological relief for some as the focus isn’t on what you’re consuming, and you don’t feel as restricted as you might on a typical diet.
TRE has received a lot of attention recently due to its many health benefits including (but not limited to) cardiovascular health, weight loss, and improved metabolic functions [1, 4]. It’s important to note that these benefits are most likely due to the calorie restriction . However, some promising research shows that TRE may be beneficial for other reasons.
TRE has a specific impact on circadian rhythms.
Your circadian rhythms are your internal biological clock that runs on a 24-hour cycle. They play a role in promoting preparatory changes in metabolic functions such as adapting to changes in light, temperature, and nutrient availability in the body . They also regulate the body’s production and secretion of endocrine factors (processes for regulating food intake, growth, and development.
Simply put, circadian rhythms work by ensuring that everything you need to live is happening in the right place at the right time of day.
Your circadian rhythms can be influenced by factors such as sleep patterns, physical activity, light and dark exposure, and nutrient intake. When disrupted, these factors can throw off your circadian windows and negatively impact hormones that influence metabolic health and organ function. These changes are associated with an increased risk of infectious and chronic diseases.
A multicenter, randomized control trial examined the effects of a 25% calorie restriction diet (participants were prescribed a 25% restriction in calorie intake based on energy requirements taken at baseline) on markers of longevity, metabolism, and biological function in 188 healthy, non-obese men and women, aged 20-50 years old, over a 2-year period .
The results found significant decreases in LDL (“bad”) cholesterol, triglycerides, C-reactive protein, and blood sugar, and increases in HDL (“good”) cholesterol and insulin sensitivity.
These results are powerful, as there was a significant impact on 4 out of 5 of the markers of metabolic syndrome. The intervention group achieved a 12% calorie restriction and maintained a 10% weight loss. This study showed that following a calorie-restricted diet pattern for two years was not only manageable but also safe.
Another randomized controlled trial found that body weight decreased in those who were following an alternate-day fasting (ADF) eating pattern . The amount of dietary fat found in the blood (triacylglycerol concentrations) was decreased and LDL (“bad” cholesterol) particle size increased in the ADF group compared to the control group. This study shows that ADF was effective for weight loss and had a protective effect on heart health in both normal and overweight adults.
Arguably the most compelling reason for adopting a TRE dietary pattern is the weight loss benefits. Although there aren’t clear indicators of what time frame is best to optimize health outcomes, some studies have examined whether having an earlier TRE window is more advantageous compared to a later window.
In a 14-week study, 90 obese participants (80% female), aged 23 to 75 years old, were split into two groups . One group had an early TRE window (7:00 am to 3:00 pm), while the other ate over a 12-hour (and greater) period. The group that practiced TRE:
The intervention group effects were equal to reducing calorie intake by an additional 214 kcal/day. Additionally, in a secondary analysis of 59 people who completed the study, the early TRE group was also more effective in losing body fat and weight than the control group.
Recent caloric reduction interventions have found greater weight loss if lunch was consumed earlier in the day .
Studies on the timing of food intake and length of overnight fasting for health outcomes are emerging. Two studies (from 2018 and 2015) revealed that a prolonged overnight fast of 13 hours or longer and/or eating an earlier dinner correlates with a reduced risk of cancer [9, 10]. Emerging research suggests that eating/fasting schedules that align with circadian rhythms have metabolic implications that are relevant to breast cancer .
The 2015 study also found that every 3-hour increase in night fasting was associated with a 4% lower 2-hour glucose measure and a decrease in HbA1c level.
In other words, a longer overnight fasting period was significantly associated with improved glycemic regulation. You’re more insulin sensitive in the morning, so eating earlier is better from a metabolic standpoint.
Hormonal regulation of glucose and glucose metabolism is balanced by our circadian rhythms .
Recent human studies have shown that TRE increased insulin sensitivity and decreased postprandial insulin, oxidative stress, blood pressure, and appetite .
Of note, this study was performed in men with prediabetes and examined early time-restricted feeding (eTRF), which is a type of TRE that involves eating earlier in the day for alignment with circadian rhythms in metabolism.
While this study was done in people with prediabetes, and may not be generalizable to a healthy population, it still may be worth trying to see if it works for your unique biochemistry, energy levels, and sleep.
TRE can be an easy addition to your daily routine, especially due to its simplicity and versatility.
To get started, keep the following in mind:
There are many methods of TRE and what works for you may not be the same as what works for your friend. Depending on your individual goals and lifestyle, one of the methods below may be best.
Refraining from eating for a specific time period (e.g., 16 hours) and then unrestricting meals during your “feeding window” (e.g., 8 hours) is known as the 16:8 eating pattern . It’s also known as the Leangains diet . This method would be a good option for beginners as it is the least intensive in terms of the number of hours that one is restricting their calories.
Engaging in unrestricted eating for 5 consecutive days of the week and then having restricted caloric intake on the other 2 days is known as the 5:2 method . It’s also known as the Fast diet .
There should be at least 1 non-fasting day between fasting or calorie restriction days. This method would be a good option for someone who did not see or feel any benefits from the 16:8 method. It’s important to note that on calorie restriction days, high-intensity or endurance training should be avoided due to a lack of energy (or calories) available in the body that is required to match your energy expenditure.
The last type of IF or TRE involves unrestricted eating every other day and minimal calories consumed on between days, which is known as alternate-day fasting . This form of fasting is the most extreme of the methods described, and may not be the best for beginners or those with certain medical conditions . You should consult with your healthcare professional before implementing this method.
Although there are many promising health benefits from following a TRE pattern, these methods are not suitable for everyone . If you fall into one of the categories below, you should consult with your healthcare professional before testing one out for yourself.
Remember that flexibility in your routine is okay — don’t forget to complement any new eating patterns you try with proper hydration, nutrition, sleep, and exercise.