Time-restricted eating is a type of eating plan that focuses on the timing of eating. Instead of limiting the types of food or number of calories that people consume, this plan restricts the amount of time they can spend eating.

A person on a time-restricted eating (TRE) plan will only eat during specific hours of the day. Outside of this period, they will fast.

In this article, we look at what TRE is, whether or not it works, and what effect it has on muscle gain.

We also provide beginner’s tips on how to get started with this eating plan.

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TRE means that a person eats all of their meals and snacks within a particular window of time each day. This timeframe can vary according to the person’s preference and the plan they choose to follow. Typically though, the eating window in time-restricted programs ranges from 6–12 hours a day.

Outside of this period, a person consumes no calories. They may drink water or no-calorie beverages to remain hydrated. In some TRE plans, people may also consume unsweetened coffee or tea with no cream.

TRE is a type of intermittent fasting. This refers to any eating plan that alternates between periods of restricting calories and eating normally.

Although TRE will not work for everyone, some may find it beneficial. Recent studies have shown that it can aid weight loss and may lower the risk of metabolic diseases, such as diabetes.

TRE may help a person eat less without counting calories. It may also be a healthy way to avoid common diet pitfalls, such as late-night snacking. However, people with diabetes or other health issues can consider speaking with a doctor before trying this type of eating pattern.

No single eating plan will work for everyone to lose weight. While some people are likely to meet weight loss goals with TRE, others may not benefit from it. It is best for a person to speak with a doctor before trying TRE or any other eating plan.

Recent studies involving people of different ages and in different research settings show that TRE has the potential to lead to weight loss and health improvement:

  • Weight loss: According to a 2021 randomized controlled trial in Nutrition & Diabetes, 30 males and females with obesity who followed 8 weeks of TRE with a commercial weight loss program saw clinically meaningful weight loss of approximately 24 pounds (lb) on average, compared with about 20 lb in the 30 people not doing TRE.
  • Metabolic syndrome and heart disease: A 2021 study in the Journal of Translational Medicine found that 20 females with obesity who followed TRE for 3 months lost approximately 7.5 lb on average from their starting study weight. The TRE group also improved risk factors for both metabolic syndrome and heart disease.
  • Gut microbiome: In a group of 25 people with obesity who followed TRE for 12 weeks, about 9 lb of weight was lost on average, along with small changes to the makeup of the gut microbiota, according to a 2022 study. But the researchers noted the clinical importance of these changes is unknown at this time.
  • Body composition: A 2022 study in Frontiers in Nutrition reviewed clinical and physical information from 43 randomized controlled trials with 2,438 study participants aged 18–79. Compared to non-intervention plans, intermittent fasting, including TRE, resulted in more weight loss and changes in body composition.
  • Type 2 diabetes: For the management of type 2 diabetes, a 2022 review in The Journal of Physiology found that TRE offers the benefit of mild weight loss and better blood sugar management.

Some research notes that health benefits may happen even if people do not lose weight as a result of trying TRE.

Cell Metabolism has published one of the most rigorously conducted randomized controlled trials to date. It found that when eight males with prediabetes who were overweight followed early-TRE for 5 weeks, several markers of heart health were improved, including:

The observed improvements in heart health occured even when the TRE group did not lose weight, and they reported a lower desire to eat in the evening. Researchers need further studies done on more people over longer periods of time to confirm these findings.

Is it better for weight loss than regular calorie restriction?

Accumulating research suggests that TRE has potential, but not all studies show it is more effective for weight loss than daily regular calorie restriction.

A 2017 review concluded that intermittent calorie restriction, including TRE, offers no significant advantage over limiting calorie intake each day.

More recently, a 2022 randomized controlled clinical trial in the New England Journal of Medicine showed TRE had no weight loss benefit after 12 months.

In the trial, 139 people with obesity followed TRE while also eating fewer calories or followed daily calorie restriction alone. When the study ended, there were no differences between the groups for weight loss.

Studies from 2019 and 2022 note that TRE results in equal weight loss to regular daily calorie restriction in people who are overweight or have obesity.

Because of this, it is possible for TRE to be an option for people who want an alternate solution to daily calorie restriction for weight loss.

Other research does not show any benefit of TRE for weight loss compared with eating regularly throughout the day with no calorie restriction. This includes when study participants receive no instruction to change their food choices or activity levels.

As the science on TRE for weight loss advances, some researchers have expressed the need for caution around who might consider following TRE.

Among people who are overweight or have obesity, some studies have found that weight loss in TRE may be due to the loss of lean mass (muscle) versus fat mass (adipose tissue).

Therefore, it is especially important for people who are overweight or have obesity and who also have comorbidities such as sarcopenia to talk with a doctor before trying TRE.

Does TRE work for long-term weight maintenance?

The current evidence base shows promise for the role of TRE in weight loss in the short term (from studies lasting less than 6 months).

However, researchers need longer-term studies with larger numbers of more diverse participants to determine whether TRE can lead to clinically meaningful weight loss that a person can maintain over time.

A 2022 study from the journal Appetite aimed to look at the barriers to or facilitators of following TRE over the long term. It used 20 middle-aged adults who were overweight or had obesity and were at risk of type 2 diabetes.

The researchers assessed how easily people could incorporate TRE into daily life following a 3-month study with structured interviews.

Seven study participants kept up with their instructions on TRE from the study, 10 adjusted their approach to follow a different version of their original instructions, and three did not follow through with their instructions.

Challenges to keeping up with TRE in the long-term included:

  • eating norms while attending social events
  • inconsistent schedules of daily life
  • irregular eating occasions
  • not meeting weight loss goals
  • absence of family support
  • feelings of guilt or self-blame

Researchers need more work to understand how TRE influences the biological, behavioral, psychosocial, and environmental facilitators of and barriers to successful long-term weight maintenance.

Research has shown that TRE does not seem to adversely affect the overall maintenance of muscle.

One 2019 study investigated TRE in 11 adults who were overweight. They followed early-TRE for 4 days, where they ate between 8 a.m. and 2 p.m., and then switched to the control schedule of eating between 8 a.m. and 8 p.m..

The authors concluded that when participants followed the early-TRE plan, they had increased activity of mTOR. This is a protein marker thought to be involved in maintaining muscle mass.

A 2020 study, in the American Journal of Clinical Nutrition, randomly assigned 16 otherwise healthy males to follow early-TRE for 2 weeks or just regular calorie restriction. It found the TRE group saw an improved ability for their muscle to use glucose and branched-chain amino acids.

A 2022 study in Scientific Reports assigned 46 otherwise healthy older males to follow 6 weeks of either TRE or their regular eating plan. The TRE group had no significant changes in their muscle mass. This suggests the participants kept their muscle throughout the study period.

In studies that paired TRE with a structured resistance training program, muscle mass was maintained or small gains in muscle health occured:

  • Muscle growth: A 2019 study randomly assigned 40 otherwise healthy and active young females to 8 weeks of following their regular eating pattern, TRE, or TRE and a dietary supplement with a link to muscle improvement. Muscle performance and muscle growth improved with no major differences between the groups.
  • Maintenance of lean mass and muscle strength: A 2020 study found that 4 weeks of TRE and a 25% reduction in calories kept lean mass to the same level as a regular calorie restriction in 26 active young males. Both groups saw an equal loss in body fat without adverse effects to their lean mass or muscle strength.
  • Muscle endurance: A 2021 study randomly assigned 21 middle-aged adults who were overweight or had obesity to complete 8 weeks of TRE or regular eating for 8 weeks. Both groups had a small increase in lean mass, muscle strength, and muscle endurance.
  • Muscle performance and protein intake: A 2016 study asked 20 young males to stick with their TRE or regular eating pattern for 10 extra months. According to the 2021 study that published the results, both groups increased their bench press and leg press performance despite losing fat-free mass. The TRE group maintained a 10% energy decrease while keeping protein intake around 1.9 grams per kilogram of body weight.

The totality of evidence suggests that in combination with resistance training, TRE may improve body composition and help people maintain fat-free mass similarly to non-TRE plans. Fat-free mass includes the body’s muscle, organ, bone, and water content.

Some researchers note that TRE may not be the best approach if primary health goals include building muscle mass and improving muscle strength because of the inconsistent eating frequency and nutrient availability for muscles.

However, TRE may be a good alternative for some people who are interested in changing their body composition or losing weight without it being problematic for maintaining muscle mass, growth, strength, performance, or endurance.

Researchers need additional longer and larger studies in different research settings with different populations to better understand the relationship between TRE and muscle health.

A person should consider talking with a doctor about the effects TRE may have on muscle health.

One of the main advantages of TRE is that it requires no special food or equipment. After getting a doctor’s approval, a person can begin a TRE plan immediately.

However, as with any eating plan, some thought and planning can increase the likelihood of success. The following tips can help to make TRE safer and more effective:

Starting gradually

People should start with a shorter fasting period and then gradually increase it over time. For example, start with a fasting period of 10:00 p.m. to 6:30 a.m. Then increase this by 30 minutes every 3 days to reach the desired fasting period.

Studies have suggested that restricting feeding periods to less than 6 hours is unlikely to offer additional advantages over more extended feeding periods.

Exercising without overdoing it

It is tempting to start a vigorous exercise plan alongside eating less for faster results. However, with TRE, this can make the fasting period more difficult.

People may wish to keep their existing exercise program the same until their body adjusts to the new eating plan. This can help to avoid increased hunger from extra workouts, which may cause burnout or failure.

Focusing on protein and fiber

Hunger can be difficult for people who do not have experience of fasting for several hours each day. Choosing foods rich in fiber and protein during the eating window can help to combat this. These nutrients help a person feel full and can prevent a blood sugar crash or food cravings.

For example, a person may eat whole grain bread and pasta rather than white or refined grains. They can choose a snack that includes protein in the form of lean meat, egg, tofu, or nuts.

Avoiding worrying about setbacks

It is normal to have days where TRE does not work out. For example, a night out with friends, a special occasion, or a slip-up may lead to people eating outside of their fixed eating window.

However, this does not mean that they should quit.

It is best to see setbacks as an opportunity to get back on track. The next day, people can recommence the TRE plan and continue toward their goal.

For most people, TRE is unlikely to be a miracle weight loss cure. However, studies have shown that it can offer health benefits without a high risk of side effects.

It can be a simple way for many people to reduce their calorie intake without complicated or strict diet rules.

Q:

Which people, situations, or medical conditions might a time-restricted eating diet suit and why?

Anonymous

A:

Time-restricted feeding seems to be beneficial for most people who are not experiencing acute illness or taking medications to lower blood sugar, for type 2 diabetes, for example.

Adolescents, young adults, or middle-aged people may all benefit from time-restricted eating if they are only lightly or moderately physically active and are interested in:

  • losing weight
  • reducing blood sugar
  • reducing gut inflammation or improving their gut microbiome

These people are most likely to experience benefits with minimal downsides.

Time-restricted eating may also be beneficial for those who are not successful with daily calorie restriction since some study results indicate that both types of diet yield similar results.

Natalie Butler, RD, LDAnswers represent the opinions of our medical experts. All content is strictly informational and should not be considered medical advice.