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The general advice for decades has been to eat small meals and snacks throughout the day to keep blood sugar in balance and energy up. But it turns out this advice may not actually be best for everyone. Along with intermittent fasting, time-restricted eating has lots of health benefits supported by research.
What Is Time-Restricted Eating?
Time-restricted eating (TRE) is the practice of eating all of your food within an eight to twelve hour window during the day. Researchers at the Regulatory Biology Laboratory at the Salk Institute for Biological Studies discovered that fasting (going without any food or non-water drinks for a period of time) may be an important part of staying healthy.
The study also found that the time in which we eat may be more important than the food itself, especially in relation to the circadian rhythm.
The Salk Study
Researchers fed two sets of mice (who shared many similarities) the same high-fat, high-sugar diet. This diet replicated the standard American diet (SAD) many people eat. One group of mice had 24-hour access to the food. The other group could only eat during an eight-hour window at night (mice are nocturnal).
After 100 days the group who had access to the high-fat diet all day and night gained weight and developed health issues including high cholesterol, high blood glucose, liver damage, and diminished motor control.
The group who only had access to food for the eight-hour period weighed 28 percent less than the first group. And despite eating the same amount of calories from the same kind of food, the time-restricted eating group did not develop the same health issues.
While this study is in mice, researchers are confident that human studies will show similar results. In fact, the researchers have done a few small human studies with good results.
Dr. Satchin Panda, the lead author of the study, commented that their research shows it may be beneficial to eat on a regular schedule and have regular fasting periods as well. The reason is that genes for digestion are more active earlier in the day while genes for cellular repair are more active at night. So it may be that eating food while the body is prepared to handle it can have health benefits.
Time-Restricted Eating Vs. Intermittent Fasting
Many people hear about TRE and think it sounds a lot like intermittent fasting. The two have some things in common but also have some differences.
Intermittent fasting is an umbrella term for any diet that restricts eating during certain times of the day. Time-restricted eating is one of those diets. But TRE focuses on aligning the times that you eat with your circadian rhythm. That means eating at the same time (and fasting at the same time) every day or most days is important.
Unfortunately for shift workers, it’s important for the eating/awake scheduled to happen during the day. This is because during the daytime the body expects food and is most able to handle and process it.
For example, with intermittent fasting, someone may eat an early breakfast and then fast for the rest of the day until they eat a late dinner. However, Dr. Panda explains that this may not be the best idea physiologically.
Melatonin, a hormone produced when light begins to fade, is responsible for preparing the body for sleep. Melatonin binds to receptors on pancreatic cells to suppress insulin secretion. So when melatonin is produced, digestion slows and your body prepares for a time of fasting.
Suppressing insulin helps blood sugar levels remain steady during the overnight fast. So eating a large meal around twilight means you’re eating at the time of day your body is least able to handle food.
So TRE is a type of intermittent fast that focuses on restricting eating to the time of day your body is most prepared to digest and use food.
Benefits of Time Restricted Eating
This kind of eating style mimics what is thought to be the normal eating patterns of our ancestors. These hunter-gatherer societies wouldn’t have had 24/7 access to food. They may only have access to a meal twice a day (when prey is out and available to be hunted). And it would make sense that replicating the eating habits of our ancestors (who didn’t have the health issues we have in modern society) might have a positive impact on our health. What researchers found was that TRE has many health benefits.
The Salk study mentioned above found that the body will continue to store fat when food continues to enter the body. But after a number of hours of fasting, the body starts to break down fat. Time-restricted eating reduces the production of fat and makes better use of it in the body.
But the time we eat also helps. Dr. Panda explains in a YouTube video interview with Dr. Rhonda Patrick that in one study, eating lunch earlier in the day (instead of 3 p.m., which was typical in Spain where the study was done) made a huge impact on how much weight loss the participants experienced. The study was controlled for activity, calories/kinds of foods eaten, etc.
A later review agreed that TRE helps reduce body fat and found that it also helps reduce cholesterol and triglyceride levels.
It’s unclear, in humans, if TRE works because it restricts calories or if there are other mechanisms at play. But the kinds of foods many people eat for late-night snacks are usually the most unhealthy, so either way, it’s a win.
Healthy Blood Sugar
TRE can also be helpful for balancing blood sugar. With constant eating, the liver continues to make glucose, raising blood sugar levels. Time regulated eating, and the long fasting time it creates helps give the liver a break from producing glucose.
Additionally, during fasting times glucose helps to build molecules that repair damaged cells and make new DNA. The Salk study found that glucose tolerance and insulin sensitivity were better when food was restricted to a 12-hour window.
A study that was conducted by the University of California San Diego had similar findings. Over two thousand overweight women were divided into two groups. One group fasted for at least 12 hours at night, while the other fasted for less time. The group that fasted for at least 12 hours had better blood sugar levels than those who fasted for shorter periods.
Often the advice for those with blood sugar issues is to eat small snacks often. This research suggests that this advice is not the best and that longer periods of fasting may be beneficial.
The regulation of blood sugar and the use of glucose for cellular repair also helps reduce inflammation. Inflammation causes many chronic illnesses including heart disease, cancer, stroke and Alzheimer’s. The Salk study found reduced inflammation as well as a better lipid profile and gene expression.
Reduced Metabolic Disease
The Salk study researchers continued to look into the concept of TRE in another study and found interesting results. The original study made researchers think that eating helps set the circadian rhythm, but the opposite may be true. What they found was that the circadian clock’s primary role may be to tell the animal when to eat and when to not eat. When the circadian clock is disrupted, chronic illness can happen. This illness may be a side effect of not eating at the times that the body is most able to handle food.
The circadian clock naturally weakens as we age. This parallels the increase in chances of metabolic illnesses. Researchers think that creating a strong circadian rhythm, by consciously controlling the hours we eat, may help keep these illnesses at bay. Considering metabolic illness (unhealthy blood pressure, blood sugar, cholesterol, etc.) is increasingly common today, these findings are very interesting!
The Salk study also found that the body only begins to breakdown cholesterol into beneficial bile acids during fasting times. This breakdown helps cause the metabolism of brown fat. Brown fat is a good fat that can improve health by enhancing the bodies ability to burn white fat, create heat, and even regulate blood sugar.
Dr. Panda explains in the YouTube video mentioned earlier that liver genes are more sensitive to the act of eating than to light. One study found that mice who were fed during the day had liver genes turn on and off at that time while the ones fed at night had liver genes turn on and off at that time. In other words, eating during the day is important for keeping the liver processing food during the day. Fasting at night is important for keeping the liver in repair mode at night. Because of this, the study found that eating during the day (not at night) can help protect against mild age-related fatty liver.
Other Benefits of TRE
Besides the benefits already mentioned time-restricted eating can also help:
- increase mitochondria volume especially in the liver and brown fat
- improve ketone body production
- speed repair processes
- lead to better aerobic endurance improvement (when feeding was restricted to 9 hours)
- increase lean muscle (if eating a healthy diet
Time-restricted eating benefits are vast, but TRE may not be right for everyone. Those with blood sugar issues or hormone imbalances may need to get these things under control before trying time-restricted eating. Additionally, when (and for how long) to fast may be different for everyone. Talk with your doctor before changing your eating habits and to discuss whether time-restricted eating is safe for you.
Also, TRE is not a silver bullet. You still have to eat healthy foods, no matter when you eat! Though research suggests that restricting eating to a smaller window of time can help the body handle a less healthy diet, the Salk study did find that TRE combined with a healthy diet has the best outcomes.
How to Begin Time Restricted Eating
- Start by going at least 12 hours overnight without food (or non-water beverages). Research has found health benefits with this length of fasting time. After you get used to 12 hours, see how you feel and whether you may want to try a longer fasting time. Some of the research suggests that the longer the fasting time the better the health benefits. Some people find that an eating window of 4-6 hours works best for them.
- It’s unclear when, specifically, is the best time to fast. However, it does seem that sticking with a consistent eating schedule is important. Based on Dr. Panda’s research it makes sense to eat bigger, more carb-heavy meals earlier in the day when insulin sensitivity is highest. Alternately, lower carb meals may be better later in the day.
- For some people, eating an early dinner (5-6pm) and then not eating again until breakfast works best.
- For others, it may be easier to delay the first meal in the morning. Just keep in mind that any beverages that are not water (like coffee or tea) count as eating. The only beverage I make an exception for are Pique Tea’s fasting-specific blends.
Time-Restricted Eating: Bottom Line
For many people, maintaining a healthy weight is an uphill battle. Counting calories, restricting fat, and avoiding their favorite foods is torture. But with the research Dr. Panda and his colleagues are collecting, a healthy weight may be as easy as having an early dinner or a late breakfast.
This article was medically reviewed by Dr. Scott Soerries, MD, Family Physician and Medical Director of SteadyMD. As always, this is not personal medical advice and we recommend that you talk with your doctor.
Have you tried TRE? What was your experience?
Discussion (15 Comments)
Thank you for this very informative article. I am in my mid seventies, broke my hip and then was further restricted by Covid. At 5’ any weight gain is noticeable. Before knowing anything about this trend I decided not to eat after 7pm. I do go to the gym 5 days a week, but since starting this restricted eating I lost 8 pounds and feel much better.