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A Primer on Fasting and Time-Restricted Eating

A Primer on Fasting and Time-Restricted Eating

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If you are reading this, you are most likely a fitness inspired individual. That means you like to find new ways to work out harder, eat healthier, and live better. You probably have tried different workout styles and diets over the years just to see if they made you feel any better or gave you any awesome results. This is a natural curiosity we all have towards new trends that arise in our industry. So, it’s no surprise that people have latched on to the idea of fasting and/or time-restricted eating. This “new” dieting strategy has certainly caught the attention of health minded people as of late.

Indeed, there are a host of potential benefits that have been attributed to fasting and time-restricted eating. Everything from off the charts fat loss, to increased energy, and even improved cancer fighting abilities have been mentioned. But, there are a lot of questions that need to be answered about these eating strategies. Do they actually work the way they claim? Are fasting and time restricted eating the same thing? As always, the explanations behind the claims are not always as sexy as we would have hoped. This article will attempt to cover the basics of fasting and time restricted eating to help you decide for yourself whether they are worthwhile.


Are Fasting and TRE the Same Thing?

If you have been paying attention for the past several years, you know that fasting has been thrown around quite a bit in the dieting world. For one, several detox diets use fasting in their protocols. But perhaps more famously, Intermittent Fasting (IF) gained popularity and has stuck around for several years now. When it was first introduced, IF offered several different strategies which all featured periods in which you abstained from eating. Some chose to fast for an entire day of a given week and then eat normally the other days. However, the majority of the IF crowd decided to follow a daily fasting schedule. This meant eating during a 6-10 hour window and “fasting” for the other 14-18 hours of the day.

This daily fasting routine is much easier to adhere to compared to the daunting task of skipping an entire day, especially since you are asleep for 8 of your fasting hours. In essence, you are only consciously fasting for 6-10 hours per day. But does this daily restriction of eating times really qualify as fasting? The definition of fasting is the abstention of food or drink for a defined period of time. However, most experts would assert that the time period should last at least 24 hours to qualify as fasting. Perhaps Intermittent “Fasting” is actually a misnomer.

There is one particular researcher who has dedicated himself to investigating these dieting strategies. His name is Dr. Satchin Panda and interestingly, he does not call it Intermittent Fasting. Instead he calls this eating strategy Time Restricted Eating. He too believes that fasting and Time Restricted Eating are not the same thing. In his view, fasting usually lasts for several days, is performed infrequently, and is done for different physiological and perhaps spiritual reasons. However, his research has also found that Time Restricted Eating may have some unique benefits as far as health is concerned.

But, before we get into the science behind fasting and Time Restricted Eating, let’s just summarize these points. Fasting and Time Restricted Eating/Intermittent Fasting are not the same thing. Both of them have distinct benefits and reasoning, but they diverge from one another. Additionally, fasting is performed periodically while Time Restricted Eating is more of an everyday, lifestyle strategy.


Time Restricted Eating and Weight Loss

Okay, so now we can get to the part you actually came here to read about. All of these reported health claims around fasting and Time Restricted Eating make them attractive, but do they really benefit us the way they have claimed? Well, it depends on how you look at it.

First, let’s look at everyone’s favorite dieting outcome: weight loss. Ever since Intermittent Fasting came onto the scene, people have been raving about its awesome fat loss benefits. Many studies have investigated the weight loss potential of Intermittent Fasting. Indeed, many of them show that intermittent fasting does in fact lead to significant weight loss over time [6]. However, when compared to a traditional, calorie restricted diet (no fasting constraints), the results are remarkably similar [5]. Neither intermittent fasting or continuous dieting is significantly better or worse from a weight loss perspective. So, in this case, it seems that intermittent fasting simply makes it easier for some people to maintain a caloric deficit, which then leads to weight loss.

Interestingly, most studies that utilize an Intermittent Fasting approach aren’t actually implementing it the way it has been popularized. Rather than using restricted eating windows, they simply employ a whole day of little to no calories, followed by a day of normal calorie intake. So, what about studies that investigate time restricted eating/feeding? Well, they are sort of unheard of as far as human trials are concerned. Instead, we can only rely on studies conducted on mice.

This is where Dr. Panda has devoted most of his resources. His studies have found that Time Restricted Feeding (TRF) of mice within an 8-12 hour period has profound impacts on their health and body composition [3, 4]. In one study, researchers fed mice a high fat, high sugar diet in order to mimic the western diet. Obese mice who were put on a TRF protocol became lean by study’s end, and lean mice who were put on the ad libitum protocol (no time constraints) became obese by studies end [1]. Furthermore, lean mice that were put on a TRF protocol managed to stay lean by studies end. The amazing result is that the calorie intake of both the ad libitum and TRF mice (lean and obese) was nearly identical. Therefore, this study showed that Time Restricted Feeding enacts some physiological change which promotes leanness and prevents fat gain in mice. However, we don’t know whether these results will translate to humans the same way.


Health Benefits of Fasting and Time Restricted Eating

So, we know that Time Restricted Eating can help you lose weight due to the caloric restriction aspect, but what about the health benefits of Fasting and Time Restricted Eating? There has been a ton of talk about the health-promoting effect of these strategies so it is worth discussing how they can help.

One big subject that is brought up is the process of autophagy. All this really refers to is the consumption of our own tissues, but the majority will focus on the aspect of clearing waste products and unnecessary cells from the body. This is an important process for our health as far as preventing cancerous cells from forming, and reducing our risk of several diseases [2]. It is true that fasting will lead to upregulation. However, autophagy is actually upregulated by any kind of caloric restriction. Obviously, the more extreme the restriction, the greater the autophagy. So, fasting has a robust effect, but so too does an extended period of caloric restriction.

Fasting does seem to help us out as far as decreasing inflammation and markers of metabolic syndrome. Although it is hard to study true fasting (abstention from any calories) due to ethical constraints, studies have been done on Fasting Mimicking Diets. These diets essentially manipulate calories, macronutrients, and foods in a way that mimics the effect that true fasting has on the body. Studies around these diets have shown that periodic fasting (5 days every month) leads to significant reductions in glucose, triglycerides, cholesterol, and C – reactive protein, which is a marker of inflammation [7]. However, subjects also reduced their body weight during these trials as a result of lower calorie consumption during the fasting periods. Therefore, it is not clear whether fasting on its own is the cause of these adaptations.

Lastly, it is worth noting the effects that fasting could have on your digestive system. Not to get too holistic on you, but our digestive system can get overburdened at times. Think of a time when you ate too much spicy food and needed to take a break from eating the rest of the day. Although there is no science to prove it, anecdotal reports suggest that taking some time off from eating can help improve digestion and perhaps even absorption of our food. Giving your intestines some time to repair and recover may help you clear out and refresh your digestive abilities. Additionally, the break from the constant outflow of digestive enzymes might regenerate your ability to release an adequate amount of them before and during meals. Both of these combined could theoretically lead to better digestion and assimilation of nutrients.



As with every new trend in the fitness industry, the claims made about fasting and time restricted eating are perhaps a bit overblown. There is no doubt that these strategies do have some cool benefits to our health and body composition. After all, they have been shown to promote weight loss and change health markers for the better. However, these benefits may not be separable from the overall caloric restriction that you can get from just about any diet. With the exception of Dr. Panda’s work in mice, no studies have been able to show that fasting or time restricted eating will outperform caloric restriction in and of itself.

However, this isn’t to say that these strategies are not worthwhile. It is always best to explore different strategies in order to find the one that works best for you. Many people find Time Restricted Eating to be much easier to adhere to than other dieting protocols. In that way, it represents a superior dieting strategy for them. Dr. Panda’s work certainly gives us some hope that Time Restricted Eating may have some unique benefits for us, but until we can see those results replicated in humans on a large scale, we’ll have to continue thinking of time restricted eating as a tool that may be superior for some people on a case by case basis.



  1. Chaix, A., Zarrinpar, A., Miu, P. and Panda, S., 2014. Time-restricted feeding is a preventative and therapeutic intervention against diverse nutritional challenges. Cell metabolism, 20(6), pp.991-1005.
  2. Glick, D., Barth, S., & Macleod, K. F. (2010). Autophagy: cellular and molecular mechanisms. The Journal of Pathology, 221(1), 3–12. http://doi.org/10.1002/path.2697
  3. Hatori, M., Vollmers, C., Zarrinpar, A., DiTacchio, L., Bushong, E.A., Gill, S., Leblanc, M., Chaix, A., Joens, M., Fitzpatrick, J.A. and Ellisman, M.H., 2012. Time-restricted feeding without reducing caloric intake prevents metabolic diseases in mice fed a high-fat diet. Cell metabolism, 15(6), pp.848-860.
  4. Longo, V.D. and Panda, S., 2016. Fasting, circadian rhythms, and time-restricted feeding in healthy lifespan. Cell metabolism, 23(6), pp.1048-1059.
  5. Seimon RV, Roekenes JA, Zibellini J, Zhu B, Gibson AA, Hills AP, Wood RE, King NA, Byrne NM, Sainsbury A. Do intermittent diets provide physiological benefits over continuous diets for weight loss? A systematic review of clinical trials. Mol Cell Endocrinol. 2015 Dec 15;418:153-72
  6. Tinsley GM, La Bounty PM. Effects of intermittent fasting on body composition and clinical health markers in humans. Nutrition reviews. 2015 Oct 1;73(10):661-74.
  7. Wei, M., Brandhorst, S., Shelehchi, M., Mirzaei, H., Cheng, C.W., Budniak, J., Groshen, S., Mack, W.J., Guen, E., Di Biase, S. and Cohen, P., 2017. Fasting-mimicking diet and markers/risk factors for aging, diabetes, cancer, and cardiovascular disease. Science translational medicine, 9(377), p.eaai8700.

About the author

About Andres Vargas
Andres Vargas

Andres is a strength and nutrition coach and the owner of The Strength Cave, an online fitness coaching company. He holds a Master's degree in Exercise Science and is currently studying for a PhD in Sport and Exercise Science. His goal is to blend science and real world application in order to provide the best...[Continue]

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