A Primer On Fasting and Time Restricted Eating

If you’re reading this article it likely means that you enjoy finding new ways to workout harder, eat healthier, and live better. You have probably tried different workout plans and diets over the years just to see if they made you feel any better or gave you specific results. This is a natural curiosity we all have towards new and popular trends. Given this curiosity, 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 battling cancer has been mentioned with fasting and TRE. However, 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 TRE the same thing? As always, the explanations behind the claims are not always as grand as people might hope.  

Are Fasting and TRE the Same Thing?

If you have been paying attention for the past several years, you are bound to have heard someone talking about fasting. Several detox diets use fasting in their protocols for purported health benefits. Perhaps more famously, Intermittent Fasting (IF) gained popularity and has stuck around for several years now.

Intermittent Fasting offers several different strategies all of which feature periods in which you refrain from eating. Some choose to fast for an entire day while other choose to fast for long periods each day. The majority of the IF crowd tend to follow a daily fasting schedule. This involves 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. Since you are asleep for 8 hours (hopefully) you really only feel like you are fasting got 6-10 hours each day.

Interestingly, some argue that this daily “fasting” routine should go by a different name. The definition of fasting is the abstention of food or drink for a defined period of time. Many 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 researcher who has dedicated his work to investigating these dieting strategies. His name is Dr. Satchin Panda and interestingly, he does not believe in the term “Intermittent Fasting.” Instead, he refers to this eating strategy as 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 found that Time Restricted Eating may have some unique benefits as far as health are concerned as well.

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.
  • Fasting is performed periodically while Time Restricted Eating is more of a lifestyle strategy.
  • Both have distinct benefits and justifications.

Time Restricted Eating and Fat 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 deliver on these benefits?

First let’s look at everyone’s favorite dieting outcome, fat loss. Since its inception, people have been raving about Intermittent Fasting and most of these rave review dealt with its apparent fat loss benefits. Indeed, many studies show that intermittent fasting does in fact lead to significant fat loss over time [6]. But before you go and crown it as the fat loss king, fat loss results from IF are remarkably similar to those obtained from a traditional calorie restricted diet with no fasting constraints [5].

What does this mean? Neither intermittent fasting nor dieting via a “normal” eating schedule is significantly better or worse from a fat loss perspective. With IF, the small window of eating seems to result in a caloric deficit which then leads to fat loss. For some, this likely just makes it easier to maintain this calorie deficit over time. 

Interestingly, most studies that utilize an Intermittent Fasting approach aren’t actually implementing it the way it has been popularized. Rather than 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? They’re 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 a positive impact 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. Despite the unhealthy diet, obese mice who were put on a TRF protocol became lean. Additionally, lean mice who were put on the ad libitum protocol (no time constraints) became obese. [1]. Furthermore, lean mice that were put on a TRF protocol managed to stay lean.

Although the calorie intake between TRF and ad libitum dieting was equal, the results were very different. This suggests that Time Restricted Feeding triggers some sort of physiological change to promote leanness and prevents fat gain in mice. However, we don’t know whether these results will translate to humans the same way.


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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.

Perhaps the most popular subject that is brought up with fasting is the process of autophagy. All this really refers to is the consumption of our own tissues. However, 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 an increase in autophagy. However, autophagy is actually upregulated by any kind of caloric restriction. 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) for ethical reasons, studies have been done on Fasting Mimicking Diets. These diets essentially manipulate calories, macronutrients, and food intake in a way that mimics the effect that full on 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 caused these effects or whether it was the caloric deficit and weight loss.  

Finally, it is worth noting the effects that fasting could have on your digestive system. It is possible for your digestive system to become overburdened. 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 digestion abilities. So the break from the constant outflow of digestive enzymes might regenerate your ability to release an adequate amount before and during meals. These potential effects could theoretically lead to better digestion and assimilation of nutrients.

Conclusion

As with every new trend in health and nutrition, the claims made about fasting and time restricted eating are a bit inflated. Fasting and TRE do have some great benefits for our health as they have been shown to promote fat loss and change health markers for the better. However, these benefits may not be separable from the caloric deficit that can be had with 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.

This isn’t to say that these strategies are not worthwhile. On the contrary. any eating strategy that allows you to stay healthy and reach your goals can be a good one. Many people find that Time Restricted Eating is much easier to maintain than other dieting strategies. For those people, TRE is a superior strategy for them.

Dr. Panda’s work certainly gives us some hope that Time Restricted Eating may have some unique benefits for us. However, 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 better for some people on a case by case basis.

References

  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 metabolism20(6), pp.991-1005.
  2. Glick, D., Barth, S., & Macleod, K. F. (2010). Autophagy: cellular and molecular mechanisms. The Journal of Pathology221(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 metabolism15(6), pp.848-860.
  4. Longo, V.D. and Panda, S., 2016. Fasting, circadian rhythms, and time-restricted feeding in healthy lifespan. Cell metabolism23(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 medicine9(377), p.eaai8700.
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