What is Intermittent Fasting?

Intermittent fasting (IF) is a variety of eating patterns, where no calories are consumed within a certain time frame. There are a number of different fasting types, however whatever you follow, it will involve fasting for at least 12 hours. Lately, intermittent fasting has been all over the news as a weight loss tool, but is it a fad or a fact? Let’s break it down. 

Examples of intermittent fasting methods include alternate-day fasting, which requires longer fasts (up to 24 hours). Practicing this method of fasting requires structure. For example 6:1 or 5:2. This means fasting for 1 day and eating as usual for 6 days, or fasting for 2 days with 5 days eating as usual. These fasts are not necessarily strict – allowing for the consumption of (up to) 25% of the energy your body requires, during the fast day. Another popular method is time-restricted feeding. This method involves consuming calories within a specific time frame everyday. Known as “window eating.”

Today, there are many different forms of intermittent fasting. The main differences between them is in the duration of the fast, and caloric deficit they may generate. So how can you know what works best for you?

A Historical Perspective: Fasting as Medicine

Fasting has gained popularity over the past few years. Yet this is not a new concept. Likewise, it has been practiced for thousands of years both medicinally and spiritually.

The goal was to “purify” the body and soul, and it was used as one of the oldest therapies in medicine.

Over 2400 years ago in ancient Greece, Hippocrates (the father of medicine), recommended fasting to his patients. He believed that eating whilst sick “impairs the body’s natural process of healing.” Throughout the years, this practice has grown and can even be seen in many religions today. In Buddhism, fasting is a common practice. It is conceived as purifying the body, and giving clarity to thoughts. Fasting can be observed in Judaism for Yom Kippur, in Islam during Ramadan, and in Christianity throughout Lent.

The Impact of Fasting on the Metabolism

Your metabolism is constantly sensing and regulating biochemical processes in your body. Some of the major roles lay in energy production, muscle building, and immune system maintenance. All these processes are interconnected to the energy and nutrients you get from the food you eat. Where there is food deprivation, there will be an effect on the body. 

Your metabolic response to fasting is complex. Energy (calories) and nutrients create an anabolic effect in the body, by activating the metabolic pathway. For example glycogenesis, (oriented towards glucose storage), adipogenesis (fat deposition), and muscle synthesis (to name a few). 

The activation of these metabolic pathways depends on multiple factors that for practical purposes will not be addressed in this article.   

By fasting, opposite metabolic pathways are induced as a result of changing hormone levels such as insulin, leptin, glucagon and more. Shifting your metabolism into a catabolic state, stimulating glycogenolysis (glucose storages depletion), lipolysis (fat oxidation), and proteolysis (muscle protein breakdown). Together this produces glucose, which is translated as energy (gluconeogenesis).

It’s important to note that these processes happen in phases, where according to different factors (mainly the extension of the fast) prompts a specific metabolic pathway.

Without a doubt, fasting has an impact on the metabolism. But, is it really useful for treating diseases or promoting health? And if so, what evidence is there supporting these arguments?

Firstly, it is important to address social media. It’s not unusual to come across blogs/vlogs and posts about intermittent fasting as a treatment or cure for many diseases. This is simply a myth. While there is strong evidence supporting intermittent fasting as a tool for specific conditions, this is not a miracle cure. Not to mention that fasting is not for everyone.

What does the research say about intermittent fasting?

1.Intermittent fasting promotes cell recycling processes

Recycling is essential for life, not only for the environment but also for your cells. Dr. Yoshinori Ohsumi is a leading scientist on the research of cell recycling. He earned a Nobel Peace Prize in Medicine in 2016, for his description of  the mechanism of autophagy triggered during fasting. Autophagy is derived from the Greek words auto (self) and phagein (to eat). Cells use this mechanism of “self-eating,” by reusing damaged proteins and other damaged structures. In addition to this, cells eliminate viruses and bacterias which play a key role in maintaining the cell’s health. By doing so, they prevent many diseases such as cancer and Alzheimer. Dr. Ohsumi’s findings were related mainly to the identification of genetic mechanisms of these processes. 

Still, a lot of research is still required in order to sequence and describe what are all the triggers and all the mechanisms involved in the autophagy.

2. Intermittent fasting contributes to weight management

Intermittent fasting has been described as an effective tool for losing weight by many authors. A recent systematic review analyzed 27 trials (18 of them were randomized and controlled trials). The results indicated that intermittent fasting serves as an effective strategy for weight loss. Resulting in weight loss of between 0.8% to 13% less than the starting body weight.

There was another randomized controlled trial published in 2019 in the International Journal of Obesity. This trial assessed the effectiveness of intermittent fasting in 322 overweight and obese subjects. The results of this study found that intermittent fasting served as a useful tool for weight loss. An average weight loss of 5kg was seen after the intervention. There were no statistical differences compared to other strategies like a simple and normal daily caloric deficit also known as “continuous energy restriction” This concludes that intermittent fasting is just as effective as other weight loss strategies.    

However, it is important to note that there are limitations in the analysis of intermittent fasting. This is because this is a term that refers to a range of strategies (as mentioned in the beginning of this post).

Due to a lack of a standardization of the strategy, the analysis of evidence varies. Meaning different strategies can lead to different outcomes. 

3.Intermittent fasting improves metabolic health

Metabolic health is the term for the efficiency of the body’s metabolism processes to sustain life. Key examples are building muscle mass, nourishing the immune system, and converting food into energy. There are multiple ways for assessing metabolic health, due to different parameters. Metabolic health is considered to have ideal levels of: blood sugar levels (glycemia) and blood lipids levels (lipidemia), among others. Today, the leading cause of death and disease is related to chronic non-communicable diseases such as diabetes, obesity, and cancer. These diseases are linked to multiple factors as well as poor metabolic health as a major contributor.

There is strong evidence pointing to intermittent fasting as a way to improve metabolic health. Different studies access the effectiveness of different types of intermittent fasting, wielding results such as improvements in:

  • insulin sensitivity
  • inflammation markers 
  • oxidative markers (oxidative stress)
  • triglycerides levels, and 
  • blood pressure

The bottom line

While intermittent fasting is a growing trend, it is rooted in ancient practices. The difference between then and now is in advances in technology and research. Today, we are beginning to better understand the molecular mechanisms implicated by intermittent fasting. Evidence is telling us that this can be an effective strategy for losing weight and improving metabolic health. 

However, it is important to remember that intermittent fasting is a tool. Just like any tool, it should be used with specific criteria according to a specific context. 

If you are looking to lose weight and improve your health, you may be considering intermittent fasting. It is essential to consult with your healthcare provider, to make sure that this practice is good for you. 

Finally, the main predictor of the success of any strategy is related to sustainability. In other words, what you can do consistently over time. For that reason, if you choose intermittent fasting, make sure you use the type of fasting that fits your lifestyle and allows you to perform at your best.

References 

  1. de Cabo R, Mattson MP. Effects of Intermittent Fasting on Health, Aging, and Disease [published correction appears in N Engl J Med. 2020 Jan 16;382(3):298] [published correction appears in N Engl J Med. 2020 Mar 5;382(10):978]. N Engl J Med. 2019;381(26)
  2. Welton S, Minty R, O’Driscoll T, et al. Intermittent fasting and weight loss: Systematic review. Can Fam Physician. 2020;66(2):117‐125.
  3. Headland ML, Clifton PM, Keogh JB. Effect of intermittent compared to continuous energy restriction on weight loss and weight maintenance after 12 months in healthy overweight or obese adults [published correction appears in Int J Obes (Lond). 2019 Apr;43(4):942]. Int J Obes (Lond). 2019;43(10):2028‐2036.
  4. Stockman MC, Thomas D, Burke J, Apovian CM. Intermittent Fasting: Is the Wait Worth the Weight?. Curr Obes Rep. 2018;7(2):172‐185. 
  5. Sutton EF, Beyl R, Early KS, Cefalu WT, Ravussin E, Peterson CM. Early Time-Restricted Feeding Improves Insulin Sensitivity, Blood Pressure, and Oxidative Stress Even without Weight Loss in Men with Prediabetes. Cell Metab. 2018;27(6):1212‐1221.e3. doi:10.1016/j.cmet.2018.04.010
  6. American Diabetes Association. Standards of medical care in diabetes. 2020
  7. Persynaki A, Karras S, Pichard C. Unraveling the metabolic health benefits of fasting due to religious beliefs: A narrative review. Nutrition. 2017. Mar 1;35: 14-20
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