What You Need to Know About Fasting: A Look at the Research

Osmosis Team
Published on Jul 14, 2020. Updated on Sep 15, 2020.

Osmosis Health Coach, Ishan Dahal, continues in his series providing health tips, this time addressing the topic of fasting. 

Dieting interventions that promise rapid improvement in health and body-composition seem to pop up periodically. In recent years, fasting has gained significant momentum. A simple internet search will reveal several articles highlighting the benefits of fasting, but it might be a good idea to dig a little deeper into these claims. Are they really valid? 

Types of fasting

Humans have been fasting for various reasons for a long, long time. Fasting is an umbrella term, and there are several ways it can be accomplished. 

Intermittent fasting

The fasting method that appears most often in popular culture is intermittent fasting (IF). People following this method have a specific time window in which they can eat, which varies by individual, but the most common is an 8-hour feeding window. 

Alternate-day fasting

Alternate-day fasting is where you eat with no restrictions one day, and fast the next day.

The 5:2 method

With the 5:2 method, you eat with no restrictions for 5 days and then fast for 2 days

The warrior diet

The warrior diet is where you fast the whole day and eat one large meal at the end of the day

Osmosis illustration of different fasting diet types.

Is fasting effective for weight loss?

Looking at the available evidence, fasting protocols do show weight loss when compared to eating normally. However, when fasting protocols are compared to continuous energy restriction protocols, the effect appears to be similar. In other words, fasting is not superior to continuous calorie restriction

This also means that the weight loss associated with fasting is most likely due to energy restriction rather than the act of fasting alone. A quote from the Molecular & Cellular Endocrinology study linked above might help bring the point home: “Intermittent fasting thus represents a valid—albeit apparently not superior—option to continuous energy restriction for weight loss.” 

So, given the evidence, how should we approach fasting? 

If you don’t like to restrict your food intake all the time, but don’t mind fasting for a few days out of the week, full-day fasting methods help you restrict calories. If you’re always busy in the morning or don’t mind skipping breakfast, limiting your food intake during the afternoon and evenings might be a way to restrict calories. 

Fasting in and of itself is not going to result in weight loss if the calories are not restricted. However, it can be an effective way of controlling the amount of calories you consume. If you consume calorically-dense food in your non-fasting days or hours, to the point where you’re eating more calories than you use, this can hinder weight loss. Thus, the majority of the time (80–90%) it’s best to stick with highly nutritious whole foods during your meals. 

Fasting is not going to be suitable for everyone. If you don’t like being hungry then fasting methods (though effective during short term) may not be effective in the long run. 

Osmosis illustration of various caloric densities.

How to control your caloric intake

There are several ways to control calories, and it’s important to find the one that works for you. Real talk for a second: if you don’t enjoy restricting your caloric intake, but want to lose weight, I would still recommend picking the best of the worst. 

If you’re going to go through all this effort anyway, you might as well add some activity to your lifestyle, too. This can be in the form of regular walks, runs, group classes, sports, and strength training at the gym. Resistance training can be a great adjustment to an effective weight-loss program. 

The benefits of fasting

Several other benefits that have been associated with fasting, including: cognitive benefits, anti- aging, autophagy (clearing out damaged cells to make room for newer, healthier ones), and increased neuronal plasticity.

A final note on the research behind fasting as a dietary practice

According to the American Journal of Clinical Nutrition, “clinical research studies of fasting with robust designs and high levels of clinical evidence are sparse in the literature.” 

Research in fasting outcomes amounts to very little. Many of the conclusions you may have read about on health and fitness blogs rely on animal models—research that includes humans as subjects is very limited. 

Although promising, there is still a significant amount of work that needs to be done before we can be conclusive about the outcomes of fasting on humans. 

Osmosis illustration of people participating in a fitness class.

Learn more from these resources

Learn more about metabolism with these biochemistry videos on Osmosis 

About Ishan

Ishan Dahal is Osmosis's health and wellness coach. When he's not working out with his Osmosis teammates or brushing up on health and wellness literature, he's spending time with his family, going on long walks with an audiobook, or contemplating what vegetables will he get next week.

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