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 when 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.
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 the short term) may not be effective in the long run.
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 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.
Additional Resources
- Intermittent metabolic switching, neuroplasticity and brain health
- Early Time-Restricted Feeding Improves 24-Hour Glucose Levels and Affects Markers of the Circadian Clock, Aging, and Autophagy in Humans
More About Metabolism with Biochemistry Videos on Osmosis
About the Author
Ishan Dahal is the Osmosis 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 he will get next week.
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