Intermittent fasting, or intermittent eating as some would call it, has become popular over the past years. Intermittent fasting is the practice of going through periods of fasting and periods of feed. The two primary types of fasting include time restricted feeding or alternate day fasting. Time restricted feeding is where you would choose a period during your 24-hour day to fast and another period to feed. Common protocols include 12:12, 16:8, and 20:4; this is the ratio of fasting to feeding. Alternate day fasting protocols include every-other-day and the 5:2 method. To follow the every-other-day fast, you would eat, then the next day you would reduce your calories by 75%. Thus, if you sustain weight at 2000 calories, on your fasting days you would consume 500 calories. The 5:2 method is similar, but here you would eat for five days and reduce calories by 75% on two days of the week.
Now that you understand what fasting is, what is the advantage? Everyone should practice fasting. I say this because when you fast, it causes processes to happen at the cellular and molecular level that can support your weight, improve your longevity, fight against chronic diseases, and improve your cognitive health. With this being said, fasting is healthy, and let's dig into the details so you can decide if fasting is something you want to do.
What does Fasting Do for Weight Loss?
As mentioned, fasting changes your body at the cellular level for the better. In fact, Varady et al (2013) found that 12-weeks of alternate day fasting caused people to lose almost 11.5 pounds. What was most interesting is that 70% of the weight lost was body fat. This is not the first study to show this. Another study showed similar results in a short, 22-day period subjects lost almost 4 pounds (2). What I found most interesting about the second study is that the subjects did not follow a diet and their metabolism stayed the same from the beginning to the end. This is interesting because when we are not “dieting” or tracking calories, we tend to revert to maintenance calories without thinking and dieting can lower your metabolism. This means people lost weight using every-other-day fasting without eating in a calorie deficit. We know this because during the 22-days the subjects were not hungrier than normal.
What does Fasting Do for Health?
Mentioned earlier is that fasting can improve your longevity meaning that it can help you live longer. At the cellular level, two primary phenomena occur when you fast. Your body increases fat oxidation, what some would call fat burning, and autophagy (1). Going long periods without eating is commonly known to increase fat oxidation because your body's primary energy source (glucose) is depleted and forced to burn other sources of energy such as fat and protein. During fasting, the same genes regulating fat oxidation regulate the process of autophogy (3). Autophogy is a fancy word for "cellular cleaning," where your body breaks down old cells and recycles the parts to make new, stronger cells. Nick English does a great job explaining autophagy in detail here. This process can improve our health and longevity to make sure a long, healthy life.
Other benefits of fasting include:
- Increasing ketones, which reduce hunger, inflammation, and promote brain health
- Promoting the growth of brain cells that are involved in learning and memory
- A possible therapy for cancer treatment
- Reducing the number of damaged cells that may cause inflammation
- Lowering blood sugar and markers of heart disease
Fasting has incredible health benefits, which is why I recommend everyone should follow some variety of fasting in their lives. Fasting gained popularity because fasting is a great weight loss tool, although, there are more benefits to fasting than weight loss. A common theme you may have noticed while reading this article is that to reap the benefits of fasting, you must be in a calorie deficit or at least calorie maintenance. This is because we do not see the same benefits of fasting if you are in a calorie surplus. Depending on your expectations, weight loss or longevity, fasting can be adapted to your lifestyle to make sure you reach your goals.
Step-By-Step Guide to Fasting
- Decide the model of fasting you want to follow - I recommend starting with a 12-hour fast, then increase from there.
- Figure out your goal.
- Outline your macro- and micronutrient needs.
- Plan your eating schedule.
- Stick with it - Nothing happens overnight. Plan on sticking with your intermittent fasting plan for at least 6-weeks to find if you are on track.
- Adjust & Repeat.
- Bujak, A. L., Crane, J. D., Lally, J. S., Ford, R. J., Kang, S. J., Rebalka, I. A., ... & Steinberg, G. R. (2015). AMPK activation of muscle autophagy prevents fasting-induced hypoglycemia and myopathy during aging. Cell metabolism, 21(6), 883-890.
- Heilbronn, L. K., Smith, S. R., Martin, C. K., Anton, S. D., & Ravussin, E. (2005). Alternate-day fasting in nonobese subjects: effects on body weight, body composition, and energy metabolism. The American journal of clinical nutrition, 81(1), 69-73.
- Morselli E, Galluzzi L, Kepp O, Criollo A, Maiuri MC, Tavernarakis N et al. (2009). Autophagy mediates pharmacological lifespan extension by spermidine and resveratrol. Aging (Albany NY) 1: 961–970.
- Varady, K. A., Bhutani, S., Klempel, M. C., Kroeger, C. M., Trepanowski, J. F., Haus, J. M., ... & Calvo, Y. (2013). Alternate day fasting for weight loss in normal weight and overweight subjects: a randomized controlled trial. Nutrition journal, 12(1), 146.