Intermittent fasting (IF) is an eating plan that switches between fasting and eating on a regular schedule. When the fasting state is long enough, fat loss can occur with preservation of muscle mass.
Many people think that fasting is hard, but that is simply not true. Our bodies have evolved to be able to go without food for many hours, several days, or even longer. We just need to retrain our bodies to take advantage of this natural mechanism that is already working inside of us.
How Does It Work?
Intermittent fasting works similarly to ketogenic diets. After a period of fasting, the body exhausts its sugar stores (glycogen). It then starts burning fat, creating ketones as our energy source. If someone eats three square meals a day with snacking in between, they will never reach a state where they burn fat for fuel because they are always working off their glucose stores.
With IF, you halt the eating early so the body can burn through the glycogen and switch to fat as its energy source. The body must learn how to become “keto-adaptive” or run off ketones efficiently without causing you to become hungry or hypoglycemic. This occurs over time as your fasting periods lengthen.
Why Switch to IF?
With intermittent fasting, timing is everything. There is less focus on what you eat and more on when you eat it. Of course, you want to eat healthy during your feeding period. But you don’t have to count calories or restrict carbohydrates.
When you stop eating early or start eating later, you naturally consume less calories. Having a “stop time” in the evening tends to keep people from late night snacking which can be detrimental to a weight loss program. When you are burning ketones for fuel, you feel more awake, alert, and energetic.
Some major health benefits of switching to intermittent fasting are:
- Mental clarity/memory: Studies have discovered that it boosts working memory in animals and verbal memory in adult humans.
- Cardiac health: Intermittent fasting can improve blood pressure, resting heart rates, and other heart-related measurements.
- Physical performance: Young men who fasted for 16 hours showed fat loss while maintaining muscle mass. Mice fed on alternate days showed better endurance in running.
- Weight loss: In animal studies, intermittent fasting prevented obesity. And in six studies, obese adult humans lost weight through intermittent fasting.
How To Start an Intermittent Fasting Plan
The two main approaches to intermittent fasting are the daily approach and the 5:2 plan.
With the daily approach, you pick a fasting window during the day. The most common way to start is with the 16:8 plan, where you fast for 16 hours and eat during an 8-hour window. You can start with a shorter fasting window, but most people won’t lose weight until they reach a fast of 15-16 hours. You may choose to fast until 11am and eat between 11am and 7pm. Other popular eating windows are from 10am-6pm or 12pm-8pm.
During your fasting period, you can drink water and other zero calorie beverages such as black coffee or tea. Once you break the fast, focus on eating something every two hours during your eating window. Although there is no specific meal plan, it is recommended to include protein in each meal.
A typical 16:8 fast can look like this:
- Before 12pm: black coffee and water
- 12pm: protein shake
- 2pm: protein bar
- 4pm: mozzarella cheese stick and a small apple
- 6pm: 6 ounces of lean protein, 1 cup of veggies and a salad
- 7:30pm: Yaso frozen yogurt bar
- 8:00pm: STOP
Once the 16:8 plan becomes easy, try a 24-hour fast one day per week. This tends to keep the weight moving and clear up any excess inflammation.
The 5:2 approach involves eating “regularly” 5 days per week. For the other two days, you limit yourself to one 500-600 calorie meal, or two 250-300 calorie meals, spaced at least 12 hours apart.
The nice thing about the 5:2 approach is it gives you more freedom and variety. Plus your appetite is curbed the day following your one meal day. This plan can be a little harder to follow as its more challenging to become keto-adapted.
Tips for Successfully Navigating an IF Plan
It can take 2-4 weeks for the body to become accustomed to IF. It’s best to pick your window and slowly work your way up to a 16-hour fast. For example, start with a 12-hour fast where you eat from 8am-8pm. The next time, try waiting until 10am and eating from 10am-8pm. Once you can easily do this, move to 15 hours and then 16 hours.
Once you break your fast, it’s recommended that you eat every 2 hours. Try not to undereat during your feeding time as it can slow down your weight loss. And don’t just binge or eat junk during your feeding time. Eat something healthy with protein at each interval to keep you full and support muscle mass.
Pay attention to the clock and stick to your fasting window. It may take you time to find your perfect window and that window may change over time or even during a week for a special occasion. For example, you may want to eat breakfast one morning, or stay out late with friends one evening. Plan ahead if you know this is going to happen and try to give yourself at least a 14-hour fast by stopping early the night before.
Most importantly, be patient with yourself and don’t give up! Remember, your body must get used to running on ketones during your fasting period. Some people adapt quickly, but for others it takes a while. If you find yourself getting lightheaded or fatigued at the beginning, you are going too fast. Take your time reaching your 16-hour window and let your body adapt.