Intermittent fasting 101: How many hours do you have to fast to reap its benefits?
05/21/2020 / By Zoey Sky
Intermittent fasting (IF) is a popular eating pattern that offers several benefits, such as promoting weight loss and the burning of fats via ketosis. IF can also minimize inflammation by triggering processes like autophagy.
But how long do you need to fast before you experience any of its benefits?
Experiencing the benefits of IF may take time for some
Don’t feel bad if a friend who’s also doing IF loses weight before you do. Even if you’re doing it right and exercising daily, how fast you experience the benefits of IF depends on how your body responds to it. So what works immediately for one person may take a while to work for you.
Dr. Vincent Pedre, an integrative physician and gut health expert, also says that the healthfulness of your habits is another factor. What you eat, your gut health and your exercise regimen can influence how IF affects your body.
Consuming calories past your fasting window, not getting enough sleep or skipping a workout can all delay or counteract its benefits. (Related: Don’t make these 7 mistakes when it comes to intermittent fasting.)
Another thing that you should know is that entering ketosis or triggering autophagy may also take some time.
Autophagy is a natural process used by cells to disassemble, clean out or recycle unnecessary or dysfunctional components in order to create new cells. This process helps reduce oxidative stress and inflammation; it may also help lower your risk of developing chronic illnesses.
How long should you fast to reap the different benefits of IF?
The ideal fasting window varies from person to person, depending on one’s overall health and habits. Pedre advises experimenting to find a duration of fasting that works for you.
The health benefits of a 12-hour fast
Dr. Amy Shah, an integrative physician, says that fasting in 12-hour increments is the minimum.
According to a study published in the journal JAMA Oncology, people who fast at least 13 hours a day may experience a 34 percent reduction in breast cancer recurrence. This could be due to the improved blood sugar regulation that results from fasting.
The health benefits of a 14- to 18-hour fast
B.J. Hardick, a functional practitioner, says that 14 to 18 hours is the ideal range for most dieters. This attainable time frame offers significant weight loss benefits than a 12-hour fast.
However, Hardick also says that some people may need to fast a little longer to induce weight loss and enjoy the other benefits of IF.
A 14- to 18-hour fast can trigger ketosis or the fat-burning state. While the specific point at which you enter ketosis depends on several factors, including what you last ate, the process usually takes place within 12 to 22 hours after a meal, when you’ve burned through your glycogen stores. Glycogen is the form in which sugar is stored in your muscles and liver.
According to Pedre, 16 hours is an effective daily fasting window for many. This means limiting your meals to an eight-hour time frame — a practice known as 16:8 fasting. The 16:8 intermittent fasting plan doesn’t specify which foods to eat and avoid, but you should focus on following a balanced diet. Eat healthy foods, such as:
- Fruits and vegetables (e.g., fresh, frozen or canned in water)
- “Good” fats (from avocados, coconuts, fatty fish, nuts, olives, olive oil and seeds)
- Lean protein (e.g., beans, fish, lentils and poultry)
- Whole grains (e.g., barley, brown rice, oats and quinoa)
Pedre notes that you won’t experience substantial benefits until you reach the 24-hour mark.
The benefits of an extended fast
Experts don’t recommend fasting for 24 hours every day because starving yourself will do more harm than good. If you want to experiment with longer autophagy-inducing fasts, it is best to strategically space them out.
Dr. Benjamin Horne, a genetic epidemiologist, suggests doing a 24-hour fast without any caloric intake a couple of times per month. He says that this is the ideal approach for preventing chronic diseases since it is feasible to do consistently over a lifetime.
But if you’re having trouble maintaining a fast or experiencing adverse effects, reconsider your fasting plans.
Experts also say that since your fasting results will eventually stall, switching things up can be helpful. Pedre suggests increasing your fasting time to a few days a week or trying a longer fast once a week.
Fasting works best when you switch the duration of your fast so you can keep your body guessing as to when you’re going to eat your next meal.
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