How many days a week should I fast on keto?

When following a ketogenic diet, intermittent fasting can be a useful tool to help get into ketosis faster, maximize fat burning and weight loss, and provide other health benefits. But how often should you be fasting on keto? There is no definitive answer, as the optimal fasting regimen depends on the individual. However, research and anecdotal evidence provide some general guidelines.

What is Intermittent Fasting?

Intermittent fasting (IF) is an eating pattern that involves regular fasting periods. Rather than eating throughout the day, you restrict your eating window to specific hours. Popular IF approaches include:

  • 16/8 method: Fast for 16 hours per day, eating all meals within an 8-hour window.
  • 5:2 diet: Eat normally 5 days per week, restrict calories to 500–600 for 2 days.
  • Alternate day fasting: Fast every other day, eat normally on non-fasting days.
  • One meal a day (OMAD): Eat one meal per day within a 1-hour window.

On fasting days/periods, you can consume zero or very few calories (water fast), or you can allow some calories, typically from keto-friendly foods like non-starchy veggies and healthy fats. The key is that you are extending the time between meals substantially.

Benefits of Intermittent Fasting on Keto

Pairing IF with the ketogenic diet offers several potential benefits:

  • Faster ketosis: Fasting depletes liver glycogen stores, helping you achieve ketosis more quickly.
  • Increased fat burn: Fasting increases circulating fats that can be used for fuel when glycogen is depleted.
  • Preserve muscle: Ketones help preserve muscle mass when fasting compared to higher-carb diets.
  • Appetite control: Fasting helps control hunger hormones like ghrelin.
  • Focus and mental clarity: Fasting may increase catecholamines that enhance focus.
  • Longevity: Fasting triggers beneficial cellular repair processes.

In short, combining intermittent fasting with keto provides fuel for the brain and body when carbohydrates are restricted, while also ramping up fat-burning processes. This makes it easier to follow the diet long-term.

How Often Should You Fast on Keto?

There are several factors to consider when determining optimal fasting frequency on keto:

1. Metabolic Flexibility

Metabolic flexibility refers to your body’s ability to switch between burning carbs and fats for fuel. Those new to keto and fasting have low metabolic flexibility. Their bodies are still adapted to burning glucose from carbs.

For these individuals, daily intermittent fasting may not be well tolerated initially. The body needs time to make the metabolic shift to fat-burning. Start with 12–14 hour fasts and work up slowly to longer durations.

2. Lifestyle Factors

Your lifestyle also impacts optimal fasting frequency. Those with busy, active jobs may struggle with longer daily fasts. Stress can make fasting more difficult too.

Listen to your body. If you feel lethargic, irritable, and unfocused during fasting periods, scale back. Try shorter daily fasts or fasting just a couple days per week.

3. Fitness Goals

Your fitness goals matter too. Those looking to maintain or gain muscle mass need adequate protein every day.Very long or frequent fasts can compromise muscle-building.

However, fasting does not appear to increase muscle breakdown during ketosis. So occasional 24-hour fasts are likely fine for muscle retention.

4. Weight Loss Goals

Frequent and longer fasting periods tend to promote quicker weight and body fat loss. This makes sense biologically, as restricting calories and boosting fat-burning hormones will drive enhanced fat loss.

If your priority is weight loss, aim for more regular fasting at 16–20 hours per day, alternate day fasting, or 24+ hour fasts a couple times per week. Monitor your body and adjust as needed.

Recommended Fasting Frequency for Keto

Based on the above factors, here are some general recommendations for fasting frequency while eating keto:

Beginners

When first adapting to keto and intermittent fasting, start with 12–16 hours of fasting per day. Try fasting from 8pm until noon, for instance.

Once this feels comfortable, expand your fasting window to 16–20 hours daily if desired. Or try alternate day fasting or one 24-hour fast per week.

Intermediate

After adapting to ketosis and shorter fasts, aim for one of these intermediate fasting schedules:

  • 16/8 or 18/6 IF daily
  • 20–24 hour fasts 2–3 times per week
  • Alternate day fasting

The 16/8 or 18/6 methods involve fasting for 16–18 hours each day, with 1–2 meal periods. This is sustainable for most people long-term.

Fasting 2–3 days per week is also a moderate approach. You can pick whatever days work best based on your schedule.

Advanced

More experienced fasters may progress to one of these advanced regimens:

  • Alternate day fasting
  • 36+ hour fasts 1–2 times per week
  • 5:2 diet (fasting 2 non-consecutive days weekly)
  • One meal a day (OMAD)

These approaches involve longer fasting durations, from 24 hours up to full day fasts. This requires higher levels of metabolic flexibility.

Listen to your body and only try advanced methods if you tolerate shorter fasts. Adjust your regimen based on energy, hunger levels, and workout performance.

Modifying Fasting Protocols

Be flexible with your intermittent fasting schedule. Some days you may feel great extending fasts longer. Other days you may need to cut them short.

Shift your eating window earlier or later depending on your social and lifestyle schedule. The consistency is what matters most.

Also, feel free to modify protocols and combine different methods depending on goals. You might do 18/6 IF several days a week, and then throw in one 24-hour fast.

Who Should Not Fast Regularly?

While most people can safely fast intermittently, some populations should use caution or avoid it:

  • Children under 18: IF is not recommended for youth still growing and developing.
  • Underweight individuals: Those with very low BMI should not restrict calories further.
  • Pregnant/nursing women: Should not drastically restrict calories or protein intake.
  • Those with medical conditions: Certain conditions may increase health risks from fasting.
  • Diabetics: Need to monitor blood sugar closely and adjust medication dosage if fasting.

People taking prescription medications, with chronic health conditions, or a history of disordered eating should consult a healthcare provider before fasting.

Minimizing Fasting Side Effects

When starting out with fasting, some temporary side effects are common. Here are some tips to minimize adverse effects:

  • Stay hydrated – Sip water, herbal tea, or bone broth throughout the fast.
  • Supplement electrolytes – Get enough sodium, magnesium, and potassium.
  • Load up on nutrients pre-fast – Eat plenty of protein, healthy fats, and veggies before fasting.
  • Exercise strategically – Move your workout to feeding periods when first adapting to fasting.
  • Get enough sleep – Fasting can impair sleep initially, so rest and nap when needed.

Pay attention to signs of low blood sugar like dizziness, headaches, nausea, rapid heartbeat, anxiety, and irritability. If these persist, you may need to reduce fasting duration and eat keto-friendly snacks or meals to stabilize blood sugar.

Sample Intermittent Fasting Schedules

Here are some example IF meal schedules to give you an idea of how fasting can be incorporated along with keto:

16/8 Intermittent Fasting

  • 7:00 am – Wake up
  • Noon – Break fast with keto coffee or bulletproof coffee
  • 4:00 pm – Eat meal 1, examples: salmon and veggies, steak and salad, chicken wings
  • 8:00 pm – Eat meal 2, examples: low-carb chili, zucchini noodles and meat sauce, keto cheese taco shells
  • 9:00 pm – Close eating window for the day

24 Hour Intermittent Fasting

  • 7:00 am (Monday) – Finish eating last meal before fast
  • 7:00 am to 7:00 pm – Fast for a full 24 hours, consuming only water, tea, black coffee
  • 7:00 pm (Tuesday) – Break fast with small keto snack like avocado, nuts, or celery with nut butter
  • 8:00 pm – Eat regular keto meal

Alternate Day Fasting

  • Sunday: Eat keto meals normally
  • Monday: Fast completely or have one small keto meal
  • Tuesday: Eat keto meals normally
  • Wednesday: Fast completely or have one small keto meal
  • Thursday: Eat keto meals normally
  • etc.

Final Tips for Intermittent Fasting on Keto

Here are some final tips to make intermittent fasting work for you on a ketogenic diet:

  • Stay hydrated, get plenty of electrolytes, and get enough sleep – this makes fasting much easier.
  • Listen to your body – be willing to adjust fasting durations and meal timing as needed.
  • Combine different fasting protocols – mix in both daily fasts and 1-3x weekly 24+ hour fasts.
  • Break extended fasts gently – start with a small snack before resuming regular keto meals.
  • Supplement if needed – take electrolytes before/during fasts and MCT oil or exogenous ketones to support energy.

The Bottom Line

Intermittent fasting and keto work extremely well together to enhance fat burning, accelerate weight loss, and provide other health benefits. The ideal fasting frequency depends largely on individual factors like metabolic health, activity levels, fitness goals, and tolerance.

Most people can sustainably keep carbs low and do some fasting daily, while also incorporating 1-3x weekly 24+ hour fasts. Pay attention to how you feel, be flexible, and adjust your fasting regimen to match your needs as you become more metabolically flexible. Pair fasting with a solid keto meal plan when eating, and you have a powerful combination foroptimal health and body composition.

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