The Basics of Fasting

When you eat matters just as much as what you eat

Senza Fasting Timer

Did you know, the Senza app includes a fasting feature to support your journey to optimal health? Our community logs thousands of fasting minutes per day. For some, these are daily intermittent fasting windows, while for others they represent extended multi-day fasts.

For those who are new to the idea and maybe a little nervous, the Senza coaches have compiled responses to the most commonly asked questions about fasting. We hope this introduction helps you decide whether to make fasting a part of your keto lifestyle.

Fasting Lingo

Let's begin with a few basic terms:

  • IF - Intermittent fasting refers to a daily pattern of eating during a shortened time window, usually of 8 hours or less.
  • Time-restricted feeding - This is another term used to describe a pattern in which calories are consumed during a shortened period of time during the day.
  • 16:8 - This ratio refers to a specific pattern of eating during an 8-hour window each day and then fasting for 16 hours overnight.
  • Fat fast - Some people consume small amounts of fat in coffee or another non-caloric beverage, during a fasting window. This type of fast may be referred to as a fat fast. Typically, the amount of fat is equal to 50 calories or less.
  • Water-only fast - The strictest type of fast is to consume only water and electrolytes (as supplements) while fasting.
  • Multi-day fast - Any fast of 24 hours or more can be considered a multi-day fast. Current research shows that cell replenishment processes accelerate when one reaches the 36-hour mark of a fast.
  • AutophagyDuring extended fasts, the body gets rid of unwanted, non-functioning cells. We call this process “autophagy.”
  • Breaking a fast - The moment when you reintroduce calories into the digestive system.

What is fasting?

A fast is a period of time during which one abstains from all food and caloric beverages. The process of fasting encourages the body to use its own stored fuel sources - glycogen (stored form of carbohydrates) and body fat - for energy. 

Why do people fast?

Fasting allows the body to use energy that normally would be used for digestion and assimilation of food to perform cellular repair and cleanup. Some of the benefits of fasting include: 

  • Blood sugar balance
  • Improved digestion
  • Balanced hunger cues
  • Deep sleep
  • Mental clarity
  • Fat loss
  • Detoxification
  • Improved exercise performance
  • Increased longevity

How do Keto & Fasting work together?

The body has an innate ability to go without food for long periods of time. However, when people eat very high levels of carbohydrate during 16+ hours of the day, they lose this ability and may experience irregular blood sugar levels, spikes and falls in energy, mental fogginess, sugar cravings, inflammation, stress and constant hunger. 

Fasting pairs well with the ketogenic way of eating to support steady, sustainable weight loss. Being in a state of ketosis - or burning fat as the primary fuel for energy - naturally reduces hunger levels, and within a few weeks it becomes easier for most people to start skipping meals and shortening the eating window.

Both keto and fasting lead to the production of ketones and tapping into stored body fat for energy. Think of it like this:

High Carb Intake > High Insulin Production > Body Fat Stores Are Locked
Very Low Carb Intake > Low Insulin Production > Body Fat Turns into Energy

When is the best time to start fasting?

Some keto’ers are eager to jump right into fasting, but they may experience symptoms like excessive hunger, fatigue, brain fog, dizziness and low blood sugar if making a sudden transition from the high-carb Standard American Diet. Try making the transition to ketosis first by limiting net carb intake to a maximum of 25 grams per day. Once the body becomes efficient at burning fat for energy, it’s an easier next step to experiment with time-restricted eating and multi-day fasting patterns. Note that your ability to fast also is dependent on other factors such as how late and what you ate the night before, your stress levels, quality of sleep, time of the month (for women), activity levels and more. 

How do you start fasting?

One of the easiest ways to start fasting is to push back your first meal of the day. Also try to finish eating all calories at least two hours before going to sleep. Gently easing into a daily fasting schedule lets your body be the guide rather than trying to follow a regimented routine straight out of the gate.

    What can you drink during a fast?

    Sip water with electrolytes, black coffee, unsweetened herbal tea (not chamomile), and non-caloric beverages like sparkling water. Avoid ‘sugar free’ or ‘calorie free’ beverages, as artificial sweeteners can trigger cravings that interfere with ketosis and blood sugar balance. 

    How do I track my fasts in Senza?

    Senza was designed for time-based logging in order to support fasting, together with food tracking. You can use the built-in fasting timer to track your intermittent fasting windows or multi-day fasts in the same place you log meals. In your Senza Food Journal, tap the green + button to start a new entry and look for the timer at the top of the screen.

    Since many people adjust the fasting window as they go, the timer will not stop automatically at the designated time. You need to manually stop the fast to save it to your journal. It is possible to edit the start and duration of a fast, after you've paused the timer and logged the fast to your journal.  


    How will fasting affect my Daily Score?

    The Senza Daily Score considers your fasting windows in evaluating your journal for the day. As long as you log a fast, the app will take this into account and generate a score, even if you ate fewer than 50% of your calories for the day. To learn more about how the daily score is calculated, see The Senza Daily Score Explained.

    What’s the best way to break a fast?

    It’s important to plan out your first meal once you decide to end your fast. Digestive enzymes start to decrease after longer periods of fasting, and eating too much, too quickly after a fast can cause GI upset. Keep your first meal simple, light and nourishing. Avoid heavy foods and intense flavors. For example, you might sip a mug of salted bone broth, have a keto-friendly soup, or prepare a simple protein with cooked vegetables on the side. 

    Where can I learn more about fasting?

    Life in the Fasting Lane Dr. Jason Fung
    Read Life in the Fasting Lane by Dr. Jason Fung, MD, an expert in intermittent fasting and low-carb diets. 
    Get the latest science on women and fasting in this post by Mark Sisson: Intermittent Fasting for Women: What We Now Know
    See the Timeline of Fasting and other infographics by @HealthCoachKait.  


      Caveats to fasting

      Fasting may be contraindicated in those with:

      • Excessive stress
      • Hormone imbalances
      • Thyroid or adrenal dysfunction
      • Type 2 Diabetes

      Talk to your doctor about risks associated with these conditions.

      Learn more about keto

      To learn more about keto and the Senza: Keto & Fasting app, see these posts:


      Content provided by Senza is not medical advice. It is intended for informational and educational purposes only.