Is not eating for 17 hours considered fasting? A Deep Dive into the 17/7 Method

October 13, 2025 •

4 min read

Scientific research suggests that fasting for at least 12 hours can trigger a metabolic switch in the body. Therefore, is not eating for 17 hours considered fasting, and specifically, a type of time-restricted eating (TRE) where you fast for 17 hours and consume all your calories within a 7-hour window.

Quick Summary

Seventeen hours without eating is a form of intermittent fasting called the 17/7 method, which is a variation of time-restricted eating. It promotes metabolic changes, including shifting the body's energy source from glucose to fat, and may offer various health benefits.

Key Points

17 Hours as Fasting: Yes, a 17-hour period without food is a recognized form of intermittent fasting, specifically the 17/7 time-restricted eating method.
Metabolic Switch: During this time, your body transitions from using glucose for energy to burning stored fat and producing ketones, a process called metabolic switching.
Enhanced Autophagy: Fasting for 17 hours can trigger autophagy, a cellular cleanup process that recycles old and damaged cell components, promoting cellular health and longevity.
Potential Benefits: Benefits can include weight loss, improved insulin sensitivity, better heart health, and reduced inflammation.
Not for Everyone: Intermittent fasting, especially longer durations, is not suitable for everyone, particularly pregnant women, individuals with a history of eating disorders, or those with diabetes.
Safe Implementation: To start safely, ease into the fasting schedule, prioritize nutrient-dense whole foods during your eating window, and stay well-hydrated with calorie-free liquids.

Understanding the Fasting State

From a physiological standpoint, fasting begins after your body has finished processing and absorbing the nutrients from your last meal, a phase typically lasting 3 to 5 hours. A fast lasting 17 hours allows the body to move beyond this 'fed state' and into a more pronounced fasting phase. During the early fasting state, which can last up to 18 hours, the body depletes its stored sugar (glycogen) and starts breaking down stored fat for energy. For many people, a 17-hour fast is long enough to initiate this metabolic switch, potentially leading to benefits like weight loss and improved metabolic health.

The Science Behind a 17-Hour Fast

Metabolic Switching: The core principle of intermittent fasting is metabolic switching. When you don't eat for an extended period, your body's primary energy source shifts from glucose to ketones, which are produced from burning fat. This is a key mechanism for potential weight loss and improved body composition.
Autophagy: A 17-hour fast also gets you into the optimal range for autophagy, a cellular process where the body cleans out and recycles damaged cell components. This can improve cellular health and has been linked to anti-aging benefits.
Improved Insulin Sensitivity: During a fast, insulin levels decrease significantly. This can increase the body's insulin sensitivity, which is beneficial for regulating blood sugar and reducing the risk of type 2 diabetes.

Potential Benefits of a 17-Hour Fast

Extending a standard 16-hour fast by just one hour may offer amplified benefits for some individuals. Adopting a 17/7 time-restricted eating schedule can yield several positive health outcomes when combined with a balanced diet during the eating window.

Weight Management: By restricting the eating window, you may naturally consume fewer calories, leading to weight loss. The metabolic switch to burning fat also contributes to reducing overall body fat.
Enhanced Heart Health: Intermittent fasting has been shown to improve various heart health markers, including reduced blood pressure and improved cholesterol profiles.
Cellular Repair and Longevity: The activation of autophagy during longer fasts can help combat inflammation and contribute to healthy aging by repairing and renewing cells.
Brain Function: Some studies suggest intermittent fasting can boost cognitive function and protect against neurodegenerative diseases by increasing a protein called brain-derived neurotrophic factor (BDNF).

Comparison: 16/8 vs. 17/7 Fasting

For those considering time-restricted eating, a common question is whether to stick to the popular 16:8 method or extend the fast to 17 hours. Here is a comparison to help illustrate the differences.


Feature	16/8 Method (Beginner-Friendly)	17/7 Method (Intermediate)
Fasting Duration	16 hours	17 hours
Eating Window	8 hours	7 hours
Ease of Adherence	Often easier to start, requiring only skipping one meal like breakfast or a late dinner.	Requires more discipline and may feel more challenging initially, especially if you get hungry earlier in the evening.
Potential Benefits	Provides solid benefits, including weight loss, improved insulin sensitivity, and reduced hunger over time.	May amplify metabolic benefits like autophagy and fat burning due to the longer fasting window, potentially leading to more significant or faster results.
Side Effects	Initial side effects like hunger and headaches are possible but tend to fade.	The extended fast may cause slightly more pronounced hunger, irritability, or fatigue at the start.
Long-Term Sustainability	Generally considered a very sustainable long-term approach for many people.	Requires a bit more effort but can be sustainable once the body adjusts.

How to Start 17/7 Intermittent Fasting Safely

To safely incorporate a 17/7 fast into your routine, it's wise to transition gradually. Start with a shorter fast, like 12 hours, and slowly extend the fasting window by 30-60 minutes every few days as your body adapts. Consistency is key to seeing results and minimizing side effects.

Tips for success:

Stay Hydrated: Drink plenty of water during your fasting period to prevent dehydration and manage hunger pangs. Unsweetened coffee and tea are also acceptable.
Choose Nutrient-Dense Foods: Focus on eating whole foods during your 7-hour window, including lean protein, healthy fats, fruits, vegetables, and whole grains. This ensures you get all the necessary vitamins and minerals.
Listen to Your Body: Pay attention to your energy levels and mood. If you experience persistent negative side effects, it may be a sign to adjust your fasting duration or consult a healthcare professional.

Who Should Be Cautious or Avoid Intermittent Fasting?

While intermittent fasting is safe for many healthy adults, it is not suitable for everyone. Certain individuals should exercise caution or avoid this dietary pattern entirely. It is crucial to consult a doctor before starting any new dietary regimen, especially for those with existing health conditions.

Groups who should be cautious:

Individuals with a history of disordered eating: Fasting can be a trigger for restrictive behaviors and an unhealthy relationship with food.
Pregnant or breastfeeding women: Fasting is not recommended due to the increased energy and nutrient needs for both mother and baby.
People with Type 1 or Type 2 Diabetes: Intermittent fasting can affect blood sugar levels, especially for those on medication, and requires medical supervision.
Those on specific medications: Certain medications, particularly for blood pressure or heart disease, may require food intake for proper absorption or to prevent imbalances.

Conclusion

Yes, not eating for 17 hours is considered a form of intermittent fasting, known as the 17/7 method. It is a more advanced version of time-restricted eating that can offer significant benefits for weight management, metabolic health, and cellular repair, largely by promoting the body's shift from burning glucose to fat. While it can be a highly effective tool when implemented thoughtfully, it is not a one-size-fits-all solution. For some, the traditional 16:8 method may be more manageable, and certain populations should exercise caution or avoid it completely. Always listen to your body and consult a healthcare provider before making significant dietary changes. For further reading on the science of intermittent fasting, you can refer to research reviews, such as those published in the New England Journal of Medicine.

Frequently Asked Questions

The 17/7 method involves fasting for 17 hours every day and confining your eating to a 7-hour window. This is a form of time-restricted eating that extends the fasting period beyond the more common 16-hour fast.

During your 17-hour fasting window, you should only consume calorie-free beverages. Acceptable drinks include water, black coffee, and unsweetened tea. Adding milk, sugar, or other calorie-containing substances would break your fast.

After about 12-16 hours of fasting, your body begins to deplete its stored glucose and switches to burning fat for energy. This process, called metabolic switching, increases the production of ketones, which can be used as fuel.

For some, the longer 17-hour fast may offer amplified metabolic benefits, such as a more pronounced fat-burning state or cellular repair (autophagy). However, the best method depends on personal preference and sustainability, as consistency is crucial for seeing results.

When breaking your fast, it is best to start with easily digestible, nutrient-dense foods to avoid shocking your system. Options include Greek yogurt with berries, a small bowl of oatmeal, or a salad with lean protein.

Initial side effects can include increased hunger, headaches, fatigue, irritability, and difficulty concentrating. These symptoms often subside as your body adjusts to the new eating pattern over a few weeks.

Yes, it is possible to exercise while fasting. Many people find light exercise like walking or fasted cardio beneficial. For more intense workouts, it may be better to schedule them closer to your eating window to ensure you have adequate energy for performance and recovery.