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What Is 16:8 Intermittent Fasting?

"Andrea is a copywriter and editor specializing in holistic nutrition, health, and wellness. She holds a Bachelor of Arts in Communication Studies from McMaster University, is a certified personal trainer with the National Academy of Sports Medicine (NASM), and Certified Nutritional Practitioner (CNP) with the Institute of Holistic Nutrition."

One popular form of IF is the 16:8 intermittent fasting method, also known as the 16:8 diet. This method restricts mealtimes to an 8-hour window and fasting to the remaining 16 hours. It is said to benefit everything from weight loss and blood sugar regulation to chronic disease prevention and neurodegenerative conditions (1)

So, if you’re thinking about trying 16:8 diet, we’re covering what you need to know before starting. We’re breaking down what 16:8 intermittent fasting is, 16 hour fast benefits, how you can get started with this method, and potential side effects you should know. 

Studies consistently show that by consolidating meal times, one can lose weight, positively change biomarkers of disease, reduce oxidative stress, and save learning and memory longer among other potential benefits (2). In addition to the long list of potential health benefits – it is popular because it’s not a traditional diet. Instead of dictating what you eat, IF focuses on when you eat. This allows for flexibility and choice within your eating patterns.

While there are several different methods, 16:8 intermittent fasting is one of the more common and popular because it allows a great deal of flexibility and can be more sustainable than other approaches.

The premise behind the 16:8 intermittent fasting plan is to break your day into two parts—the “no calories window” and the “feeding window.” Generally speaking, a 16:8 diet plan denotes a 16-hour fasting window, followed by an 8-hour feeding window. That means for 16 of 24 hours you’re consuming only water, black coffee, or black tea. For the remaining 8, you can eat as you normally would.

At first glance, you may think 16 hours is a long time to go without food, but if you’re doing the majority of your fast overnight, it can be quite simple. For example, you eat dinner at 5 pm and then fast until 9 am the next morning – that’s a 16 hour fast diet that flies by in no time! Plus, unlike the 5:2 diet or alternate-day fasting, there’s less of a risk of getting hangry.

How to Get Started

The 16:8 method may just be one of the simplest and most sustainable forms of dieting— and it’s even easier to get started.

To get started, pick your 8-hour eating window. This will be the period where you consume all your meals, snacks, and caloric beverages. For example, you may have your eating window from 8 am to 4 pm or noon to 8 pm. The former example allows you to eat a nutrient-dense breakfast and lunch, whereas the latter means you would probably skip breakfast but eat lunch and dinner. There’s no set time for the 16:8 method, so the time frame of your eating and fasting window will depend on what works best with your schedule.

If you find jumping right into this method is too difficult at first, try starting with a smaller fasting window (i.e., 12 hours) and slowly increase your window to 16 hours overtime.

While IF protocols don’t restrict what you can eat, following general recommendations for a balanced diet can help ensure you’re eating enough important nutrients throughout the week. Consuming whole, nutrient-dense foods during your feeding window can help maximize the benefits of 16:8 intermittent fasting and support overall health. An example of what that could look like is a diet rich in:

  • Whole fruits and vegetables
  • Whole grains
  • Healthy fats (nuts, seeds, olive oil, avocado, coconut oil, etc.)
  • Lean proteins (poultry, fish, tofu, low-fat dairy)

Staying hydrated is also an important part of a balanced diet. Beverages like water, herbal teas, and black coffee (in moderation) can help you stay hydrated during both your fasting and feeding windows.

Benefits of 16:8 Intermittent Fasting

Not only is this eating pattern popular because it is easier to stick to long-term than other methods, but it is well-studied and boasts a number of potential health benefits. Those benefits include but are not limited to:

  • Stimulates autophagy: If you want your body to work like a well-oiled machine, intermittent fasting may do the trick. That’s because it triggers a process called autophagy, whereby your body breaks down old, worn out, and dysfunctional proteins for cellular renovation and homeostasis, thereby enhancing cellular adaptation to stress and improving the efficiency of organ systems (3).
  • Supports longevity: Want to be a centenarian? Along with its role in stimulating autophagy and improving cellular stress resilience, IF may help you live longer. Research suggests that fasting may extend lifespan by acting on several different signaling pathways that are activated by factors like growth hormone (GH), insulin-like growth factor-1 (IGF-1), and insulin, which have downstream effects on the mammalian target of rapamycin complex 1 (mTORC1), protein kinase A (PKA), AMP-activated protein kinase (AMPK), and other factors that are known to regulate or affect aging and longevity (4)
  • Supports weight loss: One of the major perks is a simple way to help you lose weight. Research shows that IF may boost fatty acid mobilization, reduce inflammation, regulate appetite, increase insulin sensitivity, and reduce glucose, insulin, and leptin(5). A 2015 systematic review found that on average, a person weighing about 90kg could lose up to 5% of their total body weight in ten weeks following a 16:8 intermittent fasting protocol (6).
  • Improve blood sugar regulation: Impaired glucose control is linked to several diseases, including type 2 diabetes and metabolic syndrome, and studies show that IF can reduce insulin levels by up to 31% and reduce blood sugar by up to 6%, which may decrease the risk of developing metabolic diseases (7).
  • Improves heart health: Heart disease is one of the leading killers worldwide and has several notable “risk factors.” Intermittent fasting has been shown to improve several of these risk factors, including blood sugar levels, blood pressure, triglycerides, cholesterol, and various inflammatory markers (8 , 9).
  • Improves brain health: In addition to putting the brakes on the aging process, the metabolic switch has been shown to increase neuroplasticity in the brain, which helps to optimize brain function and enhance resiliency and resistance to injury and disease. Studies show that regular fasting increases synaptic plasticity, enhances cognition and neurogenesis, reduces inflammation, and upregulates autophagy in the brain (5).

Remember, results may vary based on the individual.

16:8 Diet Side Effects and Risks

While the 16:8 method tends to be easier to sustain long-term than other eating methods, it can be challenging to maintain over time. You may have to forgo the popcorn at the movie theater or push your breakfast back the following day after a late-night dinner party to keep your fasting state. 

And while there is an impressive list of potential health benefits, there is also a list of potential downsides.

For starters, depending on your current health status, intermittent fasting may also cause temporary side effects like dizziness, fatigue, weakness, headaches, or low blood sugar. Still, as your body adapts to a new eating pattern, the symptoms may subside (10 , 11, 12). Individuals may also be at risk for mild dehydration.

While many people find IF beneficial, health professionals recommend that certain populations avoid fasting. Who should not do it for 16 hours (13)?

  • Pregnant or breastfeeding women
  • Young children and teens
  • People with compromised immune function
  • Individuals who have or have had eating disorders
  • People with dementia
  • People with a history of traumatic brain injury or post-concussive syndrome

While people with pre-existing diabetes, kidney disease, or certain metabolic disorders may benefit from 16:8 intermittent fasting, they should practice it under the guidance of a medical professional. These conditions can alter the body’s balance, storage, and use of insulin and glucose, which means that the 16:8 diet could be potentially unsafe.

For everyone else, following the 16:8 intermittent fasting protocol can offer some stellar results—but don’t expect them to come easy. The 16 hour intermittent fasting diet isn’t a miracle worker and you may find that there is an adjustment period in which you feel quite hungry or tired in the beginning. But like every other diet or eating pattern, if you make a conscious effort to eat healthily, exercise often, and be consistent, the 16:8 fasting results will be well worth your while.

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