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A Nutritionist's Guide to Fasting

by Katelyn Daugherty, MS, CNS-c

Fasting is a scary word. However, fasting is the most ancient, inexpensive and perhaps the most healing diet strategy known to man. All of our ancestors did it. They didn’t have pantries and refrigerators like we do, so if there was a poor harvest or unsuccessful hunt they went stretches without food.

It’s even built into many different cultures and religions. If you look at Ramadan in the Islamic Tradition, they fast for a period of a month (sunrise-sunset); In Judaism, they fast during Yom Kippur, and the Christian lent is based on a 40-day fast.

Fasting is ancient medicine. The Ancient Greeks Hippocrates, Plato, Socrates all practiced and wrote about fasting. The mental and physical efficiency benefits were celebrated.

It's an all-around health panacea that has lasting benefits if applied correctly. AND it doesn't cost anything. Get my Quick Guide to Fasting Here.

What Happens When We Fast?

When we fast, we don’t have available access to glucose, so our body shifts to using fat for energy. Fatty acids (from dietary fat and stored body fat) are broken down for energy and converted to ketone bodies (in the liver). Ketones become the body’s primary fuel: a very clean energy.

Ketones produce significantly less metabolic waste than glucose, and produce significantly more overall energy. In particular, our mitochondria (you know, the “powerhouse” of the cell) THRIVE on ketones as an energy source.

This is where we get all the brain benefits of fasting! As you become fat-adapted you’ll notice more creativity, sharper thinking, and a clearer mind. Additionally, increased ketone produce significantly reduces the risk of neurodegenerative conditions like Alzheimer’s and Parkinson’s Disease.

Fasting for Cellular Repair

Cells in our body are routinely being broken down and replaced. In a constantly fed state, we are not allowing the body to get rid of waste and there is no time for healing and repair. When we fast, we decrease insulin and blood sugar levels and activate stem cells. This turns on autophagy, where your body breaks down the old, damaged cellular debris. Fasting is the easiest way to ensure we are “taking out the trash”. With new, healthy cells we become more stress resilient in all areas of our life (Physically, Emotionally, Metabolically).

The Importance of Easing In

Just like with exercise, you can’t expect to jump right into a fasting routine and feel great. You need time to adapt and acclimate. Think of it like building your fasting fitness level. This happens by slowly leaning into fasting, and gradually progressing it.

I like to start with a simple twelve-hour overnight fast. If you finish your last meal at 7pm, wait until 7am the next morning to begin eating. This cuts down on unconscious eating and snacking that happens between the evening meal and breakfast.

Once you are comfortable with the twelve hour eating window, you can begin to delay eating by a few more hours. Wait a bit longer for breakfast, and have plenty of water instead. Continue to experiment with your optimal eating window and see how you feel.

Most people feel well with a 16:8 intermittent fasting program. This means fasting for sixteen hours overnight, and eating within an eight hour window. If you begin breakfast at 10am, finish eating by 6pm. This approach can be shifted depending on your schedule. Perhaps you easily fast until noon, and finish dinner by 8pm.

By the time you have fasted for sixteen hours, you have started to produce neuroprotective ketones. Practicing a daily intermittent fast (IF) is gaining popularity for its benefits and practicality. As you become fat-adapted this should become easier to maintain. Your body is not producing as much insulin, you are not going through blood sugar swings, and you reduce the drive to eat every three to four hours.

After settling into a regular 16:8 schedule, it can be powerful to add one 20-24 hour fast per week. This massively increases autophagy (cellular cleanup) and reduces your risk of chronic disease significantly. This can be incorporated by simply fasting from dinner to dinner one day per week.

Hunger is a Conditioned Response

If you are waking up hungry, perhaps you need some time to retrain your brain’s conditioning to hunger. When the stomach is empty, our body produces a hormone called ghrelin. This hormone signals to the brain- “it’s time to eat!”. Interestingly, under periods of stress, ghrelin can also be increased. When we respond to this stress-induced signaling, our brain is comforted by food. Instead of relying on true physiological need for food- we enter a cycle of emotional eating.

The routine of breakfast can also ‘trick’ our brain into hunger. We think we need food in the morning, because we are used to it. (note: Recall Pavlov's Dogs?) If you can tap into true hunger signals and separate emotional/routine comforts, you’ll find it becomes easier and easier to fast for longer periods. These periods of fasting help reset your metabolic signaling cascade (involving ghrelin, leptin, and insulin).

The very first thing that should go into your body after sleeping is water. Sleep is very dehydrating for us, we are breathing off water and carbon dioxide throughout the night. When we wake, filling the stomach with water will increase the stretch (and inhibit ghrelin). Adding a pinch of sea salt can help ensure systemic hydration. This is particularly important during a fasting window because you excrete more sodium when your insulin levels are low.

Modified Intermittent Fasting

For certain populations*, a daily intermittent fast adds excess stress on the system, and becomes detrimental to health. One group at high risk for this is lean, young, menstruating females, who have high stress. This is often a combination of lifestyle stress (kids, work) and exercise-induced stress (high-intensity training). Since fasting is an inherently stressful state, the body is overwhelmed.

To avoid overloading stressors, the best strategy for this population is a cyclical fasting schedule. Begin with a fourteen-sixteen hour fast, two times per week, on non-consecutive and non-workout days. Choosing foods that are “insulin friendly” such as healthy fats, non-starchy vegetables, and animal-based proteins will maximize the benefits of this approach. Working directly with a nutritionist is a good idea to create a personalized fasting strategy.

*Note that pregnant women and competitive athletes should not practice fasting without direct supervision from a nutritionist or doctor

Pay Attention to Your Body

It is important to pay attention to your mental and emotional health during fasting. If you find yourself obsessing about your next meal, fantasizing about all the things to eat, and calculating when to eat them, you need to take a step back. If you find that you are using your eating window to eat until you’re so full you can barely move, you should re-evaluate your strategy.

If you have a poor relationship with dieting or food restriction, fasting may trigger something in you that is not healthy. Keep in ming that you don’t have to do it EVERY DAY. Listen to your body to allow you to create an approach that optimizes your health, and avoids its potential pitfalls.

Fasting Adaptation: The Goal

Once you have fully adapted to fasting, you will experience your best memory, clearest thinking, your best energy, and your body should feel very good. Ultimately, the end goal is optimizing health potential. If you find you are struggling through it, dealing with mood issues, anxiety, or performance loss... take a step back and re-evaluate your strategy. Work one-on-one with a nutritionist to find an optimal structure for you.

Key Benefits of fasting

-Weightloss without an effect on metabolism (this is not calorie restriction)

-Stable blood sugar

-Improved insulin sensitivity

-Lower blood pressure, cholesterol, and triglycerides

-Reduced inflammation

-Increased ketones

-Higher levels of HGH which aids muscle growth and fat burning

-Reduced free radical damage

Want a free PDF that breaks down different types of fasting including 16:8, OMAD, and Cyclical? Check it out below:


Want to work with a functional nutritionist to personalize your diet? Struggling with hormone imbalance, IBS, weight gain, mood changes? Let's look at FOOD FIRST. Read more about Functional Nutrition at The Facility here.

CLICK HERE to schedule a FREE 15-Minute Nutrition Consult with Kate to determine your best course of action!


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Dr. Mitchell Rasmussen - Doctor of Chiro
Kate Daugherty - Nutritionist - Function
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