Your Definitive Functional Medicine Guide To Intermittent Fasting


In my functional medicine clinic, I often see chronic inflammation as the underlying cause of many health problems. Even though acute inflammation is a normal response of a healthy body to fight off infections, chronic inflammation that never subsides can lead to cancer, autoimmune conditions, and even heart disease.

Intermittent fasting – when you go without food for a period of time – is one of my favorite go-to tools for naturally driving down inflammation.


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Intermittent Fasting Hormones + Benefits

Now, I know you are probably wondering why eating is a problem if what you are eating is made up of healthy, whole-food sources. It’s not that eating is bad, instead, fasting gives your digestive system a chance to rest thus soothing inflammation. Therefore, intermittent fasting has been shown to have some powerful benefits:

1. Lowers cancer risk

Research has shown a link (1) between a reduced risk of breast cancer and intermittent fasting.

2. Enhances heart health

Intermittent fasting has the ability to lower blood pressure and triglycerides – two markers of heart disease risk (2) – while also raising (3) beneficial HDL cholesterol.

3. Slays hormone-signaling inflammation

Intermittent fasting decreases insulin resistance, a hormonal problem that affects a staggering 50 percent of American adults! IF also increases production (4) of beneficial enzymes that increase your body’s ability to adapt to stress and fight chronic diseases like diabetes. IF is proven to increase metabolism (5) and lower insulin resistance. (6)

4. Improves autoimmune conditions

Three-day cycles of a fasting-mimicking diet under 1,000 calories per day can help improve symptoms (7) of autoimmune conditions such as lupus (8) and multiple sclerosis.

5. Encourages weight loss

Underlying hormone imbalances can often contribute to people’s inability to lose weight. For example, leptin resistance happens when your brain stops recognizing leptin’s signals to use your body’s fat stores for energy. Your body ends up continuing to store fat instead of using it for energy. Intermittent fasting can drive down inflammation that blunts your brain’s leptin receptor sites.

READ NEXT: Natural, Permanent Weight Loss Is Possible — Here’s How To Do It

6. Kills cravings

You don’t have to worry about starving while fasting! Your hunger hormone ghrelin, is decreased during intermittent fasting while your brain’s dopamine levels are increased. (4) By transitioning your metabolism from a sugar-burner to a fat-burner your body will no longer crave that unhealthy junk food. Plus, regularly fasting can also help people free themselves from emotional eating.

7. Blunts chronic pain inflammation

Intermittent fasting improves something called neuroplasticity – the ability of the brain to form and reorganize synaptic connections in response to new information – while researchers are studying (9) the role it may play in managing chronic pain.

8. Reduces brain inflammation

Mental health problems like anxiety, depression, and brain fog are on the rise, and studies are showing that IF improves (10) brain function and mood through an effect not unlike antidepressant medication. Even neurological conditions like Alzheimer’s and Parkinson’s seem to respond positively to IF, and several studies have shown (4) that IF may actually protect neurons from genetic and epigenetic stress factors, meaning it can essentially slow down brain aging.

9. Improves lung health

A study looking at people with asthma showed that intermittent fasting was able to reduce symptoms (11) as well as oxidative stress.

10. Heals the gut

Intermittent fasting lowers gut inflammation to help improve (12) inflammatory gut disorders such as Crohn’s disease, ulcerative colitis, and IBS.

The idea of intermittent fasting can be overwhelming, but you’ll be pleasantly surprised at how easy it is, especially compared to other types of eating plans. Fasting means you’ll be eating less food, thus reducing the need for intensive meal prepping. The meals you do eat will mainly focus on healthy fats, clean protein, and whole-food carbohydrates like sweet potatoes. Remember, this isn’t an excuse to binge on unhealthy food during your windows of eating!

Intermittent Fasting and Hormones:

1. Fat storing and hunger hormones: (leptin, insulin, + ghrelin)

Intermittent fasting takes center stage in its role in improving hunger, metabolism, and blood sugar affecting hormones. When patients come in with blood sugar problems I like to recommend IF due to its proven ability to increase (13) metabolism and lower (14) insulin resistance. If you have a blood sugar problem and want to try fasting it’s key to work with your doctor who can monitor you and slowly increase your length of fasting as your glucose stabilizes. Leptin resistance, another hormonal resistance pattern which leads to weight gain and weight-loss resistance, has also been shown to improve with IF.

And if you think fasting would make you more hungry, think again. Intermittent fasting has been shown to positively affect the hunger hormone ghrelin, which can directly improve (4) brain dopamine levels. This is the perfect example of the reality of the gut-brain axis connection.

2. Estrogen and progesterone

Your brain and ovaries communicate through the brain-ovary axis or hypothalamic-pituitary-gonadal (HPG) axis. Your brain releases hormones to your ovaries to signal them to release estrogen and progesterone. If your HPG axis isn’t working well it can affect your overall health and lead to problems with fertility.

When it comes to intermittent fasting, women are usually more sensitive than men. This is due to the fact that women have more kisspeptin, which creates greater sensitivity to fasting. If not done properly, IF can cause an irregular cycle and throw off their hormones. While more research needs to be done, it would make sense to logically conclude that this hormonal shift could affect metabolism and fertility too.

Now all this to say since every person is different, this doesn’t mean you can never try intermittent fasting. You may just have to go at it with a different approach. Crescendo fasting can be a great way to gradually introduce fasting into your routine.

  • Fast two nonconsecutive days a week (such as Sunday and Thursday).
  • Only do light exercise on fasting days.
  • Fast between 12 to 16 hours.
  • After a minimum of two weeks, add one more day of fasting to your routine.
  • During this time I recommend adding around 6 grams of branched-chain amino-acid supplements (BCAAs), which come in powder and capsule form. These can help improve the positive impact of fasting and help take the edge off.

3. Adrenal hormones (cortisol):

Cortisol is your body’s main stress hormone and is released by your adrenal glands which sit right on top of your kidneys. When your brain-adrenal (HPA) axis is thrown off it can lead to an imbalance in cortisol. This high and low rollercoaster ends up leading to adrenal fatigue. I’ve found that people with dysfunctions with their circadian rhythm don’t handle intermittent fasting well. However, trying a slow beginner intermittent fasting protocol or crescendo fasting could be ok with someone monitoring your progress.

4. Thyroid hormones (T3 and T4):

Your thyroid is queen of all hormones and affects every single cell in your body. No other hormone has that much power. If your thyroid hormones are not functioning optimally, then nothing is. There are many different types of thyroid problems - all of which can be effected differently by intermittent fasting. Therefore, I recommend working with a functional medicine practitioner who can work with your specific health case.

Intermittent fasting: Scheduling meals

What are the best hours for intermittent fasting? That really depends on the individual, and their comfort and experience level. Before we dive into the specific plans for each of those levels, it is important to note that with any sort of diet or lifestyle change, make sure to talk with your doctor to determine if it is the best choice for you. Although there are many benefits of intermittent fasting for women, they in particular, should be more cautious with fasting since it may impact the balance of female hormones. Adrenal fatigue and gut issues are also health problems that may need extra monitoring. If you have a history with, or currently struggle with, an eating disorder, be especially mindful of whether this is the right choice for you.

Most likely you’ll find that when you start intermittent fasting you’ll feel fuller faster after each meal that you do eat, thus keeping the meals you eat simple. Since there are many different ways to fast, I broke down each of the various plans into beginner, intermediate, and advanced along with a one-day meal plan for each. The specific combination of nutrients will help enhance the benefits you’ll already be gaining from fasting. You can use this as a guide for your specific health case and take into consideration  any food intolerances or other modifications you need to make.

How should a beginner start intermittent fasting? The 8-6 Window Plan

For any beginner, intermittent fasting can seem intimidating. Don’t worry! This intermittent fasting guide is a perfect way to break into the scene without changing things up too drastically. You will eat between the hours of 8 a.m. and 6 p.m. This is a great plan to start with since it allows you to eat breakfast, lunch, and dinner within normal hours while still getting 14 hours of uninterrupted fasting time in a day.

Breakfast: Green Smoothie – 8:00 a.m.

I like to ease into eating with an easy-to-digest smoothie. A green smoothie avoids the high-sugar content often found in fruit-based smoothies which will keep you from getting on a blood-sugar rollercoaster. Smoothies are also great for packing a lot of healthy fats into one meal.


  • 1 avocado
  • 1 cup full-fat coconut milk
  • 1 small handful blueberries
  • 1 tablespoon chia seeds
  • 1 cup greens of choice (spinach, chard, etc.)


  1. Place all ingredients in a blender and blend to combine.

Lunch: Grass-Fed Burgers – 12:00 p.m.

I love to prep multiple grass-fed liver burgers to warm up throughout the week. Up the health benefits by making a burger salad with greens packed with B-vitamins and a homemade dressing loaded with healthy fats to increase methylation and detox pathways.


  • ½ pound grass-fed beef
  • ½ pound grass-fed beef liver
  • ½ teaspoon cumin
  • ½ teaspoon garlic powder
  • Sea salt and pepper to taste
  • Desired cooking oil


  1. Place all ingredients in a bowl and mix with hands to form patties to your desired size.
  2. Heat cooking oil on medium-high heat in a skillet.
  3. Cook burgers until desired doneness.
  4. Store in the fridge in a sealed container and use within 4 days.

Snack: Cinnamon Roll Fat Bombs – 2:30 p.m.

Fat bombs are a delicious way to satisfy your sweet tooth while still giving you enough healthy fats to keep you full until dinner. The yummy cinnamon roll taste will make you forget all about the cinnamon rolls of your past!


  • ½ cup coconut cream
  • 1 teaspoon cinnamon
  • 1 tablespoon coconut oil
  • 2 tablespoons almond butter


  1. Mix together ½ teaspoon cinnamon and coconut cream.
  2. Line an 8-by-8-inch square pan with parchment paper and spread the coconut cream/cinnamon mixture at the bottom
  3. Mix together ½ teaspoon of cinnamon with coconut oil and almond butter. Spread over the first layer in the pan.
  4. Freeze pan for 10 minutes and then cut into desired-size bars or squares.

Dinner: Salmon + Veggies – 5:30 p.m.

Salmon is one of my favorite sources of omega-3 healthy fats but any type of wild-caught seafood will work as well. Serve fish with vegetables roasted in avocado or coconut oil and you have a complete superfood meal.


  • 1 pound salmon or other desired fish
  • 2 tablespoons fresh lemon juice
  • 2 tablespoons ghee
  • 4 cloves garlic, finely diced


  1. Preheat oven to 400 degrees F.
  2. Mix together ghee, garlic, and lemon juice.
  3. Place salmon on top of a sheet of foil and pour lemon and ghee mixture over the top.
  4. Wrap foil over salmon and place on a baking sheet.
  5. Bake for 15 minutes or until salmon is cooked through.
  6. Roast vegetables alongside salmon on a separate baking sheet at the same time if your oven size is big enough.

Intermediate: The 12-6 window plan

This intermediate intermittent fasting guide is exactly the same as the beginner plan but with an added 4 hours of fasting time. This is what I personally do during the workweek. Since I am not a fan of breakfast I like to sip on a few cups of herbal tea throughout the morning. You’ll be getting a full 18 hours of fasting while only eating between 12 p.m. and 6 p.m.

Make sure to drink enough water during the fasting period so you don’t get dehydrated. Herbal tea is still ok to have while fasting and in fact, tea contains catechins that have been linked to a decrease in the hunger hormone ghrelin which can help make fasting a lot easier. Since you’ve added an additional four hours of fasting each day, your first meal needs to contain enough healthy fats. The same burger from the beginner plan will be a great meal for this plan as well, especially if you add in more fats with an avocado!

Nuts and seeds are also high fat and make a great snack to munch on in between your first and last meal. Just make sure to soak them for at least 12 hours before eating to help neutralize naturally occurring enzymes such as phytates that often cause digestive distress. Any sort of clean protein source with vegetables for dinner will be a great way to finish off your day of eating.

Intermediate: The modified 2-day plan

This plan is structured a little differently than the first two. You’ll be eating clean for 5 days of the week (which days are up to you) and on the remaining two days your calories will be restricted to no more than 700 calories. Calorie restriction provides a lot of the same benefits as a full day of fasting. During the 5 days of eating you can structure your meals however you like but they still need to contain healthy fats, clean meats, vegetables, and if desired, some fruit.

On restricted days you can structure your day however works best for you, whether that is smaller meals throughout the day or two moderate sized meals. Again, you’ll want to be eating healthy fats, clean meats, and produce.  Food tracking apps like MyFitnessPal allows you to log what you are eating so you can track your calories up to 700.

High-intermediate: The 5-2 plan

Just like the modified 2-day plan you will be eating clean for 5 days of the week. However, the other two days you won’t eat anything for 24 hours and these days must be nonconsecutive. For example, you’ll fast completely on Sunday and Wednesday. Everything you do eat will again consist of healthy fats, clean protein, and produce. Remember, you shouldn’t jump right into this plan if you haven’t intermittent fasted before. Make sure to talk to your doctor before starting any fasting protocol to determine if it is the best choice for your health case.

Advanced: Every-other-day plan

Finally, the advanced intermittent fasting guide! This plan is extremely simple. Alternate between days of eating and not eating. Even though this is intense it offers some amazing benefits. On days that you are eating, you guessed it, focus on healthy fats, clean meat sources, vegetables, and some fruit. On fasting days, you are still allowed to have herbal tea and small amounts of caffeinated tea and coffee. Also, make sure to drink enough water!

This information should give you everything you need to feel confident in meal planning while intermittent fasting. Although it may seem complicated right now, fasting will become a habit and part of your natural routine. Start slow and gradually work toward more advanced fasting protocols once you have discussed this option with your doctor.

Seeking support from a functional medicine expert

It is extremely important to get support from a functional medicine expert that can help pinpoint your body’s specific functions, imbalances, and any other underlying conditions. With this guidance you can confidently follow the safest and most effective intermittent fasting plan for you.

As one of the first functional medicine telehealth clinics in the world, we provide webcam health consultations for people around the globe.

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  13. 13. Aly SM. Role of intermittent fasting on improving health and reducing diseases. Int J Health Sci (Qassim). 2014;8(3):V-VI. doi:10.12816/0023985
  14. Harvie M, Wright C, Pegington M, et al. The effect of intermittent energy and carbohydrate restriction v. daily energy restriction on weight loss and metabolic disease risk markers in overweight women. Br J Nutr. 2013;110(8):1534-1547. doi:10.1017/S0007114513000792
  15. Martin B, Mattson MP, Maudsley S. Caloric restriction and intermittent fasting: two potential diets for successful brain aging. Ageing Res Rev. 2006;5(3):332-353. doi:10.1016/j.arr.2006.04.002

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Dr. Will Cole, DNM, IFMCP, DC is a leading functional medicine expert who consults people around the globe, starting one of the first functional medicine telehealth centers in the world. Named one of the top 50 functional and integrative doctors in the nation, Dr. Will Cole provides a functional medicine approach for thyroid issues, autoimmune conditions, hormonal imbalances, digestive disorders, and brain problems. He is the host of the popular The Art Of Being Well podcast and the New York Times bestselling author of Intuitive Fasting, Ketotarian, The Inflammation Spectrum, and Gut Feelings: Healing the Shame-Fueled Relationship Between What You Eat and How You Feel.

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Gut Feelings

Healing The Shame-Fueled Relationship
Between What You Eat And How You Feel