The Pros & Cons of Intermittent Fasting According to A Nutritionist

Written By


Expert Reviewed By

Dr. Lauryn Lax, OTD, MS

Dr. Lauryn, OTD, MS is a doctor of occupational therapy, clinical nutritionists and functional medicine expert with 25 years of clinical and personal experience in healing from complex chronic health issues and helping others do the same.

Intermittent Fasting - Woman Holding A Spoon

Today we are talking about the hot topic of intermittent fasting (IF).

Forget calorie counting. NOT eating (fasting) is the new “black.”

 In fact, I’d wager that a significant percentage of those of you reading this are doing it, or have done it in the past.

I’ve been a fan of intermittent fasting myself —although I’ve never been hardcore about it and prefer to listen to my body more than a clock to tell me when to eat. I’ve also occasionally used IF as a therapeutic strategy for some patients in my clinic.

But does restricting your “feeding window” and not eating for 14 to 16 hours, really speed up your metabolism, balance your blood sugar better and help gut healing happen faster?

Answer: Not necessarily.

Emerging studies show that intermittent fasting may not be all it’s hyped up to be.

Read on to find out more.


Intermittent Fasting - Couple Eating

One randomized, controlled trial assigned 29 participants to intermittent fast— eating all of their meals between 12:00 and 8:00 p.m. each day for three months, while 57 participants followed a normal dietary pattern—eating 3 meals each day.

The results? Participants in the IF group lost an average of just 2 to 3.5 pounds—only slightly more than the control group. What’s more, most of that weight loss was not fat, but healthy lean muscle mass (their body started eating itself).

If all they had found was that intermittent fasting wasn’t as effective for weight loss as we hoped, that would be one thing. There wouldn’t be any downside to doing it, especially if you get other benefits from it (cognitive, neurological, energy, etc.). But the reduction in muscle mass does raise concern.

So what should you do with this information? If youve been intermittent fasting, should you stop? 

For what it’s worth, that’s what one of the lead researchers from the study did. He’d been practicing IF for 6 years, but after his results came in, he made peace with food and began eating breakfast again.

Although improved body composition is just one reason people may try intermittent fasting, strong research for using IF to improve gut health, mental clarity, metabolism or blood sugar balance is also slim (and most of it has been conducted in animals—not humans!) (1, 2, 3, 4).

Simply put: Eating food is not the enemy. You are not a ‘healthier person’ whether you choose to fast or choose to eat 3 balanced meals per day.

To help you determine whether or not IF is for you, let’s discuss the pros and cons of IF, followed by 4 considerations before integrating fasting into your daily life.


The not-so-hot info most Instagram bloggers won’t tell you…

#1. You May Feel More Bloated or Constipated

Despite the hype that intermittent fasting “boosts digestion,” it can actually backfire—.

Why? For one, gut motility requires food to actually work—when we eat, stomach acid, enzymes, your liver and gallbladder, and migrating motor complex jump into gear.

The less fuel, more frequently, the slower digestion becomes. Even more:  digestive fire is hotter and stronger earlier on in the day and less at night—the opposite of what IF claims.

Additionally, a healthy gut microbiome requires more nutrients—not less—in order to populate and grow healthy gut bacteria, And a healthier gut means a healthier you.

The Hazda modern day hunter gatherers are a great example of this—although their gut biomes contain several species that most Westerners would consider pathogenic, because their diet is so varied, fresh and seasonal, their guts contain tons of diversity to counter the bad guys and keep them free of all chronic disease—cancer, autoimmunity, diabetes, and heart disease.

Lastly: Constipation and bloating are natural byproducts of being “stressed out” thanks to the gut brain connection, and often go hand in hand with under-eating and/or hormone imbalance.

#2. Your Metabolism May Slow Down & Hormones Get Imbalanced.

IF is a natural hormetic stressor—a positive stressor like exercise…as long as you don’t go overboard.

Exercise is a healthy stressor that pushes your body to work hard, develop muscle, decrease inflammation and enhance your cardio-respiratory endurance. But, push your body’s tolerance or threshold for exercise a little too far (upping your miles, or decreasing your caloric intake for example), and the FIRST system that takes a “hit” for a woman is typically her hormones.

The same thing goes for fasting.

Animal studies show that female rats that are deprived of food at certain times become infertile. Their sleep, stress levels and body fat are also affected. If we fast but don’t account for missing nutrients or calories then we can end up in a similar dilemma.

While human studies on intermittent fasting still have yet to hit mainstream, our physiology is the same—excess stress increases cortisol and inflammation that throws everything else out of balance—metabolism and hormones included.

After all, if your body is under stress—like running from a bear in the wild—the last thing it wants to do is look good in a bikini…instead it wants to make sure you have enough fat and insulation and energy storage in you to protect you and see you through to the finish line…especially if it doesn’t know when or where its next meal is coming from.

In short: Stress from IF paired with possible under-eating or nutrient deprivation can slow your metabolism and throw your hormones out of whack.

#3. You May Obsess & Think About Food More

It’s no secret the female brain in particular is different than the male brain—especially when it comes to food and well-being.

For example: Women experience more food cravings and think about food twice as much as men (every 38 minutes). That said,  IF, can foster more thoughts about food in both men and women—especially if you are accidentally under eating—shorting your body enough calories.

Ever heard of the Minnesota Starvation Study? In it, 36 healthy men were fed a semi-starvation diet—about half their ideal calories over the course of several months—about 1200-1400 calories per day, the equivalent of what many people eat when they IF regularly. What do you think happened? Sure they dropped some pounds, but the biggest finding is they became obsessed with thoughts about food.

They talked about food…dreamed about food…read about food…thought about their next meal…some even lost their appetites and cravings, but the thoughts persisted—alot like IF. While you may not feel hungry, your body and hormones may and this results in talking, reading, listening and thinking about food alot.


Intermittent Fasting - Woman Slicing Watermelon

As for the positives…

#1. IF Allows Your Gut to “Rest & Digest”

The process of digestion takes work—upwards of 12-24 hours per meal. Optimal digestion occurs in the “rest and digest” state. Intermittent fasting allows time between meals—at least from dinner to breakfast— to push food through your GI tract and repair the gut lining during the fast. Research, mostly in animal models (1, 2)  reveals that IF may restore microbe diversity in the gut—as long as you don’t go overboard (too much fasting and under-eating promotes the opposite).

#2. Reduces Inflammation

IF can be a positive or “hormetic” stressor just like exercise that reduces inflammation (as long as you don’t go overboard). IF and the subsequent adaptive response, leads to increased expression of antioxidants, DNA repair, mitochondrial stimulation and down regulation of oxidative stress. Moreover IF has been shown to restore autophagy—clearing out old cells and debris. 

#3. Helps Balance Blood Sugar

Intermittent fasting helps regulate insulin and glucose in the bloodstream, as well as leptin sensitivity (your fullness hormone)—particularly for people with hyperglycemia (high blood sugar) or dysglycemia (high and low blood sugar thoroughout the day. IF encourages the body time to tap into ketone bodies (fatty acids) for fuel and not feel so “hangry” all the time—as long as you are still eating enough fuel during the day (otherwise your body will start eating itself).

4 Considerations for Determine if Intermittent Fasting is Best for You

Although fasting and intermittent fasting has many potential benefits for autoimmunity and other chronic illness, IF is not for everyone. Whether or not you should try intermittent fasting depends on several factors.

Consideration 1: Your Conditions

Intermittent fasting (IF) is generally contraindicated (not recommended) for the following people:

  • Pregnancy
  • Subclinical Hypothyroidism (Poor T4 to T3 conversion, since low stress, energy and calories help with this conversion)
  • HPA Axis Dysregulation
  • Eating Disorders/History of Eating Disorders
  • Children & Teens
  • Hypoglycemic tendencies
  • Weaker constitution (“Vata” body types)

Note: If you are a woman or yo are dealing with hormonal or hypoglycemic imbalances, thyroid issues, eating disorder issues, or HPA Axis Dysregulation, IF may not be the best option for you. Fasting can throw your hormones out of balance and mess with your menstrual cycle and sleep patterns, resulting in amenorrhea and insomnia. That’s why women, particularly those with a lean body type, need to be careful when trying IF because their bodies are much more sensitive to signals of starvation than men. This is also true if you already have hormonal imbalances or are in perimenopause. Caution is also warranted f you have thyroid dysfunction or HPA Axis Dysregulation. Added stress from a fast can exacerbate thyroid disorders and chronic fatigue, especially if you are already under a great amount of stress in your daily life. Ketosis brought about by fasting is a major strain on your adrenal glands, which are already out of whack if you have one of these conditions.

Intermittent fasting has been shown to help these individuals:

  • Sickness (such as stomach flu, cold or flu)
  • Weak immune system
  • Chronic infections (i.e. parasites, Lyme, etc.)
  • Weight loss
  • Type 2 Diabetes
  • Metabolic problems
  • Neurological issues
  • Generally healthy individuals for optimizing longevity, mental acuity and digestion (practiced occasionally)

Remember: Every body is different. Just like no one diet is best for everyone, the same thing goes for intermittent fasting—particularly if you have multiple conditions (such as being overweight with hypothyroidism and HPA Axis Dysregulation; in this case, you’d want to first address the HPA Axis Dysregulation to then benefit from the intermittent fasting positives for your there conditions).

Consideration 2: Your Relationship with Food

Determining whether fasting is or is not for you greatly comes down to your relationship with food—food rules, diet mentality, “shoulds” and “shouldn’ts.”

Are you a person who gets caught up in legalism with food and guilt if you don’t stick to the rules? Or do you listen to your body? Do you tend to use food as a distraction or emotional coping mechanism, or eat to fuel your life?

For those both with histories of disordered eating or simply the diet mentality, intermittent fasting may become just one more food rule to add to your list—leading to more stress and boxes than freedom and connection to your body.

Consideration 3: Your Daily Needs

Simply put: Undereating can contribute to HPA Axis Dysregulation, fatigue, metabolic, hormone or blood sugar imbalances over time. You may feel great at first, but if you are unable to meet your caloric needs, then say goodbye to the benefits fasting.

Note: Your needs may change depending on your season of life, age and lifestyle.

For instance, if you’re a 34 year-old mom barely running on 6 hours of sleep, waking up early to feed three hungry mouths and eating whenever you can, chances are IF is not for you. But if you’re a 56-year-old newly retiree with a relatively stress-free lifestyle, wanting to optimize your longevity, IF may be worth a spin. A 29 year-old CrossFit enthusiast? Perhaps workout days you are mindful to eat after your morning workout, but on your off days, you can go until 11 a.m. or noon until your first meal.

Consideration 4: Listening to Your Hunger-Fullness Cues

Just like our ancestors ate based on their body’s cues, seasons and food availability, you have complete permission to not overthink or overplan IF. Listen to your body. If it’s 9 or 10 a.m. and your stomach is growling…listen. If you’re sick, and can’t stomach a full meal…listen—perhaps sipping some meat broth or homemade Ginger Ale instead. IF is not rocket science, so don’t overthink it.

Q: What if I am rarely hungry?

If appetite suppression is a regular feeling (i.e. not feeling hungry often), this could be a sign of elevated cortisol and suppressed hunger cues. Mindful eating is eating to fuel your body to meet your daily energy needs—even at times when you don’t feel hunger.

How to Intermittent Fast

Intermittent Fasting - Woman Preparing Food

If you decide you can approach fasting with a healthy mindset, Intermittent Fasting is a good place to start. 

Intermittent Fasting (IF) is simple:

  1. Stop eating and just drink liquids following a meal (such as around 8 or 9 p.m. after dinner)
  2. Drink water, broth, herbal tea and minimal coffee during your 12-16 hour window
  3. Break the fast 12 to 16 hours later (such as your next meal around 8 or 9 a.m. if you just did a 12 hour fast, or around 12 or 1 p.m. for a 16 hour fast)

Note: If you are a woman or have a contraindicated condition (autoimmune disease, hormone or thyroid imbalances, eating disorder history, etc.) and you want to experiment with intermittent fasting, be sure to start slow. For instance: Maybe try pushing breakfast until 11 a.m. instead of eating right when you get up. See how your body reacts to this “mini-fast” and whether you think you might be able to tolerate a longer or more frequent fast. Another option is be to do a “bone broth fast,” during which you would not eat solid foods, yet would still be supplying your body with the necessary nutrients it needs to balance your hormones by sipping on nourishing bone broth while you fast.

How to Break Your Fast

During a period of fasting, your digestive agni (“fire”) is dampened. It needs to be rekindled gradually. Consuming heavy foods or too much at once may cause indigestion, cramping, sour belching, acidity, vomiting, loose stools or constipation, unless you take these steps as you begin to break your fast:

  1. Drink a glass of warm lemon water with a pinch of sea salt (bonus: add a few drops of fresh ginger juice, grapefruit juice or apple cider vinegar). Swish it inside the mouth 8 to 10 times. Then swallow gradually. In this manner, drink a whole glassful. If need to drink more, then have another half a glassful.
  2. One hour later, have a moderate-sized, simple meal (i.e. not a whole day’s worth of eating in one meal).
  3. Take digestive enzymes with meals. 


One word: Balance. No one ever did a study showing balance was a bad thing.

Eating 3 meals per day does not make you weak or a bad person or disturb your gut more.

In fact,  believe it or not, healthy gut bugs require more nutrients. Not less food.

The more and more dogmas and rules and food lists we place around food, the more restrictive we become, and consequently, the more our gut biome diminishes.

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