This post was written and published in 2014, I’ve updated it, and I’m resharing it today because it’s still something I get asked all the time about all the time!    

Fasting & Skipping Meals:  Benefits and Concerns

There are many reasons why someone may choose to fast or skip meals.  A few are:

• religious holidays and observations
• dieting/weight loss
• long shifts/too busy
• longevity/ health span
• other potential health benefits

The first time I was exposed to fasting came in the form of religion when I converted to Catholicism.  The word “convert” is funny to me, because it suggests I had religion in my life before that, which I did not.   Anyways, the church teaches abstaining from meat (fish and eggs are okay) on Ash Wednesday, Good Friday, and all Fridays during the Lenten season (Ash Wednesday – Easter).  So, that was my first experience with it.  (Since I know this is unique to Catholics during lent, see this article on Why Do Catholics Practice Fasting and Abstinence During Lent.) Full fasting (not consuming anything but water) or partial fasting (consuming one light meal) is also encouraged on these days, when medically appropriate. I also know of people who fast one day a week for specific reasons, sometimes for another person, special prayer, or dedication.

Religious reasons are no longer the majority of the reason why people fast anymore.  Intermittent fasting (or IF)  is now almost mainstream.  The idea of IF is to abstain from food for 12-18 hours to maximize fat burning capabilities.  For most, this means skipping breakfast in the morning, but it can also be achieved by having an early dinner.

Let’s look at some of the pros and cons of using this approach:

Skipping meals may cause:

• Your metabolism to slow down. 

The metabolic effects of fasting are perhaps the most controversial part of fasting. There is research to suggest that fasting may increase the metabolism of mice. However, we also have significant data that points to extreme calorie restriction as a method of decreasing the metabolism.  Fasting is a way of achieving that calorie restriction.; if your body thinks that no food is coming in then eventually it will slow down your metabolism to conserve calories.  Therefore you end up burning fewer calories, which could lead to weight gain.

What we don’t know is at what point that is and if it differs from individual to individual.  Remember women don’t respond as well to starvation scenarios as males do, their hormones are more sensitive. I’ve worked with many women to repair their metabolism and hormone balance after restrictive diets, including intermittent fasting.  So, typically my advice here is that women should proceed with much more caution than men.

• A dip in blood sugar.

Although diabetic patients may find this symptom more pressing, the effects of very low blood sugar levels can be felt by anyone.  Low blood sugar leads to a tired and foggy haze, which generally leads to cravings for high-energy foods like sugar and fats. Although this symptom may lessen over time, don’t believe all the hype about “feeling super energized when fasting.” Extra energy may be related to their diet when not fasting, stimulants they take, or how adapted their body is to handling fasting.

On the flip side, fasting research demonstrates its potential ability to increase insulin sensitivity.  However, this is typically related to the breakdown of fat tissue, which can happen in any calorie deficiency including fasting but also just plain old calorie restriction.

Voracious hunger.

• This insane hunger triggers the body to enter starvation mode, causing the release of hormones that tell you to EAT EAT EAT.  The overwhelming hunger can lead to overeating at the next meal, increasing fat storage.

Weight gain. 

• Along with the possibility of a slowed down metabolism, cravings and voracious hunger any weight loss experienced during prolonged fasting (greater than 24 hours) are usually regained (and often more is gained then what was originally lost.)

Fasting may have some benefits:

• Resting the digestive system. 

There is a theory out there that resting the digestive system, also rests your immune system, and gives it a chance to “recharge.” Remember, this is a theory not based on any scientific fact I could find.  (If you know of a reputable study, please send it my way, and I’ll link to it!)

• Possible promotes anti-inflammatory mechanisms.

Some observational studies have shown that some people with inflammatory conditions such as IBD, asthma, or skin conditions experience symptom improvement with fasting.  Whether the effect is long-lasting or not is unclear.

• Promotes fat breakdown/weight loss. 

Once the immediately available energy is used up, the body turns to breaking down reserves.  The process is known as “ketosis,” and results in the release of ketones from fat reserves to be used as energy. (The production of ketones as an energy source is the point of IF.)  Again, you can encourage fat breakdown without fasting. Plus, you are only likely to see weight loss if you can keep your calories in check when you do eat.

• Possible improvement in the risk of or treatment of some chronic diseases.

Some improvement of risk factors for type 2 diabetes, heart disease, and asthma have all been observed.  This is likely related to the decrease in insulin and inflammatory markers that have been found during fasting.

• Improvement in neurological health. 

Some research supports an increase in memory and cognitive function.  It seems exercise and fasting have similar effects on the brain! In researching for this post, I found this Tedtalk by neuroscientist Doctor Mark Mattson interesting.

So, Is Fasting Bad For You?

Like many things in nutrition, this topic does not have one-size fits all answer.  There are potential pros and cons that you need to consider before you try it out.  Are you healthy enough physically, hormonally, etc. ?  What is your primary motivation?    Is it religious?  Is it to experiment and see how you feel?  Or is it weight loss? If it’s weight loss, I’d say hold on second let’s discuss your options and decide if this is the best thing.

In addition, we haven’t even considered whether the fasting is involving overall calorie restriction.  (Yes, you can fast for long periods of time without actually reducing calories.) And yet another point to consider, those that practice IF also do some in conjunction with a ketogenic diet.  And that is a whole separate post with its own sets of pros and cons.  So when you hear about someone receiving a ton of benefits from fasting keep in mind that their dietary choices when they aren’t fasting may be playing a role in some of the benefits that person is experiencing.

When I was calorie counting my only concern was restricting calories, I rarely considered my body’s actual needs and rarely listened to my body at all.  I regularly ate when I was not hungry, and often fasted when I was hungry.  So, I think the most important take away is that you should always honor your body’s cues.  Skipping meals every once a while may not cause an immediate 10lb weight gain, in fact, there is a chance you may even see some benefits.  However, regularly skipping meals and ignoring your hunger cues may trigger the stress response and lead you to overeat at other meals (read: long-term weight gain.) It’s a delicate balance.

Some of my experiences:

• I used to try to stop eating after 6 pm, which led to a fast of 12-14 hours, this often helped me keep my weight down and gave me more energy.  (However, if I was super hungry, I would eat something high protein.)  Using this method, I wasn’t “skipping breakfast” one of the most significant meals of the day but instead, skipping a late night meal.
• I used to do one-day juice/smoothie partial fasts weekly.  I don’t remember feeling much of a benefit or difference.
• I never miss breakfast on the weekdays, but regularly eat just two big meals (usually a brunch and dinner) on the weekends out with family and friends.  Often my meals are richer when I eat out, so I feel fine eating two meals.  I don’t force myself to eat another one because I’m fine.

Tips from the Dietitian 

1. Honor your body’s hunger/satiety cues: Eat something when you are hungry, stop eating when you are full. (See my intuitive eating series.)
2. Make the meals you are having high quality and well balanced.  Make sure you get enough high-quality protein (chicken, fish, eggs, and beans), healthy fats (avocado, nuts/seeds, oils), and nutrient dense carbohydrates (whole grains, sweet potatoes, winter squash) to sustain your body through the fast. (My What to Eat? Meal Plans do this for you!)
3. Stay hydrated.  Drink plenty of fluids; this will help keep you full and energized. (Do you know how much water?)
4. Discuss your fasting habits with your doctor or a Dietitian (want to work with me?) to make sure it isn’t harming you.  Some obvious situations to avoid fasting in are pregnancy, or if you are underweight, have amenorrhea, cancer, or another condition affected by metabolism such as thyroid conditions.

Have you tried fasting? What kind? Intermittent, religious forms, partial?  What insights did you gain from your experience?