Intermittent Fasting

Is Intermittent Fasting Healthy?

Intermittent fasting (IF) is no doubt on the rise.  It’s another topic I get asked a lot about.  Today, we are diving in.  We’ll cover what it is, what it can help with, who should avoid it, and my thoughts.  Let’s get to it!

What is it?

Fasting has been used for hundreds of years to cure everything from excess weight to diabetes to cancer.  Does it really do that?  Probably only the weight aspect as there are no studies concluding that fasting cures cancer (but could help recovery, etc).  However, diabetes typically comes with excess weight and by losing weight and changing your diet (read: going from eating high sugar foods to eating nothing at all), there will likely be a change in the diabetes status of that individual.

Fasting has also been used for religious purposes.  There are references to fasting in Christianity, Islam, and Judaism.  There is likely reference to fasting in most religions…those are just the ones I know for sure 🙂

When most people think of fasting, they immediately think of no food for a certain number of days.  And that is a way of fasting that some use.  I would never recommend anyone try this type of fasting on their own without medical supervision.  There are fasting centers across the US that monitor individuals on fasting. 

The point is…fasting has been around for ages.  It’s not new. But is fasting healthy?

We are going to talk about fasting in reference to IF and how it can or can’t help with overall health and wellness.  There are 2 primary ways to do IF (there are many ways to fast but we are talking about the 2 most popular ways):

  1. Fasting/Feeding window – This is where you fast for 16 hours each day and feed for 8 hours each day.  The popular feeding window is from noon to 8 pm and fasting from 8 pm to noon the following day.
  2. 2 day fast – Select 2 days in each week to fast for 24 hrs and consume food normally on the other 5 days.  These 2 days should not be back-to-back.  Ideally, they would be Tuesday and Friday.  This allows for ample refeeding.  This is the least popular version of IF. 

What can it help with?

Fasting has been studied extensively and continues to be studied as the popularity around it grows.  Here are some conditions fasting can be beneficial for:

PCOS/Type 2 Diabetes

I put these both in the same category because being overweight or obese is a risk factor for both and both share insulin dysregulation as an etiology.   Animal studies have shown the IF reduces fasting glucose levels and insulin resistance (1).  This was also repeated in human studies as well (3).  However, this only works for individuals with insulin dysregulation.  There were no changes to glucose metabolism or insulin regulation in “healthy” individuals.

Weight loss

One study show that overweight individuals following IF for 8 weeks lost on average of 9% of their overall weight (1).  Previous studies have shown that even a small 5% weight loss in overweight individuals could significantly improve their health. 

Cholesterol levels

Individuals that have followed intermittent fasting noted a decrease in their LDL levels and their fasting triglyceride levels (1).  Now, it’s important to note this was in an obese population who also lost weight as a result of the study.  Weight loss, regardless of the method will likely have an impact on LDL and triglyceride levels. 

Cognition(most notably in the aging) 

As we age, we tend to have a decline in our cognition ability.  IF has been shown to be protective in the strength of our synapses (brain firing), our ability to generate new brain tissue, and overall protection of the brain (4).   Bonus for you plant-basers or vegans out there…the same studies showed low protein/high carbohydrate diets were neuroprotective as well. 

Who should avoid it?

Those with impaired sleep

It can cause more sleep troubles.  Many with sleep impairments (read: insomnia – trouble falling or staying asleep) wake up in the middle of the night and find they must eat in order to get back to sleep.  Even if you don’t have sleep troubles but start experiencing them after you try IF, this is a sign it’s not right for you.

Disordered eating

If you’ve ever had an eating disorder (ED) in the past, IF is not right for you.  ED is tricky and so is IF.  IF can create an environment where the individual becomes obsessed with determining their feeding window, thinking about what foods they are going to eat during their window, or obsessively tracking their calories inside their feeding window.  If you have an ED, are in recovery, or find that once you start IF you’re becoming obsessive…IF is not right for you. 

Passport to eat shitty

If you’re interested in IF so that you can eat foods you know are suboptimal just during a shorter timeframe, IF is not for you.  The purpose of IF is to limit the feeding window, reduce calories (within reason), and promote high quality foods.  The foods you do consume during that feeding window should be whole foods comprised of healthy fats, fruits/veggies, and excellent protein sources.  It should not be comprised of cookies, cakes, candies, and fast food.

Hormonal imbalance

If you’re female and already have hormonal concerns, IF is not right for you.  Calorie restriction/changes have a profound effect on female hormones and any significant changes can easily disrupt the delicate balance.  If your hormones are in tip-top shape, go forth and conquer IF.  If you already know you’ve got hormonal issues, don’t try it.  Either way, you need to pay attention to how you’re feeling.  If you’re female trying IF and notice changes to your cycle, it’s probably a good idea to get back on the 4 to 6 meals a day wagon.  Here are some signs to look out for:

  • Your period stops
  • You’re feeling colder than normal
  • You notice changes to your hair (i.e. experience hair loss)
  • You notice things are bothering you more than they normally would
  • You experience mood swings when you weren’t susceptible to them before

This includes being stressed.  IF is a stressor.  If you’re already stressed to the hilt, I don’t know that I would give IF a try.  Listen to your body!  It’s always talking to you. (2)

My thoughts?

One issue I see is rebound eating.  If you find that you reach your feeding window and are ravenous, you may find that you rebound eat.  This is when you are so hungry you literally eat everything you can.  This defeats the purpose of fasting and perhaps is a sign it’s not right for you. 

If you’re trying a limited feeding window, and you find that you’re hungry an hour before your window opens, then eat!  Shift your feeding window.  There’s no perfect way to do this but certainly don’t deprive or starve yourself.  If you wait that extra hour, chances are you’re going to rebound eat.

If you know you have hormonal imbalances, don't risk it for a biscuit.  Regaining control of hormonal imbalances is tricky.

Aside from that, I’m a fan.  I’ve tried it in the past but felt I became too obsessive and rebound ate so I stopped.  I tried it again recently and I’m doing better now.  I let go of the obsessiveness that can come with it.  If it’s not my feeding window and I’m hungry, I eat.  If I need to adjust based on my schedule, I’ll do that.  I also ensure that I don’t go overboard on the calories.  Last time I tried IF, I was still eating meat.  Meat tends to be higher in calories so as I was filling up on the meat products, I was hitting my daily calories pretty quickly.  Now, it’s much easier to stay within my caloric range.

So yes, fasting can be healthy and fasting can be used for weight loss.  

Have your tried IF?  Share your thoughts below in the comments.

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Antoni, R., Johnston, K., Collins, A., & Robertson, M. (2017). Effects of intermittent fasting on glucose and lipid metabolism. Proceedings of the Nutrition Society, 76(3), 361-368. doi:10.1017/S0029665116002986

Kumar, S., & Kaur, G. (2013). Intermittent Fasting Dietary Restriction Regimen Negatively Influences Reproduction in Young Rats: A Study of Hypothalamo-Hypophysial-Gonadal Axis. PLoS ONE, 8(1). doi:10.1371/journal.pone.0052416

Patterson, R. E., & Sears, D. D. (2017). Metabolic Effects of Intermittent Fasting. Annual Review of Nutrition, 37(1), 371-393. doi:10.1146/annurev-nutr-071816-064634

Wahl, D., Cogger, V. C., Solon-Biet, S. M., Waern, R. V. R., Gokarn, R., Pulpitel, T., … Le Couteur, D. G. (2016). Nutritional strategies to optimise cognitive function in the aging brain. Ageing Research Reviews, 31, 80–92.

Sunny Brigham, MS, CNS

I'm Sunny! I'm a board-certified clinical nutritionist with an MS in Clinical Nutrition. I help individuals reduce fatigue, eliminate bloat, and lose weight by healing the digestive tract and balancing hormones. I provide individual and group nutrition consultations nationwide. Join my closed Facebook group today!

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