March 26


How and Why to Intermittently Fast.

By Sunny Brigham, MS, CNS, LDN

March 26, 2018

minutes read time


Intermittent fasting (IF) is another topic I get asked a lot about. Maybe you’ve heard of it. Maybe you haven’t. Or maybe you’ve tried it.

IF can be a useful tool for burning fat, repairing cognition, and supporting healthy aging. But it’s not a tool that should be used by all. There are some downsides to IF.

In this blog, we’re 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.

However, fasting does increase the amount of nicotinamide adenine dinucleotide (NAD) in the body. NAD is what powers the brain of the cells (in summary). One could surmise that fasting increases NAD, which helps power good cells so they can overpower cancer cells. I think that’s a slight stretch though.

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. And, just FYI, diabetes can happen in non-overweight individuals as well. Weight is usually a factor but not always. It’s more eating habits than anything else.

Fasting has also been used for religious purposes. There are references to fasting in Christianity, Islam, and Judaism. There’s 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?

Is Fasting Healthy?

The short answer is…it could be. It really just depends on the condition of the individual fasting and what they’re trying to achieve.

NAD is, essentially without getting too science-y here, the fuel that feeds the brains of our cells. These brains are called the mitochondria. As we age, our NAD naturally declines. When we aren’t feeding the cell brains, they don’t really function how we want.

Fasting sparks something called hormesis. This kicks off when we have small amounts of stress on the body. Stress like exercise, fasting, and short-term limited protein intake. Not large amounts of stress that most American experience today.

It’s important to remember our bodies haven’t really evolved to what we’ve built today. Cars, buildings, lots of food, and long work hours. The inside still functions like it’s 1999 (? obviously much further back than that…but 1999 sounds better).

Hormesis sparks the production of NAD. IF is heavily studied in the aging population and find it’s very helpful for cognition. Hormesis would be why.


Let’s chat how fasting affects the metabolism. There’s information showing IF can boost the metabolism. Short-term fasting can boost the metabolism. Short-term fasting would be classified as IF. But there are some caveats here.

The whole point of IF is to burn fat as fuel. Each time you eat, you create energy in the body. If you don’t use that energy, it gets stored in your energy reserves. If your reserves are full, it gets stored as fat.

In periods of fasting, like when you’re sleeping at night, the body uses the stores to get you through the night. When the stores are empty, the body switches to burning fat for energy.

The whole point of IF is to get you into that fat burning zone. The point of IF is not to cut calories. During your feeding window, you have to take in the number of calories your body needs in order to keep the metabolism boosted.

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 problems as the origin of the disease. Animal studies have shown IF reduces fasting glucose levels and helps with insulin resistance (1). This was also repeated in human studies as well (3). However, this only works for individuals with insulin problems (creation or utilization). There were no changes to glucose metabolism or insulin regulation in “healthy” individuals.

Weight loss

One study showed 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.

Fasting helps the body burn stored fat for fuel instead of food.

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. If you want to learn more about cholesterol, check out my pretty lengthy blog here.

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. Ahem…hormesis!

Who should avoid it?

Just because it appears fasting is healthy, doesn’t mean it’s right for everyone. It’s important you keep reading. Because if any of these apply to you, don’t try fasting. It will actually make things worse!

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, then IF is not right for you. ED is tricky and so is IF. Fasting 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 not healthy just during a shorter timeframe, then IF is not for you. The purpose of IF is to limit the feeding window 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 have hormonal concerns, IF is not right for you. This would be an imbalance in your sex hormones, problems with your thyroid, or problems dealing with stress. Guys…this applies to you as well!

Calorie restriction or changes have a huge 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 who tries 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
  • Feeling colder than normal
  • Changes to your hair (i.e. experience hair loss)
  • Things are bothering you more than they normally would
  • 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, don’t give IF a try. Listen to your body! It’s always talking to you. (2)

How to IF

So…how do you do it? There are several ways you can fast. There are even meal delivery packages you can order that have fasting built int.

But, 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 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.

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 is a sign it’s not right for you.

If you’re trying a limited feeding window, and you find you’re hungry an hour before your window opens, then eat! Shift your feeding window. There’s no perfect way to do this. But 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. And it should be done before you ever consider fasting.

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 did better the second time. It’s not something I enjoy. I don’t like restricted eating so I choose not to IF. My husband likes it though!

So yes, fasting can be healthy and fasting can be used for weight loss.  But is it right for you?

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


Updated 17 May 2019




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.

  • I have Hashi’s, tried IF for 6 months – lost 28 pounds, feel much better after the course. Problem is when you don’t listen to your body. I experienced intermittent dizziness while rising from bench exercises, and metallic mouth taste, and did not associate it with kidneys. Ended up with kidney stones. Uric acid rises during fasts. So, now I’m careful to drink lots of lemon water and take a quality B complex vitamin. Kidneys are back to normal, and am more cautious with IF to listen to my body. In general, I feel IF is helping and definitely have more energy now. I do it less often as I reach my target weight. Eating clean is crucial for Hashis.

    • I don’t deny that there are a lot of benefits to IF. I’ve outlined those in the blog. But if your goal is to reduce the stress load on the body, bring your antibody levels down, and balance out your thyroid…the research is there to support that IF is not advisable in the Hashimoto’s population. I’m glad it’s working out for you though!

  • {"email":"Email address invalid","url":"Website address invalid","required":"Required field missing"}