This blog post may contain affiliate links.  We may earn a small commission for any purchases made through these links. Click here for the disclosure statement. 

I spent two weeks of my life living the IF lifestyle and here’s what I learned.

What’s the Science Behind Intermittent Fasting?

If we’re being honest, intermittent fasting has been around for centuries, dating back to our ancestors who would go long stretches in the search for food. It was more recently popularized in 2012 by the TV documentary, Eat Fast, Live Longer, as well as the book The Fast Diet. You can find additional resources on IF by Kate Harrison, in her book, The 5:2 Diet, as well as the 2016 bestselling book, The Obesity Code by Jason Fung.

The premise is simple: We eat food. The enzymes in our stomach and intestine break it down and eventually, it enters our bloodstream. At digestion’s most basic level, carbohydrates are broken down into sugars, which the body uses for energy.

Enter insulin.

If those sugars aren’t immediately used, they’re stored in our fat cells, but only with the help from our friend, insulin. Insulin, which is made in the pancreas, acts as the ‘gatekeeper’ for sugar to enter our cells.

So, when we don’t eat for long periods of time, such as with intermittent fasting, blood sugar levels go down, insulin levels go down, and the body stops stuffing itself full of energy.

To counteract low blood sugar, the body produces glucagon, which runs around freeing this stored sugar for energy from the fat cells, effectively “burning fat.”

Sounds great, right?

What does the research say?

That’s where things get a little tricky. Depending on which study you read, some suggest that IF is highly effective in overweight and obese adults. Other studies suggest that intermittent fasting is no more effective than caloric restriction and could actually lead to increased weight gain from binge eating. While most of the research for intermittent fasting has been done on rodent and overweight/obese human populations, this study on athletes suggests that, with the exception of reduced triglycerides, intermittent fasting does not confirm prior research suggesting a positive effect of IF on blood lipid profiles. Due to the unique nature of each individual’s metabolism, you’ll be hard-pressed to find a study that doesn’t discuss the shortcomings of current clinical trials. It seems researchers cannot agree on many of the variables for studies, including: food timing, differing caloric intake, ectopic and visceral fat stores, adipocyte size, insulin resistance, and metabolic flexibility.

One interesting study on women suggested:

“After four weeks of IER [intermittent eating restriction] (four consecutive days of a 70% [eating restriction] ER and three days of ad libitum eating) amongst nine normal weight young women, classified as unrestrained eaters, resulted in increased feelings of hunger, worse mood, heightened irritability, difficulties concentrating, increased fatigue, eating-related thoughts, fear of loss of control and over eating during non-restricted days.”

My Personal Experience with Intermittent Fasting

With the research firmly under my belt, I decided to treat myself as my own personal guinea pig. I adopted the common 16:8 method, meaning I would fast for 16 hours per day and my eating window would be the remaining eight hours. I kept my caloric intake the same and continued my usual workout routine. I allowed myself black coffee during my fasting period.

My average day looked like this: Wake up at 5am to workout (usually a run). I would break my fast at 11am and eat throughout the day until 7pm.

How did I feel?

As an endurance athlete, I know my daily expenditure is ‘above average.’ This is, after all, my contribution to the plethora of variables that researchers are struggling with current research. But, when combined with an appropriate caloric intake, it should be accounted for.

I felt like trash. People had warned me that there would be an “adjustment period” and to “give it time.” I felt consistently weak, tired, and irritable. I had headaches. I was constantly hungry. For two weeks. It did not change.

I didn’t sleep well. While I’ve never been a great sleeper, I consistently woke up at night hungry. I also found myself making more frequent trips to the bathroom.

I didn’t lose any weight. While by no means was my goal of this experiment to lose weight, for the sake of science, I weighed myself each morning, immediately upon arising. I started and ended the experiment at the exact same weight.

It wrecked my mental health. With almost no research that definitively shows that IF is anything more than a restricted window of eating, are we not simply calling intermittent fasting another way to restrict ourselves? As someone who has struggled with disordered eating in the past, I felt encouraged to continue to starve myself. After all, I had given myself permission to not eat for 16 hours. And if I could make it 16 hours, could I make it 17? 18? All day?

This incredible study by Stefani Ruper actually discusses the evidence of intermittent fasting with regard to sex differences. In fact, she quotes one study that shows that men experienced insulin sensitivity improvement while women did not. Moreso, she discusses this study by Martin, which details the sex differences between male and female rats undergoing starvation.

“Female rats, on the other hand, “masculinize.” They stop ovulating and menstruating. They become hyper-alert, have better memories, and are more energetic during the periods in which they are supposed to be sleep. Theoretically, according to these researchers, this is an adaptive response to starvation. The more the female rats need calories– or at least the more their bodies detect a “starvation” state– the more they develop traits that will help them find food. They get smart, they get energetic, they get active, and they stop sleeping.”

I don’t know about you, but this reads to me like a diet ad, right? Of course, I want to get smarter, have more energy, be more active! We are idealizing this idea of self-denial. Self-denial is quickly normalized as “following the plan.” We become addicted to the feeling of self-restriction. At what point do fasting and eating windows become binging and purging?

I’ve said many times, the best diet is the one that you can stick to. The evidence to support intermittent fasting as a safe, effective long-term plan for weight loss has been incredibly mixed. Any diet plan will work if you are in a caloric deficit. Any diet will work if you focus on quality calories versus fast, processed food. If you’re looking to make a lifestyle change, do so with whole foods, clean ingredients, and an active lifestyle.

For me, intermittent fasting didn’t work. It did not make me feel my best, regardless of whether I stayed on it for just two weeks, or extended it to a month, 6 months. While it may work for some people, it did not work with me. I felt called to the false enticement that is disordered eating, that void that is only satisfied by going deeper into restriction. I felt that it was a dangerous path for me to go down. My relationship with food has always been something that I have struggled with and this, to me, felt like a return to my old, unhealthy habits.

When do we cross the line between healthy habits and disordered eating?

Emily Troscianko sums it up best in her article, The Fast Diet: A Fast Route to Disordered Eating?, for Psychology Daily:

“…this is yo-yoing between extremes of self-denial and self-indulgence. And in this key respect it’s terrifyingly like anorexia: like the 23 hours of gnawing hunger building up to a single faultlessly orchestrated feast, which is all that gives life pleasure and meaning…Let’s pause and think, hard, before we exercise our privilege to make dietary choices by making one that looks very much like slipping into the realm where preference gives way to compulsion, and an eating disorder begins.”