I started this blog because I love reading scientific literature and I like to write about it. So, I thought, making a blog will be a piece of cake. Read evidence-based papers, get stoked on science, come up with analogy and BAM I’ve got myself a post! But, I learned very quickly that there is soooo much more to having a successful online writing platform. I have to find visual content to go with the posts (I gave up on taking my own photos after the first month), I had to create a website and keep it looking snazzy, find ways to market my blog and myself, and there is something called SEO that I have to start optimizing, whatever that is!

All of these added factors have led me to my first writer’s block. A small hiatus filled with a lot of procrastination, some frustration and more binging of Netflix than I’d care to admit. However, I am back in the blogosphere and coming at you live with the hottest trend of 2019, and the most requested blog topic: intermittent fasting.

What is intermittent fasting? Well, to catch anyone up who may have been living under a rock, intermittent fasting is a dieting technique that involves restricting the time that you eat, rather than altering the foods in your diet. Intermittent fasting, like all popular diets, touts many benefits other than just losing weight – including increasing your metabolism, altering your insulin requirements, and making you feel more energized all day. The truth behind these claims? Let’s get into it!

First thing’s first. There are two different kinds of intermittent fasting: time restricted feeding – where you limit the window of time that you eat every day, and whole day fasting – where you completely eliminate food for an entire day. I’ll break each of them into bite-sized pieces to make ‘em easier to digest.

If you are too busy not eating you can skip to the verdict here for time restricted feeding and here for whole-day fasting.

Time restricted feeding

What is it?

Time restricted feeding is the slightly more exciting type of intermittent fasting from a scientific standpoint and in terms of evidence-based results. Time restricted feeding (TRF) is all about limiting the amount of time that you eat during the day, allowing for long periods of time when your body isn’t busy digesting. The popular perception of TRF is that it enhances your metabolism: by taking long periods between meals, your body does a better job of taking advantage of the calories you eat, rather than just storing them as fat. In this case, it turns out that the science has less to do with digestion and more to do with sleep…

Does TRF work?

Here is the deal with TRF: there is increasing evidence to suggest that a shorter eating window – restricting eating to 12 hours of the day rather than 16 hours of the day – may actually be beneficial to your overall metabolism, and may even result in weight loss. In rats and humans alike, researchers have found that if the daily eating window is shortened to 12 hours or less, there appear to be metabolic changes that increase fat loss, and may increase energy and alertness during the day.

Moreover, the time of the day that you fast may play the biggest role in your metabolic health.

In short, it’s not about how short you make the period of time you eat, it’s about having a clear window of eating during the day and a solid chunk of time that you’re not eating during the night.

What is important to understand is that our bodies have two distinct modes. During the day, our cells make sure we are energized, ready to attack at any moment, and are able to break down the food we eat. These processes are called catabolic processes. At night, especially when we are asleep, our body gets to business storing extra energy, going to town on repairs, and fighting infection – all of which are anabolic processes. These two modes can work simultaneously, but it takes a very fine balance of the two in order to have maintain metabolic health. For example, if our body sticks in an anabolic mode too often of the time we typically get lethargic and store more energy as fat.

It’s not about how short you make the period of time you eat, it’s about having a clear window of eating during the day and a solid chunk of time that you’re not eating during the night.

Brains + Sleep

The cellular changes that need to occur to switch from day mode to night mode are extraordinarily complex. So, our bodies have their very own clock to oversee this change, it’s what you may have heard referred to as our circadian rhythm. The time keeper of this rhythm is a part of the brain called the suprachiasmic nucleus. The suprachiasmic nucleus oversees the thousands of mini clocks that reside in each of our cells and tells them when it’s day time and when it’s night time. This clock does a great job of making sure we are allotting energy to the appropriate processes.

A strong circadian rhythm is important for having a good working metabolism, for feeling more alert during the day, and for fending off sickness during the night.

But how the heck does the suprachiasmic nucleus know what time it is? Well, some of the information comes from the sunlight – that’s why having blue light blocking glasses is all the rage these days (maybe a post for another time?). But our biological clock is also strongly linked to our feeding cycle. When we eat, our internal clock is like, “Oh hey it’s time to kick up that metabolism and start being energized!” Then, after a few hours without eating, our suprachiasmic clock sends signals to our cells to tell them to use our stored energy and do the more maintenance-oriented tasks.

What researchers have found is that a strong circadian rhythm – the changes our body makes between awake time and asleep time – is important for having a good working metabolism, for feeling more alert during the day, and for fending off sickness during the night. Basically, it also makes you feel more awake when you are awake and sleep better when you are asleep. Having a strong circadian rhythm is linked to having fewer metabolic diseases like obesity and type II diabetes, and scientists think this is because your body does a better job at allotting it’s energy appropriately.

By restricting the time of eating to a shorter period throughout the day, we may increase our circadian rhythm. In fact, in a study that followed the eating patterns of otherwise healthy individuals, researchers found that when participants ate during a block of only 10-12 hours during the day and fasted the rest of the time, they lost weight, had improved energy, and slept better. However, these results could have been because the participants were doing less late night snacking on ice cream and wine….

In support of this research, there is evidence that people who work shift work – and thus are more likely to be awake and eating at weird and irregular hours of the night – have a higher risk of metabolic diseases. Experiments in mice also indicate that circadian rhythm disruptions result in a higher risk of metabolic disease.

There are other types of TRF – some people try introducing long breaks between meals during the day, or restricting their eating period to only a few hours. However, there is no evidence to support that this type of TRF leads to any health benefits.

TRF: The verdict

Time restricted feeding, as with many diet trends, may have been blown out of proportion. While there is evidence that shortening your moderately eating period may have health benefits, this doesn’t mean that the shorter your eating period is, the healthier you will be. There is no evidence that says that eating only four hours of the whole day is good for you!

What I’m saying is that setting a stricter eating schedule, maybe with less snacking late at night, could increase the strength of the circadian rhythm and improve your metabolism. The studies that have been done in humans have restricted eating periods to 10-12 hours of the day, but you may not even need to limit it that strictly to gain the effects of improving your circadian rhythm. As with most trends, the evidence is still emerging, but it seems that having a consistent and shorter eating schedule is a good idea.

Whole day fasting

What is it?

Whole day fasting is a whole other can of worms. The most popular whole day fasting diet technique is called the 5:2 diet. The idea is that you completely eliminate eating for two non-consecutive days a week, and eat as much as you want of whatever you want for the other five days. The idea behind whole day fasting is that even though you will eat more on your feeding days, you won’t make up for the entire caloric deficit that you created on your fasting days, thus enabling you to lose weight.

Does it work?

So does this way of dieting work? Well, technically yes. People on the 5:2 diet seem to lose as much weight as a person on a “regular” weight-loss diet, i.e. people who just reduce their calorie intake on a daily basis. However, compared to a regular diet, the 5:2 diet doesn’t provide any added benefits. Metabolism stays more or less the same, there are no significant changes in what types of weight is being lost (fat vs. muscle), and no big differences in how much insulin the body uses. However, people on the 5:2 diet often cite feelings of hunger, sleepiness, and agitation on days where they are fasting (surprising, I know…).

Thus, my verdict on the 5:2 is that it is an effective way to lose weight, but no more effective than a typical calorie restriction diet where you just eat a little less every day. More importantly, weight is a pretty crappy measurement of health!

5:2 Diet: The verdict

Do the 5:2 diet if you want to lose weight and be grumpy while doing it. On the other hand, limiting your food intake to a 10-12 hour block during the day is probably a good idea.