Intermittent Fasting- Should You Try It?

It seems the people out there who like to invent new diets are starting to run out of ideas. Since there’s a diet out there scaring us out of eating just about every food known to man (meat, dairy, sugar, fruit, legumes, fat, carbs, soy, pesticides, GMOs- you name it!) We’ve pretty much run out of things to avoid.

So, what better way to finally fix us all for good by not worrying about what we eat, but when we eat?

Intermittent fasting promises to be the solution to all your health woes. Excess weight? Gone! Diabetes? Cured! Fatigue? No More! Need an immunity boost? You got it! What can’t this diet do??

Now, obviously as an RD I’m extremely skeptical of any new diet that starts making headlines. Intermittent Fasting isn’t particularly new, but seems to be one of those trends that just hasn’t gone away. Over the past several years there has been an increase in the research surrounding intermittent fasting and I was curious what sort of story it tells us. Is there something to Intermittent Fasting that actually works?

So, what exactly is Intermittent Fasting (IF)?

Well, it really depends on who you ask….

Quite simply, IF is a diet/eating pattern where you limit the time throughout the day or week that you eat. During the times that you’re allowed to eat there is generally no restriction on calorie or food intake. What makes IF difficult to really asses though, is that there is a few ways in which this is done. For example…

  • Whole Day Fasting- where a person eats no food or very little food for a full 24 hour period
  • Time Restricted Feeding- where a person limits the time throughout the day they eat (for example fasting for 14-18 hours each day, and eating normally outside of that time)
  • Others still in extreme examples will fast for as long as they can, going days without eating anything (or minimal intake such as a juice fast). (Pro tip: Don’t do this!)

This can make comparing evidence a challenge. Because feeding trials are often small and short-term, we need a significant number of them to show us a similar outcome in order to confidently state that the evidence is good quality. With such variation in the type of eating pattern we can look at, it becomes more difficult to get a clear picture.

But IF isn’t just about weight loss…

There are some additional things at play here that promoters of IF use to push their way of eating over any other “diet program”. The theory is that when we fast we’re helping our body more effectively regenerate and repair our existing cells, leading to a decreased risk of disease and ageing. Called “autophagy”, this process takes place during periods of fasting and is touted by some as a legitimate way to reduce the risk of cancer.

So what does the research actually say?

Not much in my opinion.

A lot of the research on IF has been tested in animal models. Rats and mice in particular. Obviously there are some key differences between humans and rodents in both our physical bodies, but also in our mental processes. Putting rodents on a “diet” to see how they respond really doesn’t tell us anything about how humans respond to diets because we have a much more complex relationship with food. Just because rodents lost weight when exposed to restricted feeding times, or overate when given the chance does NOT mean we will act the same way. Any diet that promotes itself on a foundation of animal studies is likely 100% BS.

In human trials though one thing that is clear: IF only “works” when it comes to weight loss if the diet is paired with an overall reduction in calories. In order to lose weight a person absolutely needs to eat fewer calories than they burn, creating a calorie deficit which results in weight loss. Changing the time of day you eat but still eating the same number of total calories does not create a calorie deficit therefore does not result in weight loss. There is absolutely no magic about IF or secret weight loss trick here- it is still a matter of calories in and calories out.

You can see a few examples of studies that looked at IF and weight loss in humans here and here. Both found that when compared with a normal lower-calorie diet the results were the same with IF. There was no special benefit to fasting.

Those are just a few examples, but overall it looks like for weight loss whether or not you use intermittent fasting, the most important factor is achieving a reduction in calories overall.


What about the science on Autophagy?

Similar to the weight loss studies, most research on autophagy has only been done in rodent models, so it’s impossible to say at this point how that will play out for us in the coming years.

However, there are a few important points I want to make about this. The first is that we already know animals and humans are completely different in a lot of ways, in both how our bodies function and our psychological processes. BUT, we also need to remember that when we sleep we are fasting. This autophagy process that takes place while we fast is typically happening simultaneously with sleep. Perhaps it’s the sleep that is a factor in our cells regeneration and repair than simply going without food? Only time (and research!) will tell, but I wouldn’t put all my eggs in the IF basket just yet.

When it comes to cancer risk, we also need to remember that there are hundreds of different types of cancers out there. Some certainly have a nutrition/lifestyle link, but not all. To simply say we can “reduce the risk of cancer” by following a certain diet is essentially BS. Yes, we can reduce the risk of specific types of cancer with a healthy lifestyle, but it is not a catch-all.


What about the other benefits of IF, such as a boost in immunity or healing?

Definitely no solid evidence here. A few mechanisms have been proposed by IF advocates, but there is no solid evidence to back it up. Personally I see fasting as a bad thing for the immune system… we need nutrients to build and repair cells!


So, could IF work for you?

Maybe… it all boils down to personal preference. Anecdotally some individuals find it easier to limit how often they eat throughout the day rather than limit their portion sizes when it comes to reducing their calories.

Could IF work for you? Maybe…

The downsides of going long periods without eating are well-documented and include things like fatigue, difficulty concentrating and headaches. Skipping meals can also be a trigger for overeating in some people.

My advice? Don’t eat by the clock, or adjust your meal times based on what someone on the internet claims works. At the end of the day, IF is still just another diet. A set of rules to follow that do nothing to teach us to pay attention to our own bodies and figure out what works best for US.

Instead, listen to your own hunger and satiety cues to decide when to eat and how much. We all already “fast” each day between our evening meal or snack and breakfast in the morning, so this idea of going without food for a few hours a day isn’t particularly novel.

Many clients I counsel tell me they don’t typically feel hungry first thing in the morning. They often feel guilty for skipping breakfast, or force themselves to eat something (which is especially detrimental if it’s a fast food breakfast!)

Instead, I encourage these folks to listen to their bodies. Drink water in the morning, but wait to eat until you’re actually physically hungry. Stop eating when you’re satisfied, not when you’re stuffed. If you eat breakfast a little later in the morning, just push back lunch until your stomach tells you its time to eat. Same with dinner and any snacks you may have. Our hunger signals exist for a reason, listen to them!

So, its highly unlikely IF will be the silver bullet for health and weight loss. Like all the other fad diets of our time, its more likely to wind up on the ever- growing pile of nutrition BS. At the end of the day a common-sense, mindful eating approach is the best way to make a meaningful, lasting change to your nutrition, health, and relationship with food.


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