Intermittent fasting is a hot topic right now, but what does the research say about the potential benefits of intermittent fasting? Is it health promoting, or simply another fad? Find out what the research says, and my thoughts on this popular trend.
What is intermittent fasting?
Intermittent fasting is used to broadly describe a variety of different eating plans. What ties them all together is that they cycle between periods of eating and not eating (fasting). This may include eating normally for a few days, fasting for one, and so on. Technically, we all intermittently fast when we’re asleep. Anyone ever wonder why we literally call our first meal of the day breakfast? The most common intermittent fasting pattern is extending the overnight fast. So a person might fast for 16 hours of the day, and only eat for 8 daytime hours. This usually also involves avoiding drinking any caloric or caffeinated beverages during the 16 fasting hours as well. There’s a lot of different ways that people practice intermittent fasting, however, and this makes research difficult.
Why is it so popular right now?
Intermittent fasting has become an incredibly popular diet lately for a variety of reasons. People claim that it helps with weight loss, blood sugar regulation, mental clarity and focus, energy levels, longevity, and the list goes on… It’s also attractive to people because it doesn’t involve cutting out any foods or food groups. The only “rules” are to stick to the periods of eating and fasting. Any food you want can fit into the eating window. Sounds great, right?!
What does the research actually say about intermittent fasting?
Like I mentioned, since there’s so many different ways people intermittently fast this makes clear answers from research a bit more complicated. I’ll start, however, by pointing out that there is no strong evidence to support any of the health claims made about intermittent fasting. There is some research to suggest that intermittent fasting may help with weight loss. These results, however, are comparable to overall caloric reduction. Basically, if you take all the food you’d normally eat in a day and squish it into a smaller time period nothing will change. But, if you end up eating less food during that window than you would in a normal day, weight loss could occur. So, it seems like eating less food has more of an impact on weight loss than when this food is eaten. I’ll also mention that weight loss is not a precise science and that diets in general just plain don’t work. You can read more on that in my blog post about why you should ditch dieting for good. Most research showing any type of benefit of intermittent fasting is with animal models as well. While potentially promising, there’s a lot of differences between humans and mice or rats. Applying findings from animal model studies to humans is irresponsible at best. Basically, we need more research in humans to know what potential benefits, if any, intermittent fasting might have.
As a dietitian, what are your thoughts on intermittent fasting?
Where the research stands right now, I see zero reason to recommend intermittent fasting to anyone. I also take issue with it for a couple of other reasons… First and foremost, I don’t approve of time dictating when a person eats or doesn’t eat. I believe that people should eat when they’re hungry–regardless of what time it ends up being. Intermittent fasting just sounds like a hangry time…
Speaking from personal experience as well (which obviously isn’t research-quality), I need to eat every couple of hours when I’m awake to function normally. If I don’t eat breakfast right away in the morning, for example, it’s hard for me to focus on my work. I’ve even gotten dizzy on mornings when I’ve been too rushed to eat breakfast before starting my day. And do you think I’m going to be in the mood to exercise if I haven’t eaten yet?? No way. Even if I moved my fasting window to the nighttime and just stopped eating earlier, trying to sleep when hungry is a nightmare.
Food is a very social thing as well which I think is always important to remember. If you’re fasting until 11am, what happens if a friend wants to grab an early breakfast? If you fast after 8pm, what if a friend wants to have drinks and pizza on the weekend with you? Eating is such a social aspect of life, and anything that interferes with that is going to be a hard pass for me.
Limiting your eating to a restricted time window also increases the risk of a binge during that period. When you know you can’t eat after a certain time there’s the strong potential that you’ll eat more than you need in order to “prepare” for not being able to eat. When you end your fast for the day, you also might eat way more than you normally would. Hunger from a prolonged fast can incite a binge.
I also think that intermittent fasting really misses the point of health. By focusing solely on the time you’re eating, it misses out on possible proven health promoting behavior changes. Eating more fruits and veggies, finding joyful ways to move your body, etc. are all ways to benefit your health that don’t need to be restricted to a particular time window. Focusing on things that are actually proven to support health makes way more sense to me than attempting a diet that hasn’t proven to promote health.
In my opinion, the potential downsides of intermittent fasting, like hunger, dizziness, low energy, missing out on social events, etc. far outweigh any supposed (and as yet, unproven) benefits.
TL;DR
Intermittent fasting involves rotating between periods of fasting (generally longer than an overnight fast) and time-limited windows of eating.
Research shows that intermittent fasting is just as effective as overall caloric reduction for weight loss.
Most research on intermittent fasting has been done in animal models which makes the results difficult to apply to humans.
Most of the health claims around intermittent fasting are, as yet, unproven.
In my opinion, the potential downsides of intermittent fasting, like hunger, dizziness, low energy, missing out on social events, etc. far outweigh any supposed (and as yet, unproven) benefits.