It’s not what you eat, it’s when you eat. Well, at least that’s what proponents of Intermittent Fasting (IF) have to say. This eating plan has gained popularity again thanks to celebrities like Hugh Jackman and Jimmy Kimmel who have promoted IF as a way to lose weight, sleep better, and stay in shape.
Fasting isn’t a new idea by any means. It’s been around for millennia, and Hippocrates (c. 460 BC-370 BC), the father of modern medicine, used fasting as a way to cure illness.
Now proponents of intermittent fasting seem to be in agreement with Hippocrates. Preliminary research seems to show that IF could be beneficial in stabilizing blood glucose, lowering triglycerides, and increasing longevity of life.
In addition, IF can be used to achieve weight loss, and more importantly fat loss.
But the reasoning behind why IF tends to work, especially in regards to weight loss, isn’t for reasons why people think. It’s all based on this principle: calories consumed need to be less than calories burned for weight loss to occur.
Intermittent fasting works to create an overall calorie deficit by limiting the opportunities someone has to eat during the day. By doing this, people essentially skip one or more meals a day, thus cutting out the calories they would have eaten during those meals.
In addition, IF works to discourage someone from overeating during the day as well. Let’s say you need around 2,000 calories a day to maintain your current weight. People tend to normally eat over a 14-16 hour window. If you follow some form of IF, you limit the hours you eat by anywhere from 4-12 hours. Limiting that window makes it harder for someone to get those same 2,000 calories in, thus creating a form of calorie deficit.
That’s why when studies compare IF to traditional calorie restriction, weight loss changes are similar.
That’s not to say that there aren’t additional benefits to IF, as a lot of preliminary research points to metabolic benefits like improved insulin sensitivity, lowering blood pressure, reducing inflammation and oxidative stress, and promoting longevity to name a few.
Most of this research is new and doesn’t show effects past one year. More studies need to be done before we have conclusive evidence supporting intermittent fasting as a long-term strategy to improve health.
So, what is this diet and how can I do it? Well, IF isn’t really a “diet,” but more of an eating pattern, and there are several types. Here are the more common ones:
12/12: This is where one would eat for 12 hours and then fast for 12 hours. It’s a good way to ease into intermittent fasting if you’ve never fasted before.
16/8: This one involves fasting for 16 hours and eating during an 8-hour window.
20/4 or “Warrior”: Eating is reduced to a four-hour window followed by 20 hours of fasting. This one is a bit more extreme and modeled after the hunter/gatherer lifestyle; feasting after a long day of working and “battling enemies".
24-Hour Fast or “Eat, Stop, Eat”: As it sounds, fasting occurs for 24 hours. This one can be completed so you eat on consecutive days. For example, if your last meal is at noon on Tuesday, on Wednesday you could eat your first meal after noon.
5/2: This one includes fasting for two non-consecutive days. On fasting days, calories are restricted to ~500 calories for women and ~600 calories for men. The other five days you can eat whatever you would like, keeping in mind good eating habits.
Each one of these methods have their own benefits and drawbacks, and there is not a lot of research to say that one form is better than the other. It all comes down to personal preference for which pattern you decide to follow.
I would suggest following a more liberal pattern like the 12/12 first to get a feel as to whether IF is for you. From there you can change your eating window to find the fit that works best, or decide if fasting is useful or practical for your lifestyle at all.
However, I don’t recommend trying IF if you have any history with disordered eating, have a diagnosis of diabetes, have chronic conditions that require close dietary monitoring, or are training for an athletic event.
Here are the major takeaways when it comes to intermittent fasting. It might be a successful approach to weight loss if you’re someone who hasn’t found success with a more traditional approach, or can’t stick to food journaling. There is some research to support metabolic benefits to intermittent fasting, but more research is needed to draw definite conclusions. This is especially true in regards to long-term intermittent fasting.
Like any other approach to weight loss, this isn’t a one-size-fits-all approach. If you’re interested in trying intermittent fasting, I would encourage you to speak with a registered dietitian to figure out if it’s right for you.