On intermittent fasting. Originally published 16 Sept 2016. Last updated 15 April 2021.
About 2 years ago, a colleague of mine handed me a diet book and said: “I just finished reading this and it sounds really promising. Would you mind taking a look at it and letting me know what you think?”
It was a book on intermittent fasting. I held up to my promise and actually read it cover to cover. I gave him my feedback (which I will share with you here), which he listened to with an open mind. I thought, “Ok, here’s another fad that’s ‘in’ right now… but it’ll pass soon enough.” Well, here we are, 2 years later and we’re still discussing it. That’s not a bad thing. In fact, part of the reason the idea of intermittent fasting has grown in popularity is that there are some studies that have examined its effects on body weight. Plus, it doesn’t hurt that A-list celebrities like Hugh Jackman and Jennifer Lopez have been very vocal about their successes with intermittent fasting. While this diet approach may not improve your singing skills or give you superhero powers, it will be important to consider the pros and cons.
Let me start by describing what fasting and intermittent fasting are:
By definition, fasting means the complete avoidance of food.
Intermittent fasting means that you will still eat, but with larger lengths of time in between meals and snacks.
Some intermittent fasting programs suggest limits on how many calories you can eat. For example, some may allow one meal during a “fasting day” that makes up 25 percent of your calorie needs for a typical day. So, let’s say you need to consume 2,000 calories per day. This would mean that your one meal should be about 500 calories.
Types of Intermittent Fasting Diets
In general, there are 3 types of intermittent fasting diets:
- Alternate-day fasting: This diet has you alternate between days you can eat what you want and days you are supposed to fast.
- Whole-day fasting: Fast one to two days per week; on the other days you can eat anything, anytime.
- Time-restricted eating: This involves a routine where you only have a certain number of hours to fast and a certain number of hours to eat daily.
Does Intermittent Fasting Work?
Ok, so now that you know what intermittent fasting is like, we need to discuss whether it’s effective. There are some studies that have found benefits, such as weight loss, reduced body fat, and lower total cholesterol levels. Sounds really good, right? On the other hand, researchers have also found that intermittent fasting may be just as effective as watching what you eat and reducing your daily calories. Oh, and many of the studies on intermittent fasting were performed using animals as participants. We know that we behave very differently than lab mice.
Short-term intermittent fasting may reduce body weight and body fat because, by fasting, your body relies more on your fat stores for energy. This has been shown especially within the first 24 hours of fasting and seems to peak between 18 and 24 hours of fasting. Also, it has been shown to increase metabolism in the short term.
Is It Right For You?
At this point, you may feel convinced! These are some wonderful benefits, right? However, as always, you must ask yourself, “Is this right for me?” When we look at longer-term studies (most of the ones I mentioned earlier were done in the short-term… like 1-6 months), researchers are finding that very low-calorie diets do not have better long-term weight loss results than less extreme diets. Also, when they study these diets, they often use young, otherwise healthy folks. In fact, many participants of these studies were athletes.
Since most of us aren’t young, healthy athletes, we need to be sure that this eating pattern is right for us. Plus, there are also some risks for nutrient deficiencies, some loss of muscle mass, and the possibility that you will gain more weight (mostly fat weight) if and when you go back to a typical eating pattern. But if you’re one of those folks that find yourself snacking way too often throughout the day, or always eating too much during meals, then intermittent fasting may be a reasonable way to restrict calories for weight loss in the short-term.
Intermittent Fasting vs. Small Meals
What about consuming small meals throughout the day? This concept is based on the idea that by eating more often, we can keep our metabolisms up.
I recently read an article in an eBlast that was sent to me from a well-known organization. The article discussed tips for losing weight in the New Year. In it, the author claims that increasing meal frequency will “rev up your metabolism” and help keep those unwanted pounds at bay. Metabolism basically refers to how many calories you burn in one day. This article was saying that if you want to burn more calories (and potentially more fat), eat 5 or more smaller meals each day. It has been shown to increase metabolism in the shorter term.
While this recommendation is not completely off-base, I feel the author needs to clarify something very important here: a large portion of the calories you burn every day is due to keeping your organs functioning, breathing, powering your brain, digesting and absorbing nutrients, etc. A much, much smaller portion of our metabolism is responsible for mechanically breaking down and absorbing the foods that we eat. This is a very small percentage of the number of calories we burn each day.
Since digesting and absorbing food burns so few calories per day, you may actually end up sabotaging your weight loss and fat burning efforts by using this method. If this type of eating isn’t natural to you, then it’s possible you may not feel sated throughout the day. In turn, this may make you actually consume MORE calories in the long-term because you may end up snacking more often.
Does Intermittent Fasting Get Rid of Toxins in the Body?
I must mention claims that fasting may help remove toxins from the body. We simply don’t know whether this is true at this time. If you do hear this claim, and they claim it’s backed by science, they are likely quoting studies performed in animals… usually mice. And, since our bodies are different from rodents’, we can’t put much stock in these claims.
The Bottom Line
Intermittent fasting and more frequent, smaller meals both have their drawbacks. The key is to find the eating pattern that suits you and your lifestyle. If you can feel satisfied throughout the day by consuming smaller meals more often while still controlling your overall calorie intake, then go for it! If you can fast for long periods of time without it interfering with your school, work, or social obligations, then give it a try.
Trial with Intermittent Fasting
Although some intermittent fasting diets may be more difficult (like fasting for 20 hours and only allowing time to eat for four hours), there are other versions that may be easier to follow. For example, a 16-hour fast followed by an eight-hour eating window is very similar to eating patterns of people that regularly skip breakfast and dinner.
There are some folks that should avoid this style of eating completely:
- Those with diabetes
- Those with low blood sugar
- The elderly
- Pregnant and breastfeeding women
- I wouldn’t recommend fasting before exercise – you may end up fainting (or worse) due to low blood sugar levels
As always, definitely check with your personal physician before beginning something like this just to be safe.