clock on a plate indicating fasting window

Intermittent Fasting and Weight Loss: Does it Work?

Short Answer: Yes

Long answer: It depends. 

The better question: Is it right for you?

Intermittent fasting is a growing diet trend with over a million searches in the last month. There are many proposed benefits to fasting, with weight loss being a popular one. But is this actually effective? And if so, should you do it? In this article I will explain what intermittent fasting is, what the potential benefits are, the effectiveness on weight loss, and considerations if you want to try it. 

What is Intermittent Fasting?

Intermittent fasting refers to reducing calorie intake, well, intermittently, for lack of a better word. You eat less during some periods of time, and eat more during others. Examples include alternate day fasting, where one eats ad libitum (i.e., until full) on one day, and then fasts the next day; time-restricted feeding, where one eats only within a designated time frame (e.g. 12-8 pm); and the 5:3 method, involving 5 ad libitim eating days followed by 2-3 fasting days over the course of a week. There are a lot of opinions out there about how to do it right. (Side note: I will add that when someone makes a very black-and-white nutrition claim, you’re better off running the opposite direction.) But ultimately, there is not one right way to fast.

Why Try Intermittent Fasting?

There have been a slew of proposed benefits on fasting, ranging from the aforementioned weight loss to disease prevention and increasing longevity. There is evidence from rodent studies that suggest calorie restriction improves lifespan resulting from metabolic adaptations. 

What does this mean? 

Studies done on rodents have shown that calorie restriction causes a small amount of stress on their cells. This small amount of stress triggers an adaptation that allows the cells to grow stronger. This is similar to what happens during exercise: you push yourself a little outside your comfort zone, and you come out on the other side a bit stronger. 

Of course, anytime there is a fascinating outcome like this, the media likes to run with it. (Skipping meals makes you live longer!) And then come all of the claims, books, and so-called “experts” preaching about the benefits. One of those most popular benefits is, of course, weight loss.

Can intermittent fasting help you lose weight?

In theory, anytime you eat fewer calories than you burn, you will lose weight. So, yes, restricting calories through fasting can result in weight loss. Several studies in humans have shown it to be effective. Reasons for this are multi-factorial: It cuts down on food intake, and therefore calorie intake. Calorie counting can be tedious, as can thinking about your diet every day. Fasting restricts calories inherently so no counting is needed. It also puts no limitations on what you can eat, it simply tells you when to eat. This can be a huge advantage for someone who needs something simple to follow and doesn’t want to get caught up in whether something is healthy.

That being said, there is no evidence that it is more effective than continuous energy restriction (i.e., restricting calories more moderately, every day.) 

Is intermittent fasting safe?

Generally speaking, intermittent fasting seems to be “safe”, as in there are no immediate risks. However, studies have reported a range of side effects of fasting, ranging from increased hunger, constipation/diarrhea, and bad breath. This makes sense: when we go a long time without eating, it is hard to stick to smaller portions. Our gastrointestinal system also relies on regular and consistent food intake to support digestion. Stomach acid levels can rise and cause irritation for those prone to reflux. As for the bad breath – this can be a side effect from ketone production. All of these are inconvenient, but nothing immediately dangerous.  

There are certain groups that should be cautious when it comes to experimenting with a fasting regimen. The first are women, particularly women trying to become pregnant. There have been rodent studies demonstrating reduced fertility in those placed on fasting diets. 

There is also concern for an increased risk for eating disorders and disordered eating behaviors. Dieting in general is associated with an increased risk for the development of an eating disorder. In addition, when most people go a long time without eating, there is a tendency to overeat at the next opportunity. This could lead into negative self-talk and what is commonly known as the “binge/restrict” cycle. 

Lastly, there is the question of adherence. Fasting regimens such as alternate day fasting can be hard to stick with. Many of the fasting studies reported a high drop-out rate compared to other dieting interventions. This makes sense: it can be hard to enjoy your life when it is dictated by when you can eat. If you are missing out on socializing with family and friends because of your fasting schedule,it is my opinion that you should reconsider your goals and approach. 

Should You Try intermittent fasting?

Whether you should try intermittent fasting depends on your goals and personality. The scope of this article specifically relates to weight loss, so if this is your goal, fasting has been shown to be an effective approach. However, it is not more effective than a standard calorie restricted diet. 

Reflect on the following considerations before choosing this method:

Reasons to Try Intermittent FastingReasons To Avoid Intermittent Fasting
You’re overwhelmed with making daily meal and snack choicesYou have unpredictable eating opportunities
You want a black-and-white eating approachYou are an athlete or regularly do high intensity exercise
You don’t mind eating within an 8-12 hour time frameFood rules stress you out
You only do low-intensity exerciseYou find yourself overeating before or after fasting
You generally prefer to skip breakfast or dinnerYou have a history of an eating disorder or disordered eating tendencies
You have a healthy relationship with food and no history of disordered eatingYou are a woman trying to become pregnant
You have no issues with digestion, such as irritable bowel syndrome or acid refluxYou have digestive issues

If you fall in the left-hand category, intermittent fasting could be worth experimenting with. Even still: it is not all-or-nothing! Most resources recommend starting out slowly and gradually transitioning to your fasting goal. And if it’s not for you? Don’t stress. All of the benefits of fasting can be achieved through other means. Health is not a one-size-fits-all. You do you!

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