What is Intermittent Fasting?

If you hang out on fitness blogs or subreddits, you’ve almost certainly heard of intermittent fasting. But what exactly is this form of dieting? And what are the supposed benefits? Let’s find out.

How many times have you heard that breakfast is the most important meal of the day? This advice has become so common that it’s just accepted as fact.

But is it true?

There are studies that suggest eating earlier can help you lose more weight, such as this one in Nature. The study found that people who ate their breakfast and lunch earlier in the day lost more weight, despite having similar diets to those who ate later.

According to fans of intermittent fasting, however, skipping meals can actually help you lose weight and breakfast is no more important than any other meal.

There is some justification for this. Throughout human history, breakfast was never considered that important. People tended to eat whatever was left-over from the night before.

It wasn’t until the late 19th century when the obsession with breakfast – and a very specific range of breakfast foods – began.

At the time, people were worried about the effects of the industrial revolution on their health. Religious moralisers seized on this idea and began to teach that eating light, plain foods was vital for health and productivity. They also taught that eating a light breakfast, such as cereal, was a way to be more productive at work.

(Interestingly, one of the biggest proponents of this type of dieting was a man named Mr John Harvey Kellogg…)

This combination of advertising, moralising and preying on people’s health fears was the start of breakfast being considered the most important meal of the day. But this was just the beginning.

During the 1940s, a company selling bacon got a single doctor to say that a protein-heavy breakfast of eggs and bacon was the healthiest option. He then sent the statement to 5000 doctors and asked them to sign it. Once signed, he got popular newspapers to publish it as it if was a scientific study. Since then, bacon, eggs and cereal have been considered breakfast foods.

To add more fuel to the fire, around this time mothers were becoming more common in the work place. Companies preyed on the maternal instinct to create “healthy” cereals that were quick and easy to give children in the morning.

In other words, companies seeking more profit and religious moralisers were the drivers behind breakfast – not science.

So we know our feelings about breakfast aren’t exactly based on rigorous science. But what does intermittent fasting have to do with it?

What is Intermittent Fasting?

Intermittent fasting isn’t a diet. Instead, it’s a dieting pattern that focuses on when you eat.

The basic idea is that you skip certain meals with the goal of reducing your overall calorie intake. This may help you to lose weight faster than other methods. The most common meal to skip is breakfast, although when you fast is up to you.

While the idea is simple, there are a number of variants:

  • The most common is to only eat during a specific window in the day. This could mean you skip breakfast (the horror!) and consume all your calories between 12pm-8pm. Some people also use shorter windows.
  • A more extreme form of intermittent fasting is to avoid eating for 24 hour periods. On this schedule, you might eat dinner and then skip the next breakfast and lunch. On other days you would eat your regular three meals.
  • Some people also follow the 5:2 diet. This involves eating normally five days a week but greatly reducing your calories (by up to 75%) on the other two days. It’s not quite fasting, as you’re still eating something on those two days, but is a similar idea.
  • A less common method is to restrict certain types of food to specific windows. In our Half Day Diet review, for example, we discussed how the program recommends only eating carbs in the evening.
  • The simplest is to skip random meals. If you don’t want to regularly skip meals, you can gain some of the benefits by not eating random meals throughout the week.

There are also variations in what you can eat. Some IF protocols don’t allow you to consume anything other than water during fasting periods. Others allow small amounts of calories, such as milk in a cup of tea.

What are the Benefits?

The most obvious benefit of intermittent fasting is that it makes it much easier to control your calorie intake. It’s harder to overeat when you’re only having two meals per day. While there is more to weight loss than calories – timing and exercise also play a role – your net intake is still the most important factor.

This isn’t the only reason intermittent fasting can help you lose weight though. According to NerdFitness.com, fasting also affects the way your body operates.

When you eat, your body processes the food and uses some of it immediately for energy. But when you “fast,” your body doesn’t have a new source of food, so it’s more likely to burn stored fat instead.

Without getting into the details, the reason this happens is related to insulin sensitivity. Greater sensitivity means your body uses the food you eat more efficiently – and sensitivity increases after fasting. There is some complicated science behind this, but the result is that intermittent fasting may help promote muscle building and weight loss.

Another benefit is that IF is simple. Instead of worrying about nutrients or foods, you only need to focus on when you eat.

Other potential benefits include:

  • Spend less time preparing food. Preparing two meals per day saves time and makes it easier to eat healthily.
  • Improved self-control. When you’re hungry and food is available, it takes self-control not to eat it.
  • May improve the health of your brain and protect it from certain diseases. This is far from proven, but some people claim fasting can help improve brain health.
  • Life extension(?). There is preliminary evidence that fasting may improve certain health markers and start regenerative processes (more on that later).

For more information about fasting effects on the brain, check out this video from Mark Mattson:

Is it Proven to Help Speed Up Weight Loss?

In short, IF does help you lose weight. The debate is how much more effective it is than other forms of dieting.

The confusion is partly caused by the wide range of IF variants. Some studies that asked people to skip breakfast, for example, showed significant weight loss, while others didn’t. This is probably related to the timings used.

Another study showed that IF can lead to weight loss – but no more than regular calorie restriction. It also has not been studied in underweight people, the elderly or children, and may be dangerous for these groups.

Whatever the science says, one thing is for certain: if you overeat during your “feasting” period, you won’t lose weight. There’s nothing magic about an IF diet – it’s just a way to make controlling your calorie intake easier.

Additionally, research studies have suggested people should only fast for more than 24 hours if monitored by a doctor. This is because doing so may affect the digestive system and circadian rhythm. You should also discuss IF with your doctor if you have any conditions that affect your blood sugar regulation (such as diabetes).

IF isn’t just about weight loss though. While there isn’t a huge amount of evidence behind other claims, a study seems to suggest that IF can improve certain markers of health. There is also some research that shows fasting can cause regenerative processes to begin and even increases the lifespan of some animals.

It must be stressed that these studies are just the beginning though. It’ll be many years before we know the true benefits of IF. There also needs to be a lot more research into which variant is best for health.

Even so, there are some potentially exciting benefits to intermittent fasting. There’s also no doubt that it can help you lose weight if used correctly. So if you’re struggling to shift your extra pounds and prefer the thought of controlling when you eat over other types of diet, it might be worth trying.

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