What is Intermittent Fasting? Should You Do It?

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When it comes to weight loss, calories are king. Restricting calorie intake will lead to weight loss whereas overconsumption of calories will cause fat gain.

There are a number of popular methods and diets that will all eventually lead to weight loss. With that being said, some methods are more effective than others.

Fasting is by no means a new practice and is commonly exercised in many religions. In recent times, fasting has become a popular weight-loss method.

In this article, we will start with an in-depth look at intermittent fasting methods. We will then move on to the potential benefits and side effects associated with this approach.

What is Intermittent Fasting?

Fasting is simply abstaining from food (or drink) for a prolonged time period. The intermittent fasting approach differs greatly from conventional diets. It doesn’t specify the foods to consume or avoid, neither does it inform us of the quantities of each food.

Rather, the intermittent fasting approach focuses on meal timings and involves eating and fasting in cycles.

So, what is the significance of fasting? What is the purpose?

As briefly alluded to, calories influence changes in body composition. Calorie intake needs to be reduced in order for weight loss to occur. By performing regular fasts, we can significantly reduce the total number of calories consumed.

If this is maintained over a period of time, substantial change will take place.

To demonstrate this, let’s consider an individual who consistently consumes 2000 calories each day. By the end of the week, they amassed a total of 14,000 calories. A second individual also consumes 2000 calories on a typical day.

However, they use an intermittent fasting method where, for two days per week, they perform a fast.

By using this method, they will have consumed 10,000 calories per week. That is 4000 calories less than the first individual. As this demonstrates, intermittent fasting can significantly decrease calorie intake and consequently facilitate weight loss.

Intermittent Fasting Methods

What Is Intermittent Fasting

There are a number of different intermittent fasting methods that ultimately lead to the same outcome. Some of the following methods may be more suitable than others. Lifestyle, occupation, and personal preference will determine which method is chosen.

1. Time Restriction

The first method is to set a window for eating. Commonly used timings are the 16/8 or 14/10.

The first number refers to the number of hours fasted whereas the second number is the feeding window. Food is only to be consumed during this short window and therefore, the body goes without food for a substantial period.

By using the 16/8 timing, we could consume food during the designated eight hours of the day. Eating would be prohibited outwith of this window.

Consequently, our body would be in a fasted state for 16 hours per day. This small window gives us less opportunity to over consume calories and contribute to weight loss.

This method is popular for good reason. Firstly, unlike other methods that require full-day fasting, the time restriction method allows us to eat every day.

Because of this, we are much more likely to adhere to it. Secondly, it is one of the more convenient methods. While we sleep, we are fasting.

By simply skipping breakfast we can extend this overnight fast without much difficulty. Most people will begin their window at noon which will allow them to consume a hearty lunch and dinner.

This will keep them well-satiated and less likely to eat outwith of the window. How often this method is applied comes down to the individual. Some will perform this only once or twice per week whereas others will do so most days.

2. The 5:2 Method

The 5:2 method is similar in principle to the time restriction method. This time, however, instead of restricting intake by the hour, calories are reduced by the day.

The numbers “5:2” refer to the number of days where calories are to be consumed as normal and restricted.

A normal diet is to be consumed five days per week with calories capped for the other two days. On these two days, calories should be restricted to 500.

The conventional way of applying this method is to consume two meals on the fasted days. Typically the meals should contain 300 and 200 calories each.

If using the 5:2 approach, it is critical that these meals are high in fiber and protein. Both of these have been shown to increase satiety levels and keep us feeling fuller for longer.

When it comes to choosing the fasting days, any day can be selected – personal preference will likely determine this. However, it is important that the two days are not successive days; there must be at least one non-fasted separating them.

For this method to be effective, it’s vital that we consume a normal diet on non-fasted days. It may be tempting to reduce calories on these days too, however, this should be avoided.

3. The Alternate-Day Fast

As the name suggests, this method follows a simple structure of one day on, one day off.

On fasted days, it is recommended to aim for approximately 500 calories or 25% of our normal intake. Calories can be consumed at any time throughout the course of the day.

A more aggressive approach would be to consume nothing on fasted days, however, this may not be sustainable for many. On non-fasted days, it is imperative that a normal diet is consumed and that calories are not restricted.

With that being said, it is also important that it doesn’t go the other way. Overeating or binging on non-fasted days will wipe out the impact of the fasted days.

4. The 24-Hour Fast

While the other intermittent fasting methods do restrict calories, they allow us to eat a little food during the day. The 24-hour fast, however, is a much more extreme method and prevents us from consuming any food.

As the name suggests, we must not eat for a 24-hour period. As highlighted in an earlier example, doing this can drastically cut weekly calorie intake and lead to compositional changes.

However, be aware that this method should not be performed often. Once or twice per week would be more than enough.

Considering the body requires calories and nutrients to function effectively, this approach can have side-effects. Fatigue, irritability, headaches, and low energy are not uncommon.

Additionally, it is more challenging to adhere to a 24-hour fast. Hunger can become a real issue and, as a result, many find this approach to be too challenging.

There is no denying that this method can effectively onset weight loss. With that being said, it is not highly recommended as other intermittent fasting methods are more sustainable.

Weight Loss & Intermittent Fasting

Although weight loss often appears complicated, the driving force behind body compositional changes is simple. As alluded to earlier, calories are most important.

When too many calories are consumed, a calorie surplus is established. The body then stores these calories as fat to serve as an emergency energy store.

Conversely, when calories are restricted, the body must find energy from another source. Therefore, it begins to breakdown fat tissue to continue to supply the body with energy.

Therefore, considering that intermittent fasting significantly reduces calorie intake, it is clear that it can cause significant weight loss. While calories are most important, there are a number of other ways intermittent fasting can facilitate weight loss.

Intermittent fasting has been shown to impact a number of hormones and consequently impact metabolism. Two particularly influential hormones are insulin and human growth hormone (HGH).

Insulin regulates blood sugar levels by allowing the body to use sugar as energy or by storing it for future use.

Studies have indicated that insulin suppression can aid in weight loss (1). HGH plays a key role in maturation and development. However, it also appears to influence body composition.

One particular study prescribed subjects with a low-dose HGH treatment alongside calorie restriction. The results confirmed that increasing HGH levels can accelerate fat loss (2).

Lastly, one common concern with dieting and weight loss is the impact on muscle mass. Although a calorie deficit does burn fat, it can also cause muscle size to reduce.

Studies have found intermittent fasting to be an effective method of reducing this. It appears that fasted methods may be more beneficial than daily restrictions for retaining muscle mass (3).

Considering the above points, it does appear that intermittent fasting is indeed an effective weight-loss method.

Intermittent Fasting Health Benefits & Effectiveness

The benefits of intermittent fasting do appear to extend further than simply weight loss.

It appears that the method can significantly reduce the risk of developing chronic diseases. As mentioned earlier, intermittent fasting can lower both insulin resistance and lower blood sugar levels.

Consequently, the risk of developing diabetes is much reduced. A number of diabetics use intermittent fasting techniques to help manage their blood sugar levels. However, this should always be done under the supervision of a medical professional (4).

Intermittent fasting may also improve a range of cardiac disease risk factors. This includes lowering blood pressure, triglycerides, cholesterol, and inflammation (5).

Oxidative stress occurs as we age and cause deterioration in health and function. Research suggests that intermittent fasting may improve the body’s resistance to oxidative stress (6).

Finally, fasting can positively affect brain health and protect it from damage. This occurs through a combination of reducing blood sugar, blood pressure, and oxidative stress.

Side Effects

Although intermittent fasting can have a positive impact on health, there may be a number of side effects. The fasting method that is used will often determine the extent of these side effects.

The more extreme methods tend to cause the most side effects. Calories are the main fuel source for the body. Therefore, the body may feel the effects of dramatic calorie cuts in a number of ways.

Potential intermittent fasting side effects include:
  • Bloating
  • Constipation or diarrhea
  • Feeling cold
  • Headaches
  • Heartburn
  • Hunger and cravings
  • Irritability
  • Insomnia
  • Lethargy and fatigue

Should You Do It?

The benefits of intermittent fasting are clear.

Ultimately, there are two main considerations that are to be made before starting intermittent fasting.

The first consideration is the side effects.

As highlighted, there are a number of potential side effects associated with intermittent fasting. If we are willing to put up with these side effects, then we can proceed. However, be aware that there are other nutritional strategies that can be used that have no or few side effects.

The second consideration is sustainability.

Hunger can become a real issue with fasting and often individuals cannot continue with the diet. We need to know that intermittent fasting is something that we can consistently stick to.

Change takes time. Therefore, it would be futile to start intermittent fasting if we are unable to sustain it. Intermittent fasting may not be suitable for everyone.

Take time to carefully consider whether or not this method is the best fit. Those who suffer from a medical condition must consult their doctor before starting any new diet.


Can we drink during intermittent fasting?

Yes. Maintaining good hydration is important for health, function and weight loss.

However, considering that we are attempting to cut calories, calorific drinks, such as soda, should be limited. A useful guide is to focus on drinks that are less than 50 calories.

What can we eat or drink while intermittent fasting?

Intermittent fasting methods focus on cutting calories rather than specific foods. Therefore, we can really eat whatever we want providing we stay within the calorie target.

There are a number of useful foods that can help to reduce hunger and prevent side effects. Focus on high-fiber foods, such as whole-grains, fruit and veg, and protein products, such as meat and fish.

How much weight can be lost in a month with intermittent fasting? Once again, this is dependent on the method chosen.

Methods that involve extreme calorie cuts will yield greater reductions, however, they may also increase side effects. We want weight loss to be gradual and sustainable, ideally focusing on losing 1 to 2 pounds per week.

Most intermittent fasting methods will allow this amount of weight to be shed. Therefore, 4 to 8 pounds per month can be reasonably expected, however, there are many factors that may influence this.

How long should intermittent fasting be done to lose weight?

Ultimately it depends on the amount of weight we are seeking to lose. A severely overweight individual will have to sustain intermittent fasting for longer in comparison to a slightly overweight individual.

It is recommended to set a goal weight and assess progress on a regular basis. Once the goal weight has been attained, intermittent fasting can be stopped.

Can I take supplements while fasting?

Yes. However, it is important that the calorie content of each supplement is accounted for. Protein supplements can be particularly useful for increasing satiety and retaining muscle mass.


Intermittent fasting has consistently been found to have a positive impact on weight loss.

Additionally, they may help to generally improve health and reduce the risk of disease. Although there may be benefits, there are also drawbacks.

A number of side effects may be experienced when fasting, specifically with more extreme methods. Whether or not intermittent fasting is employed as a weight-loss method comes down to personal preference and suitability.


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