Intermittent Fasting Pros and Cons

By Chloe Bennett, B.Sc.Reviewed by Dr. Liji Thomas, MD

With the increase in the amount of evidence of the adverse consequences of being overweight, a growing proportion of society is becoming more health conscious. In order to manage their weight, many are adopting diets and different training strategies, such as intermittent fasting.

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Moving away from traditional calorie restriction, intermittent fasting has become increasingly popular in recent years. But what are the benefits and consequences of following such a plan?

What is Intermittent Fasting?

There are several types of intermittent fasting which may be differentiated by the level of calorie restriction and the frequency of eating. For some, intermittent fasting is part of their religion, for example, Muslims cannot consume any food or drink between dawn and sunset during the month of Ramadan. Some of the most common types of intermittent fasting are outlined below.

Types of Intermittent Fasting

Alternate Day Fasting (ADF)

ADF is intermittent fasting that requires one “feed day” where those following the diet can eat whenever and whatever they want within a 24-hour period. This is alternated with a “fast day” where you’re unable to eat for a maximum of 24 hours. There are variations of ADF which may make it easier to follow, such as allowing a maximum of 500 calories to be consumed on “fast days”. On fast days, those following the diet can drink no-calorie beverages such as tea, coffee and water. However, the use of sweeteners, sugar or cream with hot drinks is not recommended.

Modified Fasting Regimens

On modified fasting regimens, those who follow them are allowed to eat food regularly, but are restricted to consuming only about 20-25% of the required energy on fasting days. This program forms the basis of the popular 5:2 diet which recommends energy restriction on two days of the week while on the remaining five days, the usual calorie intake is allowed.

Time-Restricted Feeding

Those following the time-restricted feeding regimen are allowed to eat whatever they like, but instead of calorie restriction, they are restricted to eating within specified periods of time. The time frame can range from 6 to 12 hours and outside of this window only the consumption of no-calorie drinks and water is permitted.

Pros of Intermittent Fasting

Several types of intermittent fasting have been associated with different benefits for their adherents compared to other traditional diets.

Weight Loss

One of the main reasons why people adopt intermittent fasting is to manage or lose weight. Evidence suggests that intermittent fasting can be beneficial as a weight loss tool. Specific research investigating the effects of ADF on weight loss found that within a 2 to 3-week period, there was a 2.5% reduction in weight compared to baseline measurements.

Health Benefits

It has been found that intermittent fasting can have several long-term preventative health benefits. It is well researched that being overweight and obese can increase the likelihood of developing a range of life-threatening diseases such as coronary artery disease (CAD). An intermittent fasting dietary program can thus bring about a reduction in triacylglycerol concentrations, and an increase in high-density lipoprotein cholesterol. These changes lead to an overall reduction in the risk of developing CAD. Further research has also demonstrated that by adopting intermittent fasting, individuals can actually reduce the likelihood of developing age-related diseases such as Alzheimer's.

It’s easier to follow

Research has found that people find it easier to follow an intermittent fasting diet over a long-term period compared to following a calorie-restricted diet. It is suggested that as individuals only have to reduce their calorie intake every other day on the ADF diet, it is easier to achieve than lowering consumption every day. Even those who follow the amended ADF diet, where they can consume 500 calories on “fast days”, have found that much more achievable than maintaining a constant calorie deficit. Therefore, for those wanting to achieve sustainable weight loss, intermittent fasting might be extremely beneficial.

Cons of Intermittent Fasting

Those who are thinking of adopting intermittent fasting into their routine may want to consider the following negatives.

Side Effects of Intermittent Fasting

Like many diets, intermittent fasting can have several side effects. Research investigating the impact of ADF on weight loss found that participants experienced headaches, constipation and lack of energy. The reported lack of energy may be an issue for those wishing to train or exercise, which is also recommended for adults in order to maintain a healthy lifestyle.

Furthermore, varying psychological effects were reported such as a lack of concentration and bad temper. One major highlight from the research was that people were found to be more preoccupied with food as a result of intermittent fasting. This may cause further issues for those who are predisposed to certain eating disorders.

The Effectiveness of Intermittent Fasting in Weight Loss

There are conflicting research findings on the impact of intermittent fasting on weight loss compared to traditional calorie restricted diets. Some researchers suggest that intermittent fasting is not superior to conventional calorie-restricted diets.

Suitability of Intermittent Fasting

Despite the many health benefits that it offers for individuals who are overweight, obese or of average weight, intermittent fasting is not suitable for everyone. There are specific groups of society for whom this plan is not recommended, such as pregnant women, those with eating disorders and those with certain health issues.

Further Reading

• All Fasting Content
• Juice Fasting: Pros and Cons
• Is Intermittent Fasting Healthy?
• A Guide to Fasting Healthily for Ramadan