Why has this practice become so popular in recent years?
One of the main reasons is simplicity.
Let’s see what the main types of intermittent fasting are and what the evidence shows about weight loss and other health effects.
Variants of intermittent fasting
Intermittent fasting is also known as time-restricted eating; intermittent fasting alternates periods of normal food intake with prolonged periods (usually 16-48 h) of low to no food intake.
This approach lends itself to different variants, including the following:
Alternative day fast (also known as modified day (alternate) fast)
This diet can take different forms: you can eat more than 12 hours and then fast for 36 hours; you can eat more than 24 hours and then fast for 24 hours; or you can eat normally for 24 hours and then eat very little (about 500 kcal) for the next 24 hours.
This variant restricts calories rapidly or severely for 24 hours, either at regular intervals (two days a week on the 5: 2 diet) or only occasionally.
Random food skip
In this one you skip meals at random throughout the week.
Within this variant you can only eat for a specified period of time every day (from 10 AM to 6 PM, for example).
If you decide to try intermittent fasting, choose a variant that you think you can keep for at least a few weeks.
Effects on weight
Yes, intermittent fasting works, although to very different degrees in different studies. This variability could be explained by different factors, among which is the specific variant of intermittent fasting studied.
For example, simply skipping breakfast caused some weight loss in one study but not another.
In each of those two studies, the control group was given a standard breakfast, such as oatmeal, but neither group was restricted as to what they could eat for the rest of the day.
People with more weight to lose may also benefit more from an intermittent fasting approach, but one thing’s for sure: if you make up for missed meals by eating later in the day, or the next day, or the next, you will not lose weight.
The weight loss equation is simple – you need to eat fewer calories than you burn, and intermittent fasting is just one way for this to happen, but it’s one way that some people find easier than the more common approach of eating smaller meals. .
To lose weight, you must burn more than you eat, or, conversely, eat less than you burn. Some people find this goal easier to achieve through intermittent fasting than through the traditional “smaller meals” approach.
The body of evidence on intermittent fasting is still relatively small, but a growing number of studies have reported improvements in several health markers other than weight, especially lipids.
Additionally, those studies suggest that intermittent fasting may provide unique metabolic benefits over the “eat smaller meals” approach.
The most intriguing of those benefits, but also the most debated, is a longer life.
Fasting can kick-start some regenerative processes in the body, and extended lives of caloric restriction have been reported in many (but not all) animal models.
Keep in mind, however, that those animals were fed low-calorie diets or rotated during periods of fasting for most of their lives.
It is unknown if intermittent fasting can prolong human life, and if it can, which variant is better, and how many weeks, months, or years it takes to make a difference.
Assessing the potential metabolic benefits of intermittent fasting is a long-term endeavor.
As a systematic review of the literature observed in 2015, preliminary evidence looks promising, but solid research is still scant, so “more research in humans is needed before recommending the use of fasting as a health intervention.”
Preliminary evidence suggests that fasting might have unique metabolic benefits, including life extension, but these need to be confirmed by additional research in humans.
Depending on the length of your fast, you may experience:
- Stress .
Staying hydrated is particularly important; it will also help alleviate any headaches or constipation.
Some preliminary evidence suggests that a periodic reduction in caloric intake may produce physiological benefits similar to those of fasting.
A fast copycat diet is a strategy where instead of giving up food entirely, you simply eat a low calorie diet for 5 consecutive days each month.
The typical protocol involves consuming 1,090 kcal (10% protein, 56% fat, 34% carbohydrates) the first day, then 725 kcal (9% protein, 44% fat, 47% carbohydrates) in each of the next four days.
Keep in mind that intermittent fasting is not for everyone. People with impaired glycemic control should avoid fasting as it causes a worse glucose response.
Also, if you’re pregnant, underweight, under 18, or have a history of eating disorders, fasting is probably not for you.
Intermittent fasting is a viable route to help you lose weight or maintain a healthy weight. That said, limiting calories (the traditional way to lose weight) offers similar benefits.
Consistency is important, and people who consider eating less often than eating less could especially benefit from trying intermittent fasting.
There is not much evidence that intermittent fasting has unique metabolic health benefits.