Intermittent Fasting (IF) is currently one of the world’s fastest growing diet trends and a strategy many people have adopted to help them reach their nutrition goals. You most likely have heard of it – no doubt someone you know has tried it. You may even have tried it yourself.
But does intermittent fasting work? Can it really help you lose weight? What are the benefits of intermittent fasting? What do the studies show?
What is Intermittent Fasting?
Before we examine the science, first what is Intermittent fasting? Fasting is abstaining from food for a period of time, and intermittent means that it’s interval-based. So intermittent fasting is an eating pattern that cycles between periods of eating and fasting.
Generally there are no “good” or “bad” foods on an Intermittent fasting diet. Instead the focus is not what foods to eat but rather when to eat. In this way, IF is not so much a diet but rather a lifestyle choice or pattern of eating.
How do I follow an Intermittent Fasting Routine?
There are several ways of following an IF routine. The most common one is a time-restricted fasting method called 16:8 in which you eat within an 8 hour period followed by a 16 hour fast. For example, eating 12-8pm and fasting until noon again the next day. Followers of this style typically either skip breakfast or dinner and fast through the evening and/or morning.
This method is ideal for those who already have a tendency to skip breakfast or aren’t as hungry in the mornings. It can be inconvenient for those who prefer not to workout on an empty stomach or for social events if you fast during the evening.
Another time-restricted fasting method, that may be easier to follow depending on your schedule, would be fasting for 12 hours followed by a 12 hour eating window, but by far 16:8 is the most common method seen in the media.
The 5:2 method is a modified version of fasting that involves limiting calories to only 500-600 calories on two non-consecutive days (for instance Tuesday and Thursday) and eating regularly the other days of the week. Another variation of this suggests fasting on two nonconsecutive days per week with only a 25% reduction in daily calories consumed. For example, if you normally consume 2000 calories, you would limit to 1500 calories on “fasting” days. (13)
Lastly, the “Eat-Stop-Eat” method involves fasting for a full 24 hours one to two days a week and eating regularly the other days of the week. Alternately, one could fast every other day, literally eating, stopping, eating.
The real question is – Why would you want to follow an Intermittent Fasting routine?
What are the benefits of Intermittent Fasting? What does the science say about these IF benefits?
Even though IF is not a diet, many people try intermittent fasting in an effort to lose weight. (1) All of the different IF methods cited above involve skipping meals during the fasting periods. So unless you overeat during the feeding windows, then you should be taking in fewer calories overall.
According to one study, people lost about 0.55 pounds per week with intermittent fasting, but 1.65 pounds per week with alternate-day fasting. (2) It is also thought that the body burns more fat during periods of fasting. (3,4,5)
However, when comparing intermittent fasting to continuous calorie restriction with the same daily caloric intake, there is no difference in the rate or amount of weight lost. (2) The overall conclusion is that modified fasting methods of IF are no better than the standard diet of reduced calorie intake. (13) On the flip side, if you prefer fasting over calorie counting, then perhaps IF is a more convenient method of weight loss for you.
Hormonal and Cellular Benefits
When you go fast, the body essentially goes into a mini starvation mode and adjusts hormone levels to protect itself. For example, levels of growth hormone increase by 5 times. Human Growth Hormone supports fat loss, gaining muscle and cell repair. (3,4,5)
Speaking of cell repair, cells begin the repair and restoration process as well as removing dying cells no longer needed when you fast, such as at night. (Provided you didn’t eat just before bed!) (6, 7)
Healthy Blood Sugar
Fasting may improve insulin sensitivity as insulin levels tend to drop, making stored body fat more accessible. (8) In one study, fasting lowered blood sugar by 3–6% and fasting insulin levels by as much as 20–31%. (2)
Some studies show that IF may reduce inflammation biomarkers, which is beneficial for many reasons as inflammation is a key player in many diseases but also causes soreness and muscle damage in relation to physical exercise. (9,10,11,12,13)
Intermittent Fasting is not a diet but a lifestyle choice. While the benefits sound noteworthy, most IF studies have been done on rats, not humans, most of which aren’t even long term studies, so the evidence supporting the benefits of IF is largely up for debate.
That being said, everyone should find a way of eating that fits with their lifestyle and meets your nutritional needs that is sustainable and enjoyable for them. This ensures sustainability and long-term success. If IF (either time-restricted or modified fasting methods) works for you and your schedule, then give it a try!
On the other hand, if intermittent fasting doesn’t appeal to you or fit your schedule, it isn’t necessarily something you need to try. New studies are being done regularly though so perhaps there will be more conclusive information on IF in the future.