Intermittent fasting is an approach that alternates between periods of fasting and periods of eating. It doesn’t tell you what to eat or how much, it only tells you when. This is an important point to understand for later when we will compare this approach to others. There are many ways to do this but, in general, we can divide intermittent fasting protocols into three main types.
- Time-restricted eating: This is probably the most common type that asks you to fast for a certain number of hours every day. A popular split is 16/8 where you abstain from food for 16 hours which leaves you with an 8-hour window to get all your meals in. Some people start with an easier 12/12 split while others push this to a 20/4 split that leaves only 4 hours for eating every day.
- Whole-day fasting: With this type of intermittent fasting, you are typically asked to stop eating for a day once every week or so. The most popular is the 5/2 diet which makes you fast for 2 non-consecutive days each week and eat normally the other five days. Sometimes you’re allowed a very low intake of around 500 kcal during the fasting days.
- Alternate-day fasting: With this approach, you fast every other day. You are free to eat as you want on non-fasting days. During fasting days, you have to keep your calorie intake under 25% of your usual needs.
Intermittent fasting works for weight loss
There is a lot of research that looked at intermittent fasting and weight loss. A 2014 review of scientific literature showed intermittent fasting can cause significant weight loss of up to 8% of body weight over periods of 3 to 24 weeks. It also documented that participants lost up to 7% of their waist circumference, which suggests that they got rid of the most dangerous visceral fat that forms around organs. These are quite impressive results, intermittent fasting is certainly effective if you want to shed a few pounds.
Do you lose fat or muscle?
The thing is, many cyclists are not interested in just any weight loss. They are interested specifically in losing body fat while maintaining as much muscle mass as possible. A review from 2011 suggests that alternate-day fasting causes less muscle loss than regular calorie restriction. On the other hand, a 2020 randomized clinical trial found that the people in the time-restricted eating group lost a lot more muscle mass compared to the group with consistent meal timing. We likely need more studies to have a clearer picture of how to best protect muscle mass when losing weight.
How does intermittent fasting help you lose weight?
Your body switches from burning carbs to burning fat for energy when you’re fasting. Some people think that this is why intermittent fasting helps them burn their body fat. As good as high fat-burning rate sounds, weight loss always comes down to one thing. You simply have to burn more calories than you take in from food. Intermittent fasting might be able to help with that. It reduces the amount of time for eating which makes it hard for you to eat as much as you normally do so you end up reducing your calorie intake spontaneously.
A new meta-analysis from May 2022 was set up to find out whether intermittent fasting goes beyond calorie restriction or whether you can achieve the same by just cutting down on your regular meals without any time restrictions. Researchers looked at data from 630 subjects from short-term and long-term trials in men and women where calorie intake was equal for intermittent fasting groups and non-intermittent fasting groups. They included a variety of different protocols of time-restricted eating such as 16/8, 18/6, and 20/4 and even whole-day fasting and alternate-day fasting protocols. Their results speak clearly – calorie reduction is king.
Intermittent fasting is no better than normal calorie restriction
The new meta-analysis found that when calorie intake is the same for both groups, weight loss and fat loss are the same, whether you’re intermittent fasting or just reducing calories during your regular meals. The researchers concluded that the vast majority of the benefits of intermittent fasting on weight loss and other health markers are caused by the calorie deficit.
To put it all together, intermittent fasting is certainly an effective way to lose weight. If restricting your eating window works for you and helps you keep your calorie intake low, go for it! The good news is that you can choose many other dietary approaches, as long as you reduce your calorie intake, and get the same results. The next article will be all about the health benefits associated with intermittent fasting.