A major point of pushback is with people who have spent time growing their muscle mass. They’re looking to cut body fat, but they’re concerned that fasting will negatively impact their muscle. First, let’s be clear. All weight loss diets can be boiled down to one simple concept. You are reducing your calorie intake, thereby eating less calories than you burn. This forces your body to tap into that fat, to make up the difference. Converting this fat into energy, reduces your fat mass while making up the additional energy you need. In order to evaluate fasting as a way to lose fat for people interested in still preserving their muscle we need something to compare it against. Since the goal here is fat loss with a consideration for maintaining muscle, it only makes sense to compare fasting against another similarly effective method of weight loss, a typical cutting diet, which has participants eating less calories than they consume daily.
In this type of regimen, the caloric deficit shows up at the end of each day. This means that day after day, their body is constantly in a state of malnutrition. It was long thought that this was actually far and away, the best way to lose fat while maintaining muscle. The idea was that eating at a constant deficit would cause you to lose fat, but keeping protein and calories from dropping too low would help preserve muscle. Fasting, on the other hand, involves creating a deficit, but just on a larger timescale, while someone on a traditional diet is in a daily deficit, someone doing periodic fast is looking at the bigger picture, creating perhaps a weekly caloric deficit.
This is why in as little as 72 hours, you can lose one to two pounds of fat. This level of weight loss could take two to four weeks on a traditional cutting diet. Now the core fear is that during these extended windows of not eating, muscle might degrade more rapidly than it would if you lost the same amount of fat by maintaining a constant deficit over several weeks. People believe that something about an extended period with no food causes more muscle loss, but what does the science say? It may come as a shock, but not only has it been studied and proven that this isn’t really the case, but fasting may actually be better at maintaining muscle mass.
Fasting preserves more muscle mass than traditional diets
Why don’t we lose muscle? Well, to understand this, we’re going to need to take a quick lesson on hormones and what happens to them when you fast, specifically human growth hormone and IGF one. One 1992 study put subjects on a three day fast. After two days of fasting, they remeasured over the final 24 hour period of the fast. The impact of the fasting was huge, mean levels of growth hormone in the blood increased by three fold up to about 6.7 micrograms per liter. After a closer look, they found that the pituitary gland had kicked into overdrive. Not only did the number of blips of growth hormone release double, but the average size of each blip increased as well.
Fasting is a viable option for those who want to lose fat while maintaining their muscle gains. This brings us to our final study, which is actually a review. Researchers looked at several weight loss studies where participants used a fasting protocol and compared the results with studies where participants lost weight via traditional calorie restriction. One thing that jumped out at the researchers was that the participants were able to lose an impressive amount of weight fairly quickly in just two to three weeks, male and female participants lost 3% and 4% of their body weight, respectively. This amount of weight loss actually took longer to lose on many of the daily calorie restriction diets. Ultimately though, both daily calorie restriction and the periodic fasting groups lost similar amounts of body weight over their trials. Doesn’t sound so good for fasting, right? Well, hold on because everything changed when they took a deeper look and focused, not just on body, weight loss, but on what kind of weight they lost during the daily calorie restriction diets, the bodyweight participants lost, comprised on average 75% fat and 25% lean mass.
Whereas when you look at the groups who lost their weight through periodic fasting, they might have lost the same amount of body weight, but the ratio was different. On average, 90% of what they lost was fat and only 10% was lean mass. While both groups lost similar amounts of body weight, the group, which did periodic fasts maintained more lean mass, much of which is muscle. It seems like these fasting groups experienced the best of both worlds. In many ways, they dropped fat quite quickly. Thanks to the hormonal processes their muscles were mostly protected when they fasted and they still benefited from being in a calorie surplus on the days they didn’t fast. This is the beauty of these periodic fasts: participants are able to lose body fat quite quickly while keeping most of their muscle. Then over the rest of the week, they could benefit from being in a calorie, surplus and replenish any muscle they may have lost unlike the traditional dieters whose body starved day after day after day.
To compensate for the loss in muscle mass, some fasters do some resistance training during their fasts as this triggers various pathways, which further protects muscle mass. One thing you should be aware of is during a fast, your body will become more sensitive to sugars, which is why it is recommended to always break a fast with fats and proteins.
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