Intermittent fasting is a dieting approach that is steadily gaining popularity. Individuals are now beginning to see that it is a viable option for those looking to improve body composition. However, despite its effectiveness and benefits, it may not be optimal to use every day, especially for lean individuals hoping to hold on to lean body mass while dieting. Let me provide a brief explanation of intermittent fasting and then explain why you should consider scheduling fasting periods based on training.
Lean Gains Intermittent Fasting
Lean gains intermittent fasting utilizes a 16:8 fast:feast ratio. i.e. you fast for 16 hours, followed by feeding for 8, preferably with most intake coming in the post workout period. Benefits of this are based on the idea of the AMPK/mTOR “seesaw.” As one goes up, the other goes down, and vice versa. AMPK is a catabolic pathway which also includes increasing fat oxidation (fat burning). mTOR is a major anabolic pathway (increasing muscle growth).
These two pathways act as a synergy and a cyclic nature between the two is optimal for potentially losing fat and building muscle simultaneously, since you dedicate specific times of the day towards one or the other. When you fast, you may elevate AMPK (which is still up for debate, AMPK elevation my be dependent on movement and muscle glycogen status), and when you feed/train, you elevate mTOR. Simple enough. More realistically, during the fasting period, you may have an elevation in both free fatty acid availability and subsequent oxidation (Heilbronn et al., 2005), in addition to increases in catecholamines, which play a role in lipolysis (The freeing of fatty acids from tissue to later be oxidized).
Intermittent Fasting For Maintaining Lean Muscle
Based on current evidence regarding the protein synthetic response to training in trained individuals, while intermittent fasting may be good for longevity purposes, it may not be optimal for maintenance of lean muscle tissue. Also, let me preface that the next couple arguments I make are more based towards those that are of an advanced training status. If you are obese and untrained, it may be more beneficial for you to follow this protocol every day if it is something you chose to employ. Further, there are other forms of intermittent fasting that you could always consider (cheat mode, alternate day fasting, carb back loading, etc.).
If you’re a trained individual, you know how hard it can be to pack on muscle. Further, if you are lean, you also know that it can be increasingly more difficult to shed those last couple of pounds of fat, while maintaining lean mass. If so, this may apply to you.
The Untrained vs. Trained Individual
When you are untrained, the protein synthetic response for skeletal muscle post workout is very long – possibly with a duration of up to 48 hours! However, as you become more trained, that synthetic response becomes drastically shortened; potentially to as little as 8 hours. As with anything in training, your body responds to insult (training stimulus) in order to adapt the stress. That’s why you get stronger and build muscle in short. You train –> an insult to your body –> your body grows or gets stronger in order to adapt, so that the next time it happens, you’ll be better prepared.
The same thing happens with the protein synthetic response. As you become more trained, your body becomes desensitized to the stimulus and then doesn’t respond as strongly (as in the “need” for an increased protein synthetic response is lessened, in the eyes of your body).
For the trained individual, considering the last paragraph, it becomes increasingly more important for you to maximize the time of elevated protein synthesis. Now, if you’re fasting throughout the morning and training in the late afternoon, this elevated protein synthesis may transcend into the next day.. See where I’m going with this? If you go right into the next day and begin fasting, you may be wasting precious time that your body is in a protein synthetic state, further decreasing the time that you are actually “building muscle.”
So, where does that leave us? It may be a better idea to train and fast in a cyclic nature. This would be especially beneficial while actually in a dieting phase. By having a cyclic IF/Training schedule, you not only can reduce the training frequency (which is prudent when on a caloric deficit, since you have less calories to fuel growth and recovery), but you can maximize the times of protein synthetic elevation, as well as the times that you would want to have increased AMPK activation, lipolysis and fat oxidation, 16 hours prior to training.
An Example Intermittent Fasting Schedule
- Night 0, the day before beginning the diet: Last meal
- Day 1: Fasted through the night and continue fasting through the day, reaching the 16 hour mark. Then you train.
- Day 1 Post-training: Begin eating the majority of the day’s calories.
- Day 2: Protein synthesis is still elevated (how long, we don’t know, so err on the side of caution), so eat normally on these days. If you are on a caloric deficit, then it should be maintained, but you should eat more often on this day.
- Day 2 Night: begin the fast at the same time as night 0.
- Day 3: Fasted throughout the night and continue fasting through the day until training.
- Day 3: Post training: Begin eating the majority of your day’s calories
- Day 4: Protein synthesis is still elevated (how long, we don’t know, so error on the side of caution), so eat normally on these days. If you are on a caloric deficit, then it should be maintained, but you should eat more often on this day.
This cyclic style may allow those who are trained to reap the benefits of Intermittent Fasting, while maximizing the times of increased protein synthetic response. This will not only allow you to effectively lose some body fat, but you could at least take advantage of the training stimulus in an optimal fashion, and potentially put on some muscle, though that is not guaranteed.
Manipulating the Intermittent Fasting Schedule
Further, this schedule may be manipulated based on when you train. If you train around noon, it may not be necessary to follow this cyclic style. If you are well trained, it may be the case that by the time you wake up the next morning (<16 hours post training), the protein synthetic response could be decreased. Unless you have access to regular biopsies and blood testing, you’ll have to decide for yourself.
This style is simply a suggestion and a hypothesis. Always remember that most effective diet is one that you’ll actually stick to. If you are more concerned with maximizing fat loss in the quickest amount of time, then it may be more optimal for you to IF every day. You’ll have to make that decision on your own.