The intermittent fasting trend has well and truly settled in.
I get dozens of questions about intermittent fasting, so today we’re addressing the big questions and what it can really do for you.
We’ll be covering the basics, what it’s for, how it works, and if it has any value you to you. Read on if you want to cut through the hype and get to the real science behind Intermittent Fasting.
What is IF?
The big question to start with: what is Intermittent fasting (or “IF”)?
In the simplest terms, intermittent fasting is the idea that diets should cycle through restriction and refeeding phases. This isn’t a new idea, bodybuilders have been doing this forever, but the applications we’ve seen lately are pretty interesting.
16/8 is one of the most common and trendy versions of intermittent fasting. This approach says that you should be fasting for 16 hours and eating for 8. 5:2 goes even further, suggesting you restrict eating drastically for 2 days and then eat around (or just above) maintenance for 5. Other protocols exist, but the principles are similar.
The idea is that continuous energy restriction (a regular diet) tends to produce adaptive responses and plateaus. Your body gets used to calorie restriction and can easily back-shift to produce regular stalling in fat loss.
On the other hand, intermittent energy restriction like IF produces weight loss while reducing adaptive responses. This is done by having periodic refeeds, which keep your metabolism regular, support insulin sensitivity, and reduce compensatory processes.
This is a good idea in theory, but the science isn’t clear on whether or not this holds up in the real world yet…
Can you Use Intermittent Fasting Build Muscle?
Intermittent fasting is not a muscle-building diet. It’s right there in the name: fasting. This is a diet that is centred around fat loss.
The restrictions placed on the body during intermittent fasting are not conducive to building muscle, studies show already that they are likely to burn up significant amounts of muscle if not closely-controlled.
16/8 dieting isn’t as bad, since the restriction is never long enough to use up all your stored glycogen, but it does increase AMPK. This can lead to muscle breakdown, though this is comparable to a regular diet when matched for calories.
Longer periods of restriction like the 5:2 approach seem to make this worse and have a serious burden on muscle tissue. They burn up fat-free mass (muscle) at greater rates than regular diets since you’re consistently underfed.
Timing is key here, and there are some ways to reduce the risks of breaking down muscle:
- Eat lots of protein no matter whether you’re fasting or refeeding – intake should be roughly the same for both
- Refeed with lots of carbs: carbohydrate intake during a refeed is key to restoring energy balance and signalling for muscle growth
- Stay with strength training. This favourably targets fat loss and maintains muscle mass during a diet.
Intermittent fasting isn’t inherently going to ruin your muscle, but studies have yet to show it as a way of building muscle on a diet. This kind of study does exist for regular, consistent energy restriction, so IF is definitely lagging behind on the muscle-building front.
Is Intermittent Fasting Effective for Burning Fat?
Intermittent fasting is definitely a viable method for burning fat. This has nothing to do with the fasting itself: it’s just a way of reducing your overall calorie intake by restricting total feeding.
There’s no magic here. IF can be a great choice for you if you struggle to eat less, but don’t mind eating less often. This is also a great way of making behavioural change – especially if you’re the kind of person that snacks or “grazes” during the day.
During intermittent fasting, you’re entirely restricted from these behaviours. During eating hours, you’re likely to get full rather quickly, especially if you’re focusing on high-quality, nutrient-dense, energy-sparse foods like vegetables.
The problem is that studies don’t suggest that IF fat-burning is any greater, faster, or better-balanced than regular dieting. The research is all pretty clear that intermittent fasting is one way – but not the best way – of dieting!
Using IER for your own goals
So, what can you do to make intermittent energy restriction – and intermittent fasting specifically – suit your goals?
There are a few ways of making it fit the general goals of a leaner, stronger, more muscular physique. This is intermittent energy restriction but in a way that actually works for you.
The idea is to take a normal diet and get the benefits of intermittent fasting without the restrictive process. There are a few ways that I deal with adaptation to fat loss with my London-based personal training clients that you might use to get all the benefits of intermittent fasting without the difficult bits or risk of muscle-loss.
- Restrict and Refeed Without Fasting
Intermittent fasting has some good ideas, but they don’t need to stay within this framework.
Restriction and refeeding actually work best in shorter cycles. The science tell us that restriction should last 4-7 days before a refeed. This means you can build a simple restriction/refeed pattern that keeps your metabolism responsive and supports muscle maintenance/gain alongside fat loss:
4 days of restriction (75% of maintenance calories, 80% of maintenance carbs)
1 day of refeeding (120% maintenance calories, 120% maintenance carbs or more)
This allows you to lose weight at a good rate (usually a few pounds, or roughly a kilo, per month) but also falls into the range for muscle maintenance/gain we discussed above!
- Periodised Dieting
Sounds fancy, but in reality this is just the process of taking “blocks” in your diet with different focuses. Plateaus happen in response to chronic calorie restriction, but a good diet isn’t just the same calorie intake forever.
Regular maintenance and recompositioning blocks can keep fat loss consistent. For example, an 8 week “cut” could be followed by 2-4 weeks of maintenance dieting where we focus on dietary habits, gaining strength, and enjoying healthier foods.
This also keeps your metabolic activity regular and stops resting energy expenditure from getting too low.
- Keep Your Diet Narrow
Avoid excessive carb restriction, but make sure to limit somewhat during a cutting diet. This will ensure effective insulin sensitivity, which is key to good metabolic health as well as muscle growth during the refeeding process.
Calorie restriction is the centre piece of any diet. We’ve discussed calorie restriction before but using around 0.5% bodyweight loss per week is a good place to start (roughly 10% calorie restriction). This is true whether you’re fasting or using a consistent restriction approach!
Diets shouldn’t be so fast that they burn muscle, so take the time to lose weight while building/maintaining muscle! A hard fast can pose real problems to your overall body composition, so take your time whatever diet you use.
- Carb restriction and timing
Carbs are key on a diet, even more so when you’re looking at a restriction/refeed approach. This means you need to be smart about how you take in your carbs.
Firstly, your diet shouldn’t reduce carb inake below 80% of maintenance – they’re key to supporting muscle. When you’re not getting enough carbs during a fast, you’re going to break down muscle to produce glucose.
Timing your carbs is important. Refeed days should be the day before, or of, your toughest training sessions. This allows you to produce better results, stimulate muscle, and producing energy abundance.
You should use carbs with higher-GIs, usually associated with white or processed foods, closer to workouts. Out-of-training carbs should be slow-releasing, consistent energy sources such as the traditional brown rice, or nutrient-dense pulses. If you’re eating sweets at night, you’ve messed up.
We said it earlier, but it’s the overall theme for this discussion: Intermittent fasting works, but it’s not necessarily better than any other diet out there.
The risks associated with restrictive fasting can be a serious problem for your metabolism and it may not suit you. It’s a diet that poses a higher risk to your muscle mass, which can also undo the benefits by reducing your overall resting energy requirements!
If used properly, IF can be a good choice if it suits your preferred style of eating and dieting. However, this doesn’t make it a perfect diet or a magic bullet for health, and you can get the benefits of this type of diet in other ways. There’s very little unique about the way this diet works, it’s just a novel option that suits some people better.
We’ve described a simple approach to dieting that produces short- and mid-term refeeds to support metabolic health. These offer the same benefits with an improved chance of muscle-gain and reduced muscle breakdown.
This is a single example, and there are definitely alternatives that suit most fitness goals as well. Applying the principles of an intermittent energy restriction is crucial, but intermittent fasting is just a single, trendy, example.