Fasted exercise has popularized over the last few years, with claims ranging from “burning body fat” to “decreased hunger”. Fasted exercise occurs when people train before breakfast as a result of their own preferences or intermittent fasting.
The idea of fasted exercise commonly refers to fat burning. While the theory behind fat burning is viable, the research isn’t always as simple as we first believe.
Throughout this article, we will be looking at why fasted exercise isn’t quite what it’s made out to be, and if it’s worth doing. We will be taking a particular focus on fasted weight training, as this is something that is not commonly discussed.
What is Intermittent Fasting?
Intermittent fasting is a term used to describe periods of fasting and eating. You’ve probably come across intermittent fasting in a range of popularized diets, including the 5:2, and alternate day diet. However, the most common form of intermittent fasting is the 16:8 diet. During the 16:8 diet, you’ll fast for 16hrs, then consume your food during the remaining 8hr period.
Early intermittent fasting research studies suggested intermittent fasting led to better weight loss, cardiovascular health, neuroprotective effects, reduced risk of cancer, and increased life expectancy. However, many early studies were performed in rats, so their results aren’t fully valid. Later studies suggest intermittent fasting leads to weight loss, lower cholesterol, and lower blood pressure in overweight individuals. On the other hand, studies involving lean participants showed weight was only maintained following a period of intermittent fasting.
Intermittent Fasting: Endurance vs Weight Training
Fasted cardio is the most common form of fasted training, due to its connection with fat burning. The idea of increased fat burning on an empty stomach is feasible. When we are in a fasted state, our insulin levels are at their lowest. One of insulin’s roles is to restrict the breakdown of fat. Therefore, by exercising when our insulin levels are low, it’s feasible to presume fat breakdown is less restricted and therefore leads to greater fat breakdown.
Additionally, our glycogen stores are also at their lowest in a fasted state, therefore suggesting our bodies will be more inclined to use fat during exercise. Both these ideas surrounding fasted cardio are true. Studies have shown we burn more fat when in a fasted state.
However, this doesn’t mean we have a greater level of fat loss overall. When we burn more fat during a workout, we burn less fat over the day (Paoli et al. 2011), which appears to negate the increased fat burn during fasted training. When we look at long-term studies investigating the effects of fasted cardio, we don’t appear to see any real benefits of training in a fasted state. A meta-analysis concluded the amount of fat and weight lost overtime does not differ between individuals exercising in a fed or fasted state.
Weight sessions are notoriously high-intensity workouts. During a weight training workout, we are lifting weights for 5-60 seconds, with 1-5 minutes rest per set. While the total workout time may be long, the actual time lifting weights isn’t. However, when we are working, we are performing at a high-intensity. During high-intensity exercise, our bodies favor carbohydrates as their main source of energy, rather than fat. As we’ve discussed, carbohydrate stores are at their lowest in the fasted state. Therefore, lifting weights while in a fasted state might not be optimal.
Many people lift weights to build muscle mass. You’ve probably heard of the idea that you must eat every couple of hours to build muscle. With this in mind, it’s rational to think intermittent fasting will only hinder our muscle-building ability. However, studies have shown periods of fasting up to 40 hours don’t result in muscle loss and other further studies have shown fasted training does not impact changes in body composition. Therefore, weight training for the goal of muscle growth might not be hindered by fasted training.
Weight training is performed for a variety of reasons including improving body composition, strength training, and improving performance. When we think about fasted weight training, we must consider our reasons for lifting weights. If we want to maximize our results from resistance training, we need to pay attention to the role carbohydrates play in our session.
Benefits of Fasted Weight Training
An empty stomach makes training a lot more comfortable, especially when it’s high intensity like weight training. Training fasted can make us feel lighter and less full, allowing us to work harder with ease. While we are able to work harder, we have the potential to make greater progress in our workouts.
Some of us feel like working out in a fasted state provides us with more energy during the workout, leading to improved progress in the gym. Maybe it’s because we have less food sat in our stomach, there’s not a whole lot of reasoning behind it.
Fits Into Our Schedule
For many of us with busy lives, working out before breakfast is the only time we get to train. Therefore, we train fasted as an indirect consequence of our schedules. When it comes to exercise timing the most important factor is adherence, if that means training before breakfast, then so be it.
What to Look out for with Fasted Weight Training
Restricted Muscle-building Potential
We’ve discussed how fasting doesn’t appear to lead to muscle loss, but it may restrict our muscle gain. Muscle is made of protein, therefore to build muscle we must be consuming protein. A study concluded four 20g servings of protein consumed throughout the day were more effective than two 40g servings regarding muscle building. During periods of fasting we typically consume 1-2 meals per day, therefore we are potentially restricting our muscle-building potential when fasting.
As we’ve discussed, high-intensity exercise such as weight training utilizes carbohydrates over fat as their preferred source of energy. When we are in a fasted state, our carbohydrate stores are at their lowest, meaning we might find it difficult to perform at a high intensity during our lifts, resulting in stunted progress in our weight training.
To build muscle, we need to be in a calorie surplus. Fasted training reduces our eating window, therefore giving us less time to consume larger volumes of food. Many people struggle to eat in a calorie surplus, and this is made even harder when we have less time in the day to eat.
Expert Advice on Fasted Weight Training
Eat a Big Meal The Evening Before
We’ve mentioned carbohydrate stores are at their lowest in a fasted state, but we need carbohydrates for weight training. To ensure our carbohydrate stores are as high as possible, we can top them up before we go to bed, so the loss overnight is minimized. Focus on having a carbohydrate-rich meal before bed such as oats, pasta, or rice.
Work With Your Routine
Workout whenever fits your routine. Exercise provides huge health benefits, therefore is essential in our lives. Don’t think just because you can’t train in the evening when you’re in a fed state, you shouldn’t train at all.
Consuming a carbohydrate-rich sports drink pre-workout, or intra-workout can increase your blood glucose levels, allowing your body to utilize carbs during the workout without having to consume real food.
Once you’ve finished your workout, consume a carbohydrate and protein-rich snack as soon as it’s convenient. After a fasted workout, your body will need to be replenished to aid recovery and muscle repair. If you’ve begun the workout in a fasted state, it’s extra important you get these nutrients in ASAP.
Seek Professional Medical Advice
For many of us, training fasted is perfectly healthy and safe. However, for some people, fasted training can cause a significant drop in blood glucose levels resulting in dizziness, nausea, and headaches. Before starting any new training program or eating habits you should consult your physician or dietitian on what is best for you.
Different people have different preferences when it comes to training fasted. Some of us prefer working out fasted as it’s more comfortable and makes us feel more energized. Others prefer working out in a fed state because they feel like they have more energy.
Fasted weight training doesn’t seem to provide any real benefits, but also doesn’t show any real adverse consequences either, as long as we have enough carbohydrate stores to sustain us through our workout session.
So, is it worth it? It really is down to personal preference. If you do prefer to workout fasted, just make sure you’ve topped up your carbohydrate stores by having a sports drink or big meal the night before.
Frequently Asked Questions
Is it OK to lift weights on an empty stomach?
For most of us, yes. However, some of us might find training on an empty stomach actually gives us adverse, or even harmful consequences. Before engaging in fasted workouts you should consult your physician or dietitian on what is best for you.
Does fasted weight training burn muscle?
Technically, we are always ‘burning muscle’ during exercise, regardless of whether we are fed or fasted. When we lift weights, we are breaking down muscle. Growth and repair in our muscles occur with nutrition, specifically protein. When we consume insufficient amounts of protein, we will lose muscle. However, if we consume sufficient protein throughout the day, we will gain, or at the very least maintain muscle mass. Therefore, in terms of ‘burning muscle’, we should be more concerned with our nutrition, rather than worrying about whether we’re working out fasted or fed.
Can you build muscle fasted?
Yes. To build muscle, you need to be in a calorie surplus with sufficient protein to support muscle gain. Building muscle in a fasted state is a bit harder than fed, but it’s not impossible. Ensure your eating in a calorie surplus and getting protein through the day and you’ll be able to build muscle. Also, prioritize your post-workout nutrition.
When should I eat after fasted weight training?
Eat a carbohydrate protein-rich meal as soon as you can. To recover and repair your body after training, you need to be consuming protein and carbs. Because your body has been starved for so long, getting in those nutrients is essential. Saying this, the most important thing is fitting in with your schedule. If eating a meal isn’t possible, think about having a carbohydrate and protein-filled shake straight after your session.