The long-standing debate: should I eat before my workout or complete it fasted? Which strategy will optimize performance and why? Well, like any nutrition strategy out there, there are pros and cons of both. What strategy you should implement is contingent on numerous factors, topped with caveats on caveats.

Whether you workout fasted or ‘fed’ depends on your fitness goals, the type of workout, the duration, your genetics, and being cognizant of any underlying health conditions you may have. These are just a few of the considerations to keep top-of-mind when choosing a nutrition timing strategy.

The fact is, there’s no one size fits all when it comes to pre-workout nutrition. Our bodies are all different and to find the strategy that works for you, it’s important to experiment. Be open to unlearning old mindsets and routines that would stymie your progress. Trial and error and tracking moods/energy levels is how I’ve come to many conclusions regarding nutrition, and guess what? Those assumptions are always challenged and shifting as new fitness and nutrition research is mixed into the wellness discourse.

Before we dive in, it’s also important to note that I’m a morning gal; like, the type of person who enjoys getting up before the sun rises and will consistently hit the sack before your grandparents do. I realize that those who workout in the evenings or afternoons will most likely have a very different experience than me. Since I prefer to base my blog posts on personal experience, I won’t be doing a deep dive on what nutrition regimen works best for you later-in-the-day athletes…that’s not in my wheelhouse. However, you may still find odds and ends from this article that are still applicable to you. I won’t pull some Gwenyth Paltrow pseudoscience bullshit on you, so be sure to reference the additional resources of real scientific journals linked at the bottom of this post.

Non-Fasted or ‘Fed’ Workouts

What is a fed workout?

Let me start by stating the obvious. A ‘fed’ workout is exactly what it sounds like – eating before a workout or working out in a fed state. After consuming a meal, you can be in a fed state for up to 4-6 hours on average. When you work out in this state, your body uses the calories consumed as a form of energy; allowing you to workout longer and with more intensity than, say, a fasted workout.

Benefits of fed workouts

The fed state is what we’ve been conditioned from birth to utilize as athletes. Experts have emphasized the importance of a proper pre-workout meal, but why? Well, in short, by consuming the right pre-workout nutrition, we can maximize our performance while also repairing muscle damage post-workout. Geoffrey Woo and Zhill Olonan did a systematic review and meta-analysis of the effects of a fed-state on post-exercise metabolism and it was determined that eating in a fed state was more beneficial for longer forms of exercises, but not for workouts in shorter duration.

There are also different groups of people that can benefit from being in a fed state, from powerlifters and endurance athletes to an individual that exercises solely to round off a healthy lifestyle.

It also comes down to preference. Some people feel lightheaded when they workout fasted or feel that they don’t have enough energy to push through challenging workouts. If you enjoy eating before your workout, then keep doing you – BUT I have a hunch that because you’re already this deep in the article, you may be interested in testing out the fasted strategy. 

In sum, if you’re trying to optimize your performance for long workout durations, a fed state is probably the way to go. If you decide to go this route, then it’s important to understand and experiment with different pre-workout macro splits.

What to eat while in a fed state

When you exercise, your body uses glycogen as its main source of energy. Where do you get glucose from? Sweet, glorious, god-blessed carbs. Eating carbs pre-workout can help increase our glycogen stores and in turn provide us more sustained energy during our workouts. Carb-loading is a strategy that endurance athletes use repeatedly to help top off their glycogen stores before a big race. This involves eating a carb-rich diet for 1-7 days before race day.

But what about protein and fats? Are these macros essential for fueling our workouts as well? Consuming protein either by itself or with carbs has shown to help increase muscle protein synthesis. In the article, Pre-Workout Nutrition: What to Eat Before a Workout, several of the mentioned studies point to the conclusion that, “the benefits of eating protein before exercise include: a better anabolic response, or muscle growth, improved muscle recovery, increased strength and lean body mass, and increased muscle performance” 

If you’re planning prolonged exercise then your body switches to burning fat stores, so higher-fat foods might be a good choice for fuel. It could be beneficial for you to eat a pre-workout meal that includes a mix of carbs, protein, and fats, but it’s always good to go heavier on the carbs.

My Experience

I’ve been working out in a fed state for most of my life. Since I do workouts in the mornings, consuming breakfast pre-workout has become habitual for me. Up until last Spring (2019), I truly believed that if I didn’t consume food pre-workout, I would burn muscle. To be honest, I had a bit of a fixed mindset when it came to fasting vs. fed workouts. I knew about intermittent fasting (IF), but couldn’t allow myself to get on board with it. When I finally started to let go of my old routines and habits when it came to nutrition and training, I was able to welcome new information and try it out for myself. I saw transformative changes to my physique and energy levels. I’ll flesh this out a bit more in the following section, but let’s first get into the reasoning behind this choice.

Before I ate lighter meals or did my workouts in a fasted state, I would consume heavy pre-workout meals. My go-to was typically a bowl of oatmeal with greek yogurt, protein powder, nuts, and peanut butter (usually topping 600 calories). This carb-heavy breakfast would sit in my stomach for at least 1-2 hours, sometimes longer. Once I finally digested, I found my workouts to still be okay; not great, not even good, but just okay.  I did break this habit and started eating different foods, such as a bowl of oats  (less the nuts/nut butter) and protein powder which was closer to 250-300 calories, a pear/apple and a protein shake (water and whey isolate mixture), or just a banana. The lower calorie meals prior to workout were a significant help.

Even though I now do about 90% of my workouts fasted there are some cases where I will eat pre-workout or intra-workout (ie. long runs/ 13+ miles or on race day). If I don’t eat a lot the night before or wake up starving, I’ll also have a light snack before my workouts. For long runs, I need the fuel to help keep my energy levels stable and to avoid the dreaded “bonk”. I’ll also execute a carb-loading strategy the day before; consuming a carb-heavy diet to get my energy to peak levels and topping off my glycogen stores. During my run, I’ll consume nutrition in the form of gels, chews, stroopwaffels, or might pop into a grocery store to grab a banana.

Fasted Workouts

What is a fasted workout?

Although it may seem pretty self-explanatory, let’s first elucidate what a fasted state encompasses. Simply put, a fasted state is when your body hasn’t eaten for several hours (usually 8-12 hours), but with some people, that timeframe can be even more condensed. It really depends on how quickly your body can digest meals. The most common way to workout in a fasted state is first thing in the morning, when your last meal was the night prior and you can sleep off the ‘fed’ state. However, if you are a person that prefers working out in the afternoons or evening, it is still possible to workout fasted by allowing your body a certain gap in time from your last meal.

Benefits of fasted workouts

The first and most common benefit is that fasted workouts could potentially, burn more fat. In fact, several studies have shown that you can essentially burn up to 20% more fat working out in a fasted vs. non-fasted state. Depending on your meal the night before and how late you ate, you should have a bit of glycogen left in your body to use to fuel your morning workouts while also burning fat. Did you catch my tone of uncertainty in the first sentence? The reason being is if you’re only doing fasted workouts for the potential weight loss benefit, you might want to reevaluate your stance – especially if you find your workout difficult to get through without eating before-hand. Here’s why.

In fitness YouTuber Jeff Nippard’s video Does Fasted Cardio Burn More Fat? (What The Science Says), he explains, “just because you burn more fat during the cardio session itself, doesn’t imply that you will lose more fat overall”.

He goes on to explain the results of a study titled, Body composition changes associated with fasted versus non-fasted aerobic exercise, where 20 young women were put on a 500 calorie deficit per day diet over a 4 week period. The women were split into two groups: one group performed 1 hour of fasted cardio 3x per week and the other did 1 hour of cardio in a fed state. After 4 weeks, there was no fat loss difference between the groups, meaning they were equally effective. To summarize, even though it is well established in the scientific community that fat oxidation increases post-fasted cardio, over time, there doesn’t seem to be any particular differences in body composition.

However, it’s important to note that there isn’t conclusive evidence on shorter-term effects. Here’s the takeaway: if you only do fasted cardio for the potential weight loss benefits, it doesn’t seem to matter whether you’re fasted or fed so long as you’re in a calorie deficit at the end of the day.

Another perk of not eating before a workout is the whole issue surrounding digestion (as I previously mentioned).  It can be a lengthy process to not only digest your meal, but also be able to use that food for fuel. Your body is drawing blood to help with digestion vs. using that energy to kill your workouts. When working out fasted you can avoid the issue of how much to eat and how soon before a workout altogether.

Another popular reason to use a fasting strategy is performance-related. When you start working out fasted, you’re teaching your body to access different fuel sources. Instead of using sugar or glycogen, your body is tapping into your fat stores to use as energy. In the Evidence-Based Athlete’s article, Does Fasted Cardio Enhance Fat Loss?, Brandon writes:

Long term fasted cardio appears to lead to chronic molecular adaptations favoring fat oxidation. Mechanistically this implies that fasted training may help athletes like those that compete in endurance events since fat is an important fuel for those activities OR those that compete in a sport like CrossFit that requires some flexibility in fuel substrate utilization.

The preferential fuel substrate utilization may give endurance athletes more of an advantage in training or on race day.

Lastly, fasted cardio can help improve insulin sensitivity. Basically, the more your body operates in a fasted state, the less insulin your body releases. What does this mean? Well, in short, insulin can help you accumulate fat and high insulin levels are associated with diabetes. Brandon writes, “if you have blood sugar regulation issues including exercise-induced hypoglycemia, type 2 diabetes, pre-diabetes, etc. – this may very well help improve those conditions.” A quick disclaimer: this isn’t to be taken as medical guidance. Please educate yourself and consult an accredited professional.

If you’re new to the fasting game, a quick word of advice: like any adjustment to a new diet or training regimen, your body is going to need some time to adapt. For so many years, you’ve been eating before your workout so it’s going to be a bit of a shock to the system. When I got back on the fasting train after a long break, it took around 3 days of fasted workouts to get my body to adjust again. I found myself suffering energy-wise one day, and then experiencing severe hunger pains the next.

My Experience

After the end of a long relationship with a person I cared deeply about, I wanted a big change. My workouts felt monotonous; performing the same routine day in and day out. My diet was okay, but I was eating out a lot (as in visiting my favourite Indian restaurant about 3 times a week…yikes). I was also consuming alcohol too often and needed to cut it down.

That’s when I started researching everything I could on diet & nutrition. One of the first diets I wanted to try out was IF and specifically, doing my workouts (strength & cardio) in a fasted state. I read a library of articles on how fasted cardio can help you burn more fat.

I figured I had nothing to lose, so may as well give it a go. I started implementing new exercises I learned from YouTube and also doing my workouts in a fasted state. Within a month I started noticing material differences with my physique; specifically, more vascularity and leanness.

When I first jumped on the fasted workout train, I did suffer for more than 3 days (as I mentioned above). It actually took me a few weeks to fight through the hunger pangs and random bouts of low energy in my workouts, but slowly, my body acclimatized and I started to reap the many rewards of working out fasted.

My mind felt more alert and clear. I felt more energetic and didn’t have to wait around for my food to digest. I could just hop to it whenever I was ready to workout. Gone were the days that I would be able to feel the oats sloshing around in my stomach while I ran.

I leaned out and started to build muscle, letting go of the long-held belief that I would lose mass if I worked out in a fasted state. I also took Branched-Chain Amino Acids (BCCAs) pre & intra-workout which helps preserve muscle.

The fasting regimen isn’t perfect. There are days where it doesn’t work for me and I need to workout in a ‘fed’ state. I’m flexible and would recommend that you try to be as well. Basically, I’ve figured out a mental checklist of what needs to happen in order for me to have a successful fasted workout:

• Eat a good amount of carbs the night before (~50-75g). I usually eat my last meal around 8-8:30pm.
• In order to have enough glycogen to do my workouts with zest, I need to workout within 2 hours of waking up or I get too hungry and my workouts suffer.
• My workouts are under 2 hours (any more and I need to eat). These are for my regular workouts (strength/cardio). If I’m doing a run for 2 straight hours or longer, I’ll definitely need to consume some calories intra-workout.
• I curb my appetite in the AM with coffee and a mixture of BCAAs and creatine.
• My menstrual cycle fucks up everything so approximately a week before, I get very hungry. If I ignore my body’s signals, I’ll get bitchy, so I tailor my fasted workouts around my hormones.

When you shouldn’t workout in a fasted state

Like anything, there are of course some stipulations and some warnings that I would be remiss without mentioning.

If you’re a runner, then there’s the obvious (and dreaded) ‘bonk’ which basically means that your body has depleted its glycogen stores in its entirety and it’s now switched over to fat-burning mode. The ‘bonk” is also synonymous with ‘the wall’. If you haven’t experienced it yourself, every kilometer starts to feel like hell. In a marathon, this is typical ~the 30k mark, but it varies. If you’re planning to do a race or a long training run then do yourself a favor and eat beforehand. Also carry nutrition on you in the form of gels, chews, or whatever else you can squeeze into your belt or pockets.

Similar to the point above, if you’re trying to optimize performance, you might want to consider working in a ‘fed’ state to give your body the required energy to push through high intensity and tough workouts.

Then there’s the health perspective. In my article, My 2 Week 16:8 Intermittent Fasting Experiment, I outlined words of caution for particular groups of people: 

Pregnant or nursing mothers, the elderly with chronic conditions, children, those struggling with eating disorders, or individuals with either type 1 or type 2 diabetes need to be closely monitored when adopting an IF regimen.

I know I’m redundant, but need to stress the importance of doing your own research aside from this article.

Conclusion

In sum, both nutrition strategies can be applied depending on the type of workout you’re doing, your fitness goals, and also being cognizant of any existing health conditions you may have.

If you’re just doing fasted workouts for fat loss and suffering through your workouts due to lack of energy, you might want to rethink your approach. At the end of the day, it’s a calorie deficit over sustained periods that will really move the mark in your weight loss journey.

If you’re like me and have been working out in a fed state pretty much your entire life, I’d recommend slowly integrating fasted workouts (ie. a few times a week before making it a religious habit). 

Listening to your body is important. If I didn’t eat enough before or am feeling really hungry in the morning I will eat a snack before my regular workouts. I want to enjoy my runs and I know if I have low energy and severe hunger pangs, I’ll hate and suffer through them.

Overall, I think a flexible nutrition plan is the best kind and again, what works for some, may not work for others. Experiment for yourself, track your energy levels, and optimize, optimize, optimize. 

Additional Resources/Further Reading

Exercise Training and Fasting: Current Insights

Body composition changes associated with fasted versus non-fasted aerobic exercise

Exercise before breakfast increases 24-h fat oxidation in female subjects

Beneficial metabolic adaptations due to endurance exercise training in the fasted state