… And what to do instead

Most of my clients have weight loss goals. Many of them come to me hoping to be shown the perfect fat-burning diet, the personal-trainer-approved fat-blasting workout plan, and the secret of faster, more effective fat loss.

So they are often surprised when we lock horns over a simple topic: fueling workouts.

Fuel your workouts, please.

Despite articles from mainstream magazines like this one and this one, which do a great job of presenting the pros and cons, fasted workouts linger in the collective imagination as a panacea for fat loss. It doesn’t help that celebrities continue to promote fasted workouts (and fasting in general) as one of the “secrets” of their physiques on social media.

(Because we all know the best place to go for nutrition advice is IG celebrity accounts)

Fasted exercise is also appealing to many of my clients for more practical reasons, too, like…

  • Exercising early in the morning (because, you know, jobs and families and stuff!)
  • Not being in the habit of eating before exercise
  • Not feeling like eating before exercise

But fasted exercise can be problematic. And this is why I pester my clients to fuel workouts well, and will continue to bang my fueling drum until they start actually doing it.

The reality is that fasted exercise sometimes offers specific benefits to specific populations (primarily for certain types of exercise), and it’s not necessarily helpful for fat loss or physique change for non-athletes. In fact, it may hinder the results you really want!

In today’s blog post, I’m going to break down why.

(And if you’re one of my clients reading this, this is why I have been bugging you.)

We’re going to cover why fasted exercise can…

  • Raise your body’s stress levels, inhibiting your metabolism
  • Prevent muscle gain (and thus body composition change)
  • Slow down your exercise progress
  • Hurt your mindset

… in four principles that I’ll explore in detail.

In my next post, we’re also going to discuss some very simple solutions to fueling smarter – when and how to do it, what kinds of foods work best, and how to hack that early morning workout without digestive distress.

Let’s dive in!

Principle #1: Get the most bang for your buck

When people get too literal about fat burning, they hear that fasted exercise can burn proportionately more fat than “fueled” exercise (which is true). Then it’s easy to jump onto the fasted exercise bandwagon.

The problem is that this fat-burning edge is extremely marginal.

The two populations who benefit most from fasted exercise are (1) extraordinarily lean people who are targeting the last of the last spots of stubborn fat (for example, a female bikini competitor who is trying to tackle a tiny bit of fat on her thighs), and (2) endurance athletes who are training their bodies to utilize more fat for energy so that they can go the distance more efficiently. And even for these two populations, fasted exercise isn’t always the solution, and in any case, the exercise in question is usually lower-intensity cardio.

For people who are already 1%-ers, marginal is worth it. If you’re trying to go from 13% body fat to 12% body fat, or squeak a few seconds off your ultra-marathon time, you’re going to try almost anything that could help.

But when we’re talking about an average person, even a fit average person, marginal is usually not worth it – especially when the big-picture negatives can outweigh the minor positives. Instead, we want to make lifestyle changes that have the biggest bang for the buck.

Takeaway: Fasted cardio is not going to make that big of a difference for most people for fat loss.

Principle #2: Don’t unnecessarily increase stress

Exercise is a natural stressor. Exercise causes us to push ourselves and adapt to new levels of physical challenge – the result is that we get faster, stronger, and more tolerant of physical “stress” like heavy weights or a long workout session. Most of us are aware of this to some degree.

But what many people don’t realize about stress is that as our liver depletes glycogen overnight, our level of cortisol (a “stress” hormone) naturally rises in the wee morning hours. Cortisol isn’t a “bad” hormone – it’s part of what governs our circadian rhythm, waking us up in the morning and making us more alert.

But when you combine a naturally high level of cortisol and also try to do a good workout in a high-cortisol state without food… you are, ironically, not predisposing yourself to lose fat.

This is because even though, yes, fasted exercise uses more fat for fuel than “fed” exercise, it might not burn as many calories overall (which is critical for actual physical fat loss). This is because…

  • Elevated cortisol cautiously suppresses metabolic rate until we eat again (because your body is trying to be more conservative with energy expenditure until you can replenish glycogen)
  • This causes us to burn fewer calories from the workout overall, and afterwards
  • The lack of incoming food causes the body to use amino acids (i.e., protein and muscle!) for fuel along with fat… not good for body composition!

The easy way to get around this is to simply eat protein and/or carbohydrates before working out (we’ll get into more specifics later in my next blog post). This allows cortisol to drop naturally, your metabolic rate to bump up, your nutrition to fuel your workout, and your body to protect muscle.

Takeaway: A little bit of food prior to exercise mitigates the stress of exercise, allowing your body to get a better workout, actually burn more calories during and after, and protect muscle and body composition.

Principle #3: Prioritize fitness and body composition, not just “fat burn”

I alluded earlier to people getting “too literal about fat burning.” This is a real problem, because not only does it fuel our cultural obsession with being as thin and small as possible (especially for women), but it also short-circuits what could be a genuine change in physique.

This is because most people misunderstand how “fat burn” or “fat metabolism” actually behaves.

When a study or article says that a specific type of exercise helps to burn more fat, it doesn’t necessarily literally mean that you’ll lose more fat in a way that changes your appearance. It just means that you’re, proportionately, using more fat for energy than glycogen – but using more fat doesn’t mean you’re losing more fat, especially if it’s low-intensity exercise, because you may not have as big an energy output overall… which is ultimately what matters for fat loss.

I’m all for low-intensity exercise (my clients know I encourage a robust walking habit and am a fan of walking desks). But I’m also a huge proponent of truly changing your fitness and your physique – not just losing weight. And part of that process absolutely has got to be gaining muscle.

Muscle is extremely metabolically active. That means that when you put on muscle, you are actually raising your resting metabolism and making each workout more impactful. You are making yourself more likely to lose fat over time.

Gaining muscle, improving exercise performance, and healthy weight management all go hand in hand.

So where does fasted exercise come in?

Two of the reasons I don’t love fasted exercise is that it is not possible to deliver as high an energy/power output when you’re exercising without fuel, and it is also more likely that you will break down muscle for fuel. So the workout might feel really hard, but you’re not actually working as hard as you could.

Over time, you simply won’t make as much progress with your workouts (and… not to ride too hard on calories, but you also won’t burn as many calories during and after workouts). Strength will plateau, and you’ll miss out on the benefits that solid training will have on your physique.

Takeaway: even for non-athletes who are focusing on fat loss, exercise performance and muscle gain improve metabolism, and fueling these goals should be a huge priority on a fat loss journey.

Principle #4: Embrace fueling yourself

Finally, another reason I don’t love fasted cardio is that it perpetuates the “less is more” approach to weight loss that has created a lifetime of yo-yo dieting for so many people.

For most people, there are low-hanging fruits of diet improvement just waiting to be picked… and “hacks” like fasting distract from these easy lifestyle changes. Simple habit tweaks that start at the grocery store can be punted aside in favor of “fat burning tricks” like fasted cardio.

While exercise helps people maintain a leaner body composition (and especially helps with weight management after weight loss), weight loss is not a calories-in-calories-out game of doing enough exercise to burn fat. The problem is that it’s easy to follow mental logic that doesn’t apply to the way your body actually works. If you think, “I’ll just eat less and exercise more,” you may miss some of the nuances of weight loss… like the fact that your body depresses metabolism when it senses that it’s being stressed out and insufficient calories are coming in.

Plus, any kind of fasting can be an eating disorder trigger for people who have struggled. If you’re recovering from an eating disorder, or simply know that you’ve had disordered eating chapters in your life… fasted exercise is probably not for you. Rigid rules that encourage you to to get into a “less is more” mindset aren’t compatible with recovery.

If you really want to lose weight and keep it off (even if it’s just a little bit to improve body composition), you’re playing the long game. You have to take good care of your body. You have to fuel yourself to make real change.

Takeaway: Self-care has to replace self-hatred in order for real progress to happen. And part of self-care is fueling yourself, even if you look at yourself and see excess body fat that you’d like to lose. Your body still deserves to be fueled and will benefit from being fueled for exercise. In the long run, this will help you with your weight loss journey or physique transformation journey.

In my next blog post, I’m going to share some practical tips for fueling workouts – even if you wake up early in the morning or don’t feel like eating!

Rachel Trotta

I am a Certified Personal Trainer, Fitness Nutrition Specialist, Physique and Bodybuilding Specialist, and Women's Fitness Specialist. I live in New Jersey in the NYC metro area, and I coach clients online all over the world. As a trainer and health writer, my mission is to make healthy living sustainable for the average person. I’m also a wife, mom, nature lover, runner, avid cook, weightlifting aficionado, history nerd, travel addict, and obsessive podcast listener. Get in touch!

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