Fitness, Personal Training, & Exercise Science

Fasted vs. Fed Training: Which Benefits Your Clients More?

June 15, 2023

Here’s a summary of the most crucial things to know about fasted vs. fed training—including definitions, advantages and disadvantages, and how to know when to use what for your client—so you can better coach your client through their weight loss journey.

What Is Fasted Training? What about Fed Training?

First things first. Let’s understand the differences between “fasted” and “fed” training:

  • Fasted training: Refers to when your client trains on an empty stomach. But what’s an empty stomach? Well, research on the topic suggests that your client would be training “fasted” if they haven’t eaten anything 4-6 hours before working out.
  • Fed training: It’s pretty much what it sounds like; this is when your client trains after eating (fewer than four hours beforehand). 

Fasted Training Does Not Burn More Fat

With this in mind, your client’s belief that training fasted would lead to better weight loss results doesn’t appear so far-fetched anymore.

When your client is in a fed state, their blood glucose will be high—so their body prioritizes the use of glucose for fuel when exercising. But when they’re in a fasted state? Since blood glucose levels are tightly regulated, training in a fasted state essentially “forces” your client’s body to burn fat in a desperate bid to preserve muscle and liver glycogen levels.

Wait a minute. Does that mean your client was right? In other words: Could training in a fasted state increase fat-burning and, subsequently, speed up weight loss?

Here’s the fun part: Only half of the statement is true.

Yes, fasted training does indeed help your client burn more fat during the session since it’s the next best fuel source after glucose (which the body doesn’t have). But that doesn’t mean anything for fat loss.

At the end of the day, calorie balance determines if your client loses—or gains—weight. Just because your client burns more fat as fuel doesn’t mean they’re in a calorie deficit.

Research agrees.

Study after study proves that energy balance is the ultimate determinant of weight. Take, for instance, this 2017 meta-analysis published in the Journal of Functional Morphology and Kinesiology.

After analyzing five studies that compared fasted to fed training, researchers concluded that “weight loss and fat loss from exercise is more likely enhanced through creating a meaningful calorie deficit over a period of time, rather than exercising in fasted or fed states.”

Bottom line?

No matter how frequently your client trains fasted for that temporal increase in fat oxidation, they won’t lose weight as long as they’re still eating in a calorie surplus. 

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That Said, Fasted Training Isn’t Harmful

Having your client train in a fasted state wouldn’t help them lose weight faster than if you were to get them to eat something before exercising. That much is clear now.

But what if your client prefers to train in a fasted state? Or, what if they run on an extremely tight schedule—and can’t squeeze in time for a bite before turning up for their gym session?

Would this negatively impact their exercise performance or potential muscle gains? Thankfully, it doesn’t appear to. Let’s explore in greater detail.

Exercise Performance

Since the energy pathways for aerobic and anaerobic exercise differ, let’s explore how fasted training affects cardio and strength training performance separately.

So, first up: cardio. This one’s going to be pretty straightforward.

According to a 2018 meta-analysis that looked at twenty-three studies on fed vs. fasted cardio, researchers found no difference in exercise performance when workouts lasted less than an hour.

Note: While rare, if your client is doing cardio sessions longer than an hour, you should advise them to get some food into their system before working out for optimal performance. It could be something quick, like a protein shake or energy bar.

Next, strength training.

One of the most convincing pieces of evidence that fasted training doesn’t negatively impact resistance training exercise is this 2013 study published in the Journal of the International Society of Sports Nutrition.

Researchers looked at the effect of fed vs. fasted resistance training during Ramadan (Note: The participants involved fasted for about fifteen to sixteen hours before training) in Muslim recreational bodybuilders. The findings?

Both groups—i.e., fed and fasted—maintained the same training volume and reported similar levels in rates of perceived exertion!

To further convince your client: Several other studies have found that various strength training performance indicators (e.g., 1 RM strength) can be maintained even when muscle glycogen stores are low.

Muscle Loss

Would fasted training hurt your client’s muscle gains? The answer is no.

See: The previous section has already established that fasted training doesn’t appear to affect training volume. Building upon that, we know that training volume is the critical determinant of muscle hypertrophy.

Thus, it’s safe to say (based on the scientific literature currently available) that your client wouldn’t be sacrificing muscle gains by exercising on an empty stomach. 

Another 2012 study also shows that participants who engaged in fasted cardio (vs. fed cardio) didn’t lose any muscle mass by the end of the study period.

Educate Your Client on What to Prioritize for Weight Loss Instead

Putting this all together, you have to make the following two points exceedingly clear for your client when explaining the differences between fasted vs. fed training:

  • Fasted training doesn’t lead to better weight loss results.
  • That said, fasted training doesn’t appear to hurt neither exercise performance nor muscle growth.

Meaning? The decision on whether they should be training in a fasted or fed state is ultimately up to them.

You can also take the chance to educate your client on “weight loss fundamentals.”

This is an opportunity to tell them that instead of fixating on whether they should be training in a fasted vs. fed state for better weight loss results, they should be focusing on making sustainable lifestyle changes that’ll help them stick to a calorie deficit.

And for that, they’ll need to be mindful of the following.

Create a Reasonable Calorie Deficit

While eating in a calorie deficit is non-negotiable for weight loss, make it clear to your client that it isn’t the larger the deficit, the better. Cutting out too many calories too soon (more than 500 calories) is harmful for two reasons:

  •   Typically involves eliminating foods from the diet: With so many calories to cut, your client would more likely than not be tempted to eliminate whole foods (or even food groups, like carbohydrates) from their diet. That doesn’t bode well. Dieting in an unsustainable way—i.e., eliminating foods from the diet—has been correlated with less dieting success and, in turn, less weight loss.
  •   Risks muscle mass loss: The greater your client’s calorie deficit, the greater their risk of losing precious muscle mass. Since muscle mass is metabolically more active (i.e., burns more calories at rest) than fat mass, your client would end up finding it even more challenging to stick to a calorie deficit. Worse still, a loss of muscle mass also appears to dysregulate hunger and appetite. So it’s a double-whammy; your client gets hungrier—and yet, less satisfied during meals!

Eating Enough Protein

When your client is eating in a calorie deficit, one of the most important things you should do is ensure they’re eating enough protein. The general recommendation for protein intake is anywhere between 0.73 to 1 gram per pound (or 1.6 to 2.2 grams per kg) of body weight.

Maintaining a higher intake of protein throughout a calorie deficit helps with two things.

The first is hunger management.

Protein is one of the most satiating macronutrients around. That’s why studies have consistently found one thing: Higher protein intakes tend to provide more satiety and less hunger. Undeniably useful for when your client has to stick to a calorie deficit.

Plus, protein intake also helps preserve precious lean mass during periods of calorie restriction!

One of the best studies that showcase this is a 2010 study published in Medicine & Science in Sports & Exercise. Researchers compared low-protein intake and high-protein intake’s impact on lean body mass over a short-term calorie deficit. Here are the findings:

  •   Low-protein intake group (1 gram per kg per day): Participants lost about 3.5 pounds (1.6 kg) of muscle mass.
  •   High-protein intake group (2.3 gram per kg per day): Participants only lost 0.66 pounds (0.3 kg) of muscle mass.

A more than five-fold difference!

And, as mentioned earlier, since your priority is to help your client preserve lean muscle mass in a calorie deficit, you’ll need to remind them to eat enough protein throughout the day.

Of course, sourcing protein from whole foods is ideal. For most clients, though, that isn’t always achievable. So let your client know that it’s also okay to supplement their protein intake with protein shakes and bars.

Training Hard in the Gym

Here’s the thing. Having your client eat a high-protein diet (alone) isn’t enough to preserve muscle in a calorie deficit. Instead, you’ll have to make sure they’re also keeping up with their resistance training sessions.

Think about it this way.

Strength training sends a clear signal to your client’s body: “Hey, I still need all this muscle mass to lift heavy stuff in the gym! So, you better hold on to it.”

Without the stimulus of resistance training, your client could eat 3 grams of protein per kg of body weight (Note: they shouldn’t)—and still lose muscle mass in a calorie deficit. So, how can you ensure that your client is training hard enough?

An easy strength and conditioning principle to leverage is something called “progressive overload.”

This is where you increase the demands on your client’s neuromuscular systems over time to create and sustain physiological adaptations from resistance training.

An important thing to note: Progressive overload isn’t all about pushing additional weights on your client. Maintaining their training volume as they’re losing weight—which they should be since they’re in a calorie deficit—can also be considered progressive overload.

That’s because their “load lifted to lean mass ratio” would have increased.

Of course, there are other “creative” ways to incorporate progressive overload into your client’s training plan, too. Good examples include changing up your client’s tempo and programming shorter rest periods.

Fasted vs. Fed Training: Let Your Client Choose

While the idea of burning more fat is enticing, choosing between fasted and fed training doesn’t matter as much as your client thinks. What you could do is share with them about how weight loss actually works—and have them focus on what really matters: sustainable lifestyle changes.

And if you’re interested in specializing in weight loss management as a personal trainer, be sure to check out this comprehensive course.

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