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's Fasted Training? Fed Training is what?
The first thing to do is understand Fed Training. 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. They can train in a fasted condition. 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. Is that a sign your client was correct? So, could fasting increase fat burning and, consequently, weight loss?
Here’s the fun part: Only half of the statement is true.
Fasted training is a great way to help clients burn fat faster than glucose. However, this doesn't necessarily mean that you can lose fat.
Studies support this assertion.
Research after research has shown that energy balance is the most important determinant for 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.”
It doesn't matter how many times your client fasts for that temporal rise in fat oxidation. They won't lose any weight if they eat in excess calories.
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. Now that is all clear.
However, what happens if your client wants to work out in a fast-paced environment? 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?
This could negatively affect their ability to exercise or hinder potential gains. Thankfully, it doesn’t appear to. Let’s explore in greater detail.
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. This could be something simple, such as an energy bar or protein shake.
Strength training is next.
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.
In a study of Muslim recreational bodybuilders, researchers compared the effects of fasted and fed resistance training. These were the results.
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.
Would fasted training hurt your client’s muscle gains? It is not.
See: The previous section has already established that fasted training doesn't appear to affect training volume. Based on this, it is clear that the key determinant for muscle hypertrophy and training volume are.
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.
- Fasted training does not appear to affect exercise performance or muscle growth.
So what does that mean? Meaning?
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. Because muscle mass burns more calories when it is active metabolically than fat, clients will have a harder time sticking to a diet. 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.
It is important to maintain a higher protein intake in the face of calorie shortages.
Hunger management is the first.
The most satisfying macronutrient is protein. That’s why studies have consistently found one thing: Higher protein intakes tend to provide more satiety and less hunger. Your client will find it invaluable when they have to maintain a strict diet.
Protein can also help preserve your client's lean mass when you are restricting calories.
One of the best studies that showcase this is a 2010 study published in Medicine & Science in Sports & Exercise. The effects of low-protein and high-protein diets on body mass were compared over short-term deficits in calories. 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.
This is a fivefold increase in muscle mass!
As mentioned, your goal is to keep your client's lean muscles mass intact in a low-calorie environment. You will need to remind them that they should eat sufficient protein every day.
The best way to get protein is from whole food sources. 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. It is not enough for your client to eat a high protein diet. You'll need to ensure that they are also participating in resistance training.
It's as simple as that.
The body receives the message that strength training has a positive effect on it: "Hey! I still need to have all these muscle mass in order to lift heavy things at the gym!" It's important to keep your client on track.
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. How can you make sure your client is working hard?
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.
It is important to remember that progressive overload does not mean adding weight on the 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.