G-Flux Redux: Explained

by Chris Shugart

An Interview with John Berardi, Ph.D.

How to flick the metabolic switch to get bigger, stronger, and leaner while eating more food than you do now.

This,” John Berardi told us a couple of years ago, “is 100 percent, without a doubt, absolutely critical to building your ultimate body.”

That certainly got our attention. What was he talking about? A new supplement? A new training program? Not really.

He was talking about energy flux, or energy turnover, known as G-Flux to the cool kids.

Why should you care? Because if you’re like most Testosterone readers, you’re always chasing one of two goals: You either want to build slabs of muscle without adding layers of fat, or you want to lose body fat rapidly without losing a lot of lean body mass.

If G-Flux can help you do both, then this is Holy Grail stuff. We talked to Dr. Berardi to get the scoop.

Q: John, you wrote about the idea of energy flux a while back here on Testosterone. For those who missed it, give us a quick and dirty explanation.

G-Flux represents the relationship between the amount of energy you ingest through your diet and the amount of energy you burn through the sum total of your metabolic activity.

Q: So, the old energy-in vs. energy-out thing? And by “energy” we mean calories?

Exactly. However, the idea of G-Flux goes one step beyond. You see, in the old model of calories-in vs. calories-out, the discussion revolved around energy deficit vs. energy surplus. So, you’d tally up your input and output and you’d come up with a number.

However, with G-Flux, physiology can be profoundly changed – regardless of the energy-balance state or that input-output number.

For example, if I were eating 2,000 calories a day and burning 2,500 a day, I’d be in a negative energy balance of 500 calories. And you’d expect me to lose weight.

But if I bumped up my G-Flux by boosting my intake to 3,000 calories, and my expenditure to 3,500, my calorie deficit would be the same. So you’d expect my physique to be in the same state as in the former situation. And a classically trained dietitian would suggest that there’s no difference between the two.

However, the research paints a different picture. This boost in G-Flux would most likely lead to an increase in lean mass, a decrease in fat mass, and an increase in metabolic rate.

Q: And who doesn’t want that? So what happens if you go the other way with lower calories?

That’s a great question. Basically, the reverse happens. If you’re “fluxing” at 3,000 and 3,500 calories, and you drop down to 2,000 and 2,500 calories, you’d likely carry less lean mass and more fat mass, and your metabolic rate would drop.

You’d still lose fat, mind you. But the whole point of G-Flux is that you gain a greater control of your body and force it to carry more muscle mass and less fat mass at any given energy-balance point.

Q: This is a cool theory. Any research to back it up yet?

Absolutely. Here are a couple of studies that people can start with.

  1. Goran MI et al. Effects of increased energy intake and/or physical activity on energy expenditure in young healthy men. J Appl Physiol. 1994 Jul;77(1):366-72.
  2. Bullough RC et al. Interaction of acute changes in exercise energy expenditure and energy intake on resting metabolic rate. Am J Clin Nutr. 1995 Mar;61(3):473-81.
  3. Bell C et al. High energy flux mediates the tonically augmented beta-adrenergic support of resting metabolic rate in habitually exercising older adults. J Clin Endocrinol Metab. 2004 Jul;89(7):3573-8.

But beyond the research, there are more real-world examples than you can count. Many of the Olympic athletes I work with, specifically the strength and power athletes, train between 15 and 20 hours a week while eating a huge caloric load. They carry lots of muscle mass with minimal body fat – most of that muscle built with their high-G-Flux training plans.

Q: And how about physique athletes?

They’ve used the G-Flux principles for decades to prepare for bodybuilding, fitness, and figure contests. If you watch how they prepare for shows, they typically increase both exercise volume and food intake anywhere from 10 to 16 weeks out from a contest. Of course, with physique competitors, the calories eventually drop as they get very lean and close to the event. But their first step is to increase G-Flux.

So this isn’t just some dry laboratory thing. It’s what the best athletes on the planet are doing to look the way they do.

Q: Okay, say a guy is eating 1,800 calories a day in an effort to get lean. His fat loss stops. His instinct is to lower calories more. What does G-Flux tell us?

Well, for starters that doesn’t seem like much food to me. To be quite honest, there aren’t many scenarios where a guy should be eating 1,800 calories a day.

If he’s below average height, 150 to 160 pounds, and is trying to get ready for a bodybuilding contest or photo shoot, okay. But if he’s larger and is “stalling out” at 1,800 calories a day, he clearly doesn’t get the G-Flux picture. If he did, he’d realize he needs to be exercising way more so that he can successfully lose fat at higher calorie intakes.

And trust me, it’s very possible. I have 105-pound figure girls (drug-free, mind you) who are still losing fat on 1,800 calories a day. They’re simply exercising enough to ensure fat loss at this intake level.

Q: Okay, so what exactly is G-Flux doing for us?

Physiologically, it’s better to exercise as much as you can while eating as much as possible – as long as you’re gaining muscle and losing fat – than the reverse.

Why? Well, on the exercise end, increased exercise volume and frequency means improved nutrient partitioning – more calories go toward muscle growth and/or energy provision and fewer to fat cells. It means better insulin sensitivity. It also means additional opportunity to stimulate protein turnover, tissue remodeling, and positive adaptation.

And on the food end, more calories mean sustained sympathetic nervous system activity, maintained metabolic rates, and, perhaps most important to the entire process, better vitamin, mineral, and antioxidant status.

When we don’t exercise enough, our energy intakes necessarily have to be lower so we don’t OD on calories. And when we don’t eat enough high-quality food, we end up with deficiencies in vitamins, minerals, and phytonutrients.

Sure, we’re not talking scurvy and rickets here. However, subclinical deficiencies mean suboptimal function, including slower metabolic rates, big food cravings, poor digestion, cranky moods, declining health, increased risk of disease, and poor exercise intensity and quality.

Not good for losing fat. Not good for health. Not good for lean mass preservation, or for sticking to your plan.

So, when we’re talking about a fat-loss diet, the best prescription is to eat as much food as we can get away with while still losing fat. How’s that possible? Easy. Exercise more.

Q: So back to our example of the guy whose fat loss is stalled out. He should just exercise more?

Generally, the best fat-loss approach is this one:

First, be sure you’re eating enough nutrient-rich food to begin with. Typically 12 to 18 calories per pound of body weight is in the ballpark of where you should begin a fat-loss plan. If you’re not doing this, this is where you start. Spend a few weeks eating a high-quality, sufficient-calorie diet.

Also be sure you’re exercising about five hours a week to begin with. If not, when it’s time to start losing fat, begin by getting your exercise volume up to five hours per week.

Follow the plan above. If progress stalls out for more than a week, it’s time to drop the calories a bit. Taking them down by about 10 to 15 percent will do the trick to get your progress kick-started again.

Next, if progress stalls out for more than a week, it’s time to up the exercise once again. Add 1.5 to 2 hours per week and your body fat will get moving.

If progress stalls again, drop the calories once more. This time take them down another 10 to 15 percent. If progress stalls after that, it’s time to take the exercise up once again. Another 1.5 to 2 hours should do the trick.

Now, keep in mind that these numbers are guidelines. They’re not set in stone. The point is to follow a logical progression of first adding exercise, then dropping your food portions, if necessary. And that fits in with G-Flux perfectly. Remember, it’s optimal to lose fat with the highest possible food intake.

Also keep in mind that typically, even in the case of physique athletes preparing for shows, it’s usually not necessarily to go above 10 to 12 hours of exercise per week. So don’t go too nuts with the progression.

Bottom line: If you’re going for the ultimate level of leanness and are doing 10 to 12 hours of exercise per week while having dropped your calories by 20 to 30 percent below “maintenance,” you should be losing fat. If not, you either weigh 100 pounds, you’re doing something wrong, or you need to get a full medical work-up to look at your digestive, absorptive, metabolic, and hormonal health.

Q: Cool. Now let’s take a deeper look at mass plans. The idea is to eat more than maintenance calories and build a lot of muscle. The problem with many people: excess fat gain, leading to freak-out. What does an energy-flux plan offer us here?

Oh, that’s simple. By up-regulating G-Flux, you can gain more muscle mass without that excess fat gain. Now, it’d be silly to say no fat gain. Because some fat is usually gained when people are expressly trying to gain mass. But this amount of fat gain can be managed, and it takes more exercise and more food to do so.

Of course, the food and exercise selections aren’t arbitrary. This is the biggest mistake I see people making. They hear about G-Flux and just randomly crank the exercise volume while stuffing their faces.

The training program has to be solid and the food intake has to be high, but not so high that you’re packing on a bunch of fat. Of course, it’s harder to overeat on a higher-volume, properly designed training plan. But yes, it’s still possible to gain too much fat even if your exercise volume is very high.

Q: Most people’s take-home message with G-Flux is, “Eat a lot, train a lot.” Then they say, “Yeah, no shit. I already knew that.”

That’s not an appropriate take-home message. G-Flux is all about training more, as long as your program is properly planned, and eating more, assuming a nutrition plan that’s well-designed. It’s really pretty simple.

Of course, the caveats here are the most important part. The training has to be good and so does the diet. However, most people, even Testosterone readers, still struggle with both. So it’s simple and not simple at the same time.

As far as the “already knew it” part, sure, most exercisers sorta already know this. However, knowing and doing are two completely different things.

So if you’re not really applying the principles of G-Flux to your plan, then “already knowing it” is pretty useless to you, isn’t it? And I’d wager that most people simply aren’t maximizing their G-Flux.

Q: But what about the people who say, “Yeah, cool plan, but I don’t have time to train that much”?

If someone has that attitude, there’s not much convincing I can or am willing to do.

Q: Fair enough. Now, just so readers can get their heads around this amount of exercise and the type of exercise, can you give us a sample week?

The real key here is to make sure you’re training a mixture of muscle qualities. I’m not talking about five-plus hours per week of strictly bodybuilding-style training, strictly strength sessions, or strictly conditioning sessions.

Instead, I’m talking about training in a very similar way to my Olympic-level athletes, albeit lower in volume and without the sport-specific training and practice. This means some weight training for strength, some weight training for power, some sprints and/or conditioning work, and some low-intensity recovery work.

Here’s an example of the type of program I’d build for someone who wanted to get bigger and stronger while improving body composition.

Day 1: (1 hour)
Dynamic warm-up
Lower-body-dominant max-strength workout

Day 2: (1 hour)
Dynamic warm-up
Upper-body-dominant power workout

Day 3 (0.5-1 hour)
Low-intensity recovery workout
For example: yoga, Pilates, hiking, walking, bike riding, etc.

Day 4: (1 hour)
Dynamic warm-up
Upper-body-dominant strength workout

Day 5: (1 hour)
Dynamic warm-up
Lower-body-dominant power workout

Day 6: (0.5-1 hour)
Total-body conditioning workout
For example: interval circuits with body-weight exercises, kettlebell exercises, med-ball exercises, tire flipping, sled dragging, etc.

Day 7: Rest/recovery

If you’re doing far less exercise than this right now, you’ll want to build up to this volume slowly. Further, within this template, you’d want to periodize your volume. For example, week one might be a medium-volume week, week two a high-volume week, week three a low-volume week, and week four a very high-volume week. Then, during week five you might start this cycle over with a new set of exercises.

And here’s another example. This time, it’s the type of program I’d build for someone who wanted primarily to get leaner while preserving muscle mass, or even adding a little.

Day 1: (1 hour)
Dynamic warm-up
Full-body-circuit conditioning workout
For example: interval circuits with body-weight exercises, kettlebell exercises, med-ball exercises, tire flipping, sled dragging, etc.

Day 2: (1 hour)
Dynamic warm-up
Lower-body weight training

Day 3: (1 hour)
Low-intensity recovery workout
For example: yoga, Pilates, hiking, walking, bike riding, etc.

Day 4: (1 hour)
Dynamic warm-up
Full-body-circuit conditioning workout
For example: interval circuits with body-weight exercises, kettlebell exercises, med-ball exercises, tire flipping, sled dragging, etc.

Day 5: (1 hour)
Dynamic warm-up
Upper-body weight training

Day 6: (1 hour)
For example: 100-meter repeats, 200-meter repeats, etc.

Day 7: (1 hour)
Low-intensity recovery workout
For example: yoga, Pilates, hiking, walking, bike riding, etc.

Again, as above, if you’re doing far less than this, you’ll want to build up slowly. Further, remember to periodize your volume with successive weeks.

Q: How do you respond to those who worry about overtraining?

Overtraining is a very real phenomenon, although I guarantee that most people reading this have never been overtrained. I bet they’ve never even met someone who’s legitimately overtrained!

I’ve worked with Olympic athletes in a dozen different sports. And I’ve worked with physique athletes in bodybuilding, fitness, and figure. In fact, the number of athletes I’ve directly assessed or created programming for probably exceeds a thousand. And in all of these, I’ve not seen more than two cases of what’s known as “overtraining syndrome.”

CNS fatigue, on the other hand, is something that I see more trainees suffering from – both elite athletes and recreational types. So this can very well become an issue with high levels of G-Flux if someone isn’t careful. But it’s not G-Flux, per se, that’s the problem. It’s doing too much CNS-demanding exercise with too little active recovery. With this said, avoiding CNS fatigue is pretty easy.

The first way is commonsensical: Build up your exercise volume over time. None of my elite athletes start training 15 to 20 hours overnight. They increase volume progressively over time. That way, your work tolerance can keep pace with your workload.

The second way is to periodize your training, something very, very few coaches do well. Testosterone contributor Eric Cressey is one of the best. Observing how he uses periodization has taught me a lot about preventing fatigue and overtraining. His programs undulate in terms of volume and intensity within a given week as well as between weeks. Interestingly enough, if you do this properly, you’ll rarely need time off from the gym.

The final way is to properly mix training modalities. For example, when some low-intensity work is thrown into the mix, CNS recovery is much improved. This is because high-intensity work stimulates the sympathetic nervous system (fight or flight), while low-intensity work stimulates the parasympathetic nervous system (rest and digest). The balance between these two types of exercise is important, as originally proposed by Hans Selye in the 1950s. It’s sort of a yin-and-yang thing.

Q: Okay, so let’s say we increase our training – and we do it right. Next we’ve got to eat more. We have to be careful when we tell people to eat more, right?

You bet. When we’re talking big-time fat loss, you still have to eat pretty clean if you want to see all six abs, regardless of the faster metabolism and improved nutrient partitioning.

However, when we talk mass gain or body recomposition in general, the interesting thing is that when G-Flux is high, it’s actually way harder to overeat to the point of fat gain. So the body is much more forgiving of dietary indiscretion.

Of course, that doesn’t mean you’ve got carte blanche at Mickey D’s. But it does mean that you don’t have to obsess about every food selection or calorie count. Here, following the “10 Habits” outlined in my Precision Nutrition System is a perfect start. In summary, they are:

  1. Eat every 2 to 4 hours
  2. Eat lean, complete protein with each feeding
  3. Eat fruits and/or veggies with each feeding, for a total of around 10 servings per day
  4. Based on your body type and goals, use appropriate carbohydrate timing
  5. Eat a healthy balance of fats, about one-third of each type (saturates, monos, and polys)
  6. Ditch most calorie-containing drinks like soda and fruit juices
  7. Focus on whole, unprocessed foods first
  8. Eat whatever else you want 10 percent of the time
  9. In most cases, prepare/pack your food in advance
  10. Incorporate lots of variety; don’t fall into a food rut

Q: Okay, all very cool-sounding, but how about an example of someone who’s G-Fluxed his or her way to a better body?

These people aren’t hard to find. In my original G-Flux article I profiled five of them. One recent example of a client I helped is Amanda Graydon. Amanda started out fit, strong, and healthy. Yet she always wondered what it would be like to take her body to the proverbial “next level.” Here’s what she looked like in her “before” pictures:

And here’s what she looked like after 10 weeks of G-Flux training and Precision Nutrition eating:

Finally, here’s what I look like standing next to this little hottie:


Q: Okay, don’t rub it in, Berardi! Got any other examples?

Yep, here’s a cool one – Greg. At his heaviest he was close to 300 pounds, as seen below.


He lost 100 pounds and spent a few years yo-yo dieting between 190 and 230. Then he had health problems that dropped his weight to a cadaver-like 165, and then a very over-fat 240.

When Greg began using the principles of G-Flux, he upped his exercise volume quite a bit while boosting his calorie intake. And within the next few months he dropped from 219 at 18 percent body fat to 178 at around 8 percent, as you can see below.


Even better is this: After reaching his goal and losing about 40 pounds of body weight, mostly fat, he decided to G-Flux his way to increased muscle mass. In the next two months he gained about five pounds while dropping his body-fat percentage.


Q: Okay, so let’s say you’ve convinced the person reading this to give G-Flux a go. What’s his first step? Does he need to keep a food log and figure out where he is now in terms of calories per day, or what?

For most people, a food log and calorie counting aren’t required. There are only two variables to control here – calorie intake and expenditure – and expenditure is the driver.

So the best first step is to increase your training volume to about five hours per week. Ease your way into it, and make sure your program includes a mixture of high-intensity and recovery activities.

Once this is in place, make sure you’re eating the right foods at the right times. Most want to start counting calories here, but with a high level of G-Flux, you probably don’t need to count to be lean and muscular. Instead, spend your time on figuring out how to implement the 10 habits.

Next, based on your goals and on how your body is changing, you’ll start adjusting the exercise volume and your food intake. If you want to gain muscle mass and strength while improving body comp, you might be fine at 5 to 6 hours of exercise per week.

However, if you want to get aggressive with the fat loss, you might need to work your way up to 7 to 9 hours per week while continuing to tweak the amount of food you’re eating.

Q: Cool stuff, as always. Blatant plug time: Where can Testosterone readers go to get more info on this?

I highly recommend picking up a copy of the Precision Nutrition System. It includes seven guidebooks and a gourmet cookbook.

The principles of G-Flux are built into the Precision Nutrition System, so not only will readers get a greater appreciation for G-Flux, they’ll be able to figure out the optimal diet for them as well.

Q: Thanks for the interview, Dr. Berardi!