Nutrition for Athletes: John Nelson and Mandy Macri

Based on Episode 59 of the Just Fly Performance Podcast, a conversation between host Joel Smith and John Nelson and Mandy Macri of Elite Level Performance.

Good nutrition for athletes is not really about the meal plan; it is about what the body actually processes from that plan. That is the argument John Nelson and Mandy Macri make from their gym, Elite Level Performance in Collierville, Tennessee, where they pair muscle testing and neurology with a hands-on nutritional assessment. Their favorite example is protein: a young athlete can pour down shakes and still test with a system that cannot break the protein down or clear it out, so the effort never reaches the muscle. Nelson reads the body through movement and manual muscle testing; Macri reads it through a urine and saliva sample that scores how efficiently the athlete turns food into usable energy. Put together, they treat nutrition as a performance variable you can measure, not a guess.

Key Takeaways

• Treat nutrition as a function problem, not a food problem. Macri scores the body on energy in versus energy out, so the question is not just what an athlete eats but how well the body assimilates and clears it.
• Eating protein is not the same as absorbing it. An athlete can chug protein and still show an overload in the kidneys, which means the fix is digestion, not more powder.
• Sugar and electrolyte overload can shut an athlete down. The kids who struggle come back high in sugar and salts, and that overload tracks with fatigue, poor recovery, and muscles that will not fire.
• A nutrition problem can surface as a failed muscle test. When Nelson finds a muscle or reflex point chronically failing, he reads it as an internal flag and sends the athlete to Macri for testing.
• The tools are cheap and simple. A urine and saliva sample, a roll of pH paper, and an efficiency score do most of the diagnostic work.

Why nutrition for athletes comes down to energy in versus energy out

Macri’s whole framework rests on a testing method most coaches have never heard of. She uses RBTI, Ream’s Biological Theory of Ionization, and she is quick to translate it out of the jargon.

RBTI stands for Ream’s Biological Theory of Ionization, and that’s just a long, fancy way for energy in versus energy out.

From a small urine sample and a small saliva sample she reads where an athlete’s sugars sit, where the electrolytes sit, how the body processes protein, and how fast things move through the digestive tract. When those numbers fall in range, the body pulls in the minerals it needs and clears what it does not. When they do not, the cost lands on the athlete.

Any imbalance in that, and you’re not recovering, you’re not sleeping, and you’re creating an environment where your body is having to work too hard.

The practical takeaway for a coach is the reframe itself. An athlete who is not recovering may not be undertrained or lazy; the body may simply be spending its energy on digestion and cleanup instead of on adaptation. Macri’s point is that you can put a number on that instead of guessing.

The hydration and sugar problem coaches keep missing

Ask Macri what most young athletes actually eat and drink and the picture gets bleak fast.

Peanut butter crackers and Goldfish and Cheetos and Mountain Dew, and the only water they get is what they brush their teeth with in the morning.

Gatorade is not stocked at Elite Level Performance, and Macri hands out better alternatives rather than lecturing. What changes behavior, she has found, is not a rule but a number the athlete can see.

I can show them an efficiency rating, like, “Your body is operating at 15%. Do you think that you could feel a little bit better if we could get you to 85% just by getting you off the Cokes and the Starbucks?”

The common thread she finds in the athletes who struggle is an overload: too much sugar, too many electrolytes, and a system that cannot clear the protein it is fed. For a coach, the application is to stop treating hydration and fueling as an afterthought handed to a sponsor’s sports drink. Water, sleep, and a cleaner diet are the first interventions, and they are free.

Eating protein is not the same as absorbing it

Protein is the question every athlete asks, and Macri’s answer runs against the grain of the supplement aisle. She is not against protein; she is against assuming that swallowing it means using it.

Protein is extremely important, but it is also the hardest thing for your body to break down. Just because you’re eating it doesn’t mean it’s making it into your body to do any good. And to add another layer to that, protein’s gotta get out.

Because she has a number in front of her, she can catch the counterintuitive cases the eye would miss. A kid who is trying to gain weight and told to eat more protein may already be swamped.

If this kid is barely eating any protein and I see a number that shows an overload of protein in his system, the last thing I’m gonna do is tell this kid to go eat more protein. And without that number, he would never have known that.

Her fixes target digestion first: a little HCL to get the stomach acid working, an enzyme to help break things down, and attention to elimination, before anyone reaches for more grams. Nelson frames the same problem from his side of the gym.

If it can’t assimilate it the right way, it’s gonna compensate somewhere.

For a coach, the lesson is to stop answering “how much protein?” with a bigger scoop. The bottleneck is often absorption, and absorption is fixable.

Gut health, enzymes, and the immune system

If digestion is the gate, the gut is where most of Macri’s athletes are losing the battle. She sees enzymes as a small lever with an outsized effect.

A simple enzyme deficiency might be the only thing standing in your way between making the gains you want to make and staying exactly where you are.

She walks parents through the same idea because it starts young. A childhood of repeated antibiotics, she argues, leaves an athlete with almost nothing to build on.

So many kids have been on antibiotics their whole childhood, they have absolutely no gut bacteria.

Her position is that the immune system starts in the gut, so enzyme support, gut bacteria, and the basic building blocks of digestion come before any exotic supplement. The application for a coach is patience: an athlete who is constantly sick or slow to recover may need the gut rebuilt before training loads have anywhere productive to go.

When a nutrition problem shows up in a muscle test

Nelson’s half of the assessment is physical and neurological, but it keeps pointing back at what Macri measures. When a muscle or a reflex point fails his manual testing again and again, he does not just chase the muscle.

If we’re finding things that are failing, or these neurolymphatic points that are failing, then that’s an automatic indicator to me that from an internal standpoint, there’s something going on. There’s an inflammatory response there.

His logic is that the muscles sit low on the body’s list of priorities. If the internal systems are struggling, the body pulls resources away from movement to keep the essentials running.

Your body’s gonna start pulling away from the other processes that it needs to focus on, like digestion, blood flow, liver, kidney regulation, heart regulation, managing salt, sugars, all that good stuff.

He also refuses to solve movement with activation drills alone, which is where the nutrition link becomes practical rather than mystical.

If a kid doesn’t move efficiently, it’s gonna show up in an activation, not the other way around. You’ve got to be able to get the kid to move efficiently to get things activated. Don’t activate and expect the movement to change.

For a coach, the takeaway is a cross-check: a stubborn activation problem that never holds may not be a coaching failure. It can be an internal signal, and Nelson’s move is to hand that athlete to Macri for a nutritional read before grinding on the same drill.

How Elite Level Performance assesses an athlete

The striking part of Macri’s process is how low-tech it is. The instruments are simple; the interpretation is the skill.

I take a small urine sample and a small saliva sample, and I’m using very basic instruments to give me a reading to see where your sugars are, where your electrolytes are, and how your body processes protein, both assimilating it in and your kidneys filtering it out.

Urine shows what the body is getting rid of; saliva, because of its enzymes, gives a read tied to the liver. She measures pH with a roll of pH paper, careful to note she is looking at digestion, not blood pH. If a coach wants a single place to begin, she is blunt about it.

Really, of all the things that Reams does, pH is the most important. Always start there.

For coaches who want to learn more without a formal program, Macri points to the work of Dr. Reams and to author Andrew Badeaux, whose books she recommends for making sense of the readings. The practical entry point is small: buy the pH paper, learn what the numbers mean, and start paying attention to digestion as a training variable.

Frequently asked questions

How much protein should an athlete eat?
Macri uses a basic basal metabolic rate calculation to give an athlete a target, but she stresses that the number eaten matters less than the amount absorbed and cleared. If her testing shows protein already backing up in the kidneys, telling that athlete to eat more protein is the wrong move. Fix digestion first.

Why isn’t the protein I eat building muscle?
Because eating protein and absorbing it are two different things. Protein is the hardest macronutrient for the body to break down, so weak stomach acid, an enzyme deficiency, or poor elimination can leave most of it unused. Macri works on digestion, HCL, and enzymes before adding more grams.

Is Gatorade bad for athletes, and what should they drink instead?
Elite Level Performance does not stock Gatorade. Macri points athletes to water first and offers better alternatives, because the pattern she sees in struggling athletes is an overload of sugar and electrolytes. Her approach is education: show the athlete an efficiency number, then let the drink choice follow.

What is RBTI (Ream’s Biological Theory of Ionization)?
It is a testing method that treats health as energy in versus energy out. From a small urine and saliva sample, Macri reads sugars, salts, protein processing, and pH, then scores how efficiently the body turns food into usable energy. Numbers in range mean good absorption and recovery; numbers out of range mean the body is working too hard.

Can nutrition affect muscle activation?
Nelson thinks it can. When a muscle or a neurolymphatic point tests weak over and over, he reads it as a flag that something internal is off rather than a simple firing fault, and he sends the athlete to Macri to test the internal terrain before continuing to drill activation.

About the authors

John Nelson is the owner of Elite Level Performance in Collierville, Tennessee, where he integrates neurology, applied kinesiology, and manual muscle testing into athletic training and treatment. He holds a master’s degree in health and sport science and works with athletes from high school through the professional ranks.

Mandy Macri Nelson has been with Elite Level Performance since 2012 after two decades in health and fitness. A naturopath and NASM Corrective Exercise Specialist, she uses RBTI testing to assess how athletes process sugar, electrolytes, protein, and pH, and builds nutrition from that read.

Joel Smith is the host of the Just Fly Performance Podcast and the founder of Just Fly Sports, a former collegiate strength and track and field coach who focuses on speed, power, and athletic development. Listen to the full episode with John Nelson and Mandy Macri on Just Fly Sports.