Why Protein Should Anchor Your Diet (And Where Carbs and Fat Fit In)

Ask ten people what matters most in a diet and you'll get ten different answers — calories, carbs, "clean eating," intermittent fasting. But once total calories are set, the research is clear on what matters next: protein is the macronutrient that moves the needle most for muscle, body composition, and performance. Carbohydrates and fat still matter, but they play supporting roles. Here's why, based on the nutritional science in The Renaissance Diet 2.0.

Protein: The Building Block You Can't Substitute

Protein is made of amino acids — the literal building blocks of muscle tissue, enzymes, tendons, ligaments, and much of the rest of your body's structure. Your body constantly breaks down and rebuilds protein in a process called protein turnover, and net muscle growth only happens when you're replacing that loss with a surplus of amino acids from food. Unlike carbs and fat, which the body can partially manufacture or substitute for one another, nine of the twenty amino acids humans need are "essential" — they can only come from the diet.

This is why protein has an outsized effect on body composition compared to the other two macronutrients. Research consistently shows that while variations in carb and fat intake do affect performance and body composition, variations in protein intake affect them considerably more. Protein is also uniquely anti-catabolic, meaning it actively protects existing muscle from breakdown, and it has been shown to increase satiety (fullness) more than an equal number of calories from carbs or fat — a real advantage for anyone managing hunger during a diet.

How much protein you need depends on your goal and calorie situation:

• General health minimum: about 0.3g per pound of body weight per day

• Athletes: roughly 0.8–2.0g per pound per day depending on sport

• Strength and power athletes: around 0.9–1.0g per pound per day is optimal

• Fat loss (hypocaloric) phases: 1.0g per pound per day as a baseline, up to 1.5g for more aggressive diets, since catabolism risk rises as calories drop

• Muscle gain (hypercaloric) phases: around 1.0g per pound per day — more than this doesn't meaningfully add muscle and just crowds out carbs

That last point matters: more protein isn't automatically better. Because all three macros share the same calorie budget — a concept the book calls the Caloric Constraint Hypothesis — eating protein far beyond what's useful just displaces the carbs and fats your body also needs to perform and recover.

Carbohydrates: The Fuel That Powers Everything Else

If protein is the building material, carbohydrates are the energy that makes the construction happen. Carbs are the body's preferred and most efficient fuel source, especially for the nervous system and for muscle contractions during anything above light activity — nearly all sport and resistance training relies heavily on carbohydrate (specifically muscle glycogen) for fuel.

Carbs matter for muscle building in two major ways beyond fuel. First, eating carbs allows you to train harder and recover faster, which itself drives more muscle growth. Second, carbohydrate intake triggers insulin release, a hormone that — especially in combination with resistance training — leans anabolic (muscle-building) rather than fat-storing in lean, active individuals. Training under chronically low-glycogen conditions has repeatedly been shown to increase muscle loss, which is a strong argument against very low-carb approaches for anyone trying to build or preserve muscle.

Carb needs vary widely by activity: as low as 0.3–0.5g per pound per day just for health and micronutrient intake, but 1.0–3.0g per pound per day (and higher for endurance athletes on hard training days) to properly fuel performance and support muscle retention. On a fat-loss diet, carbs shouldn't be neglected either — dropping below roughly 1.0g per pound per day risks depleting glycogen enough to hurt training quality and accelerate muscle loss.

Within the macronutrient hierarchy, carbohydrates rank second behind protein for most goals — but they can temporarily outrank protein in situations like heavy endurance training, where immediate glycogen depletion has faster, more severe consequences than a short-term protein shortfall.

Fat: Necessary, But the Smallest Lever

Dietary fat rounds out the three macronutrients, and it's essential — quite literally, since Omega-3 and Omega-6 fatty acids can't be produced by the body and must come from food. Fat supports hormone production (including testosterone and estrogen, both important for muscle growth and retention), helps absorb certain vitamins, and provides raw material for compounds that regulate inflammation and muscle repair.

That said, of the three macronutrients, fat has the smallest measurable impact on body composition and performance. It's also energy-dense at 9 calories per gram, more than double protein or carbs at 4 calories per gram each, which makes it an easy way to hit calorie targets without eating a large volume of food. A minimum of about 0.3g per pound of body weight per day is enough to meet essential fat needs and support hormone production for most people; beyond that minimum, fat intake mostly becomes a flexible tool for fitting your remaining calories after protein and carb needs are met.

In the macronutrient hierarchy, fat sits below both protein and carbohydrates — carbs are simply a better fuel for training and the nervous system, so when calories are limited, fat is generally the macro to trim first.

Putting It Together

None of these three macronutrients operates in a vacuum — they all draw from the same daily calorie total, so raising one always means adjusting the others. But they are not equally important. Protein builds and preserves the muscle tissue itself and should be the first macro you lock in after setting your calories. Carbohydrates fuel the training that builds that muscle and support the hormonal environment for growth, making them the second priority. Fat, while essential for health and hormone production, has the least direct influence on body composition and performance, and can generally flex around your protein and carb targets. Prioritize protein, fuel with carbs, and let fat fill the rest within your calorie budget. For tailored nutritional guidance, we offer training in Salt Lake City, Utah, and virtually.

Reference

Israetel, M., Davis, M., Case, J., & Hoffmann, J. (2018). The Renaissance Diet 2.0: Your scientific guide to fat loss, muscle gain, and performance. Renaissance Periodization.