Skeletal muscle is about 40% of an adult’s body weight, and that matters for nutrition coaching.

Skeletal muscle: the hidden driver of a smart nutrition plan

Here’s a fact you’ll hear a lot in serious nutrition conversations: skeletal muscle typically makes up about 40% of an adult’s body weight. That number isn’t just trivia. It’s a practical guidepost for how we shape diet, training, and overall plans for clients. Yes, the figure can shift based on age, sex, activity level, and body composition, but the idea remains the same: muscle isn’t just “stuff you can lift”—it’s a major player in metabolism, energy needs, and how the body responds to food.

What 40% really means, in plain terms

Muscle is metabolically active tissue. That means it burns calories even when you’re sitting on the couch, scrolling through your phone, or sipping your morning coffee. More muscle mass typically translates to a higher resting energy expenditure (REE). In turn, that affects how many calories a person needs to reach goals like fat loss, muscle gain, or simply maintaining weight.

The 40% figure also helps explain why two people who look similar on the scale can have very different body compositions. If one person has more skeletal muscle and less fat, their weight might be similar to someone with more fat and less muscle—but their energy needs, appetite signals, and response to training will feel very different. It’s a reminder that body weight alone is a rough proxy; muscle mass matters in its own right.

Who tends to have more muscle—and why

Age, sex, and activity all tug on that 40% number. In younger adults, hormones such as testosterone support greater muscle investment, which is why men often have a higher percentage of skeletal muscle than women. That doesn’t mean women can’t build impressive muscle or that men can’t lose it; it just highlights that biology sets a baseline, and training can move the needle.

Training status is the big lever. Regular resistance training, especially with progressive overload, nudges muscle mass upward. Athletes in power and strength disciplines may push the muscle percentage higher than the average, while endurance athletes might have a leaner appearance with a different distribution of lean tissue. And then there’s aging: as we mature, there’s a gradual decline in muscle mass and function if we aren’t actively countering it. The antidote is clear—consistent resistance work combined with enough protein and overall nutrition.

Why this matters for nutrition coaching

If you’re helping clients navigate fat loss, performance goals, or simply staying healthy as they age, the muscle story matters in concrete ways:

• Energy needs are not static. More muscle can raise the baseline calories your client burns, which influences how you set calories for weight goals. If you assume a fixed calorie target without considering muscle, you risk undershooting energy needs for training or overdoing fat loss.

• Protein becomes a central tool. Muscle preservation and growth hinge on adequate protein, especially when energy intake is adjusted for weight loss or when training volume is high. In practice, many practitioners aim for roughly 1.6 g/kg/day for those seeking gains or maintaining muscle during a calorie deficit, with broader ranges from about 1.2 to 2.0 g/kg depending on goals, training load, and individual tolerance.

• Training integration matters. Nutrition and resistance work go hand in hand. A plan that pits aggressive fat loss against heavy training without enough fuel or protein will blunt results and can raise injury risk. The food plan should support training quality, recovery, and long-term adherence.

• Special populations require nuance. Older adults may benefit from higher protein per meal and periodic protein-rich snacks to counter sarcopenia. Those recovering from injury or illness may need adjusted protein and energy targets to support muscle maintenance during healing.

Practical takeaways you can apply now

Here are some actionable ideas to weave into client conversations, without turning the plan into a lab project:

• Prioritize resistance training 2–3 days per week, with progress over time. Exercises that target major muscle groups—squats, presses, pulls, rows, and hips hinges—pack the most muscle-building punch. If a client is new to lifting, start with fundamentals and gradually add load.

• Talk protein per meal, not just per day. Spreading protein across 3–4 meals helps with muscle protein synthesis. Aim for roughly 25–40 grams of high‑quality protein per meal, depending on body size and appetite. Include leucine-rich sources (like dairy, poultry, eggs, or soy) to maximize the anabolic response.

• Build a balanced plate around workouts. Carbohydrates help fuel training and replenish glycogen stores, supporting performance and recovery. Healthy fats support hormones and overall health. The exact mix isn’t sacred; it’s about hitting personal needs and food preferences so the plan sticks.

• Don’t fear a modest energy deficit when fat loss is the goal. A smaller deficit paired with strong protein intake and resistance training tends to preserve muscle better than a steep cut. It’s not glamorous, but it tends to work longer.

• Consider older clients separately. They often benefit from a slightly higher protein target per meal and continued resistance training to combat sarcopenia and maintain functional capacity.

• Use accessible gauges for progress. Not every client has a DEXA scan in the wallet. You can track simple, practical markers: strength improvements, tightness of clothes, performance in training, occasional body measurements, and even bioimpedance scales if available. These aren’t perfect, but they offer a realistic sense of change over weeks to months.

How to assess muscle without a lab visit

If you don’t have fancy equipment, you’re not out of luck. A few practical methods can help you keep tabs on muscle status:

• Body composition estimates. Bioelectrical impedance devices and home scales can give rough lean mass readings. They’re imperfect—hydration and time of day can skew results—but when used consistently, they show trends.

• Circumference tricks. Arm, thigh, and chest measurements can reflect muscle growth when paired with training. Consistency is key: measure the same spot, at the same time of day, with the same tape.

• Strength as a proxy. Steady gains in lifting numbers (more reps at the same weight, or heavier weights for the same reps) usually signal muscle adaptation. It’s a practical, real-world signal that something is working.

• Training quality over vanity. If your client feels stronger, recovers well, and can handle the planned workload, muscle mass support is likely in play. That’s a win worth acknowledging.

A couple of real-life coaching touches

Let me explain with two quick scenarios you might recognize:

• A 32-year-old man who lifts twice a week and wants leaner arms and a stronger squat. He’s hitting protein targets around 1.6 g/kg/day and isn’t shy about lifting heavy. Over 8–12 weeks, you notice his squat numbers climbing and his body composition improving modestly. Muscle has clearly responded to the mix of protein and progressive overload, and fat shows a gentler decline because the training is helping him stay in a lean‑mass-preserving balance.

• A 46-year-old woman who’s starting resistance training after years of mostly cardio. She’s curious about “where her muscle is.” You set expectations that muscle gain will come slowly, but with consistent effort and a protein-friendly plate, she begins to feel stronger, and her clothes fit differently. The changes aren’t flashy, but they’re meaningful for long-term health and metabolic comfort.

A thought on the bigger picture

Muscle is one of those things you don’t notice until it’s gone—until you look in the mirror and see fatigue in your posture or you feel energy dips you can’t seem to shake. That’s why this 40% number isn’t just a party trick; it’s a reminder to weave training and nutrition into a cohesive plan. It’s also why a nutrition coach’s toolkit should always include strategies to protect and build lean mass, especially during times of life change, stress, or big goals.

Bringing it home: the take-home message

• Skeletal muscle makes up about 40% of adult body weight, but the exact share varies by age, sex, and activity.

• For nutrition coaching, this figure translates into practical actions: tailor protein intake, design training plans that emphasize progressive resistance work, and monitor energy balance to support both fat loss and muscle preservation.

• You don’t need fancy equipment to stay on top of changes. Use simple measures, reliable training progress, and consistent nutrition to guide clients toward their goals.

• Remember to tailor advice for different life stages. Older clients, athletes, and those recovering from illness may need tweaks to protein and training emphasis.

• The core of a strong plan is clear: combine resistance training with adequate protein, distribute protein across meals, and align energy intake with training and goals.

If you’re working through resources for NAFC-related content, this muscle-matters angle is a powerful through-line. It ties together physiology, nutrition, and real-world coaching—three things that clients feel in their day-to-day lives. And when you can speak to those connections with confidence, you’re not just giving information; you’re offering a practical, human-guided path to healthier habits and better performance.

A final nudge

Next time you sketch a plan for a client, pause on the numbers for a moment and think about the muscle you can help them build, protect, and feel good about. It’s not all about the scale. It’s about a metabolic ally that shows up in training sessions, daily energy, and the way clothing fits on a Tuesday afternoon. That’s the kind of insight that makes nutrition coaching resonate—clear, relevant, and a little bit inspiring.