Every protein recommendation sounds like it was written for someone else. You scroll past the grams-per-kilo targets, the post-workout shake advice, the timing windows — and file them under lifting nutrition. Your sessions are on the bike or the trail, your priority is carbs, and you've quietly exempted yourself from the conversation.
What you haven't accounted for is what happens inside your muscles when you do a lot of cardio. Your body breaks down its own muscle protein and burns it as fuel — not to build, not to repair, just to keep going. And the replacement cost lands at the same number you've been scrolling past.
Do you need more protein if you do a lot of cardio
Endurance athletes require roughly 1.8 grams of protein per kilogram of body weight per day — landing in the same range as the resistance training ceiling of 1.62 g/kg. Per-meal protein needs after endurance exercise actually exceed the resistance equivalent: 0.49 versus 0.24 g/kg. Carbohydrate remains primary for endurance performance.
— Witard et al. 2025 · Sports Medicine
The answer collapsed a boundary most people assume is wide open. The endurance-specific protein requirement, when measured directly rather than extrapolated from lifting data, landed at 1.8 grams per kilogram of body weight per day. The resistance training ceiling, measured in a different population entirely, sits at 1.62.
The gap that's supposed to separate cardio nutrition from lifting nutrition doesn't show up in the data. Same range. Same ballpark. The category you built — carbs for cardio, protein for lifters — exists in habit, not in physiology.
The convergence makes sense once you look at what cardio does to protein in real time. During endurance exercise, your body burns through amino acids — the building blocks of protein — at roughly 6 percent of the total energy cost. Muscle protein is broken down to supply them: some burned directly inside the muscle as fuel, some shipped to the liver and converted into glucose. Every session draws from the same pool that lifters replenish after their last set.
The per-meal math hits even harder. After endurance exercise, the protein dose needed to maximize muscle repair works out to roughly 0.49 grams per kilogram of body weight. After resistance exercise, the equivalent dose is 0.24. The comparison rests on a single dose-response study, and the exact number deserves more data. But the direction is clear: per-meal protein needs after cardio don't trail a lifter's. They exceed them.
For a 70-kilogram runner, that means about 34 grams in one sitting — nearly double what a lifter needs.
The daily number shifts with what kind of session you ran. Standard training days: 1.8 g/kg. Low-carbohydrate training: 1.95. Recovery days, when the body rebuilds what the session consumed: above 2.0. Most of this data comes from trained men, and the numbers may shift as female-specific evidence catches up.
There is an upper bound, and it cuts lower than more-is-better logic would suggest. At 3.6 grams per kilogram per day, muscle repair and growth were actually suppressed — not enhanced, not neutral, actively reduced. The finding comes from a single study in trained runners, and a single data point is not a permanent ceiling. But the principle it reveals holds: past a threshold, the same nutrient that supports recovery begins to undermine it.
None of this rewrites the carb playbook. Carbohydrate remains the primary fuel for endurance performance, and adding protein to your mid-ride nutrition doesn't improve output when carb intake is adequate. The instinct that cardio runs on carbs was always right. The instinct that protein belongs to someone else was the part that broke.
The boundary between cardio nutrition and lifting nutrition dissolved at the protein line. Beneath it, a bigger assumption starts to crack — that the right protein target is ever one number. Age, training volume, body composition, and energy balance all move it. The evidence behind the daily protein recommendation starts where this category collapse ends.