Nutrient timing is really two questions wearing one name, and they have opposite answers. Timing your protein barely matters once your daily total is adequate. Timing your carbohydrate genuinely matters — but only when your next session is close. Almost every confusing thing written about this subject comes from merging the two.
The short version
- The protein window is not supported. Once total daily protein is controlled for, the timing effect on muscle growth disappears.
- The carbohydrate window is real but conditional. It applies when the next session is under about 8 hours away.
- With 24 hours between sessions, the consensus says eat carbohydrate “according to what is practical and enjoyable.”
- 1.6 g of protein per kg per day is where extra protein stops adding muscle in the pooled data.
- Aggressive refuelling is 1.0–1.2 g of carbohydrate per kg per hour for the first four hours — a specific protocol for a specific situation, not everyday advice.
- Pre-sleep casein raises overnight muscle protein synthesis. Whether it beats eating the same protein earlier is still unresolved.
The protein half: timing loses to total intake
The cleanest test is a meta-analysis that looked at protein timing across 23 studies and 525 participants. Unadjusted, timing showed a small effect on muscle growth. Then the authors controlled for how much protein each group ate in total, and the effect fell to 0.14 ± 0.11, P = 0.20 — no longer significant. Their conclusion: total protein intake was the strongest predictor.
A larger 2018 analysis in the British Journal of Sports Medicine reached the same place and added a number worth memorising: “protein intakes at amounts greater than ~1.6 g/kg/day do not further contribute” to gains in fat-free mass. On timing specifically: “the specifics of protein supplementation (eg, timing, postexercise protein dose or protein source) play a minor, if any, role.”
The International Society of Sports Nutrition says the same thing in the language of biology: “the anabolic effect of exercise is long-lasting (at least 24 h), but likely diminishes with increasing time post-exercise.” And it names the condition under which timing stops mattering at all: “the benefits of protein timing in relation to the peri-workout period seem to be lessened for people who are already ingesting appropriate amounts of protein (e.g. ≥1.6 g/kg/day).”
What to do instead of watching the clock. The position stands converge on the same practical shape: 20–40 g of high-quality protein, or 0.25–0.40 g/kg, every three to four hours, totalling 1.4–2.0 g/kg a day. That distribution takes care of the peri-workout period automatically without anyone timing anything.
The carbohydrate half: here timing is real
Glycogen is a different problem. It is a physical store that refills at a limited rate, so when you need it back quickly, when you start matters.
The joint position stand of the Academy of Nutrition and Dietetics, Dietitians of Canada and the American College of Sports Medicine sets the trigger by the next session rather than by the clock. Its “speedy refuelling” row applies to “< 8 h recovery between 2 fuel-demanding sessions”, with carbohydrate at 1–1.2 g/kg/h for the first four hours, then a return to normal daily intake.
Note what the table does not contain: any comparable urgency for longer gaps. Speedy refuelling is the only recovery row in it. Once more than eight hours separate two sessions, the stand simply directs you back to daily fuel needs — 5–7 g/kg/d for a moderate programme of about an hour a day — with no instruction about when within the day to eat it.
| Time until your next hard session | What the consensus says to do |
|---|---|
| Under 4 hours | Aggressive refeeding, about 1.2 g of carbohydrate per kg per hour |
| Under 8 hours | Carbohydrate as soon as practical: 1.0–1.2 g/kg/h for the first 4 hours, then normal meals |
| 24 hours or more | Timing is your choice. Hit the daily total — 8 g/kg/day or more restores glycogen fully within 24 h |
For most people training once a day, the third row is the one that applies. The ISSN puts the same point positively: “maximal glycogen levels are restored within 24 h if a diet contains ≥8 g/kg/day.”
Why the two halves differ
It is worth understanding, because it makes the rules memorable rather than arbitrary.
Glycogen is a warehouse with a delivery rate. You emptied part of it, refilling has a ceiling of roughly 1.2 g/kg/h, and if the next session is in six hours you simply cannot refill in time unless you start now. The urgency is arithmetic.
Muscle protein synthesis is a switch that stays on. Training elevates it for at least 24 hours. Feeding protein during that window raises the response, but the window is a day long, so arriving 90 minutes late does not miss it. As the review that examined this concluded, “evidence-based support for such an ‘anabolic window of opportunity’ is far from definitive.”
Before training
Two consensus documents give the same number: 1–4 g of carbohydrate per kg, consumed 1–4 hours before exercise. The range is wide on purpose — a small snack an hour out and a full meal four hours out both fit.
Whether eating beforehand helps at all depends on how long you are going. A meta-analysis of 37 studies found feeding improved performance in exercise longer than 60 minutes (effect size 0.3, P = .012) and made no difference under 60 minutes — an effect size of exactly 0, P = .687.
During training
| Session length | Carbohydrate during |
|---|---|
| 45 minutes or less | Not needed |
| 45–75 minutes | Small amounts, including a mouth rinse |
| 1–2.5 hours | 30–60 g per hour |
| 2.5 hours or more | Up to 90 g per hour, using a glucose–fructose mix |
The reason the ceiling moves at the top of that table is a transporter: glucose absorption “becomes saturated at a carbohydrate intake of around 60 g/h.” Adding fructose, which uses a different route, lifts oxidation rates by up to 75% — and in one trial produced 8% more power than glucose alone.
Pre-sleep protein: promising, unresolved
Casein before bed is the one timing intervention with genuinely interesting data. The ISSN position is that “pre-sleep casein protein intake (30–40 g) provides increases in overnight MPS and metabolic rate without influencing lipolysis”, and the underlying research found muscle protein synthesis roughly 22% higher overnight than with placebo, with at least 40 g needed for a robust effect.
The catch, stated by the researchers themselves. The twelve-week training study that showed muscle and strength benefits compared pre-sleep protein against a non-protein placebo. So it cannot separate the timing from simply eating more protein. As a 2019 review puts it: “Whether pre-sleep protein ingestion has surplus benefits compared with protein supplemented at other time points throughout the day remains to be established.” Its most defensible role is as an extra meal that lifts your daily total.
What to actually do
- Hit the daily totals first. Protein 1.4–2.0 g/kg, with 1.6 g/kg as the point where more stops helping. Carbohydrate scaled to your training load.
- Spread protein across the day in 20–40 g portions every three to four hours. This is the whole of protein timing.
- Ask one question after a hard session: when is the next one? Under eight hours, refuel immediately. Otherwise, eat normally.
- Match carbohydrate during exercise to duration, not to habit. Under 45 minutes, nothing is needed.
FAQ
Do I have to eat protein right after training?
No. The timing effect disappears once total daily protein is accounted for, and training elevates muscle protein synthesis for at least 24 hours. Eating within a couple of hours is sensible; a stopwatch is not required.
Does the carbohydrate window exist?
Yes, conditionally. It matters when your next hard session is under about eight hours away. With a full day between sessions, the consensus explicitly leaves timing to your convenience.
How much protein per day?
Position stands say 1.4–2.0 g per kg. Pooled data puts the point of no further benefit at about 1.6 g/kg/day. The current Dietary Guidelines set a general target of 1.2–1.6 g/kg.
Should I take casein before bed?
It reliably raises overnight muscle protein synthesis at 30–40 g. Whether it beats eating that protein earlier in the day has not been established, so treat it as a convenient way to reach your daily total rather than a special mechanism.
Do I need carbs during a one-hour workout?
Not for sessions of 45 minutes or less. Between 45 and 75 minutes small amounts may help, including a mouth rinse. The real bands start beyond an hour.
Where this fits
What to eat after a session, including glycogen refuelling protocols and rehydration numbers, is in recovery nutrition. How the answers change between endurance, lifting and interval work is in fuelling different types of training. And the claims that grew out of this topic — the 30-minute window, per-meal protein ceilings, fasted cardio — are checked in sports nutrition myths.
Every figure here is linked to its source in the text: position stands of the International Society of Sports Nutrition, the joint Academy of Nutrition and Dietetics / Dietitians of Canada / ACSM position statement, the International Olympic Committee consensus on carbohydrates, and peer-reviewed meta-analyses and reviews in the British Journal of Sports Medicine, the Journal of the International Society of Sports Nutrition, Sports Medicine, Nutrients, Frontiers in Nutrition and the Scandinavian Journal of Medicine & Science in Sports. Checked against those sources on 2 September 2026. Educational information, not medical advice — see our medical disclaimer.
This content is for educational purposes only and is not medical advice. Always consult a qualified healthcare professional for personalised guidance.
