Nutrition periodisation is the deliberate variation of macronutrient intake — particularly carbohydrates — to match the metabolic demands of each training phase. Just as training load is periodised across a season (base building, build phase, peak, race, recovery), nutritional strategy should shift in parallel. A single dietary approach maintained year-round means the athlete is almost certainly over-fuelling easy weeks and under-fuelling hard ones — or vice versa — and missing opportunities to drive specific metabolic adaptations through strategic fuel availability.
The concept gained significant research attention following work by Burke, Hawley, and colleagues demonstrating that fat oxidation capacity could be meaningfully increased by training in carbohydrate-depleted states, while separately showing that high carbohydrate availability was necessary for quality high-intensity efforts. The synthesis of this body of work suggests that "train low, compete high" — training periodically in low-carbohydrate states to drive fat oxidation adaptations, while fully fuelled for quality sessions and races — is a more sophisticated and effective approach than either always-high or always-low carbohydrate availability.
The Four Training Phases and Their Nutritional Requirements
A standard endurance season cycles through four broad phases, each with distinct metabolic demands:
- Base phase (high volume, low intensity): Zone 1–2 aerobic work, building aerobic infrastructure. Moderate carbohydrate availability (3–5g/kg/day) is appropriate. Deliberate "train low" sessions (fasted morning runs, two-a-days with depleted glycogen from the first session) drive fat oxidation adaptations. This is the phase to build metabolic flexibility — not to maximise carbohydrate availability at all times.
- Build phase (moderate volume, increasing intensity): Lactate threshold work, tempo sessions, race-pace intervals. Carbohydrate requirements increase substantially (5–7g/kg/day). Quality sessions must be fuelled — under-fuelling threshold work reduces adaptation stimulus and increases injury risk. "Train low" sessions are reserved for easy low-intensity days only.
- Peak/race-specific phase (lower volume, highest intensity): VO2max intervals, race-pace work, final specificity training. Highest carbohydrate availability of the season (6–10g/kg/day). No deliberate glycogen depletion. Every hard session should be fully fuelled and followed by immediate recovery nutrition.
- Recovery/transition phase (very low volume, unstructured): Active rest and deconditioning prevention. Significantly reduced carbohydrate intake (2–3g/kg/day) to match dramatically reduced energy expenditure. Maintaining high carbohydrate intake during recovery phases leads to unnecessary weight gain that must be managed before the next base phase.
Train Low Sessions: Protocol and Precautions
Training in a low-carbohydrate state upregulates fat oxidation enzymes, increases mitochondrial biogenesis, and improves the metabolic machinery for sustained aerobic work. Specific protocols:
- Fasted morning training: Easy runs or rides of 60–90 minutes performed before breakfast, after an overnight fast. Suitable for Zone 1–2 only. Add electrolytes. Limit to 2× per week maximum.
- Sleep low/train low: Complete an evening glycogen-depleting session (tempo intervals), consume a low-carbohydrate dinner (high protein and fat), sleep, then perform a morning aerobic session before breakfast. Most potent "train low" stimulus — also highest fatigue and injury risk. Use sparingly (1× per week maximum, only in base phase).
- Two-a-day glycogen depletion: Complete a glycogen-depleting morning session without carbohydrate recovery, then perform an afternoon easy aerobic session in the depleted state. Lower intensity commitment required than sleep low protocol.
- Never train low for quality sessions: Threshold runs, interval sessions, group rides with surges, and any race-pace work should always be performed with full glycogen availability. Attempting quality work in a depleted state ruins the session quality and negates the intended adaptation.
Protein Periodisation
Protein requirements also shift across training phases. During base building with high volume, tissue repair demands are elevated — 1.6–1.8g/kg/day supports muscle maintenance under high volume. During peak phase with lower volume but higher intensity, acute muscle damage per session is higher — increase to 1.8–2.0g/kg/day. During recovery phase, 1.4–1.6g/kg/day is sufficient and helps manage total energy intake while preserving muscle mass. Protein timing remains constant across all phases: 20–40g within 60 minutes of key sessions, and before sleep (30–40g casein) to maximise overnight protein synthesis.
Practical Weekly Structure
A periodised nutrition week in base phase might look like: fasted easy run Monday morning, fully fuelled threshold session Wednesday evening with 60–90g carbohydrate in the 2 hours prior, moderate carbohydrate intake Thursday–Friday for recovery, sleep-low protocol Saturday (depleting ride Friday evening, low-carb dinner, Sunday long run first 90 minutes fasted then gel/drink after), recovery Sunday afternoon fully fuelled. Track carbohydrate intake across the week rather than day-by-day — weekly totals matter more than daily precision for most athletes.
Use the NorthLine Carb Loading Calculator to calculate precise carbohydrate targets for your peak phase and race week — when carbohydrate availability should be maximised and the "train low" approach fully abandoned in favour of glycogen supercompensation. The Race Day Nutrition Planner pairs with this to ensure your fuelling strategy on race day builds on the nutritional base you have built across the season.