A science-based protocol for maximizing glycogen stores before Ironman and 70.3 racing. Covers the 36 to 48 hours pre-race, race morning, and GI risk management during the taper.
36 to 48 hrs pre-race
Ironman and 70.3
Calculator included
Important: The targets and timing in this protocol are based on published sports nutrition research and are intended as general guidance only. Individual responses to carbohydrate loading vary significantly based on training status, GI tolerance, food preferences, and race-day conditions. These calculations should be practiced in training before race day and reviewed with a qualified coach or sports dietitian before implementation. Nothing in this tool replaces the guidance of a qualified professional. If you have questions about how this protocol applies to your specific situation, book a free consult with a BPC coach →
The science in brief. Muscle glycogen is the primary performance-limiting substrate in events lasting more than 90 minutes. A well-executed carbohydrate loading protocol can increase muscle glycogen stores by 50 to 100% above baseline, delaying fatigue and supporting sustained race-pace effort. The current evidence supports a target of 10 to 12 g/kg body weight per day for 36 to 48 hours pre-race in trained endurance athletes. Sources: Burke LM et al (2011) J Sports Sci; Hawley JA et al (1997) Eur J Appl Physiol; Thomas DT et al (2016) Academy of Nutrition and Dietetics Position Paper.
Training low-carb or fat-adapted? If you have been following a low-carbohydrate or fat-adapted training approach, your body's capacity to store and oxidize glycogen may be temporarily reduced. Research from Burke et al (SUPERNOVA studies, 2017-2020) demonstrates that chronic fat adaptation can impair carbohydrate oxidation efficiency at race-relevant intensities. Talk to your coach before following this protocol -- you may need a longer carbohydrate reintroduction period in the days before loading begins.
Your personal CHO targets
Enter your body weight to calculate your daily carbohydrate targets for each phase of the protocol.
Units:
lbs
Normal training
--
g / day
Taper days (days 5 to 3)
--
g / day
Loading days (T-2 and T-1)
--
g / day
Race morning (2 to 3 hrs out)
--
g total
Protocol timeline
The protocol begins with the taper, which reduces training load and primes the body for glycogen supercompensation. Loading follows in the 36 to 48 hours before race start.
Normal trainingBaseline carbohydrate intake5 to 7 g/kg/day
During normal training, carbohydrate intake should support training load. For most Ironman athletes this is 5 to 7 g/kg/day, distributed across meals and timed around key sessions. This is not loading -- it is maintenance.
Taper day (days 5 to 3 before race)Gradual carbohydrate increase6 to 8 g/kg/day
As training volume drops, modestly increase carbohydrate intake to 6 to 8 g/kg/day. The reduction in training stress combined with maintained or slightly elevated carbohydrate intake begins to elevate glycogen stores above normal resting levels. Keep fat and protein intake consistent -- do not add total calories aggressively yet.
Training load: sessions are short and low intensity. Reduce volume by 40 to 60% from peak training weeks. One brief race-pace effort per day is acceptable to maintain neuromuscular readiness.
Loading (T-2 -- 2 days before race)Begin aggressive loading8 to 10 g/kg/day
Begin aggressive loading. Target 8 to 10 g/kg/day from high-glycemic, low-fibre carbohydrate sources. Reduce dietary fat and fibre intake significantly -- both slow gastric emptying and can cause GI distress when carbohydrate volume is high.
Food choices: white rice, white pasta, white bread, bagels, boiled potatoes (no skin), sports drinks, rice cakes, bananas, fruit juice, pretzels. Avoid whole grains, legumes, cruciferous vegetables, and high-fat foods.
Training load: rest or a short 20 to 30 minute very easy spin or jog only. No intensity.
GI note: some athletes experience bloating and discomfort at these intake levels. Spread intake across 5 to 6 smaller meals rather than 3 large ones. Do not try foods or quantities you have not practiced in training.
Loading (T-1 -- 1 day before race)Continue loading8 to 10 g/kg/day
Continue loading at 8 to 10 g/kg/day. Maintain the same low-fibre, low-fat food approach. Finish your last large meal by early evening -- aim to stop eating significant quantities at least 10 to 12 hours before your expected race start to allow full gastric emptying.
Hydration: glycogen storage requires water -- approximately 3 g of water is stored per gram of glycogen. Expect to feel heavier and fuller than normal. This is physiologically expected and does not represent fat gain. Ensure adequate fluid intake throughout the day.
Training load: rest only, or a brief 10 to 15 minute activation ride or jog at very easy effort.
GI note: avoid new foods, high-fat restaurant meals, and excessive fibre. The night-before dinner should be familiar, practiced, and predictable. Save culinary adventure for after the race.
Race morning3 to 4 hours before start2 to 3 g/kg (Ironman) / 1 to 2 g/kg (70.3)
The race morning meal tops off liver glycogen (which is depleted overnight) and provides additional substrate without causing GI distress during the swim. Target 2 to 3 g/kg for Ironman or 1 to 2 g/kg for 70.3 and shorter events, consumed 2 to 3 hours before race start.
Practical targets: for most athletes this means 60 to 120g of carbohydrate from familiar, practiced sources -- white rice, a plain bagel, oatmeal (if practiced), a banana, sports drink, or a combination. Keep fat and fibre very low.
If race start is early and the gap between waking and start is under 2 hours, reduce to 0.5 to 1 g/kg from liquid or easily digested sources (sports drink, white bread, banana) to minimize GI risk.
GI note: this meal must be practiced in training under race-simulation conditions. Do not eat more than you have tolerated in long training sessions. When in doubt, less is more -- you can supplement with on-course nutrition; you cannot undo GI distress at mile 10 of the run.
High-carbohydrate food reference
Low-fibre, low-fat sources preferred during the loading phase. Values are approximate per standard serving.
White rice (1 cup cooked)
~45g CHO
White pasta (1 cup cooked)
~43g CHO
Plain bagel (large)
~55g CHO
White bread (2 slices)
~30g CHO
Boiled potato (1 medium, no skin)
~30g CHO
Banana (large)
~30g CHO
Sports drink (500ml)
~30g CHO
Fruit juice (250ml)
~25g CHO
Rice cakes (2 plain)
~15g CHO
Pretzels (30g)
~23g CHO
Oatmeal (1 cup cooked)
~27g CHO, moderate fibre
Honey (1 tbsp)
~17g CHO
Managing GI risk
GI distress is one of the most common causes of DNF and performance loss in Ironman racing. The pre-race period is the highest-leverage window for prevention.
The evidence. Jeukendrup et al (2014) identified GI problems in up to 90% of ultra-endurance athletes during competition. The primary modifiable risk factors in the pre-race period are high-fat intake, high-fibre intake, dehydration, and unfamiliar foods. The loading protocol above is designed to minimize all four.
Eliminate dietary fibre progressively from T-3 onward. By T-1 your diet should be almost entirely fibre-free.
Reduce dietary fat to less than 20% of total calories during loading days. High fat slows gastric emptying and compounds GI stress when carbohydrate volume is high.
Eat nothing on race morning that you have not eaten before a long training session. This is not the time to experiment.
Avoid NSAIDs (ibuprofen, aspirin) in the 48 hours pre-race. They increase intestinal permeability and significantly elevate GI distress risk during racing. Pfeiffer et al (2012) demonstrated this association in Ironman athletes specifically.
Spread loading intake across 5 to 6 smaller meals. Large single meals increase bloating and reduce absorption efficiency.
Stay well hydrated throughout the loading phase. Glycogen storage requires approximately 3g of water per gram of glycogen stored -- expect to gain 1 to 3 kg of water weight during loading. This is normal and expected.
Sources
Burke LM et al (2011). Carbohydrates for training and competition. J Sports Sci. 29(Suppl 1):S17-27.
Hawley JA et al (1997). Carbohydrate loading and exercise performance: an update. Eur J Appl Physiol. 76(5):411-419.
Thomas DT, Erdman KA, Burke LM (2016). Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and Athletic Performance. J Acad Nutr Diet. 116(3):501-528.
Burke LM et al (2017). Low carbohydrate, high fat diet impairs exercise economy and negates the performance benefit from intensified training in elite race walkers (SUPERNOVA). J Physiol. 595(9):2785-2807.
Burke LM et al (2020). Crisis of confidence averted: Impairment of exercise economy and performance in elite race walkers by ketogenic low carbohydrate, high fat (LCHF) diet is reproducible (SUPERNOVA2). PLoS One. 15(6):e0234027.
Jeukendrup AE et al (2014). Nutrition for endurance sports: marathon, triathlon, and road cycling. J Sports Sci. 29(Suppl 1):S91-99.
Pfeiffer B et al (2012). Nutritional intake and gastrointestinal problems during competitive endurance events. Med Sci Sports Exerc. 44(2):344-351.