Carb-loading: How to do it properly
Preparing for a marathon, long-distance cycling event, or triathlon requires more than just logging miles on the road. What you put into your body in the days leading up to race day plays a critical role in your endurance and stamina. Carbohydrate loading, often referred to as carb loading, is one of the most proven nutritional strategies for endurance athletes aiming to optimise energy stores and avoid hitting the wall.
When implemented correctly, a structured carbohydrate loading protocol can significantly delay muscle fatigue and elevate your overall exercise performance. However, carb loading is frequently misunderstood, leading many athletes to make critical nutrition mistakes right before competition.
Here is a comprehensive guide on how to carb load properly, including science-backed protocols, exact dietary targets, and practical guidance from Nutrition & Co, where expert dietitians provide tailored sports nutrition consultation and adult performance nutrition services.
What Is Carbohydrate Loading?
Carbohydrate loading is a deliberate dietary strategy designed to maximise the storage of glycogen in your muscles and liver prior to prolonged endurance events.
When you consume carbohydrates, your digestive system breaks them down into glucose. Your body utilises this glucose for immediate fuel, while surplus glucose is synthesised and stored as muscle glycogen and liver glycogen.
During high-intensity endurance exercise, muscle glycogen serves as your primary fuel source. Under standard daily dietary conditions, baseline muscle glycogen stores provide sufficient energy for approximately 90 minutes of continuous exercise. Through a targeted carbohydrate loading strategy, athletes can elevate glycogen stores to nearly double their baseline levels, providing a sustained energy reservoir for long-duration efforts.
Who Needs to Carb Load?
Not every workout or athletic effort requires a carb loading phase. Because the primary objective is preventing glycogen depletion over multi-hour events, carbohydrate loading is specifically recommended for continuous exercise lasting longer than 90 minutes.
Events That Benefit from Carb Loading
Marathons and Ultra-marathons (such as the London Marathon or Manchester Marathon)
Long-Distance Triathlons (Half-Ironman and full Ironman distances certified by Ironman UK)
Endurance Cycling Events (Sportives and century rides organised via British Cycling)
Cross-Country Skiing and Multi-Hour Multisport Competitions
Events That Do Not Require Carb Loading
If your event lasts less than 90 minutes, such as a 5k or 10k running race, a standard gym session, or a short sprint-distance workout, traditional carbohydrate loading is unnecessary. In short-duration events, baseline glycogen stores are already sufficient, and attempting to carb load can leave you feeling unusually heavy or sluggish on competition morning.
How to Carb Load Properly: A Step-by-Step Protocol
Historical approaches from the 1960s required a harsh "depletion phase" consisting of exhaustive exercise combined with a low-carb diet, followed by a loading phase. Modern sports science guidelines from The British Dietetic Association (BDA) have demonstrated that this depletion phase is completely unnecessary and counterproductive.
Today, standard UK performance guidelines recommend a 36 to 48-hour carbohydrate loading protocol paired with a structured training taper.
Step 1: Calculate Your Daily Intake Targets
To maximise muscle glycogen supercompensation, aim to consume 8 to 10 grams of carbohydrate per kilogram of body mass per day during the 1 to 2 days preceding your race, keeping in line with anti-doping and athletic health guidance from UK Anti-Doping (UKAD) and general dietary energy principles from the NHS Starchy Foods Guide.
Athlete Weight | Daily Carbohydrate Target (8–10 g/kg) | Total Daily Carbohydrate Calories |
55 kg (8 st 9 lb) | 440 – 550 grams | 1,760 – 2,200 kcal |
65 kg (10 st 3 lb) | 520 – 650 grams | 2,080 – 2,600 kcal |
75 kg (11 st 11 lb) | 600 – 750 grams | 2,400 – 3,000 kcal |
85 kg (13 st 5 lb) | 680 – 850 grams | 2,720 – 3,400 kcal |
Step 2: Shift Your Dietary Composition
Carbohydrate loading does not mean eating larger, heavier meals overall. Rather, it requires shifting the proportion of your daily calories toward low-fibre, high-carbohydrate foods while reducing dietary fats, fibre, and excessive protein.
Primary Food Sources: White basmati or jasmine rice, refined pasta, white bagels, crumpets, white bread, porridge oats, pancakes, pretzels, ripe bananas, fruit juices, and isotonic sports drinks. If you require help structuring these meals around specific training schedules, book a consultation directly through Nutrition & Co or check out their latest advice on the Nutrition & Co Blog.
Foods to Reduce Temporarily: High-fat meals, takeaway foods, high-fibre vegetables, large raw salads, and heavy meat dishes that cause quick fullness.
Step 3: Taper Your Physical Activity
Your body cannot fully top off glycogen stores if you are actively burning them during hard training sessions. Combine your high-carbohydrate intake with a strict training taper, drastically lowering exercise volume and intensity during the final 48 to 72 hours before race day.
Common Mistakes to Avoid
Consuming Too Much Dietary Fibre: While fibre is an essential component of a healthy daily diet, consuming high amounts during a carb load can lead to gastrointestinal distress, bloating, and unwanted pit stops during your event.
Relying Solely on a Massive Dinner the Night Before: Attempting to complete your entire carb load during a single massive bowl of pasta the night before an event often leads to indigestion and disrupted sleep without adequately saturating muscle glycogen stores.
Fearing Water Weight Gain: Each gram of stored glycogen naturally binds approximately 3 grams of water in muscle tissue. Expecting a temporary weight increase of 1 to 2 kg (2 to 4 lbs) is normal and indicates successful glycogen storage; this hydration is utilised by your body during exercise.
Overindulging in High-Fat Foods: Carb loading is not an open invitation to eat high-calorie junk foods like pizza, fish and chips, or pastries. High fat content delays gastric emptying and interferes with efficient carbohydrate absorption.
Frequently Asked Questions (FAQ)
1. Will carbohydrate loading cause permanent weight gain?
No. Any scale weight increase experienced during a carbohydrate loading protocol is temporary water weight tied directly to muscle glycogen storage. Because every gram of stored glycogen binds roughly 3 grams of water, fluid accumulation occurs naturally. This stored water is released and utilised by your muscles as you burn glycogen during your event.
2. What are the best UK supermarket foods for an effective carb load?
The best choices are easily digestible, low-fibre carbohydrates that can be consumed without causing GI fullness. Ideal options from local shops include white rice, standard pasta, plain bagels, crumpets with jam, scotch pancakes, pretzels, porridge oats, ripe bananas, tinned fruit, applesauce, and sports drinks. If you want a complete list of performance foods tailored to your sport, visit Nutrition & Co. You can also refer to the public nutritional advice on the British Nutrition Foundation website.
3. How can gluten-free or plant-based athletes carb load?
Gluten-free athletes can easily meet carbohydrate targets by consuming white rice, rice cakes, potatoes, sweet potatoes, gluten-free pasta, corn tortillas, gluten-free oats, and fruit juices. Plant-based athletes can utilise these same staple sources alongside maple syrup, golden syrup, and fruit purees while keeping high-fibre beans and lentils lower during the loading period to prevent digestive discomfort. You can also review sports nutrition resources from The British Dietetic Association (BDA) or contact our team for additional plant-based fueling tips.
Ready to Fuel Your Next Race Day?
Nailing your carbohydrate loading strategy can mean the difference between hitting a new personal best or hitting the wall halfway through your event. Every athlete’s body is unique, and calculating exact macronutrient targets tailored to your weight, sport, and training load takes the guesswork out of race preparation.
If you want a bespoke, evidence-based nutrition plan designed specifically for your upcoming marathon, triathlon, or cycling event, the specialist dietitians at Nutrition & Co are here to help.
Book Your Personalised Sports Nutrition Consultation Today and smash your race-day performance goals!
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