Pre-Race Weight Check: Why You Shouldn’t Try to Lose Weight in the 48 Hours Before a Marathon

Introduction

“I still have 2 kg to lose before race day—should I eat less these two days?” This thought is not uncommon among runners, especially those running their first marathon and particularly sensitive about their weight. However, trying to lose weight in the 48 hours before the race may be one of the worst decisions you make in your entire training cycle. This article explains why your dietary strategy in the final 48 hours before the race should be about “adding” rather than “cutting.”

What Is Your Body Doing in the Final 48 Hours Before the Race?

In the last 2 days before a marathon, your body is in a critical “charging phase”:

Muscle Glycogen Supercompensation

A marathon requires a large amount of glycogen as fuel. Under normal conditions, muscle glycogen stores are approximately 15–18 grams per kilogram of muscle, but through pre-race carbohydrate loading, you can increase glycogen stores to 25–35 grams per kilogram of muscle—equivalent to a 60–80% increase in reserves.

Weight changes from glycogen loading:

• For every 1 gram of glycogen stored, approximately 3 grams of water are also retained
• A 65 kg runner who fully loads glycogen can store an additional 300–500 grams of glycogen
• Accompanied by approximately 900–1500 grams of retained water ≈ a weight increase of 1–2 kg

This 1–2 kg increase represents part of the energy reserves you need to complete 42.195 km—it is “useful weight,” not “excess weight.”

Optimizing Muscle Hydration

• Adequate hydration keeps muscles at optimal contraction efficiency
• Muscle flexibility and explosive power both decline in a dehydrated state
• Proper pre-race hydration (urine a pale yellow) is one of the foundational conditions for race performance

Final Tissue Repair

The taper week gives muscles ample time to repair the micro-damage accumulated from training. During this period, your body needs adequate protein and micronutrients—not caloric restriction.

The Specific Harms of Trying to Lose Weight Before the Race

The Correct 48-Hour Pre-Race Nutrition Strategy

Day 2 Before the Race (48 Hours Out)

Primary goal: Begin increasing carbohydrate intake while reducing dietary fiber

• Carbohydrates: 8–10 grams per kilogram of body weight
• Reduce high-fiber foods (raw vegetables, legumes, whole grains) to avoid pre-race gastrointestinal issues
• Protein: maintain normal intake (1.4–1.6 g/kg)
• Reduce high-fat foods (excess fat delays gastric emptying)

Suitable meal options in Taiwan:

• White rice, noodles (instead of brown rice)
• Bananas, white toast, steamed buns
• Chicken breast, fish, eggs (protein sources)
• Adequate water intake (2–3 liters per day)

Day 1 Before the Race (24 Hours Out)

Primary goal: Continue replenishing glycogen and ensure gastrointestinal stability

• Continue a high-carbohydrate diet
• Eat familiar foods for dinner (do not try new dishes), 1–2 hours earlier than usual
• Avoid foods that may cause gastrointestinal discomfort: high-fat, high-fiber, heavily spicy foods, and alcohol
• If needed the night before the race, a glass of low-fat milk can help (aids sleep while also providing protein)

Race Morning

• 2–3 hours before the race: a breakfast of 200–400 grams of carbohydrates (plain rice porridge, white toast, bananas)
• 30–60 minutes before the race: you may take in 50–100 grams of fast-absorbing carbohydrates (energy gels, bananas)
• 1–2 hours before the race: continue hydrating (about 400–600 mL), but do not drink too much to avoid gastrointestinal discomfort while running

Psychological Management of Pre-Race Weight Anxiety

Many runners’ “pre-race weight anxiety” stems from an excessive need to control race performance. Here are suggestions for adjusting your mindset:

• Change your evaluation criteria: Do not look at the scale in the final 2 days before the race; instead, assess your readiness based on “training completion” and “glycogen loading status”
• Accept the temporary weight gain: A 1–2 kg weight increase means your glycogen stores are full—this is a good thing
• Trust your training: The past months of training have already determined 90% of your result. The final 48 hours cannot change your training outcome, but they can ruin a good race

Conclusion

In the final 48 hours before a marathon, your only task is to maximize energy reserves, not to chase a lower number on the scale. Glycogen-filled muscles, a fully hydrated body, and completely repaired tissues—these are the true assets that will carry you across the finish line. The extra 1–2 kg on the scale will be converted into the energy that drives you forward over the 42 km course. Trust the science, trust your training, and step onto the starting line fully fueled.

Related Reading

• Carb Loading 3 Days Before a Marathon: A Complete Guide to Food Choices and Portion Calculations
• Weight Management During Race Preparation: Goal Setting and Control Strategies for the Final 8 Weeks
• 48-Hour Pre-Marathon Itinerary Planning: Scheduling Transportation, Accommodation, and Meals
• Nutrition Planning for Marathon Preparation: Dynamically Adjusting Training Volume and Caloric Intake