Common Nutrition Mistakes That Can Sabotage Your Marathon Training

Training for a marathon is a test of endurance, consistency, and often overlooked smart fueling. What you eat before, during, and after your runs can make or break your performance. According to sports dietitian Nancy Clark, RD, author of Nancy Clark’s Sports Nutrition Guidebook, marathon nutrition mistakes are surprisingly common and fixable.

Here are nine nutrition missteps that can compromise your training and race-day success, along with expert-backed strategies to keep your body running strong from mile 1 to 26.2.

1. Not Eating Enough

Cutting calories may seem like a shortcut to a faster time, but undereating can leave you sluggish and underpowered. Your body needs sufficient fuel to sustain long training sessions.

What to do instead:

• Eat a pre-run snack (100–300 calories) an hour before your workout

• Refuel within 30 to 60 minutes after your run

• Maintain consistent energy intake throughout the day

2. Overeating After Long Runs

Logging double-digit miles doesn’t give you free rein to eat with abandon. Many runners fall into the “sedentary athlete” trap training hard but sitting most of the day.

Try this:

• Refuel with a mix of protein and carbs within an hour

• Keep portions balanced and nutrient-dense

• Be mindful of overall daily movement outside of training

3. Skipping Breakfast

Heading out for a long run on an empty stomach is a recipe for burnout. Without pre-run fuel, your blood sugar drops, making runs feel harder than they should.

Before long runs or race day, aim for:

• 100 to 300 calories of carbs (toast, oatmeal, banana)

• Easy-to-digest foods to avoid stomach upset

4. Not Hydrating Properly

Dehydration can sabotage performance and slow recovery. Calculating your personal sweat rate helps you determine how much fluid you really need.

How to do it:

• Weigh yourself before and after an hour-long run (without drinking)

• A 2-pound loss = 1 quart of sweat = drink ~8 oz every 15 minutes during your runs

5. Not Fueling During Long Runs

Your body burns through stored energy in about an hour. Waiting until you’re hungry to eat mid-run? That’s already too late.

Keep energy up with:

• 200–300 calories per hour (think: sports drinks, gels, bars, or dried fruit)

• Practice during training to learn what your body tolerates best

6. Inadequate Post-Run Recovery Nutrition

Protein shakes are great but alone, they’re not enough. Your muscles need carbohydrates to replenish energy stores and support muscle recovery.

Recovery meals should include:

• A 3:1 ratio of carbs to protein

• Easy options like chocolate milk, PB&J, chicken with rice, or spaghetti with meatballs

7. Poor Carb-Loading Strategy

Carbs are key to sustaining energy throughout the race. But not all carbs are created equal, and your fiber tolerance matters.

Smart carb-loading tips:

• Avoid processed carbs that cause sluggish digestion

• Don’t overdo high-fiber foods like beans or dried fruit close to race day

• Practice your pre-race meals during training

8. Trying Something New on Race Day

New foods or drinks on race day can wreak havoc on your gut. As Clark says, "More marathons are won or lost in the portable toilets than at the dinner table."

Stick to:

• Foods and snacks you’ve tested during training

• Restaurants or meals you’re familiar with if traveling for a race

• Your usual timing and portions for breakfast and pre-race snacks

9. Celebrating with Booze Too Soon

Yes, you earned that celebratory drink but be cautious. Alcohol on an empty stomach and a dehydrated body can intensify its effects and slow recovery.

If you’re planning to drink post-race:

• Hydrate with water first

• Eat a carb-rich meal or snack before reaching for alcohol

• Beer may be a better choice due to its water content but moderation is still key

The Bottom Line

Marathon training is about more than hitting your mileage goals. Smart nutrition supports your energy, recovery, and overall performance before, during, and after race day. Avoid these common mistakes, and you’ll give yourself the best chance at a strong finish and a healthy training journey.

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