Running burns a significant number of calories, and if you’re not deliberately eating enough to replace them, your body will pull from its own reserves. The fix is straightforward in concept: eat more than you think you need to, protect your muscle mass with strength training and protein, and time your nutrition around your runs. In practice, this takes some planning, because running suppresses appetite in many people and the calorie gap can grow quietly over weeks.
How Many Extra Calories Running Actually Burns
A useful starting point: running burns roughly 100 calories per mile. That’s a rough average. A 120-pound runner burns closer to 11.4 calories per minute, so a 10-minute mile costs about 114 calories. A 180-pound runner burns around 17 calories per minute, making that same mile cost 170 calories. If you’re running 30 miles a week and weigh 160 pounds, you could be burning an extra 3,000 to 4,000 calories per week on top of your baseline metabolism.
To calculate how much you actually need to eat, multiply your basal metabolic rate by an activity factor. For someone exercising hard most days, that multiplier is around 1.725. If you’re logging 10 or more hours per week of running and cross-training, it climbs to 1.9. Most runners underestimate where they fall on this scale, especially when mileage creeps up during training blocks. The result is a slow, steady calorie deficit they never intended.
Eat Enough Carbohydrates to Refuel
Carbohydrates are the primary fuel your muscles burn during running, and they need to be replaced after every session. For recovery, aim for 1.2 to 1.5 grams of simple carbohydrates per kilogram of body weight within 30 minutes of finishing a run. For a 150-pound (68 kg) runner, that’s roughly 80 to 100 grams of carbs in that post-run window. Good options include a banana (about 25 to 30 grams of carbs), a sandwich on whole-grain bread, low-fat chocolate milk, or a sports drink paired with a snack.
Adding protein to that post-run meal at a 3:1 or 4:1 carb-to-protein ratio enhances glycogen replenishment. In practical terms, that means if your post-run snack has 90 grams of carbs, pair it with 25 to 30 grams of protein. Cottage cheese with fruit, a chicken sandwich, or a protein shake blended with a banana and oats all hit this ratio naturally.
Throughout the rest of the day, prioritize calorie-dense whole foods. Nuts, nut butters, avocados, olive oil, whole-grain pasta, rice, and dried fruit pack a lot of energy into small volumes. If you struggle to eat enough solid food, liquid calories are your friend. Smoothies with oats, protein powder, full-fat yogurt, and fruit can easily reach 500 to 700 calories without making you feel stuffed. A low-fat liquid meal replacement before a run can also help if you’re someone who can’t eat solids close to exercise.
Protein Needs Are Higher Than You Think
Most runners know protein matters, but few eat enough of it. Recent research using advanced measurement techniques found that endurance athletes need about 1.8 grams of protein per kilogram of body weight per day. That’s 50% more than the recommendation for sedentary adults. During intense training blocks or periods where you’re restricting carbohydrates, that number climbs to 2.0 grams per kilogram.
For a 155-pound (70 kg) runner, that works out to roughly 126 grams of protein per day. Spread this across meals rather than loading it into one sitting. Aim for about 0.5 grams per kilogram of body weight per meal, which comes to around 35 grams per meal for that same runner. This per-meal dose maximally stimulates muscle protein repair after exercise. On rest days, keep protein intake at 2.0 grams per kilogram, since your body is still actively repairing tissue between sessions.
Add Strength Training to Protect Muscle
Running alone won’t preserve your muscle mass. High-volume endurance training, especially without adequate calories, triggers your body’s stress response. Chronically elevated cortisol activates protein breakdown pathways in skeletal muscle, ramping up tissue degradation while slowing new protein construction. The result: you lose muscle, not just fat, and the scale drops in ways that hurt your performance.
The most effective countermeasure is resistance training two to three days per week. This is the frequency recommended by the American College of Sports Medicine for healthy adults, and research shows it captures 80 to 90% of the strength gains you’d get from more frequent lifting. You don’t need to train like a bodybuilder. Full-body sessions focusing on compound movements (squats, deadlifts, lunges, rows, presses) provide enough stimulus to signal your body to hold onto muscle. Keep sessions moderate in volume so they don’t interfere with your running recovery.
When weekly training volume is held constant, lifting two days per week produces similar strength gains to lifting three or more days. So if you’re pressed for time, two solid sessions will do the job.
Recognize the Warning Signs of Underfueling
If you’re already losing weight you didn’t intend to lose, pay attention to other signals. Relative Energy Deficiency in Sport (RED-S) is a condition caused by chronically taking in fewer calories than your body needs for both daily life and training. It affects runners of all genders and experience levels, and its symptoms are often subtle enough to dismiss.
Key warning signs include:
- Recurring injuries: repeated stress fractures or muscle strains that seem out of proportion to your training
- Sluggish recovery: soreness and fatigue that linger longer than expected between runs
- Persistent tiredness: feeling drained even on easy days or rest days
- Hormonal disruption: irregular or missing menstrual periods in women, decreased libido or low testosterone symptoms in men
- Declining performance: running slower despite consistent training, reduced endurance, or worsening coordination
Prolonged energy deficiency also lowers your basal metabolic rate, which means your body starts burning fewer calories at rest. This slows digestion, drops heart rate, and creates a vicious cycle where eating feels harder because your gut processes food more slowly. It also reduces bone mineral density, raising the long-term risk of stress fractures and osteoporosis. If several of these symptoms sound familiar, the solution isn’t to train through it. It’s to eat substantially more.
A Practical Daily Framework
Rather than counting every calorie, focus on building habits that keep your intake consistently high. Eat before you run, even if it’s just a sports drink or a banana 30 minutes beforehand. Eat within 30 minutes of finishing, prioritizing that 3:1 carb-to-protein combination. Then eat regular meals and snacks throughout the day, including calorie-dense options at every sitting.
If your weight is still dropping, add 300 to 500 calories per day and monitor for two weeks. Liquid calories (smoothies, chocolate milk, homemade shakes with nut butter and oats) are the easiest way to increase intake without feeling overly full. Cooking with olive oil, adding cheese or avocado to meals, and snacking on trail mix between meals can also quietly add several hundred calories a day. The goal is to match your energy output consistently, day after day, so your body stops dipping into its own stores to cover the gap.