Whether you’re logging early miles on the Lakefront Trail or building toward the Chicago Marathon, nutrition is one of the most talked-about and most misunderstood parts of training. It’s often framed around what to cut out rather than what your body needs to perform and recover.
Good nutrition for runners isn’t just about race day. Adequate fueling plays a direct, well-documented role in injury prevention, particularly for bone health and tendon recovery. Both are closely tied to the running injuries we treat every week at RESPORT Chicago’s Old Town clinic.
This guide covers the fundamentals of running nutrition: fueling for training and racing, post-run recovery nutrition, and the nutrients most relevant to runners. The emphasis throughout is on adequate, sustainable fueling, not restriction.
Why Adequate Fueling Matters More Than Most Runners Realize
Running is a high-energy-demand activity. Consistently under-fueling relative to your training load carries real risks that go well beyond feeling tired.
This is worth stating clearly, because a lot of casual running culture emphasizes restriction or “earning” food through mileage. The evidence points the other way: adequate fueling is foundational to staying healthy as a runner, not something to minimize.
RED-S in Runners
Relative Energy Deficiency in Sport (RED-S) is a well-documented condition affecting athletes who consistently take in less energy than their training requires. It can affect bone density, hormonal function, immune function, and recovery capacity. It’s also associated with a meaningfully higher risk of stress fractures and other injuries.
RED-S isn’t limited to elite athletes. It can affect recreational runners training at high volume without matching their intake to their output, including many of the Chicago runners stacking up miles during a summer marathon build.
If you’re training at meaningful volume and notice any of the following, talk with a medical provider or sports dietitian rather than assuming it’s a normal part of training hard:
- Consistently low energy
- Changes in your menstrual cycle (for female runners)
- Frequent illness
- A stress fracture or recurring bone-related injury
Carbohydrates for Runners: Your Primary Fuel
Carbohydrates are the foundation of nutrition for runners. They’re the body’s preferred and most efficient fuel for running, especially at moderate-to-high intensities. They’re stored as glycogen in the muscles and liver and can be accessed quickly during exercise.
Adequate carbohydrate intake supports both training quality and recovery. It’s also one of the nutrients runners most often under-prioritize, usually after absorbing low-carbohydrate diet trends that aren’t well suited to endurance training.
Sports nutrition guidelines generally scale carbohydrate needs to training volume. Runners doing higher weekly mileage or more frequent high-intensity work need proportionally more, since glycogen stores must be replenished to support performance and recovery.
Rather than chasing a rigid number, most runners do best by making carbohydrate-rich foods a substantial, consistent part of their diet, especially around training days. Persistent low energy during runs or unusually slow recovery can be a sign your intake isn’t keeping up with your training.
Protein for Runners: Recovery and Tissue Repair
Protein plays an essential role in muscle repair and adaptation after training. It also supports the connective tissue and tendon adaptations covered throughout our injury guides. Endurance athletes generally have somewhat higher protein needs than sedentary people.
Running-friendly protein sources include:
- Lean meats and poultry
- Fish
- Eggs and dairy
- Legumes
- A combination of plant proteins, for runners on a plant-based diet, to cover all essential amino acids
Spreading protein across the day, rather than eating most of it in one meal, is generally more effective for ongoing muscle repair and adaptation.
Fats: Often Underappreciated
Dietary fat is an often-overlooked part of nutrition for runners. It supports hormone production and the absorption of certain vitamins. It’s also an important fuel source during lower-intensity, longer-duration running.
Runners who significantly restrict fat may unknowingly compromise both performance and broader health, including the hormonal function tied to RED-S. Nuts, seeds, avocados, olive oil, and fatty fish provide healthy fats. Fatty fish also supplies omega-3 fatty acids, which are associated with anti-inflammatory properties.
Micronutrients Especially Relevant to Runners
Iron Deficiency in Runners
Iron deficiency is a genuinely common concern among runners, particularly female runners, distance runners, and those following vegetarian or vegan diets. Iron plays a central role in oxygen transport.
Low iron can contribute to fatigue, weaker performance, and impaired recovery. It’s sometimes mistaken for being “out of shape” or overtrained when the real issue is a nutritional deficiency.
If you have persistent, unexplained fatigue alongside declining performance despite consistent training, ask a physician to check your iron status. Supplementing without a confirmed deficiency isn’t generally recommended and can carry its own risks.
Calcium and Vitamin D
Calcium and vitamin D are directly relevant to bone health, which matters enormously for stress fracture prevention. Vitamin D supports calcium absorption, so the two work together. We cover the bone-injury side in more detail in our Guide to Common Running Injuries.
These nutrients deserve extra attention if you:
- Train at high volume
- Run mostly in low-sunlight conditions, as many Chicago runners do through the long winter months
- Restrict dairy or other calcium sources without an adequate alternative
B Vitamins
B vitamins play various roles in energy metabolism and red blood cell production. Most runners get enough through a varied diet that includes whole grains, lean proteins, and leafy greens. Runners on more restrictive diets should make sure their intake is sufficient.
Fueling Around Training and Racing
Pre-Run Nutrition
For runs longer than about 60–90 minutes, or higher-intensity efforts, having carbohydrate available beforehand supports better performance. It also lowers the chance of significant energy depletion, often called “hitting the wall” or “bonking.”
In practice, that means a carbohydrate-containing meal or snack in the hours before your run. Timing and portion depend on your individual tolerance, since some runners handle eating close to a run better than others.
Fueling for Long Runs and Races
For runs or races lasting beyond roughly 90 minutes, taking in carbohydrate during the effort helps maintain blood sugar and glycogen as your stored fuel runs down. Sports drinks, gels, chews, and other easily digestible sources all work.
Practice your race-day fueling during long training runs first. If you’re training for the Chicago Marathon, your summer long runs along the lakefront are the place to test products and timing. Race day is not the time to try something new.
Post-Run Recovery Nutrition
The period after a hard or long run is an important window for recovery. A combination of carbohydrate (to begin replenishing glycogen) and protein (to support muscle repair) is the goal.
The popular “30-minute window” has been somewhat overstated in casual running culture. Research suggests the window for meaningful benefit is considerably more flexible. Eating a balanced recovery meal or snack within a couple of hours after a significant session is a reasonable, practical guideline.
Staying Hydrated
Adequate hydration supports both performance and recovery. Needs vary with your sweat rate, the climate, and effort intensity, so paying attention to your body and adjusting for conditions works better than any single universal number.
Running in Chicago’s summer humidity demands far more attention to hydration than a cool fall run along the North Branch. For runs longer than about an hour, especially in warm weather, adding electrolytes to plain water helps replace what you lose through sweat.
Electrolytes can help prevent cramping. In more extreme cases, they help prevent hyponatremia (dangerously low blood sodium), which can result from drinking large amounts of plain water without electrolyte replacement during very long efforts.
Read our full Hydration for Runners Guide.
How Nutrition for Runners Connects to Injury Prevention
The link between nutrition for runners and injury risk is more direct than many people realize:
- Energy and carbohydrate intake support the recovery processes that let tendons and muscles adapt to training stress, connecting directly to the work in our [guide to strength training for runners](INTERNAL LINK: strength training for runners).
- Calcium and vitamin D support the bone density that’s central to stress fracture prevention.
- Avoiding RED-S protects against hormonal and immune consequences that can compound injury risk well beyond nutrition alone.
That’s why we treat nutrition as a genuine pillar of running injury prevention in Chicago, alongside training load, strength work, and running mechanics, not a separate, secondary consideration.
Frequently Asked Questions
Do I need to eat differently on rest days versus running days?
Your energy needs are lower on rest days than on hard training days. Still, consistent, adequate overall nutrition, rather than dramatic day-to-day swings, tends to best support recovery and long-term training consistency.
How do I know if I'm not eating enough for my training volume?
Signs can include persistent fatigue, declining performance despite consistent training, frequent illness, poor recovery between sessions, changes in menstrual cycle for female runners, or a history of stress fractures. If you notice these patterns, discuss your nutrition with a medical provider or sports dietitian.
Should runners avoid carbohydrates to lose weight?
Significantly restricting carbohydrates isn't well suited to running, since carbs are your primary and most efficient fuel. Runners with weight or body composition goals are usually better served by a qualified sports dietitian who can balance those goals with adequate fueling for training and health.
What should I eat before a long run?
A carbohydrate-containing meal or snack in the hours beforehand generally supports better performance. Ideal timing and foods vary by person, so practice during training rather than experimenting before an important run or race.
Do I need supplements as a runner?
Most nutritional needs can be met through a varied, adequate diet. Some deficiencies, particularly iron and sometimes vitamin D, are common enough among runners that targeted supplementation may be appropriate. This is best guided by a deficiency confirmed through bloodwork.
How does nutrition connect to stress fracture risk?
Adequate calcium and vitamin D, along with enough overall energy to avoid RED-S, play a meaningful role in bone density. That directly affects your vulnerability to stress fractures.
Is intermittent fasting compatible with serious running training?
It depends on your training volume, goals, and how it’s implemented. It isn’t a universal recommendation for runners, given how important carbohydrate availability is around training. Discuss it with a sports dietitian familiar with endurance training.
Where can Chicago runners get help with nutrition and injury prevention?
RESPORT Chicago’s Old Town clinic works with runners across the North Side on running analysis, strength guidance, and injury treatment. Our team can help connect you with appropriate nutrition resources as part of a complete plan.
Fuel Your Chicago Training the Right Way
Nutrition for runners works alongside training load, strength work, and running mechanics as a pillar of both performance and injury prevention. Getting it right means prioritizing adequate, consistent fueling, not restriction.
RESPORT Chicago’s Old Town clinic offers Running Gait Analysis, strength guidance, and injury treatment for runners from Lincoln Park, Old Town, and across the North Side. We can also help connect you with nutrition resources so your plan covers every part of healthy, sustainable training.
Ready to build a complete approach to healthy running? Book an assessment at RESPORT Chicago.
Questions? Contact our team — we’re happy to help you determine whether ESWT is right for your condition.
The RESPORT Chicago clinical team medically reviewed this article. It is intended for general educational purposes and is not a substitute for personalized guidance from a physician or registered dietitian. If you’re experiencing signs of inadequate fueling or disordered eating patterns, please speak with a medical provider.
