More Fatigue on Your Runs May Come Down to These Key Nutrients. A Dietitian Explains How to Fill the Gaps for More Energy.

When your usual pace suddenly feels harder, your legs feel less responsive to intensity, or you cannot seem to recover between runs, you probably first question your training. But it’s not always the workouts themselves.A crucial factor to consider: Can your nutrition support your hard work? And we’re not just talking about carbohydrates and protein.Endurance runners have substantial energy and nutrient needs, thanks to training increasing energy demand. You need calories, vitamins, and minerals to support oxygen transport, tissue repair, immune function, and bone remodeling—not just for your health, but for performance and injury prevention too.At the same time, many runners’ fears of GI issues may influence nutrient intake quality, while busy schedules can make eating enough more challenging, and food restriction can remove important nutrients from the diet when the body needs them most.Proof: In a study examining nutrient intake in 95 endurance athletes, researchers found a high percentage of participants consumed inadequate amounts of calories (77 percent of athletes), carbohydrates (96 percent), and dietary fiber (50 percent). Up to 97 percent of athletes also missed out on essential omega-3 fatty acids with anti-inflammatory effects, along with vitamin D, vitamin E, vitamin K, folate, magnesium, potassium, and choline, with more than 50 percent of participants missing each of these key nutrients.Female athletes were also more likely than male athletes to fall short on protein and vitamin B12, whereas male athletes appeared to have lower intakes of fiber, an omega-3 known as ALA, and water. This evidence suggests that eating patterns that appear healthy on the surface or may fit the description of a “higher carbohydrate diet” do not always provide enough nutrition to match energy expenditure.There is an important distinction, however, between a low dietary intake and a true nutrient deficiency. A runner may consume less than the recommended amount of a nutrient without having a clinically diagnosed deficiency or insufficiency. Symptoms, health history, dietary assessment, and sometimes blood testing are needed to provide a clear picture.Athletes have higher energy demands, higher energy output, and also lose some nutrients through sweating; therefore, ensuring adequate intake of nutrients over time is important for health, recovery, and showing up consistently for training if performance is a goal. Here’s what to keep in mind to make sure you’re getting enough from your diet to support your training.First, Ask Whether You’re Eating EnoughBefore you go straight to adding a multivitamin or other supplements, assess your total daily energy intake. Many nutrient deficiencies often begin with or occur secondary to low energy availability (LEA), which occurs when the body does not receive enough energy to cover both exercise and essential physiological functions.In chronic LEA, the body is left trying to support training while also maintaining reproductive hormones, bone health, immunity, recovery, and normal cellular functions.No supplement can compensate for chronic underfueling. The foundation for healthy training and optimized performance remains enough total nutrient-dense food, sufficient carbohydrates, adequate protein to support repair, and enough dietary fat to support hormonal function and the absorption of fat-soluble vitamins.Once you have that foundation in place, these are a few nutrient gaps to recognize, as they appear more prevalent in runners and may or may not be detected in bloodwork.IronWhy it’s so important for runnersIron is one of the most important nutrients for endurance runners because it is directly involved in oxygen transport and energy production. You need it to make hemoglobin, which carries oxygen in the blood to muscle.When iron stores decline, running at your usual pace can start to feel harder. You may experience higher fatigue, reduced endurance, difficulty completing quality workouts, slower recovery, and higher fatigue between sessions.Where to get itTo support iron intake, regularly include foods such as beef, poultry, seafood, eggs, lentils, beans, tofu, pumpkin seeds, and iron-fortified cereals. Cooking in a cast iron skillet can also help to boost iron content in those foods.The body absorbs heme iron from animal foods more efficiently than nonheme iron from plant foods. But pairing plant sources with vitamin C can improve that absorption. Try lentils with tomatoes, tofu with broccoli, beans with bell peppers, or iron-fortified cereal with berries.Coffee and tea can interfere with iron absorption. If you have low iron, drink your caffeine before your iron intake, with a gap in time.Vitamin DWhy it’s so important for runners: Vitamin D supports calcium absorption, bone remodeling, muscle function, and immune regulation. Rather than suddenly losing aerobic capacity, a runner with inadequate vitamin D may experience impaired muscle function, frequent illness, or an increased susceptibility to bone stress injury.Where to get it: Even if you eat a varied diet, it’s hard to get enough vitamin D from food sources. But you can find it in fatty fish, egg yolks, fortified dairy milk, and fortified plant beverages.Vitamin B12 and FolateWhy it’s so important for runners: Vitamin B12 is required for normal red blood cell production, DNA synthesis, and neurological function. Vitamin B12 deficiency can decrease the body’s ability to transport oxygen and contribute to fatigue and reduced exercise capacity.Similarly, folate plays a role in DNA synthesis and red blood cell formation. Because training continually creates a need for tissue repair, cellular turnover, and red blood cells, you need adequate folate to help with each process.Where to get it:Vitamin B12 deserves particular attention among vegan runners because you’ll find dependable natural sources in animal foods including meat, fish, dairy foods, and eggs. B12 is also found in fortified cereals, fortified plant beverages, and fortified nutritional yeast.Folate is found in leafy greens, beans, lentils, citrus fruit, avocado, and fortified grains.MagnesiumWhy it’s so important for runners:Magnesium contributes to energy production, glucose metabolism, nerve transmission, bone health, and normal muscle contraction and relaxation. Therefore, magnesium deficiency can lead to fatigue, muscle weakness or cramping, impaired neuromuscular function, and reduced exercise tolerance.Where to get it:Food sources include pumpkin seeds, almonds and cashews, beans and lentils, whole grains, leafy green vegetables, soy foods, and black beans.ZincWhy it’s so important for runners:Zinc plays a role in protein synthesis, tissue repair, immune function, wound healing, and numerous metabolic reactions involved in helping you actually adapt to training. Avoiding illness and recovering from training and illness are important to maintaining consistency in training, a key element to performing well on event day.Where to get it:Zinc is found in oysters, shellfish, beef, poultry, dairy foods, beans, lentils, nuts, seeds, and fortified cereals. Depending on the food, soaking, sprouting, fermenting, and using leavened breads can improve mineral availability.Alpha-Linolenic Acid (ALA)Why it’s so important for runners:Alpha-linolenic acid, commonly called ALA, is important because it is an essential fatty acid that you must get from diet—the body cannot make it. Like all omega-3s, ALA helps tame inflammation, which runners experience postworkout, and it supports heart and brain health.Where to get it:You’ll find ALA in ground flaxseed, chia seeds, walnuts, hemp seeds, soybeans, and soy foods. Add a tablespoon of ground flaxseed or chia seeds to oatmeal, cereal, smoothies, or yogurt. Toss walnuts into snacks, salads, and grain bowls.In addition to ALA, many of these foods also contribute fiber, magnesium, protein, and other nutrients that support overall dietary quality.Eicosapentaenoic Acid (EPA) and Docosahexaenoic Acid (DHA)Why it’s so important for runners: Like ALA, EPA and DHA are essential fatty acids you must eat in the diet. EPA and DHA have attracted considerable attention in sports nutrition because of their potential effects on inflammatory responses, muscle soreness, immune function, cardiovascular health, and neuromuscular function.Some research suggests that EPA and DHA supplementation may reduce muscle soreness or influence certain markers of exercise recovery and submaximal exercise physiology. However, these effects have not consistently translated into improvements in endurance performance. Keep in mind, for runners, the ability to recover and maintain immune function does lead to better consistency in training, which supports improved performance.Where to get it:EPA is a long-chain omega-3 fatty acid found primarily in salmon, sardines, herring, mackerel, and anchovies. Runners who eat fish should aim to include two 3- to 4-ounce servings per week.DHA is another long-chain omega-3 fatty acid found in many of the same foods as EPA, including salmon, sardines, trout, herring, mackerel, and some shellfish.ALA can be converted into DHA, but only in small amounts, so it’s important for runners to include both sources. This is why eating walnuts or flaxseed is not nutritionally identical to eating fatty fish. Both can be valuable, but they provide different forms of omega-3 fatty acids.FiberWhy it’s so important for runners:It’s common for runners to experience GI issues, which can then have a large negative effect on performance. Maintaining a healthy gut, as well as the immune system, with a healthy level of fiber intake can help ensure you can tolerate your race-day nutrition plan.Where to get it:Fiber-rich foods include beans and lentils, whole grains, fruits and vegetables, and nuts and seeds. These foods also provide vitamins, minerals, and polyphenols that runners may miss when the diet becomes overly dependent on processed carbohydrates and sports nutrition products.An important note: If you’re eating a very high-energy diet, you may not need to increase fiber in direct proportion to additional calories. Attempting to consume extremely large amounts can create fullness, bloating, or gastrointestinal distress that makes it harder to meet total energy and carbohydrate needs.While it makes sense to consume lower-fiber foods such as cereals, bagels, or waffles prior to runs, daily nutrition should still emphasize fiber-rich, nutrient-dense complex carbohydrates such as oats, whole grains, beans, lentils, fruits, vegetables, potatoes, and whole-grain breads throughout the rest of the day.How to Reduce the Risk of Nutrient GapsYou don’t need a perfect diet, but you do need enough food, sufficient variety, and consistency across the training cycle by making sure you get enough of these key nutrients.Use these habits as your foundation:Adjust total food intake when training volume increases Include carbohydrate at meals and around training Eat fruits and vegetables in several colors each day Include calcium-rich foods two to four times per day Eat iron-rich foods regularly Include nuts, seeds, beans, lentils, or whole grains most days Include a regular source of ALA, such as chia seeds, ground flaxseed, walnuts, or soy foods Include fatty fish approximately two times per week, or evaluate an algae-based source of EPA and DHA if you do not eat fish Build fiber intake through whole foods while adjusting the amount and timing before important runs Include dietary fat from foods such as olive oil, nuts, seeds, avocado, eggs, and fatty fish Use fortified foods when natural food sources are limited Build a specific replacement plan whenever you eliminate a food group Dr. Namrita Brooke is a full-time endurance sport coach and sport nutritionist advising active individuals and amateurs to professional athletes. She is also an adjunct professor in the Department of Movement Sciences and Health at University of West Florida. Professionally, she also serves on the Board of Editors of the Sports Nutrition Care Manual and remains involved in nutrition and exercise-related research, student mentorship, and coach development. Namrita's personal athletic experience ranges from ultra-endurance mountain biking to off-road triathlon, cross-country mountain bike racing, gravel cycling, duathlon, cyclocross, running, and trail running. Her research background includes hydration and sports drink research, and the interaction of nutrition, physical activity, and the brain.