Nutrition for Endurance Athletes: Q&A with Claire Shorenstein (MS RD CSSD CDN)

For this month’s blog post, we sat down with Board-Certified Sports Dietitian Claire Shorenstein (MS RD CSSD CDN) to ask common questions we hear from clients related to nutrition nutrition for runners and eating for performance. We dive into fueling while training in the summer heat, nutrition mistakes to avoid while injured, supplement use, protein needs, marathon training, and more below…


*To learn more about Claire and her work with endurance athletes, visit her website You can also follow her on Instagram (@eatforendurance) and subscribe to her show, The Eat for Endurance Podcast.


What nutrition advice do you have for injured athletes? 


This varies based on what the injury is! My recommendations change if it is a bone injury or post-surgery versus a muscle strain, etc. Moreover, if the athlete is on complete rest from exercise, nutrition needs change compared to an individual who is still running and/or cross training. However, no matter the kind of injury, there are increased caloric and protein needs when the body is healing. Possibly not as high as during peak training, but certainly not as low as a fully sedentary, healthy person. Protein is key in mitigating muscle mass loss as much as possible while healing and especially while resting from sport.


Many might notice appetite changes, whether that is related to depression or anxiety revolving around the injury or decreased energy expenditure. It is a common myth that you don’t need to eat very much during this time period and a common fear that you will gain weight while injured. Don’t fall into the trap of under-fueling! Nutrition is a key component in allowing your body to heal. Quality foods – lean proteins, plant-based foods (fruits, vegetables, beans, legumes, nuts, seeds, whole grains), anti-inflammatory foods (e.g. those rich in omega 3’s like fatty fish or certain nuts and seeds)…these choices will support your body through the repair process. And don’t be afraid to enjoy treats as desired throughout this process. Yes, it’s true that you can’t “get away with” everything you may have enjoyed during training if you’re drastically less active, but being overly rigid or restrictive with your diet will likely backfire (e.g. overeating later, cravings etc) and it doesn’t put you in a good place emotionally. Focus on consuming foods that make you feel good – physically and mentally. 


Another mistake I often see is injured athletes increasing their overall activity levels via cross training and not matching their nutrition appropriately. For example, I’ve had clients who can’t run anymore but suddenly they’re cycling or doing other forms of exercise five to six days a week, often at high intensity and/or long duration. These athletes may perceive that this isn’t quite the same as marathon training, for instance, but their energy expenditure is still high, and the last thing you want is to underfuel and overtrain while injured. 


Lastly, it’s important to note that while some injuries are unavoidable – you trip and fall, for instance – many injuries result from under-fueling, over-training, or other issues with an athlete’s nutrition or training program. So if you’re injured, I recommend taking a look at how you might have gotten to this point and how to prevent it from happening again. And if you’re not injured, examine the health of your fueling approach and training, and make any necessary adjustments to prevent risk of injury in the future.


We’re getting a lot of questions regarding hydration needs while exercising in the summer heat and humidity (which is no joke in New York City) – what do you recommend athletes pay attention to in order to maximize performance?


During endurance training, a runner’s average sweat rate is between 24-32 oz of fluid per hour of activity. However, this varies dramatically by athlete and by environmental conditions! Sodium losses are similarly individual (500-1500 mg/L, or even higher in some cases). All to say, there is no one-size fits all approach to hydration. 


To get a ballpark of where you’re at, I recommend performing your own sweat test at home with a scale. Ideally, choose a workout that is about an hour (we don’t want you to go to the bathroom, as that will produce inaccurate results). Weigh yourself before and after exercise (preferably naked for a more accurate measure). Make note of any fluids you consume during exercise, in ounces, if any. For every pound you lose, that equates to 16 oz of fluid. So if you lose 1lb and consume 16oz of fluid during a 60-minute run, your sweat rate is 32oz/hour. You can perform this test in different situations (time of day, weather conditions, harder efforts, different sports) to learn your body’s unique fluid needs and how they fluctuate. Aim to consume roughly 75-90% of the fluid lost per hour that you exercise, and practice this in training so that you can execute your hydration plan successfully on race day (with adjustments for weather, of course). The goal is never to lose more than 2% of your body weight during a given training session – this will lead to cognitive and performance impairments. If you don’t have access to a scale, a good starting point based on sports nutrition guidelines is to consume 14-28oz of fluid per hour of exercise, and adjust as needed.


Rehydrating after a session is equally important. Aim to replenish 125-150% of your fluid loss in the hours afterwards (pace yourself to avoid feeling ill). Electrolytes consumed in food may be enough for certain individuals (salt your food!), but if you’re a heavy sweater (anything more than 1.2L/hour) or if you exercised for over two hours, then you may require electrolyte supplementation to replenish losses and to help you retain the water you’re consuming. 


For very heavy sweaters (>1.2L/hour), long workouts (>1.5-2 hours), or harder workouts, especially on hot, humid days, it’s important to include electrolytes during your workout. A good starting point is to consume 500-700mg of sodium per liter of fluid consumed. Note that I did not say per hour – this is the one thing we think of as per liter, not by time, because we want to think about the concentration of sodium as it relates to your fluid intake. Tracking your intake can get tricky especially if you use gels because they all vary quite a bit in sodium content, and typically are quite low. If you’re consuming sports drink, it’s much easier to hit electrolyte targets (not to mention, adds more much-needed carbs and fluid). Other options include salt pills, salty foods (like salted pretzels), or even carrying a tiny takeout packet of table salt that you can dip into as needed. Read labels and find out how many mg of sodium your favorite sports nutrition products contain to see where you’re currently at with your salt intake. Save your wrappers after a long run and tally up mg of sodium and divide by the number of liters of fluid you consumed to see how you did! You can also pre-hydrate ahead of your training session with sports drink or other electrolytes. Note that both under and over salting can lead to nausea and other GI issues, so do take stock of how you’re doing with your electrolyte intake to make sure you’re at least getting in that minimum amount (500mg/L), and don’t pop salt pills like candy! It’s much easier to over-salt yourself with salt pills because you can’t taste them. By contrast, have you ever had something salty during or after a long run and have it taste like the best thing in the world? Yeah, that’s your body saying – I need salt, give me more!


This question is common amongst female runners we see in the clinic – is it necessary to supplement with iron and magnesium if you are highly active?


When it comes to supplementation, the starting point always is performing labwork, followed by a food-first approach in addressing any deficiencies. If no deficiency exists, there is no performance benefit to supplementing any micronutrients (even a multivitamin) as long as the athlete is consuming a balanced, adequate diet (key word is adequate – you must be eating enough relative to your exercise energy expenditure to avoid being at higher risk for deficiencies). 


Generally speaking, micronutrient requirements vary by age group and gender. For instance, the Recommended Dietary Allowance (RDA) for iron for women (not pregnant or lactating) ages 19-50 are 18mg/day, and 8mg/day for women 51+. Men require 8mg/day ages 19+, with higher needs during adolescence (11mg/day). As for Magnesium, the RDA for adults 19-51+ years is 400-420mg daily for men and 310-320 mg for women (not pregnant or lactating). 


Iron is considered a nutrient of concern for athletes, for a variety of factors. Iron depletion or deficiency may result from low iron intake, inadequate energy intake (this can be intentional or unintentional), periods of rapid growth, training at high altitudes, menstrual blood loss, foot-strike hemolysis, blood donation, or injury. Furthermore, we lose iron in sweat, urine, and feces. Thus, this is an important nutrient to keep tabs on. Be sure to get your ferritin (iron stores) tested, among the other common iron biomarkers. Do not take any iron supplements 24 hours prior to your test, and avoid high intensity exercise right before your test as well. 


I highly recommend also getting Vitamin D tested, as this is another nutrient of concern for athletes (it’s key to absorbing calcium, among many other key roles), and it’s harder to get in food. Also, if you live in the Northeast, it’s very common for Vit D to be on the lower side. In my practice, this is the most commonly supplemented micronutrient. 


If your test results reveal a deficiency, then we tweak the diet and may temporarily use supplementation to reach normal levels. For iron, consume a variety of foods rich in well-absorbed iron (heme iron, from animal products, and/or non-heme iron from plant foods along with Vit C-rich foods for increased absorption). Examples of iron-rich foods include lean beef, whole eggs, oysters, chicken, turkey, fortified cereals, lentils, beans, tofu, pumpkin seeds, cashews, and spinach. 


Magnesium is an electrolyte lost in sweat, but not in as high of a concentration as sodium. Sometimes I have my clients add in Magnesium powders or pills if they’re constipated (supplements can sometimes help) or having sleep issues (consuming at night also sometimes helps), but mostly, we’re looking at foods not supplements. Magnesium is found in plant foods like legumes, dark green leafy vegetables, nuts, seeds, whole grains, and fortified cereals, as well as in fish, poultry, and beef. So unless you’re a very heavy sweater (or to be honest, even if you are), you’re likely okay just getting it in the diet. Magnesium commonly is under-consumed though so do evaluate your dietary intake to make sure you’re regularly consuming magnesium-rich foods. 


How do you calculate protein needs?


For endurance athletes, 1.6-1.8 grams of protein per kilogram of body weight is a good starting point. This is much higher than the protein needs for the average healthy sedentary adult (0.8 – 1g per kg body weight). Intakes of 2g+ per kg body weight is not necessary or helpful, except for in specific types of situations (e.g. if calorie intake is lower and you want to maintain lean body mass, during certain types of injuries, if training volume is extremely high – but all of these situations are temporary). Once you calculate out your individual protein goal range, aim to spread out your protein intake throughout the day in more moderate amounts (e.g. consume every 3-5 hours and post-workout). Another helpful protein guideline is post-workout, aiming for 0.3-0.5g protein per kg bodyweight, as part of a balanced meal with carbohydrates of course. 


For runners training for a fall marathon, what nutrition changes should they start to make in preparation?


This is a HUGE topic in the sports nutrition world, so I will give a very brief overview! We covered the hydration piece above, which is a key component to overall fueling success. Before your long runs or harder workouts, prioritize having a meal or snack that is rich in carbs with a small amount of protein (8-10g). Training the gut, in terms of tolerating your pre-run meal as well as during your run sports nutrition, takes TIME so start gut training as early as possible in your training cycle. For longer runs (>60-90min), aim to consume 30-60g of carbs per hour (this guideline is for everyone, regardless of age, gender, or body weight). This equates to a gel or equivalent roughly every 30-45 minutes, and note that the harder your effort, the faster you will burn through your carbs! Play with different products and see what works best for you. Most runners don’t love consuming fuel during a run, and what works for you is highly individual, so the goal is to find calories that are tolerable to YOU. Some runners like to research what products will be available along the course on race day to streamline their nutrition, but I highly recommend carrying the products you plan to use (and bring an extra just in case). Don’t stress about the simple sugars – this is the time we need them. Your working muscles need and want easy to digest, simple carbs, and these calories are an investment in your performance. After your training session, get a balanced meal and snack as soon as you are able (~20-40g protein, or use that 0.3-0.5g/kg guideline). The recovery window does not suddenly slam shut, but 30-60 minutes after a training session is a great eating opportunity, since your body is primed for it. If you don’t eat soon thereafter, it can throw your body off for the remainder of the day.


While we are not licensed professionals in nutrition, the team at Perfect Stride is well-equipped to help with your injury, movement, and training needs. Reach out to us today for a free 15-minute discovery call to learn more about our rehab and performance services to maximize your athletic goals. 


More articles you may find interesting

Search for a topic of your interest

“I have been to several PT practices over the years, and Perfect Stride deserves five stars. I worked with Vikash, who was knowledgeable and thorough and got me back on my feet – literally! Although I did not work with any of the other therapists, I observed they maintain the same high standard as Vikash. And Austin does a great job of keeping everything running smoothly. I am glad my doctor recommended Perfect Stride!”


– Brian C

Find out whether you have the necessary mobility for running




We understand that making decisions about your health are very important and can be difficult. To better assist you
in making this decision and answering your questions about how Perfect Stride can best help you, we offer FREE 15 minute discovery calls with a Doctor of Physical Therapy.

Call Now Button