Fueling: Carb, Sodium, & Hydration Roles

Let’s break it down: what’s important during my long run and why?

Rebecca Youngs, MS, RD, LD

Sports Dietitian, Fit For Life Physical Therapy

Before we talk about the key nutritional elements to focus on DURING a long run, we need to address a few basics and how these factors could impact our run later in the day:

1. Fiber: fibrous foods (think: salad, raw vegetables, fruits with seeds and skins, whole, sturdy grains, etc.) can be hard on the gastrointestinal (GI) system and can reck havoc on ours run. Avoid highly fibrous foods the night before and the morning of a long run. Ideas of foods to consume before you run: white bagels, toast with a small amount of nut butter, banana + graham crackers, fruit snacks, oatmeal, or a granola bar. 
2. Hydration: going into a long run already dehydrated is recipe for disaster when it comes to cramps, diarrhea, and side stiches. If you look ahead and notice the weather for your long run day is going to be hot and humid, start hydrating 1-2 days before! Use electrolyte powders, water dense foods (cucumber, watermelon, juicy fruit) and beverages like tea and coffee (yes, they count!) to ensure you are starting your run hydrated.
3. Meal timing: larger or more “regular” meals should be eaten 3-4 hours before your long run so that food can digest. If you are not having a full meal before your run, or you only have 30 minutes- 1 hour before you start, try to get in simple, quick digesting carbohydrates (fruit snacks, dried fruit, half a gel, pretzels, half a banana, etc.) so that it can empty the stomach quickly. 

Now that we have some basics down, what role do carbohydrates, sodium, and hydration play during a longer run?

Carbohydrates

The purpose of fueling during a long run specifically, if the run is going to be longer than 90 minutes, is to replace the carbohydrates that we burn for energy so that we can sustain activity at a high rate. In our body, the storage form of these carbohydrates is known as glycogen. Think of glycogen as the stocked up frozen veggie you grab from the freezer once you’ve gone through all the fresh ones in the fridge. Once we burn through any of the carbohydrates we just ate before our run, and all our carbohydrates stored in the form of glycogen, our body will switch to trying to burn fat for energy. Although this is possible, and our body can use fat to create glucose, it is not very efficient and takes much longer for this process to happen. So, if we are trying to rely on fat, we will likely become way more fatigued at a faster rate than we would using glycogen. How do we overcome this? We take in carbohydrates in the form of chews, gels, carbohydrate rich fluids, or simple carbohydrate rich foods. If we actively take in carbohydrates (30-40 minutes into a long run and every 20-45 minutes based on pace and intensity), we don’t have to completely burn through our glycogen (freezer veggies) and possibly risk having to use fat for fuel. Additionally, the intensity of our exercise helps to dictate which type of fuel, carbohydrates or fat, will be used most efficiently, and guess what? As endurance exercise intensity increases, we rely more heavily on carbohydrates. 

Ingesting carbohydrates during exercise also maintains blood sugar levels within the body helping to prevent bouts of hypoglycemia, or low blood sugar which has symptoms ranging from confusion and dizziness, to sweating and weakness. If you struggle with blood sugar issues or are a diabetic, meet with a sports dietitian to come up with a personalized plan! In general, consuming a carbohydrates source with a small amount of complex carbohydrates will allow slower release of glucose which can be beneficial to avoiding blood sugar highs and lows.

Some carbohydrate products have now added caffeine to the mix. Caffeine is considered an ergogenic aid, meaning it can increase athletic performance and increase the time it takes to feel fatigued. In some, higher doses of caffeine may cause side effects such as increased heart rate, trouble focusing, or GI distress, but lower doses, around 150-200mg, have been studied and still have performance enhancing benefits without the added side effects. The use of caffeine during activity is very individual. Using caffeine should be trialed before an event or race. Athletes should start with low doses of 100-200mg of caffeine. 

For well-trained athletes who are used to taking in maximum amount of carbohydrates, or may struggle with GI issues, gels, chews, or drinks with multiple transportable carbohydrates should be considered. The mixture of two different carbohydrates, mainly glucose and fructose, added to gels, bars, chews, and sports drinks have been researched heavily in endurance activities. Ingesting both glucose and fructose leads to much higher oxidation rates of carbohydrates. What does this mean? Glucose tends to be oxidized or converted into energy at a much faster rate than fructose. The transporter in the small intestine that gets glucose into our system only works with glucose, so once we have filled up “the seats on the bus”, we can’t add anymore glucose. This can lead our energy levels and to plateau. Fructose is absorbed by a different transporter than glucose, so if we consume a carbohydrate source with both glucose and fructose, we can fill up double of the seats, burn double the amount of carbohydrates, and get energy into our system much faster. 

So, how do we choose between a solid like a chew, a gel, or a drink? Personal preference! Research comparing the rates of oxidation between various forms of carbohydrates has shown that there is no difference between varying forms! If you have never used carbohydrates on a long run, try a few different brands and types!

Hydration and Electrolytes

Every runner knows that they are going to sweat and sweat a lot on long runs. Sweat rates will differ per athlete, but on average we can lose 1,000mg of sodium in just 2 pounds of sweat. The electrolytes and minerals that we lose in sweat are sodium, chloride, magnesium, potassium, and calcium. Losing just 2% of our body water through sweat can decrease aerobic capacity! Our goal is to avoid this! Dehydration can also be life threatening for some athletes, so it is important to have a solid hydration plan in addition to your fueling plan. There are some drinks that can be used as BOTH a form of hydration/electrolytes, and fuel, but not all! Additionally, some electrolyte powders or drinks may not be as effective as you think! The absorption of fluids and solutes (think: electrolytes) occurs in the small intestine. There is a special transporter in our small intestine called the sodium glucose transporter 1 (SGLT-1) that sodium and glucose “ride on” to get into our small intestine. When SGLT-1 transports glucose and sodium across the small intestine, a large amount of water movement occurs with it. So, to maximize how quickly and efficiently we are getting both water and electrolytes into the small intestine, we want our fluid choice to have a small amount of glucose along with our electrolytes since this will allow water to be absorbed much quicker. Even though there is glucose in these drinks, some may not have enough to be used as both a fuel and way of getting in fluid or electrolytes. If you are a heavy sweater (sweats that stings your eyes, gritty or pasty feeling on your skin after a run, streaks of white on your skin or clothes) you may need to supplement with additional sodium through salt sticks, soy sauce, or ketchup packets (yes- it works). 

Now that we have the science down and what carbohydrates, water, and electrolytes do to our athletic performance, how do we choose? There are so many types of fuel out there and it can be very overwhelming. Use the table below to help guide your search! Each athlete is very different, and everyone should spend a little bit of time trying a few products, flavors, and brands to determine the best option for them. The key to nailing down a fuel and hydration plan is by practicing on long runs BEFORE race day! 

Rebecca Youngs, MS, RD, LD