You slip on the fastest sneaks, consistently drag your butt to 6:00 a.m. spin class, and never skip post-exercise stretching. But if your eating habits aren’t on point? Then sorry, but you’re leaving fitness results on the table.
Alex Larson, LD, RDN, a Minnesota-based registered dietitian nutritionist, works exclusively with endurance athletes, and nearly everyone she’s coached—from beginners to expert-level competitors—“has had gaps in their nutrition that affected performance, energy, or recovery,” she tells SELF. Even more concerning, certain fueling mishaps can increase your chances of injury and even harm your overall health.
These mistakes aren’t always glaring. Sometimes they’re small, innocuous-seeming habits you may not even be aware of. Other times, they’re actions you intentionally take because someone—maybe your workout buddy, fave spin instructor, or a GymTok influencer—erroneously extolled their virtues. In either case, take heart: These missteps completely fixable! In fact, making a few small tweaks to your fueling habits “can make a big difference,” Larson says.
Read on for some of the most common nutrition mistakes sports dietitians see that wreak havoc on people’s workouts—plus what to do instead. Read on for all the intel you need to level up your exercise routine.
1. You don’t eat before tough morning sessions.
There are plenty of reasons why people roll out of bed and work out on an empty stomach, including feeling strapped for time, being worried about GI discomfort, or (falsely) believing it’ll improve their performance. And while fasted exercise may be okay for short or low intensity morning workouts—think: light 20-30 minute resistance work, yoga, or walks—if you’re doing heavy lifting sessions and endurance exercise lasting 45 minutes or more, you really should prioritize fueling first, Kelly Jones, MS, RD, CSSD, a board-certified specialist in sports dietetics and owner of Student Athlete Nutrition, tells SELF.
Unfortunately, a lot of people have missed this memo. In fact, jumping into a workout on empty is the most popular—and problematic—fueling mistake that Colorado-based sports dietitian Alyssa Lieb, MS, RD, sees people make.
So why’s it so bad? For one, when you exercise, your muscles need fuel to perform their best, and carbs are the best source of that fuel. The thing is, your body can only store a certain amount before you need to replace them by eating more. And if you haven’t eaten in many hours (you know, like…while you’re sleeping), it doesn’t take long to deplete that stash.
When that happens, your brain recognizes that you’re low on energy, and to conserve it, it reduces your ability for high intensity movements, Jones says. The result? You feel sluggish, fatigued, and your performance tanks, Larson explains.
More concerning, though, is that fasted workouts are linked with an increased risk of bone injuries. One 2024 study, published in the European Journal of Sport Science, found that endurance athletes who currently practiced fasted training were 1.61 times as likely to have a bone injury than athletes who ate beforehand. What’s more, if you don’t fuel up before hitting the gym, you’re missing out on an important window to get calories in. Research shows that people who do fasted workouts end up eating fewer calories over the course of the day. Taking in less cals than your body needs can increase the risk of issues like relative energy deficiency in sport (REDs, where your body doesn’t have enough energy to function properly), Lieb says. In short, fasted workouts can not only sabotage today’s gym sesh—they can also set you up for some more concerning longer-term health issues.
What to do instead: This doesn’t need to be complicated. In fact, having too elaborate of a meal beforehand can backfire by triggering GI issues. So keep things simple: If you’re waking up and hitting the gym or the roads very soon after, eat some carbs with very little fiber and no protein five to 15 minutes before breaking a sweat, Jones says. Examples include dates, a spoonful of honey, or even juice or a sports drink, she says. Worried that it won’t sit well with your stomach? “Start small,” Lieb advises. “Whatever you can get in is better than nothing.”
If you have a little more time––think: 30 to 90 minutes before your workout—nibbling on a more substantial snack with a balance of different macros (not just carbs) is ideal, Jones says. This could look like a banana and peanut butter with half of a whole grain English muffin. Everyone is different in terms of what foods they can comfortably stomach and when, so it may take some trial-and-error experimentation to figure out what combo is ideal for you, Jones caveats.
2. You overdo it on fiber.
Colorectal cancer rates are rising, especially among younger people, and eating enough fiber is one of the best things we can do to reduce our risk, according to Lieb. “Fiber definitely matters,” she says. But there’s some nuance here: Eating too much of it before a workout—say, a big ol’ salad before your afternoon spin class, or a large apple on your way to run club—can cause some not-so-pleasant GI issues. That’s because even though fiber is a carb, it’s a complex one and we don’t fully digest it like we do other, simpler carbs. “Our bodies can’t process it, which is why it’s so good for our gut, because it basically just helps keep things moving through our digestive system,” Lieb explains. But that also means it hangs out in our system for a long time, which makes it more likely to get bounced around during exercise and cause problems like bloating, diarrhea, and gassiness. This is why eating fiber-filled snack or meal too close to a workout–for example, scarfing a heaping bowl of oatmeal topped with berries, nuts, and seeds shortly before you head out on a run—can seriously backfire.
What to do instead: Load up on fiber after your workout, and stick to more easily digested carbs (say, white toast, graham crackers, or a banana) beforehand. Keep in mind the daily recommended amounts of fiber—25 grams for women and 38 grams for men—and strive to meet those benchmarks by prioritizing the nutrient during the meals and snacks that don’t directly proceed your sweat sessions.
3. You’re laser focused on protein—and nothing else.
A simple scroll of FitTok shows that protein is all the rage right now. And while overall daily intake of it truly is important, it’s not something you want to hit heavy right before you break a sweat—especially if you’re doing a cardio-centric workout, Lieb explains. One reason? Similar to fiber, protein takes a while to digest, so if you have a ton of it right before you get moving, you run the risk of GI unpleasantness.
Another reason is that carbs are your muscles’ preferred source of energy. That isn’t to say your body can’t power your movements using protein; it can, but the process isn’t as quick or efficient, especially if you’re doing high-intensity exercise, like sprinting or jumping, Lieb explains. So, if you overdo it on protein to the detriment of carb intake, you’re basically shortchanging your performance.
What to do instead: There’s admittedly a lot of nuance here. Consuming some pre-workout protein, like a tablespoon or two of peanut butter, can be okay—especially if you’re embarking on a longer session (think: a two-hour marathon training run) and eating carbs too, Lieb says. That’s because it’s a filling macronutrient that can prevent hunger pangs from striking mid-exercise. But if you’re doing, say, a 45-minute gym workout, reaching for quick digesting carbs is going to be your better bet, Lieb says. Either way, make it a goal to load up on protein after you exercise, and also during times of the day that aren’t directly before a workout.
4. You swear off all processed foods.
Processed foods (especially ultra processed foods, or UPFs, like packaged sweet and savory snacks, flavored yogurts, frozen meals, and energy drinks, just to name a few examples) have been vilified lately, as various research links a diet high in UPFs to a slew of negative health outcomes. But that’s not the complete story, as SELF reported previously, and swearing off this entire food category isn’t realistic or even recommended for most people. In fact, Lieb sees certain processed foods—like graham crackers, sports drinks, and fruit snacks, for example—as optimal sources of pre and mid-workout fuel. That’s because they digest quickly, giving your muscles quick access to energy, and they often don’t cause GI issues. Plus, they’re really convenient, making them a feasible fueling option for people who may otherwise just not eat.
What to do instead: To be clear, we’re not advocating for a full-on, UPF-only diet. “I talk with a lot of athletes about the difference between what you’re eating around a workout and then what you’re eating in your day to day life,” Lieb says. Just know that as long as you’re meeting your overall nutritional needs—for example, you’re gobbling enough fruits, veggies, whole grains, lean proteins, and fiber in the rest of your day—“eating some candy to fuel your run is not only totally fine, but it’s probably the optimal situation,” Lieb says.
5. You neglect post-workout food.
We’ve all been there: You finish that bootcamp workout at 5:00 p.m. but your dinner reservation until 7:30. You don’t want to ruin your appetite, so you hold off on eating. No biggie, right? Turns out, this is a biggie…specifically, a big no-no. That’s because waiting too long to eat after exercise can delay muscle repair, increase soreness, and leave you drained for your next session, Larson explains.
What’s more, the ideal post-workout snack includes a mix of carbs and protein, and if you skimp on carbs specifically, you can reduce your body’s stores of muscle glycogen, the go-to fuel for exercise, which can shortchange your performance in your next workout. On the protein front, that macronutrient is important for muscle recovery, so “having it available when muscles are the most stressed may be helpful,” Jones says. And the International Society of Sports Nutrition recommends consuming protein every three to four hours to maximize muscle repair and growth, Jones points out. So if you take pre-exercise meal timing into consideration, waiting much more than two hours after your workout to eat protein likely means going more than four hours without this powerhouse nutrient, she explains.
What to do instead: Aim to eat a snack that mixes carbs and protein—like chocolate milk, a smoothie, or a turkey sandwich—within 60 minutes of a workout, Larson suggests. Or, if you can have a full performance meal—which Jones defines as a starch, protein, veggies and/or fruit, as well as some healthy fats—within 60 to 90 minutes of a tough workout, you may not need that post exercise snack, she says. Meal examples include a marinated shrimp, rice and veggie bowl; peanut noodles with tofu and snap peas; or a veggie omelet with sourdough, she says.
6. You pound pre-workout.
There’s no debate that caffeine can level up your workout performance (tons of research backs this up), which is why Jones is a fan of sipping coffee pre-exercise or leaning on caffeinated gels during endurance training and racing. But constantly reaching for specific energy drinks and pre-workout bevs can cause you to take in large amounts of other stimulants, like glucuronolactone, taurine and guarana, that aren’t well studied. This means we don’t know what dosing of these stimulants is safe. Plus, keep in mind supplements are poorly regulated in the US, so it’s hard to know what substances (and how much of them) are actually in pre-workout and energy drinks, unless they are third-party tested, Jones explains.
To boot, if you’re hyper-focused on caffeine and pre-workout drinks, you may neglect adequate fluids, carbs, and electrolytes for energy and hydration, Jones points out. And, if you take in too much caffeine—think: over 6 milligrams of caffeine per kilogram of bodyweight a day, which, for a 150-pound person, equates to about 400 milligrams, the equivalent of about four cups of brewed coffee—it can trigger the excessive loss of fluids and some minerals, including electrolytes. That can be a problem, since just a 2% fluid loss can result in decreased physical and cognitive performance, according to Jones.
What to do instead: Rather than reaching for pre-workout, Jones encourages highly active folks to choose coffee or beverages such as Yerba mate over energy drinks, and also add electrolytes to water. With coffee and Yerba mate, “you can be more confident knowing you are getting caffeine as your stimulant, with estimates of quantity known depending on your brewing style,” she explains. Some of her go-to electrolyte products include NOW effer-hydrate tabs, Skratch daily hydration, and Designs for Sport hydration.
Related:
- 5 Foods You Really Want to Avoid Before Working Out
- 7 Best Whey Protein Powders for Truly Tasty Shakes
- 9 Common Snacking Mistakes You’re Probably Making—and What to Do Instead
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