Your Workouts Could Be Making You Sick — Here’s What You Need to Know
Thanks to the ever-increasing popularity of diets like keto and paleo in recent years, countless people are cutting back on carbs in hopes of shedding some pounds and getting shredded. But here’s the problem: carbohydrates are your body’s primary energy source when you’re exercising at a high intensity. So, if you’re regularly cranking out grueling workouts without supplying your muscles with what they need for fuel, you could come down with “exercise flu.” Not only that, but experts say you may actually struggle to build muscle, too — or worse, lose some of the muscle you already have. So, what is exercise flu? We talked to two fitness experts to find out.
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To be clear, just because you’re working out while sticking to a low-carb diet doesn’t mean you’ll suffer from the exercise flu. However, Barry’s Bootcamp, CrossFit, Orange Theory, F45, and other forms of high-intensity interval training (HIIT) can be extremely strenuous on the body. That means you’ll need to be mindful of how many carbs you’re eating — because if you’re cutting them out completely, your endurance and performance will likely be limited, and you may start feeling under the weather after that sweat session is over.
The good news? Exercise flu can totally be avoided. Here’s what you need to know.
What Is the Exercise Flu?
It’s not uncommon for people to feel a little crummy after giving up carbs. In fact, many people have reported experiencing headaches, fatigue, nausea, dizziness, “brain fog,” gastrointestinal discomfort, decreased energy, and even heartbeat alterations after starting diets like keto. This is typically known as the “keto flu” or the “low-carb flu.” The exercise flu does trigger similar symptoms — however, the difference is that it’s brought on by the combination of intense exercise and a low-carb diet (as opposed to just the diet alone).
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“Some people experience it when under-eating relative to their training demands,” explains Paul Kriegler, an RD and program manager at Life Time.
According to Kriegler, if you have the exercise flu, you’ll probably feel lethargic, worn out, nauseous, or chronically sore.
What Causes Exercise Flu?
When you eat carbs, they’re broken down into glucose that then turns into blood sugar — which your body relies on for fuel during exercise. If you’re not getting enough carbs in your diet, your body will undergo “gluconeogenesis” to make that sugar instead.
“Gluconeogenesis is the process the body uses to break down protein or fat into sugar in order to fuel itself when carb-intake is restricted,” explains Curtis Christopherson, Founder of WRKOUT.
Christopherson notes that the resulting symptoms can include headaches, irritability, weakness, vomiting, nausea, muscle soreness, and cramping.
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“When dietary carbohydrates are scarce, our liver can use certain amino acids and fatty acid backbones to generate glucose,” adds Kriegler. “Any symptoms experienced while this is happening internally are likely not caused by gluconeogenesis itself, but rather by whatever is causing the low-carbohydrate availability.”
The bottom line? If you’re looking to bulk up or build strength, you’ll want to be careful of eliminating too many carbs from your diet. Because if you don’t eat enough of them, your body will be forced to make its own glucose — and it’ll break down your muscle to accomplish that.
But Wait — Isn’t Low-Carb Healthy?
Proponents of low-carb diets say that restricting carbs can help with weight loss, insulin resistance, and reducing high blood pressure, among other benefits — and there is some research to back this up. That makes it an ideal lifestyle choice for people with diabetes and other metabolic diseases. Some studies have shown that the keto diet may help your body to use fat as fuel during exercise as opposed to the glycogen stored in your muscles, thus preventing you from getting tired. However, these findings are more relevant to people who are performing low-intensity workouts or exercising for more than two hours. Plus, Alan Aragon, a co-author of The Lean Muscle Diet, previously explained to AskMen that carbs yield two to five times more energy than fat does.
When it comes to power-based and high-intensity physical activities, low-carb diets seem to be at a disadvantage. Here’s why: carbs have been shown to play a key role in the anaerobic and ATP energy systems (the body’s main fuel sources for exercise), promote recovery after exercise, improve resistance to fatigue during exercise, and help to reduce muscle breakdown during recovery. Studies have also demonstrated that eating carbs can improve exercise performance, particularly when it comes to endurance.
“Exercise of any kind, but especially high-intensity exercise, creates a much greater demand for fuel,” explains Christopherson. “Low-carb diets essentially involve replacing the body’s primary and most efficient fuel source. While it is not impossible to exercise on a low-carb diet, it is much more difficult to adequately fuel the body for exertion.”
How Can I Avoid Exercise Flu?
According to Kriegler, cutting carbs is warranted if you have an intolerance or metabolic disorder. However, if you don’t struggle with these kinds of issues and you participate in high-intensity training, he doesn’t recommend dramatically restricting carbs. It may be helpful to work with a nutritionist along with a personal trainer to come up with a dietary plan and workout regimen that’s tailored to your goals and lifestyle.
Rather than eliminating carbs altogether, Christopherson suggests just reducing your intake to reap many of the benefits of low-carb diets without the risk of flu-like symptoms. Studies have shown that for active people, a high-protein, moderate-carb diet seems to be ideal for muscle growth and body composition.
FYI, you should also be mindful of how much fat you’re getting in your diet.
“One common mistake is that people tend to experiment with reducing carbs while only consuming lean protein sources — so in effect, they’re going low-carb and low-fat at the same time,” adds Kriegler. “This is a scenario in which someone would be too low-carb to fuel workouts, too low-fat to get into nutritional ketosis, and potentially so high in protein they’re stuck in gluconeogenesis-driven glucose-dependent metabolism.”
And if you ever suspect that you’ve already come down with a case of the exercise flu, remember this: it’s important to honor your body’s limitations and avoid strenuous exercise until symptoms subside.
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