Low-Carb Strength Training and Cardio: What You Need to Know

Woman doing weight training

 

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Depending on your fitness goals, finding the type of exercise that works best for you can be an asset to weight management, building muscle, and improving physical and mental health.

What we eat (and how much we eat) provides the fuel we need for activity, whether it be getting dressed, doing chores, or working out. If you’re following a low-carb diet, you may be wondering how exercise is affected carb restriction.

It is possible to safely combine a low-carb diet and exercise, but it will help to understand how your body uses carbs to fuel different types of activity. Here’s everything you need to know about low-carb strength training and cardio.  

Aerobic v. Anaerobic Metabolism

Carbohydrates are your body’s preferred source of fuel for intense exercise. Fat and protein, while essential components of a balanced diet, don’t provide the same level of energy for high-performance exercise.

There are two types of metabolism your body can use: aerobic and anaerobic. Endurance activities like running and cycling use aerobic metabolism while the muscle activity required for lifting weights is anaerobic.

Aerobic activities use carbohydrates, fat, and protein for energy. Your body uses aerobic metabolism to fuel many tasks, including your basal metabolic rate (the energy required only for your body’s basic functions).

Aerobic metabolism makes use of several energy sources, so it's efficient than anaerobic metabolism, which requires glucose.

Anaerobic metabolism draws on your body's glycogen stores. Your body primarily stores glucose in your liver, but it's also found to a lesser extent in your skeletal muscles.

A byproduct of anaerobic metabolism is lactic acid. The buildup of lactic acid in your muscles during a workout leads to feelings of fatigue and soreness. Some athletes may “carb load” before a competitive sporting event in an effort to prevent this.

Carbs as Fuel

Knowing your body prefers to use carbs for energy, you might be wondering how reducing your carb intake will affect your exercise performance. If you are eating fewer carbs, you'll want to make up those calories with healthy fats and protein.

Keep in mind that scientific research on low-carb diets and average exercisers is limited and even contradictory. While the information available can help you better understand the potential outcomes, pay attention to how your individual body and metabolism respond to any adjustments you make to your diet and activity level.

The weight loss potential for a low-carb or Ketogenic diet is well known, but some research has demonstrated low-carbohydrate-high-fat diets may alter body composition in ways that could affect athletic performance.

In the past, researchers working with lab rats proposed low-carb diets lower bone mineral density. However, more recent studies following people on long-term low-carb diets to treat medical conditions (such as epilepsy) indicated carb restriction over time doesn’t seem to have a negative impact on bone density.

Athletes performing higher intensity endurance exercise on a low-carb diet have reported reduced efficiency during the first few weeks cutting carbs—though most felt their bodies seemed to recover within two to four weeks.

One study demonstrated a typical pattern for endurance athletes: reduced energy initially, which corrects as their bodies adjust to burning fat instead of carbs.

In other studies, athletes didn’t experience any change in exercise performance when they ate fewer carbs. In fact, some athletes reported that as their bodies adapted to dietary changes, they experienced increased exercise efficiency and even felt their performance had improved.

Keto-Adaptation

The adjustment process is often referred to as "keto-adaptation" or "fat adaptation.” During this time, the body gets better at using stored fat for energy during exercise.

Carbs are your body’s preferred source of energy. Depending on the intensity of your workout, you may not begin to burn fat until you’ve been exercising for a set period of time—anywhere from 30 minutes to 2 hours.

Using fat for energy takes longer and is, therefore, better suited for fueling low-intensity exercise. High-intensity exercise benefits more from the efficient and readily-available energy provided by carbs.

During your first week on a low-carb diet, you may want to take it easy with your exercise routine. If you’re feeling fatigued, or like you aren’t performing at your usual capacity, you may be more vulnerable to injury.

To stay limber and active, you may want to stick to gentle stretching, yoga, conditioning exercises, and walking until your metabolism has transitioned.

In the period after a workout, known as the recovery phase, carbs support muscle growth, help repair weakened or strained muscles, and prevent break down of muscle.

However, a high intake of carbs is not necessary to achieve these benefits. While it doesn’t necessarily preclude a low-carb diet, there’s limited evidence reducing carbs has a positive effect specifically during the recovery phase.

The reduction in dietary carbs necessary to trigger keto-adaptation is still debated.

Most low-carb diets allow for 50-150 grams carbohydrate each day, but keto diets are typically reduced to 30-50 grams.

Keto-adaptation may be of limited use in short-burst anaerobic exercise, however, this doesn’t mean weight lifters won’t experience other benefits of a low-carb diet. In fact, athletes prefer to “carb-cycle,” meaning they switch from ketogenic levels of carb intake to normal, even elevated, levels.

Listen to Your Body

It’s important to note that when studies on diet and exercise are done in humans, researchers may be looking primarily at intense exercisers—even elite athletes. If you do light to moderate regular exercise, your experience won't necessarily be the same as those included in these studies.

The best guide will be paying attention to your individual experience when pairing a low-carb diet with exercise. Let your body’s response inform your decisions—whether it be adding or reducing carbs, increasing the frequency and intensity of your workouts, or adding an entirely new exercise to your routine.

As always, talk to your doctor before starting or changing your diet or fitness routine. While these changes can have positive results, you’ll want to approach these lifestyle adjustments with care, attention, and support; especially if you have any chronic health conditions.

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