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Why Carb Loading Is a Bad Idea

Carb Loading Is a Bad Idea

Story at-a-glance -

  • Carb loading may temporarily increase exercise performance, but these benefits may be cancelled out by water weight gain and bothersome digestive symptoms
  • If you’ve been following a low-carb, high-fat, Paleo-style diet, your body is likely fat adapted and will require very few carbohydrates for fuel, even during exercise
  • Many professional athletes are rethinking carb loading, as low-carb, high-fat diets provide more long-lasting fuel and have an overall better impact on metabolism

By Dr. Mercola

Carb-loading is a strategy commonly used by endurance athletes, such as marathon runners, in the days leading up to a long run or race. The idea behind carb-loading is to saturate yourself with carbs so your muscles will have plenty of glycogen to use as fuel while you exercise. For instance, Runner's World states:1

"The easiest way to achieve a simple, successful carb-load is to include carbohydrate-rich foods at every meal and snack [starting as early as five days prior to your race].

This means bread, pasta, rice, cereal, potatoes, and fruit should be mainstays. Simple sugars and refined grains… get the green light in the days leading up to the race."

This can work well for really fit athletes who have an intense workout regimen or a race on the horizon, but even then it has the potential to backfire if done incorrectly, or if you ordinarily follow a low-carb diet.

There are some compelling reasons for professional athletes to rethink carb-loading, in part because high-fat, low-carb diets provide more long-lasting fuel and have an overall better impact on metabolism.

Meanwhile, carb loading is totally inappropriate for the vast majority of non-athletes who exercise casually, as this type of regimen could lead to weight gain, digestive issues, and even chronic disease.

The Downsides of Carb Loading

There are a couple of serious issues with the idea of carb loading the night before, or in the days leading up to, a marathon or other intense sporting event. Carbs are stored in your muscles and liver in the form of glycogen, which your body uses as fuel. Once this fuel runs out, fatigue sets in and your performance suffers.

Carb loading helps to increase your glycogen stores so that you'll have more energy and be able to run farther before running out of fuel. However, if you're burning carbs as your primary source of fuel, you'll still need to refuel during a marathon.

And if you need to refuel your body in the midst of the event anyway, then your previous carb loading was, mostly, all for naught. Sport scientist Ross Tucker, PhD, told Fittish:2

"…just like you don't plan to drive all the way across the USA without filling up [your gas tank] again, you don't run the NYC marathon without planning to take any carbohydrates during the race.

And so when we have the opportunity to constantly refuel, and provide the body with carbs [in-race drinks, gels, bars], then the loading phase becomes rather more redundant/unnecessary."

Not only is it largely unnecessary, but it can backfire too, causing you to put on extra pounds of water weight (as your body stores water with carbs). The extra weight from carb loading could easily cancel out any performance benefits, according to Tucker.

He recommends following your normal diet in the three days leading up to a race, and perhaps slightly increasing your carbs, and focusing on how to adequately refuel your body during the course of the race as your best option, but even then there are important caveats…

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If You're Fat Adapted, You Need Very Little Carb Replacement, Even During Exercise

If you've been following a low-carb, Paleo-style diet, or a high-fat, moderate-protein, low-carb diet like the one described in my nutrition plan, your body is probably already fat adapted.

Our ancestors were adapted to using fat as their primary fuel, but nearly all of us are now adapted to using sugar or glucose as our number one fuel source instead. One way to tell if you're fat adapted or not is to take note of how you feel when you skip a meal. If you can skip meals without getting ravenous and cranky (or craving carbs), you're likely fat-adapted.

Also if you are overweight, have high blood pressure, diabetes, or are taking a statin drug you most likely are not adapted to burn fat as your primary fuel.

Being able to rely more on fat for energy during exertion spares your glycogen for when you really need it. This can improve athletic performance and helps burn more body fat.

As explained by former Ironman triathlete Mark Sisson, if you can handle exercising without having to carb-load, you're probably fat-adapted. If you can work out effectively in a fasted state, you're definitely fat-adapted.

Replacing non-vegetable carbs with healthy fats, and fasting intermittently, are among the most effective ways to encourage your body to change from burning carbs to burning fat.

So for those of you already following a Paleo diet or similar, you're likely quite efficient at burning fat for fuel and will require very little carb replacement even during intense exercise.

There is some evidence that switching to a higher-carb diet just before a race (after you've been on a low-carb diet) can help to "top off your tanks" to boost your performance… but this is highly individual. For many, this strategy may backfire, as the sudden carb consumption may lead to headaches, nausea, bloating, and other symptoms as well.

Many Athletes Are Ditching Carb Loading for Low-Carb, High-Fat Diets

Athletic superstars like NBA players LeBron James and Ray Allen claim to have switched to a low-carb diet with beneficial results.3 Other athletes jumping onto the high-fat, low-carb diet include Ironman triathlete Nell Stephenson, pro cyclist Dave Zabriskie, and ultra-marathoner Timothy Olson. Former Ironman triathlete Ben Greenfield is said to have followed a ketogenic diet while training for the 2013 Ironman World Championships and experienced improved stamina, stable blood sugar, better sleep, and less brain fog.4

What's the Right Pre-Workout Nutrition?

Only when your glycogen stores are depleted will your body move to using fat as its fuel. And it's this fat-adapted state that results in improved energy utilization and other benefits, like stem cell regeneration and tissue repair, along with decreased body fat, reduce inflammation, and increased insulin sensitivity.

If you carb load prior to exercise, you will actually be inhibiting fat burning and many of the metabolic benefits of exercise, even if it enhances your performance temporarily. For this reason, fitness expert Ori Hofmekler recommends flooding your body with stress-activated food nutrients (SAF nutrients) prior to a workout. These nutrients mimic the effects of intermittent fasting and exercise. He explains:

"Once ingested, SAF nutrients demonstrated the capacity to increase animal and human survivability. Some of these nutrients have shown to mimic the anti-obesity, anti-diabetic, and anti-aging effects of exercise and fasting on the body. The point is, food rich in those exercise-mimicking nutrients is ideal for pre-workout. Not only that it can prevent setbacks with the fat burning and healing impact of exercise, it may actually enhance that impact.

…Note that some of the most potent SAF nutrients are no longer part of our diet. These hard-to-find nutrients occur in barks, roots, pits, and peels, which we don't normally eat. However, some foods within our reach contain high levels of exercise-mimicking SAF nutrients such as phenols, caffeine, theobromine, catechins, and immune proteins and thus can potentially yield powerful synergy with physical training."

So where are these nutrients found?

  • Whey protein from grass-fed cows
  • Organic black coffee
  • Unsweetened cocoa
  • Green tea

Exercising while in a fasted state is actually ideal (see below), but if you feel weak or nauseous while exercising on an empty stomach a high-quality whey protein shake can be an ideal pre-workout snack. A study published in the journal Medicine and Science in Sports & Exercise demonstrated that consuming whey protein (20 grams protein/serving) 30 minutes before resistance training boosts your body's metabolism for as much as 24 hours after your workout.5 It appears as though the amino acids found in high-quality whey protein activate certain cellular mechanisms (mTORC-1),

This in turn promotes muscle protein synthesis, boosts thyroid, and also protects against declining testosterone levels after exercise. In practical terms, consuming 20 grams of whey protein before exercise and another serving afterward may yield the double benefit of increasing both fat burning and muscle build-up at the same time. You can play with the dose, as that is an average (depending on your weight and stature, you may need half that amount or up to 50%-75% more).

Exercising While Fasting May Be Best of All

When you exercise while intermittent fasting, it essentially forces your body to shed fat, as your body's fat burning processes are controlled by your sympathetic nervous system (SNS), and your SNS is activated by exercise and lack of food. The combination of fasting and exercising maximizes the impact of cellular factors and catalysts (cyclic AMP and AMP Kinases), which force the breakdown of fat and glycogen for energy. On the other hand, eating a full meal, particularly carbohydrates, before your workout will inhibit your sympathetic nervous system and reduce the fat burning effect of your exercise.

Instead, eating lots of carbs activates your parasympathetic nervous system, (which promotes energy storage—the complete opposite of what you're aiming for). One study found, for example, that fasting before aerobic training leads to reductions in both body weight and body fat, while eating before a workout decreases only body weight.6  

Exercise and fasting together also yields acute oxidative stress, which actually benefits your muscle triggers genes and growth factors, including brain-derived neurotrophic factor (BDNF) and muscle regulatory factors (MRFs), which signal brain stem cells and muscle satellite cells to convert into new neurons and new muscle cells, respectively. This means that exercise while fasting may actually help to keep your brain, neuro-motors and muscle fibers biologically youngThe combined effect of both intermittent fasting and short intense exercise may go way beyond helping you to burn more fat and lose weight; it may help you to:

Turn back the biological clock in your muscle and brain

Boost growth hormone

Improve body composition

Boost cognitive function

Boost testosterone

Prevent depression

This strategy would probably not be appropriate for long endurance exercise, but for the vast majority of casual exercisers, it can be quite beneficial. One of the easiest ways to do this for most people is simply to exercise before eating breakfast, as you've been fasting since your dinner the night before.

Proper Sports Nutrition Is Highly Individualized

There are no one-size-fits-all nutrition requirements when it comes to physical exertion. What works best for you will depend on the type of activity, your level of fitness, your diet, and your personal goals. If your goal is to be an elite athlete who runs the fastest marathon, your nutrition requirements will obviously be very different from someone who is trying to build muscle or lose weight.

For many people, fasting prior to exercise will give you the best of both worlds, helping you to build muscle and burn fat. But again it depends on the workout. It's not wise to start a marathon on "empty," for instance, as your body will require massive amounts of energy (but even then, if you're fat adapted this doesn't mean you need to load up on bread, pasta, and other unhealthy carbs).

If you are already fat adapted and a competitive athlete, it is probably not the best idea to regularly train fasted, as it will impair the intensity of the workout and reduce some of the benefits you are seeking to gain. Another exception to fasting before exercise is if you are doing strength training. When you are fasting for 14-18 hours you typically deplete most of your glycogen stores, which makes it difficult to lift your maximum weight to failure.

Hence, if you are doing heavy lifting to failure, you may want to avoid training while fasting. In these cases it is likely helpful to consume some healthy slow-releasing starchy carbs the night before working out so your glycogen stores won't be depleted in the morning. Then, have whey protein as a pre-exercise meal to grant sufficient supply of branched-chain amino acids for optimum muscle fueling during your workout.