If you’re trying to lose weight, you may be cutting back on the number of carbs in your diet. Cutting back on carbs isn’t necessarily a bad thing if you’ve been eating a high-carb diet and aren’t losing weight, but you need a certain amount of healthy carbs in your diet if you’re exercising regularly. The key is to choose carb sources from high-fiber, whole foods rather than processed ones that have little nutritional value and raise your blood sugar level rapidly. Why are carbs more important if you exercise? There are three main reasons carbs are important. Here’s why you need them.
Carbohydrates Are a Major Energy Source during High-Intensity Workouts
Your body can use carbohydrates and fats as energy depending upon the intensity of your workout but it increasingly taps into carbs as exercise intensity increases. A very low-carb diet makes it more challenging to get through a high-intensity workout without feeling fatigued as a result of low muscle glycogen stores. You may find yourself “hitting the wall” quickly on a low-carb diet, making it hard to maximize the intensity of your workout.
If you work out at a moderate or low intensity, your body can easily tap into fat stores as fuel and you won’t feel the same degree of fatigue, especially after your body adapts to a low-carb diet. Still, research shows that higher intensity workouts have a metabolic effect, activating hormones that boost fat burning. Plus, they gear up your body to burn calories for hours after you finish. If you go too low-carb, you won’t be able to push yourself to an intensity that’s high enough to give you these benefits.
Carbohydrates Help to Preserve Lean Body Mass
Most people think of protein as being the anabolic macronutrient, but carbohydrates have anabolic properties too. That’s because they preserve lean body mass during periods of long or intense exercise and during periods of low-calorie intake or starvation. When blood sugar levels start to drop, your liver has the ability to make glucose from other components through a process called gluconeogenesis. One of those components is amino acids from the breakdown of proteins.
What happens if you don’t get enough? If you do a long workout in a carb-depleted state, your blood sugar levels will begin to fall after a period of time. This activates a hormone called cortisol. In turn, cortisol turns on a protein called myostatin that breaks down muscle tissue so your liver can use some of those amino acids to make glucose. Eating carbs before a workout blunts the release of cortisol and has a protein-sparing effect. That’s important if you want to hang onto your lean body mass.
Your Brain Needs Carbs
Your brain can’t use fatty acids from fat directly as fuel. It needs glucose. As an alternative fuel source, it can use ketone bodies your liver makes from the breakdown of fats when it’s in a carb depleted state but it’s not your brain’s preferred energy source.
According to research published in the European Journal of Clinical Nutrition, your brain needs 200 grams of carbs a day or more for optimal functioning, although there’s a lack of consensus on this. It may depend upon the individual and the ability of their brain to adapt to ketones. The brains of people on a low-carb diet adapt to variable degrees to being on a low-carb diet. If your brain hasn’t adapted, you can experience brain fog, memory issues and fatigue on a very low-carb diet.
Very low carb diets have been linked with mood swings and change in levels of serotonin, a neurotransmitter that impacts mood. Plus, it can interfere with your workout. Research shows when blood sugar levels drop, your brain reduces muscle activation during exercise. That means your performance will suffer. Just remember, your brain loves glucose and functions best when it has enough of it.
Too Many of the Wrong Carbs Isn’t Good Either
What happens if you eat a diet high in processed carbs? It increases insulin levels. This suppresses fat oxidation or the breakdown of fats for fuel and increases conversion of carbohydrates to fat. It also raises triglyceride levels.
The key is to consume high-fiber carbs like vegetables, low-glycemic fruits and modest amounts of whole grains. If you’re limiting the number of carbs in your diet, at least make sure you’re not carb-depleted before going into a workout. The more often you train and the harder you train, the more important it is to consume carbs. Volume and intensity should impact the percentage of carbs in your diet. Another way to do it is to consume carbs before and after an exercise session, along with protein, and limit them the rest of the time. This will help reduce the catabolic effects of exercising in a carb-depleted state.
The bottom line? If you’re making healthy, fiber-rich carb choices, you can be more liberal with the number of carbs you eat. Where you’ll get into trouble is eating too many processed carbs. Don’t train in a carb-depleted state and choose your carbs wisely.
References:
Eur J Clin Nutr. 1999 Apr;53 Suppl 1:S101-6.
Medicine and Science in Sports and Exercise. 35: 589-594.
Exercise Physiology. Fifth edition. McArdle, Katch, and Katch. (2002)
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Why You Should Eat Your Carbs with Protein
Is Going Low-Carb the Best Way to Get Lean?
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