Thoughts on “Low-Carb” Diets

Recently, I’ve received a lot of questions about eating for exercise, most involving protein – how much to eat, when to eat it, the best protein supplements, etc. Most people are surprised to hear that while protein is certainly an important piece of the puzzle, the main nutrition component to consider for exercise is carbohydrates. My pancake-loving bias aside, here’s a healthy does of physiology and biochemistry to back me up.

Yes, muscles do need protein for growth and repair, the minimum per day being 0.8 g/kg of bodyweight. However, think about it: skeletal muscles are organs. No, they aren’t as complex as the heart or lungs or liver, but they are organs. They are made up of cells that contain mitochondria, an organelle whose main function is to convert glucose (a six-carbon molecule found mainly in carbohydrate foods) into energy (in the form of ATP) so that the cell can continue to function.

Like most body cells, muscle cells prefer to use glucose for energy, which is easiest to access when packaged in carbohydrates. If need be, glucose can also come from protein, but it has to be created through a process called gluconeogenesis. This process involves converting amino acids (the building blocks of protein) into glucose, which is more time and energy consuming than using glucose from carbohydrates.

The “Protein-Sparing” Effect 

Gluconeogenesis can involve amino acids from either dietary protein or body protein. If the amino acids are derived from dietary protein, that protein can’t be used for muscle synthesis and repair – it’s used to create glucose for energy. If using body protein, the first type to be broken down is skeletal muscle. In the grand scheme of things, skeletal muscle is less essential than organs such as the heart, liver, kidneys, lungs, pancreas, etc. No matter your weight, activity level, or age, eating a balanced diet including adequate carbohydrates prevents protein from being used for energy, thus resulting in a “protein-sparing” effect.

Beyond Muscle Mass & Exercise

The “protein-sparing” function of carbohydrates is important not only in fueling exercise but also because protein fulfills other vital roles in the body. It maintains organ systems, fortifies the immune system to fight infections, balances blood sugar levels, and is the building block of many hormones and neurotransmitters. By eating carbohydrates, you prevent your body from using dietary protein for energy, thus allowing it to be used for its many vital functions beyond just muscle repair and synthesis.

One last (and perhaps most important) reason why the body needs adequate carbohydrates is simple: all body cells need energy, preferably from glucose. The brain is especially dependent on glucose since unlike other cells, brain cells can only use glucose for energy. The exception to this is severe starvation, in which brain cells can use ketone bodies (an end product of fatty acid oxidation), which is a situation that the body does not prefer.

If blood glucose becomes too low, the brain perceives this as a life-threatening situation. It’s scared that it won’t have enough food to keep the body working at full speed. The brain’s response to this stressful situation is to send instructions to different organs in the body to synthesize and release hormones that increase blood glucose. These hormones include:

• Growth hormone
• Glucagon
• Adrenaline (epinephrine)
• Cortisol

Do those stress hormones, adrenaline and cortisol, look familiar? You might have heard about them because of their role in the “fight-or-flight” response. Well, low blood glucose is one of the triggers for that response. These hormones, when elevated for too long, can cause inflammation and trigger the break down of body muscle stores.

All in all, carbohydrates are really important just to be a happy, functioning human being. They’re important to keep your skeletal muscles in tact. They’re important to decrease inflammation in the body. They’re important to spare dietary protein for its many essential functions. Eat carbohydrates!

What are food sources of carbohydrates?

Not surprisingly, when I explain the importance of carbohydrates, people usually mention bread.

“So you want me to eat bread after exercise?”

“Oh, I don’t like bread though.”

“My roommate is gluten-free so it’s hard to keep bread around.”

While bread is certainly a source of carbohydrates, a variety of other foods contain this macronutrient. To truly go “low-carb,” you’d be cutting out a lot more than just bread and pasta. To put this into context, here’s a list of some foods and their carbohydrate content:

Reference point: 1 slice whole grain bread = 15 g

• 1 medium banana = 30 g
• 1 medium apple = 20 g
• 1 cup blueberries = 20 g
• 1 cup sliced carrots = 12 g
• 1 medium sweet potato = 26 g
• 1 cup diced butternut squash = 16 g
• ½ cup beans = 21 g
• 1 cup milk (8 oz) = 12 g
• 6 oz plain Greek yogurt: 7 g

Eating a low-carb diet isn’t as easy as it may seem, eh?

But…but…but…

Yes, I’ve also heard countless testimonials about “low-carb” diets, including weight loss, improved energy, clearer skin, etc. With a little more investigation, I usually find that these “low-carb” diets are really just about cutting back on refined grains (products made from white flour and white rice) and added sugar; it’s usually processed foods that are being reduced, not necessarily carbohydrates as a whole. The dietary pattern often still involves a wide variety of fruits, vegetables, legumes, dairy, and some whole grains. Perhaps without even knowing it, a person practicing this whole-foods dietary pattern would probably still be getting the 200-250 grams/day of carbohydrate recommended for the average adult.

All foods can be a part of a healthy diet!

 The key to nutritional balance is variety – an array of fruits, vegetables, whole grains, legumes, nuts, seeds, and lean protein. Processed foods, such as refined grains and added sugars, aren’t the main staples of a nutritious diet, but they absolutely still appear. After all, these foods provide pleasure and are often involved in joyous social situations, which are not fun to miss out on. All foods can be a part of a healthy diet; no dietary change is worth it if it’s unsustainable, causes stress and anxiety, or sucks the fun out of life.

No matter your dietary preferences, nutritional needs, or eating behaviors, it’s important to have a healthy relationship to food. Let go of the need to follow any dietary restrictions that aren’t warranted by a medical diagnosis, and eat in a way that works for your body and lifestyle. Maybe this includes bread, maybe it doesn’t. Either way, I hope it includes carbs!

For more info:

“Guidelines for the Casual Exerciser”

http://www.todaysdietitian.com/newarchives/111609p18.shtml

“Busting the Top 10 Carb Myths”

http://www.todaysdietitian.com/newarchives/0416p30.shtml

“The science of ‘hangry:’ Why some people get grumpy when they’re hungry”

http://www.cnn.com/2015/07/20/health/science-behind-being-hangry/

“The Fundamentals of Good Nutrition Actually Haven’t Changed for Decades”

http://www.foodnavigator-usa.com/R-D/David-Katz-reThink-Food-Nutrition-advice-doesn-t-keep-changing