First off, we need to define exactly what a low carb diet entails. A low carb diet (LCD) can be defined as a calorie intake that consists of 20% or less of the calories coming from carb sources. Before I get started, I suggest just taking home the general message Iʼm attempting to convey and not worry about all of the complicated terms. Now lets get to it.
#1-INCREASED RISK FOR MUSCLE LOSS:
The reason for this is quite simple. Itʼs generally accepted that a majority of people will exercise and diet to attempt weight loss. If you practice this in conjunction with a low carb approach, there is a strong likelihood that muscle loss will occur. When we exercise @ moderate to high intensities our working muscles become highly reliant on carbs to support the increased demand of exercise. This means that we recruit glycogen (stored glucose or blood sugar) stores directly from the target muscle to get the job done. Now what about if this glucose is not available to us? The next best option is for our body to break down stored glucose from the liver (hepatic glycogenolysis) and deliver it to the muscle until this reserve runs out. The next reserve comes from body protein (muscle) and this protein is sent to the liver and then converted to glucose through a process called gluconeogenesis. The breakdown of fat for fuel supply in this type of condition simply takes too long and our body has to seek a faster alternative route to immediately supply the muscle with energy. “A rate limit exists for fatty acid use by active muscle (Mcardle, 162).” Lastly, the scary thing is that this process can occur even when we are not exercising that hard. According to the RER (Respiratory Exchange Ratio), we will begin burning a lot more carbohydrates (or protein/muscle if there is no carbs) at around 120-140 beats per minute. The RER is a scientific energy model that indicates which type of energy our body uses at specific heart rates and training intensities. The take home message here is that we will use muscle for energy by default if carbs are unavailable. Below is a list of links containing studies that support the information stated above:
#2-DECREASED THYROID OUTPUT:
The Thyroid Hormonal Gland is a complex piece of anatomy located at the neck that promotes increased muscle building and calorie expenditure, among many other things. Carbohydrates are a nutrient that serve a role in creating and maintaining a healthy and active Thyroid. “When you restrict carbohydrates and overall calories for any significant length of time your thyroid levels will down regulate causing an overall slow down in your metabolism (Ferrugia, 130).” The Thyroid produces GH (Growth Hormone) which not only plays a secondary role in fat loss, but promotes muscle and tissue growth as well. What all of this really means is that if your Thyroid production is reduced from eating less carbs, then rest assured muscle loss and decreased calorie expenditure will follow.
#3-POOR PROTEIN SYNTHESIS (MUSCLE BUILDING):
Now I just briefly touched on one of the pathways in the body that performs muscle building, but there are more. Insulin is a storage/anabolic hormone released from certain cells in our pancreas that assists in shuttling amino acids which are the building blocks for muscle into the muscle cell. Insulin also activates other parts of the cell responsible for muscle growth. Check out this study from PubMed; http://www.ncbi.nlm.nih.gov/pubmed/16545079. Carbs create the greatest release of this hormone. Thus, if carbs are low, so is this hormone, and so is muscle building and other essential functions in the body. Moreover, stored glucose (aka glycogen) in the muscle promotes greater muscle building (via increased gene expression), and when carbs are low, so are these stores, and so is muscle building. And thatʼs not all. Insulin is also an antagonist to the catabolic (breaking down) hormone Cortisol. Whenever we diet or live life in general, its preferred that we try to minimize levels of this hormone as much as possible, or keep it at normal doses in the body. Insulin turns down this hormone, but if carbs are low, so is Insulin, so cortisol stays higher and we are worse off, and muscle loss along with a host of other adverse undesirable outcomes will result.
#4-INCREASED HUNGER AND APPETTITE:
When we elect to lower or not consume carbs, we stay hungrier for at least two reasons. First, glycogen (glucose or sugar stores) do not fill up our muscles and liver. “To make matters worse, the impaired ability of glucose to enter the muscle cells keeps glycogen stores lower, which can increase appettite (Clark, 439).” Secondly, Ghrelin is a hunger hormone produced from cells in the stomach that is inhibited through increased carbohydrate consumption. “Nutritionally, carbohydrates appear to play a primary role in regulating ghrelin levels with dietary fat having less of an impact, the effect of protein is currently unclear. In one study, a high carbohydrate/low-fat diet generated weight loss without the normal increase in ghrelin levels (Mcdonald).” So if you want to undoubtedly feel fuller and potentially be more successful dieting then eat some carbs.
#5-LOWER DOPAMINE AND SERATONIN LEVELS:
Dopamine and Seratonin are neurotransmitters (chemical messengers) that are secreted in parts of the body, and they are responsible for giving us that feel good euphoric feeling that we like so much. Essentially, they play a key role in emotional state balance. Unfortunately, when we decide to lower carbs we lower the respective levels of each of these important chemicals. Here is a great article from world class physiologist and fat loss expert Lyle Mcdonald; http://www.bodyrecomposition.com/nutrition/carbohydrate-intake-and-depression-qa.html.
On a final note, Iʼve browsed over some literature that suggest Dopamine may have a direct role in fat loss. I will know more in the future on potential pathways and how it directly affects fat loss physiology, so stay tuned.
Well this concludes Part #1 of the series. In Part #2, I will be including 5 more reasons why low carb diets fail. I hope you enjoyed this and learned something new on the subject of low carb dieting.