How Low Carb Diets Work

Why should I be on a low carb diet?

How does a low carb diet work?Many of my patients will ask me why they should be on a low carb diet.   This is a hotly debated topic in the medical literature and among medical professionals.  In order to address this topic, there needs to be a bit of background.

From a basic nutrition standpoint, there are essentially 3 macronutrients.  These are protein, fat, and carbohydrates.  Proteins are long chains of amino acids and they are typically derived from animal products such as beef, chicken, fish, egg, and milk.  They can also be obtained from vegetable sources such as soy, legumes, wheat germ, mushrooms and others.  Fats are long chains of  carbon and they are typically derived from similar sources as protein.  Nuts, seeds, and avocados are vegetarian sources of fat.  Carbohydrates are either sugar molecules (glucose, sucrose, fructose) or chains or polymers of these sugars.  They are typically derived from vegetable sources.  In our current culture, they are often seen in refined form where the sugar is separated and purified from the source.  An example of this is how sucrose or table sugar is refined from sugar cane.  The last macronutrient, which I did not count in the 3 that I had listed, is alcohol but this is a topic for another blog post.

Why is a low carb diet beneficial?

In order to understand why a low carb diet is beneficial for you, you have to understand how these individual macronutrients are processed in the body.  Let’s reverse the order that we started on above and discuss carbohydrates first.  When a mixed meal is digested and absorbed in the body there is a preferential order that nutrients are processed in (Sonko BJ, et al. AJCN 1994;59).  Carbohydrates are metabolized first, then protein and then fat.  Carbohydrates once absorbed and broken down in the body will stimulate an insulin response.  Most people will know insulin as the hormone that is used by diabetics to keep blood sugar from rising.

This is a good place to start.  Insulin keeps sugar down but where does it go?  There are really only 3 places that it can go.    It can be immediately used in energy use by daily activities, it can be stored as glycogen and it can be stored as fat.  Considering that getting on a treadmill and running for 30 min will burn about 300 calories, the immediate use of energy by sitting in an office is not going to immediately spend our 1200 calories in our carbohydrate laden lunch.  Glycogen is the next option. Think of glycogen like the battery in your hybrid car.  It is a place that will take you a ways but you are not going to go on a road trip without accessing the fuel tank in the hybrid to go more than 20 miles.  Also our glycogen stores in our body are fairly limited and most of the time, we run on full.  So there is not a lot of opportunity to store our lunch as glycogen.

Continuing with the hybrid car analogy, fat will be the fuel tank and the last option for our absorbed carbohydrate.  Insulin acts on a wide number of tissues in the body.  But for the sake of an easy explanation, it stimulates the production and storage of fat using glucose as the ingredient (or precursor as biochemists like to say). One of the main functions of insulin is to drive the activity of an enzyme called lipoprotein lipase which stimulates the uptake and collection of free fatty acids into storage in fat cells. Insulin makes you gain weight.

Next let’s look at protein.  Protein is broken down after carbohydrates.  Protein will also generate insulin but to a much smaller degree.  Part of the function of this insulin will be to cause protein to be absorbed in muscle tissue.  If you are using your muscles, such as exercising, then the muscle will need this protein.  If you are not exercising, then the protein can be broken down via long biochemical pathways to be used as a fuel source.

Fat is the last macronutrient.  Absorption of fat will not cause a rise in insulin.  If you have a mixed meal as discussed above, then high insulin levels from the carbohydrates will cause your body to store the fat into fat stores.  But if your carbohydrate intake is low, you will not have high insulin levels and the fatty acid will be metabolized.  Furthermore, in keeping insulin levels low, this will increase the activity of an enzyme called hormone sensitive lipase which will break down the contents of a fat cell (or adipocyte) and release the fat into the circulation to be used as energy.

So while this is a long explanation, I hope that this can be helpful to see why ingesting fats and proteins can be helpful to you in your weight loss efforts.

Here’s to your health,

Carl Knopke, M.D.

Need some low carb recipe inspiration? Check out this recipe for delicious mahi mahi.


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