To Carb or Not to Carb? That is the Question!

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pondering, choices, hmm

Are carbs the bad guy?

Carbohydrates have been given a bad wrap for quite some time but I think that it’s time to shed some light on the topic about how carbs are potentially one of the best fuel sources for our body to use for almost all activities. This blog doesn’t aim to tell you what to do because, as with most things… it depends! It depends on your particular situation and the outcomes you’re after but hopefully after reading this, you will have a bit more of an idea of the role carbs play in physical performance and be able to make a more informed decision. 

First things first, our body utilises a compound called adenosine triphosphate (ATP) for energy. By breaking one of the phosphate bonds and turning it into adenosine diphosphate (ADP) energy is released that we use for heaps of different processes in the body such as muscle contraction and firing of nerve impulses. We get ATP from 3 primary fuel sources, fats, carbs and proteins. 

Which fuel source our body uses is based on the activity we are completing and oxygen availability. When we are at rest with plenty of oxygen available, our body will predominantly use our fat tissue as its fuel source due to the low intensity nature of what we’re doing (study, low-intensity walking, scrolling through instagram, reading this blog, etc.). Fat is the most energy dense fuel source but it requires 4 times more oxygen to turn it into ATP.

On the other hand when we begin to change the pace of the activity we are completing (higher-intensity walk, jog, weight lift, run, sporting matches such as rugby, football, afl etc.) the fuel source will shift toward one more applicable for the situation. As oxygen becomes a more valuable resource at higher intensities we will switch to carbs as the more efficient option. There isn’t one specific moment where we are using 100% carbs or 100% fats, but it is a combination of the two macronutrients (carbs and fats) being used, with one having dominance during the activity. A good example of this can be found in the table below. At lower intensities (lower % of VO2 Max) you can see that free fatty acids (essentially fat) are the primary fuel source and at higher intensities (higher % of VO2 Max) muscle glycogen (from carbohydrates) are more predominant.

figure 1: relative contribution for each fuel source depending on the % of intensity. (in trained cyclists - Hargreaves, M., Spriet, L.L., 2020. )

figure 1: relative contribution for each fuel source depending on the % of intensity. (in trained cyclists – Hargreaves, M., Spriet, L.L., 2020. )

Cellular response – what carbs do in the system.

When we eat carb sources such as rice, pasta, breads, vegetables, fruits, etc. they get broken down into simple sugars (glucose, fructose, galactose) that are easily digestible and absorb rather quickly. These are then used throughout the body in various processes such as fueling our autonomic systems (breathing, heart beating, thinking, digestion, etc), while also fueling muscles for movement!

This can typically be found in the body as blood glucose levels (BGL’s), muscle glycogen, and liver glycogen. When the body has enough glucose to complete all the required processes it will then store excess glucose as glycogen. Glycogen is typically stored in the muscles and the liver of the body, with the liver helping to determine if glucose is stored as glycogen or fat. Our glycogen stores can be used for many different reasons like, flight or fight response, long distance events, and repeated short explosive efforts. The process of breaking glycogen to the usable form of glucose is called glycogenolysis, this just means the breakdown of glycogen into glucose. Glucose is also the primary source of fuel for our brain as it is able to permeate the blood brain barrier (which is a barrier that separates our central nervous system (brain and spinal cord) from the rest of the body). In a pinch or as an adaptation to a high fat and protein diet, the brain can use ketones as a fuel source but when carbohydrates and therefore glucose are available it will use this first.  

High carb vs low carb diets?

There is quite a bit of discussion about which is better, a high carbohydrate vs a low carbohydrate diet. There is a case for both, but it ultimately depends on what you’re looking to achieve. Our bodies naturally turn to using carbohydrates as a primary fuel source for most of our activities outside of rest where we use primarily fats. Ideally it is recommended to use a higher carbohydrate diet with extra loading surrounding periods of heightened activity to optimise the glycogen stores in the body, this will mean that we have plenty of fuel for the activity. There have been a few studies that show low carbohydrate diets decrease performance whereas higher carb diets had less of a decrease. Lower carb diets can be used to potentially help in periods where body recomposition is the goal but there is evidence suggesting that there are performance decreases after long periods of time without higher carbohydrate intake. 

How can you make an informed decision?

The best way to guide your own decision is to find out what works best for you, discussing nutritional options with an accredited sports nutritionist or dietitian will give you the best outcome.

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