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KATHLEEN HERNDER RD, CDE

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Too tired to get through your workouts? What may not be getting enough of in your diet.

October 18, 2016

Tell me if this sounds familiar: you're going to the gym and being mindful of what you eat to try to become more fit. The thing is, when you go to the gym, you always feel exhausted and have a hard time getting through your workouts. You’re getting enough sleep, eating enough protein and maybe even taking pre-workout supplements but you're still struggling even though you're not over-training. The most probable cause? You're not eating enough carbohydrates.

 

 

That's right, I said carbohydrates. They seem to get a bad wrap in the media and granted, many people eat more sugar and refined carbohydrates than are good for them. Following a diet that is lower in carbohydrates may work for some healthy individuals as long as their diet is well planned to ensure they are getting adequate vitamins, minerals, and fibre, which may require help from a dietitian. If you're hoping to improve your athletic performance, however; this is probably not a good way to go.

 

To explain why this is, first we need to discuss what your muscles use for fuel. Most of the time your muscles use a mixture of both carbohydrates and fat for fuel but this will change depending on the intensity of activity. During low intensity activity, your muscles can use a higher amount of fat compared to carbohydrate but as you increase in intensity, your body relies more on carbohydrates for fuel. This is known as the "crossover concept," which is illustrated below.

 

Image source: The Science of Sport 

 

In other words, for walking and light jogging, you may get away with not using a lot of carbohydrates but once you get into running, sports, and high-intensity training like fitness classes, your body needs carbohydrates for fuel.

 

Where does your body get the carbohydrates from to be used as fuel? There is a combination of glucose in the bloodstream and glycogen, which is the storage form of carbohydrate stored both in muscle tissues and in the liver. When your body starts running low on glucose in the bloodstream, it will start breaking down the glycogen into glucose that can be used by your muscles through a process called glycogenolysis.

 

 Interestingly during a low-carbohydrate diet, the initial weight loss that comes off quickly is due to the loss of glycogen, not fat loss! Every gram of glycogen stores four grams of water and the average individual in a well fed state has approximately 350g of glycogen but this can be as much as 900g in a muscular individual- that's anywhere from around 4-10 pounds of glycogen and water that you lose that comes right back once you increase your carbohydrate intake back to normal levels.

 

Back to Performance:

 

If you aren’t consuming enough carbohydrates and are doing moderate to intense activity, you’re likely going to deplete the glycogen and glucose available for your muscles, which is associated with fatigue. In other words, if you don’t have enough carbs, you’re going to be tired during your workout and not have optimal performance. Research is a bit mixed on lower intensity activities and performance with lower carb diets but when it comes to intense activity like interval training or HIIT (high intensity interval training), research shows performance is compromised on a low carb diet. 

 

There is some evidence that forcing your body to rely less on carbohydrates by training on low carbohydrate stores increases your body’s ability to use fat as a fuel at higher intensities, which is commonly known as ‘Train Low, Race High.’ The evidence on if this improves performance since it spares carbohydrates is not quite there yet but you can train your body to require a smaller amount of carbohydrate. I will be writing on this more in the future but it is important to realize that you don't want to do this sort of training all the time as it would not go well for speed training, for example but would be good for a low-intensity workout.  In other words, even if this is something you're using in your training, you don't want to be carbohydrate depleted for all your workouts because your training will suffer.

 

So how much carbohydrate do I need?

 

So the next question how much carbohydrate do you need in your diet for optimal training? The answer to this really depends on the intensity of your training. If you are going to the gym for 30 minutes, a few times per week for example, a well balanced diet that includes whole grains, fruit and vegetables, and beans and lentils will likely be sufficient. For low training levels, 3-5g/kg of carbohydrates per day (~1.5-2g/ pound per day) is what would be recommended. To give you an idea, or a 170 pound person, this would be around 230-385g of carbohydrate per day. For more intense training, like say training for a half marathon, 5-7g/kg (~2-3g/pound) per day would be recommended, which for that same 170lb person would be 385-540g of carbohydrate per day.

 

Example of what typical days for low and general training might look like for that 170lb person:

Nutrient breakdown from Canadian Nutrition File 

 

As you can see, the day on the left for low intensity training is simply a general healthy, balanced diet and to increase the carbs for general training, I made a few swaps like veggies and hummus for fruit and a small muffin and added an evening snack. If you are doing endurance training like a marathon, 7-10g/kg per day of carbohydrate would be recommended and for ultra endurance events like an Iron Man, more than 11g/kg per day of carbohydrates may be required.

 

If that sounds like a scary amount of carbs, start small!

 

I know if you've had the low carb mentality drilled into you, it can be a tricky thing to think about increasing the carbs in your diet but I encourage you to try it out for a few days to see what happens to your performance! You might even start with trying to include more easily digestible carbohydrates like oatmeal or fruit at least an hour before your workout and see if you notice a difference in your energy levels and the quality of your workouts.

 

 

What about timing?

 

If you're doing training involving sessions longer than 90 minutes, this is when we start looking more at carbohydrate intake before, during, and after activity to ensure you have adequate glycogen storage before activity, during activity, and that you re-fuel your muscles with glycogen following a workout. For more information on this, check out this post on what to eat before and this post on what to eat during activity and after for refuelling!

 

If you want help adjusting your diet to improve your performance, you can click here for more information and book an appointment.

 

Happy training, and enjoy adding some more carbs back into your diet!

 

 

 

 

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