Not Just a Man's World

As promised last week, this week I am doing a series of three posts to provide some more in depth information about three key nutrition areas that I have tried to target in the improvements to Chris’s diet:

• Omega 3 and 6 ratio
• Acid-base balance
• Different carbohydrate sources

I’m explaining why these are areas to look at when planning your diet and why, in particular, they matter to Chris with his muscle and strength gaining goals.

For the final instalment I am going to briefly address the issue of how different carbohydrate sources are processed by the body and how this should impact on our pre-workout carbohydrate choices.

Are all carbohydrates created equal?

Not really.  When I was first introduced to the principles of carbohydrate in relation to weight training, I learned that carbohydrates provide the glycogen energy source that is stored in the muscles.  Weight training and anything else that uses your muscles uses up these stores and then you need to take in more carbohydrates to replenish these glycogen stores.

However, glucose from carbohydrates is actually stored in three different places.

1. Directly in the bloodstream for immediate use as energy.
2. In skeletal muscle as glycogen.
3. In the liver, again in the form of glycogen.

The liver and glycogen storage

The liver’s key function is to serve as our detoxification organ, breaking down environmental toxins, hormones and other toxic materials in the body and making them more water-soluble so that they can be flushed out of the body, either through urine or faeces.  Additionally, the liver not only stores glycogen but regulates release of glycogen and the subsequent glucose levels in the blood.

The liver itself doesn’t measure the glucose levels in the blood.  This role is carried out by the pancreas which then releases hormones to signal to the liver that it should release more or less glucose into the blood.  If more glucose needs to be released then the pancreas releases the hormone glucagen as a signal to the liver, if less glucose needs to be released then the pancreas releases insulin.  Diabetes occurs when this ability to produce insulin is impaired in the pancreas so that the pancreas cannot signal to the liver to stop releasing glucose.

The liver is capable of storing up to 10% of its volume in glycogen.  Once the liver’s glycogen stores are full, any carbohydrates being sent to the liver are converted to triglycerides.  These are long-chain fatty acids which break down insulin sensitivity and can lead to non-alcoholic fatty liver disease.  This is where the liver becomes marbled with fat and ceases to be able to carry out its normal detoxification roles, leading to a build-up of toxins in the body.

In actual fact, the liver can also synthesise glucose from certain amino acids, lactate and glycerol through the process of gluconeogenisis.  As such, there is no such things as essential carbohydrates, since the body is perfectly capable of producing these itself, provided you give it the right building blocks.

If you want an easy introduction to the way the liver stores glycogen and how an excess of liver-related carbohydrates can impact on the liver, Robb Wolf discusses this in detail towards the end of the first 10 minutes of Episode 9 of the Paleolithic Solution during which he is talking about dairy and inflammation.

Which carbohydrate sources are sent to the liver?

While carbohydrates should, theoretically, be stored in the order of bloodstream, skeletal muscle tissue then the liver, certain forms of carbohydrates go directly to the liver without first ensuring that the other sources are full.  

An easy way to divide these is between glucose and fructose.  

While fructose is a carbohydrate, it is processed in the liver (to convert it to glycogen for storage and then convert it to glucose to be released into the bloodstream once it is needed), whereas glucose is sent to the glycogen stores in the muscles first.

The problem with fruit as a pre-workout carbohydrate source

Fruit is a good source of carbohydrates but looking on Wikipedia, the chart of fructose/glucose ratio for common foods shows that some of the most commonly eaten fruits have very high ratios.  The two fruits we used to use as the primary carbohydrate sources in most of our pre-workout snacks, apples and pears, have ratios of 2:1. 

For workout carbohydrates we really want the glucose to be replenishing the skeletal muscle stores, so using something that is then stored in the liver is not ideal.

In addition, fructose apparently disappears from the blood twice as quickly as glucose.

I’ve got a few other concerns about high fructose intake too:

• too much fructose can eventually lead to diabetes;
• fructose is connected to higher oxidation and inflammation; and
• fructose bypasses the key rate-limiting step that controls how fast we convert sugars into energy.

What can I use instead?

The obvious choices are pasta, bread, rice and potatoes.  However, if you are on a paleo diet then these mostly come off the list.  For this reason, sweet potatoes and yams are tolerated by most athletes on the paleo diet as acceptable carbohydrate sources when consumed as part of the pre-workout food.

After one week of eating sweet potato Chris is already struggling with the sweetness of this and I’ve had to move him onto normal baked potatoes pre-workout.  This is certainly proving to be a big shift for us in our diet mindset and one of the biggest hurdles to overcome.

What do you do for workout-related carbohydrates – particularly if you are following a paleo diet?

Related posts:

1. Workout nutrition: protein, fat or carbohydrate?
2. Low carbohydrate diets
3. Blog-watch: low-carbohydrate diets
4. Improving nutrition for muscle gain