We’ve been getting a few questions from runners who are struggling to get going on the LCHF diet, particularly because they feel like they are getting a lactic acid build up in their legs. They feel that their legs are heavy and they are wondering if the lactic acid build up is normal on the LCHF diet?

The first thing to clear up is that it is probably not lactic acid build up. Everyone has a lactic threshold, and the build up only starts once you reach this point. As soon as your Heart Rate drops down again and you stop running, your body starts to recover from this.

There is a common feeling of heaviness in the legs in most runners, when they start their run. After a couple of kilometres this generally eases up and you find your rhythm.
Warm ups become critical on the LCHF diet for this reason; and you will probably find that it does take you longer to warm up. You need to factor this in to your training and racing, and make an effort to start slower.

If it is not a lactic acid build up, what is it?

It is not too clear why this happens; but it appears that fat circulation is a more lengthy process to get going than being fueled by carbohydrates. However once up and running, the body seems to generate energy better when you are fat adapted than if it were running on carbs. So while you are starting slow and battling to get over the heaviness in your legs, once you are warm you just get stronger and stronger.

This is why the LCHF diet is such a great fit for ultra distance runners. As a Comrades Marathon runner this is ideal, as you can do the bulk of your run at an optimal level. If however you are doing speed work and you want to have a bit more power earlier in your run, factor in some carbohydrates that day to help with more rapid energy output.