Early morning workout: To eat or not to eat?

Walk into any fitness facility in the early morning hours and interview exercising individuals about their pre-workout eating habits and you will most likely receive a large variety of responses. It is a common belief that if one works out early in the morning, it is imperative to consume a small meal prior to commencing exercise. The belief stems from the notion that the working muscles will be devoid of energy if one has not eaten since the night before. While there is a benefit of a pre-workout meal as discussed in this article, the prior concept of “muscle energy” is completely false.

Muscle glycogen = workout fuel

During most resistance training the muscles will primarily run off glucose, which is stored in the muscles, liver and blood. Replenishment of muscle glycogen to normal levels (around 400g in the average individual) starts immediately post exercise with the ingestion of carbohydrates. Furthermore, consuming meals throughout the next 24 hours that contain a variety of carbohydrate sources will help fully restore muscle glycogen.

With early morning training, there is physically not enough time for an early morning meal to be digested and converted into a usable fuel source prior to engaging in exercise. In terms of athletic performance, the literature recommends that the last full meal be 3 – 5 hours pre-workout, and consist of 80% high glycemic load carbohydrates.

What happens overnight?

While muscle glycogen levels will not deplete significantly over night, the brain’s demand for glycogen as fuel will drain liver glycogen. It is common for a night time fast to deplete the liver from roughly 90g of glycogen storage to 20g, due to the brain’s 0.1 g/min glucose utilization rate. Since the main role of liver glycogen is to maintain blood glucose levels, basically a glucostat, regulating liver glycogen would be the primary focus of the pre-workout meal.

While consuming a quick shake or bar while running to the gym before dawn will not have an effect on muscle glycogen, it will prevent a hypoglycemic state by promoting glycogen release from the liver into the blood. The blood contains around 5g of glucose, with levels dipping in the early morning following sleep, and if that hypoglycemic state goes unabated, dizziness, nausea and reductions in motor skills will have a negative effect on exercise performance.

Despite early research indicating that consuming a high-carbohydrate meal within an hour of exercise will cause rebound hypoglycemia, further research has since refuted that finding, with a large variety of studies demonstrating that hypoglycemia can be avoided if carbohydrates are ingested gradually within 45 minutes of exercise. Practically, consuming food upon waking will maintain normal blood glucose levels, and decrease the risk of hypoglycemia; with the only caveat being the ability to stomach the meal.