I test out a lot of theories, research, and diet and fitness programs so I can best determine what works and what doesn't.
The most recent of them was exercising on an empty stomach - in particular, performing cardio first thing in the morning.
I'm not really a morning person to begin with, so this was challenging for me. In fact, I think I may have been a tad unapproachable on my workout days, because I did notice that loving husband gave me a wide berth on those mornings.
Recently, there has been an influx of fitness programs alleging that exercising first thing in the morning - before that bowl of oatmeal - leads to greater fat loss.
The notion of exercising on an empty stomach has been around for years, and is based on the fact our glycogen levels (the main way the body stores glucose for fuel for later use) is lower in the morning.
You see, the body prefers glycogen as a fuel. When we workout, our body will use glycogen first and then when that runs out it will start to burn fat. So, the theory rests that the lower the glycogen stores are in the body, the quicker it will use those stored fat cells as a fuel.
I found I couldn't maintain the intensity I normally train at because of low glycogen stores. So, I was happy to find a study that weighed the benefits of working out before and after breakfast.
The study used 16 men, same median age and same fitness level, over a two-week period. The men either fasted and worked out or had a 673-calorie Mediterranean breakfast (25 per cent protein, 53 per cent carbohydrates and 22 per cent fat) and then worked out. Other than that, the subjects followed the exact same diet.
All subjects followed the same exercise schedule: 36 minutes on a treadmill at 65 per cent of their heart rate reserve.
The two measurements taken (at baseline and then throughout the two weeks) were the participant's oxygen consumption and respiratory exchange.
These two measurements are the best methods to determine which group burned more fat, the fed or the fasted, and they were recorded at 12-hour and 24-hour intervals after the exercise session.
The first measurement, oxygen consumption, is the measure of energy. The more oxygen consumed while exercising, the greater the calorie expenditure.
This is why we burn more calories running than walking.
Within the two groups there was a slightly higher calorie burn for the fed group, both 12 and 24 hours after the treadmill session.
The fed group read 4.5 ml of oxygen per kilogram, per minute while the fasting group read 4.2 in a 12-hour period. After 24 hours, the fed group dropped down to 4.3 and the fasting group to 4.0.
The secondary measurement, respiratory exchange ratio (RER), measures what macronutrients are being used by the body. During exercise we use carbohydrates and fats as primary fuel sources, and then protein as a last resort.
As RER rises, the body uses more carbohydrate for its needs; as RER declines, it burns more fat. I don't know about you, but I would prefer fat to be used as my body's primary fuel source.
The fed group won this one too. It scored lower in RER, and went down even lower 24 hours after the exercise session.
What does all this mean? Working out after breakfast will score you an exercise session that will burn more calories and use a higher percentage of fat as a fuel.
My recommendation: have a light breakfast before a training session, about 60 to 90 minutes prior, to provide your muscles with the fuel to burn and the ability to build.
P.J. Wren is a personal trainer and fitness writer in the Delta area. Follow her on her blog at www.gofitgals.wordpress.com.
