Study on fed versus fasted steady-state cardio
One recent study published in the Journal of the International Society of Sports looked at the difference from doing steady-state cardio in a fasted vs. fed state with interesting results.
In the study, 20 healthy young women were each given an individualized, calorie-restricted meal plan.The women were then divided into two groups. Both groups performed an hour of cardio, which includes a 5 minute warm-up and cool down at 50% maximal heart rate (MHR) and 50 minutes of steady-state cardio at 70% (MHR). They did this 3 times a week in the morning for 4 weeks.
The difference between the two groups was that one group performed cardio on an empty stomach followed by a meal-replacement shake, while the other group consumed the shake before they did the cardio.
The results after the 4 weeks showed that both groups lost weight and fat mass. However, there was no significant difference between groups. Nor was there a significant difference between fat-free mass (e.g. muscle) between groups.
In summary, the researchers conclude that changes in body composition due to the combination of aerobic exercise and a calorie-reduced diet are similar regardless of whether the person is fasted or fed.
Schoenfield, BJ et al. 2014. Body composition changes associated with fasted versus non-fasted aerobic exercise. J Int Soc Sports Nutr. 11: 54.