Does fasted cardio accelerate fat loss?
The main theory behind fasted cardio is if you train on an empty stomach when glycogen and insulin levels are lower you should be able to preferentially use stored fat for fuel.
This theory also has evidence to support it. Ingesting glucose during an aerobic workout has shown to decrease lipolysis (the breakdown of fatty acids). Fasted training has also shown to increase fatty acid oxidation versus fed cardio.
However, this is what is known as acute research, it shows us what happens in the short term but not necessarily how this pans out in the long term. Most people just want to know if they have to do fasted cardio to get better fat loss.
One six week trial on high intensity-interval training compared fasted to fed training and showed no significant differences in body mass, fat mass or fat free mass between conditions.
One four week trial compared fasted vs fed cardio during a dieting phase and showed no significant differences in body composition either.
A meta analysis on the topic also showed no significant differences between fasted and fed cardio on measures of body composition
To summarize, the research to date suggests that fasted cardio is not superior to fed cardio for weight loss, when dietary intake is the same.
Interestingly though, performing cardio training prior to breakfast has been shown to reduce total daily food intake which of course would help promote faster weight loss.
So long story short, pick whichever you prefer and whichever fits your schedule although some people may find that fasted training is a good strategy to help keep their daily food intake lower.
- Influence of glucose ingestion on fuel-hormone response during prolonged exercise.
- Lipolytic suppression following carbohydrate ingestion limits fat oxidation during exercise.
- Beneficial metabolic adaptations due to endurance exercise training in the fasted state.
- Body composition changes associated with fasted versus non-fasted aerobic exercise
- Interval training in the fed or fasted state improves body composition and muscle oxidative capacity in overweight women.
- Effects of aerobic exercise performed in fasted v. fed state on fat and carbohydrate metabolism in adults: a systematic review and meta-analysis.
- Skipping Breakfast Before Exercise Creates a More Negative 24-hour Energy Balance: A Randomized Controlled Trial in Healthy Physically Active Young Men