Q: “Cardio on an empty stomach – will it really help me burn more fat?”
— Thomas F., via Facebook

Answer by Sara Jane McShane, Fitness Author and Personal Trainer:

Fasted cardio and fat loss is a commonly debated topic in fitness. Some believe fasted cardio is more effective at burning fat, while others believe it can actually decrease performance and limit fat loss long-term Which one is correct? Here’s a look at both sides of this hotly-debated topic.

Fasted Cardio

This fat-loss method was first hypothesized to be successful because without food readily available for energy, your body would turn to its fat stores as the energy for your workout. This method is seen by its proponents as a quicker way to drop a few unwanted pounds and a great way to meet a goal. However, the research has cast doubt on this theory. Studies have demonstrated that fasted cardio does not increase fat burning over a 24-hour period as opposed to consuming milk before exercise. That is not to say that milk is the best pre-workout, but rather that some carbs before your workout may help you burn more calories throughout the day.

Unfasted Cardio

There are several studies to draw from; the aforementioned milk study used milk glucose to test “unfasted” cardio. Ten males were used as the subjects and all of the results concluded that unfasted cardio actually helped these individuals burn more fat than fasted cardio. Again, this is not to say that milk is the answer to weight loss, but research shows that consuming calories consistently can actually help utilize our energy stores better. This, in turn, can aid fat loss.

The Verdict

The majority of data available concludes that fasted cardio does not, in fact, offer additional benefits, and in some cases can actually hinder results. However, there are a lot of individuals—many of them elite bodybuilders and other athletes—who have reported great success with fasted cardio over the years. But as with many aspects of fitness, there is no one-size-fits-all answer. There is a very wide range of what is normal, and what might work for somebody else, particularly an elite athlete, might not work for you.

Through my experience, I would say to avoid fasted cardio unless having any kind of food in your belly makes you nauseous when you train. I have observed that the best way to ensure you are burning fat is through HIIT (high intensity interval training) to ensure your metabolism stays elevated for longer periods of time, while regulating your nutrition. The key number to remember 3,500. As in, there are 3,500 calories to one pound of fat. Burning an extra 500 calories more than you eat per day will help you burn one pound of fat per week. Total calories consumed versus total calories expended is what ultimately determines success or failure. The timing of when you eat is of secondary importance.