Better Fat Loss by Skipping Breakfast? Not So Fast.

Anyone who’s followed us here at Feisty for any length of time knows we’re not huge fans of fasted training. When you don’t support your training with enough calories and/or carbohydrates, your performance and health can eventually suffer. And if you’re training longer than an hour, research shows having fuel in your system is advantageous.

Still, you may have heard that if you want to improve fat burning, going out on empty is the way to go. But research doesn’t necessarily support that. 

Fasted Versus Fed

Let’s take a look at a new systematic review and meta-analysis of randomized clinical trials that had some interesting findings. For this study, the researchers wanted to know whether working out on an empty stomach (fasted) is better for your blood sugar and lipid metabolism than working out after eating (fed), especially in healthy adults.

They looked at 28 different randomized clinical trials involving 302 healthy adults. These studies compared how the body responds to acute bouts of exercise (not long-term training) in a fasted state versus a fed state. They focused on metabolic markers including:

• Blood sugar (glucose)
• Insulin
• Free fatty acids (FFA)
• Triacylglycerol (a type of fat)
• Respiratory exchange ratio (how the body uses fat vs. carbs for energy)

What they found in a nutshell:

• Fasted workouts led to larger increases in blood sugar and insulin afterward compared to fed workouts.
• Fasted workouts also resulted in larger decreases in free fatty acids levels. 
• There was no difference in other fat markers (like triacylglycerol) or in how the body burned carbs vs. fat (RER).

So, there wasn’t any metabolic magic happening with the fasted workouts, and some of the markers were slightly unfavorable. It’s also important to note that even if you’re using proportionally more fat during a fasted workout, that doesn’t necessarily result in more fat loss. 

Recent research on postmenopausal women echoes this. In this 12 week study of 25 physically active women, average age about 60, researchers split the women into two groups: one exercised after eating (fed) and the other exercised while fasting. Both groups did the same multicomponent training (i.e. mixed training that includes strength training, aerobic exercise, and flexibility training within a single session). After 12 weeks, both groups had a small reduction in their waist circumference, with no difference between the fed and fasted groups in body composition or blood markers. 

Sure, there’s evidence that fasted training can enhance our ability to use fat as fuel during exercise. That said, women already tend to be good fat burners, and training and exercise by itself provide most of that adaptation. Plus, it can impair workouts lasting longer than an hour.

The bottom line is fasted workouts aren’t magic. If you’re taking a walk, doing some yin yoga, or going out for a chill spin on your bike, going out on empty is no big deal. If your goal is performance or building strength, eating beforehand may help nail those goals and make it easier to meet your active nutritional needs, especially when you’re doing longer, harder sessions.