Eat before or after exercise for better fat burn?

For a quick and easy way to burn fat during exercise, research shows that exercising in a
fasted state increases fat burn and stabilizes blood glucose levels (Bennard & Doucet, 2006).
This method is also called intermittent fasting before a workout. Here’s how it works, when
you have your last meal of the day, typically dinner around 5-6 pm, don’t eat again before bed.
Wake up the next morning, and head straight out the door for your morning run, treadmill run,
elliptical, bike ride, or whichever is your normal cardio routine. If you’re a coffee drinker,
maybe a cup of coffee will be ok before your workout but don’t load it down with sugar,
creamer, and other additives. Exercise sessions should be easy and slow paced and not on days
of high-intensity, sprinting type of workouts. Furthermore, exercise sessions should be kept less
than 2 hours before reaching the point of glycogen depletion (a.k.a. bonking). If you are
planning on working out longer than 2 hours, then begin refueling around the first hour to hour
and a half into your workout routine. Once you’ve completed your exercise, give yourself about
2 more hours before eating, and you’ll notice huge losses in fat after a few weeks. Another
interesting fact found in this study is that there was no difference in fat burn when consuming
either a high-GI (Glycemic Index) food or a low-GI food post-exercise (Bennard & Doucet,
2006). Again, aim to eat healthy and stay away from the donuts to prevent killing your workout
session. If you do the math, a normal slow paced cardio session may allow you to burn around
400-500 calories per hour. Consuming one Gatorade could easily balance out your calorie intake
almost making your workout useless in the end, so stick to water and protein for your morning
breakfast.

When you sleep in bed at night, your bodies will slowly burn glycogen stores in your
muscle; but nowhere near the rate of reaching depletion. In order to burn fat, your body will
need to first burn the triglycerides (stored glucose) in your body before beginning fat burn. If
you were eat immediately upon waking up, then your only adding to the amount of energy stores
that will have to be burned before initiating fat burn. Most people’s cardio routines will never
take them to the point of actual fat burning, so this method of introducing intermittent fasting
into your diet will help enormously. Here’s the caution though, this method should only be used
2-3 times a week. Never use this training method continuously from day to day in order to avoid
a metabolic drop due to sustained negative calorie balance. In addition to abusing your
metabolic system, due to overuse of intermittent fasting, immune system depression can also
happen which will put you into a higher probability of injury and sickness (Allgrove et al.,
2009). It all comes down to training smart.

References

Allgrove, J. E., Geneen, L., Latif, S., & Gleeson, M. (2009). Influence of a Fed or Fasted State
on the s-IgA Response to Prolonged Cycling in Active Men and Women. International Journal
of Sport Nutrition & Exercise Metabolism, 19(3), 209-221.

Bennard, P., & Doucet, É. (2006). Acute effects of exercise timing and breakfast meal glycemic
index on exercise-induced fat oxidation. Applied Physiology, Nutrition & Metabolism, 31(5),
502-511.