Fasting before evening workouts have pros/cons to consider

Every week it seems something new is coming out regarding the effects of fasting. In particular many are looking at the potential combined effects of fasting before exercise. If both fasting and exercise have potential benefits, the two together should be even better right? This seems to be the common thought process but not always the case. Most studies though have looked at the impact of overnight fasting on exercise. A recent one came out looking at the impact on evening workouts for a new perspective.

Effects of fasting

Most people experiment with fasting for one of two common reasons. One is weight loss and the other is improving metabolic health and adaptations. Weight loss comes from being in a caloric deficit and is true for any diet one may be following. It makes sense then that if reducing the time available to eat that overall less calories will be consumed. Pairing that with some extra physical activity to burn more calories, more weight is lost. Can’t argue with that side of things.

The metabolic adaptations are aimed at increasing the body’s ability to burn fat. Without eating anything (carbs in particular) the body is still needing energy from somewhere. To get that energy and keep functioning, fat is what gets utilized more. By forcing the body to use fat, it becomes better at that process. Just like when we practice something, the more we do it the better we get. So, if the body is using more fat and we are consuming less calories, the weight being lost should be coming mostly from fat. Then adding in some exercise on top of that may accelerate all of these things theoretically.

Exercise while fasting

In theory all signs point to a greater energy deficit for more weight loss and increased fat usage. But the exercise piece of this is going to be a bit of a struggle. As most of us have experienced firsthand, when hungry we usually aren’t feeling the best. This can result in a worse training session due to decreased performance. While more fat may proportionally be getting burned in that workout, less overall energy is likely being used meaning less overall fat burned.

In the latest study this was shown in males and females that when asked to give peak performance, they came up short when fasted. Even when given an all you can eat buffet afterwards though, a bit more food was consumed in the fasted group but it didn’t offset the amount from skipping a meal earlier. So overall a caloric deficit was still the result. Interestingly though this increased intake post-exercise was only seen in males. Females ate equal amounts in both groups and resulted in even greater caloric deficit as a result.

Is this a good strategy?

The infamous response is, it depends. In the short term it can help with some weight loss and fat loss. This comes at a cost though where you aren’t getting the most out of your workouts. Especially for athletes looking to improve performance, this can be a big problem. It also can make it tougher to recover properly. The body needs energy and in particular protein to repair itself after those hard trainings. If in a constant deficit and not getting enough protein you’re going to feel more sore and performing worse. Rough combination there. Whether considering fasted exercise in the morning or evening like this study, there are trade-offs that need to be considered.

Study referenced: click here