Is Weight Training or Cardio Better for Fat Loss?

The fitness space is full of myths and misconceptions, but one of the most pervasive is the idea that if you want to lose fat then your training should focus on cardio and if you want to build muscle then your focus should be weight training.  It’s hard to know where exactly these ideas found their prominence or why they are still so widely believed, but in this post I’ll offer some facts to provide clarity around the issue.

Anyone who has shown the slightest interest in improving their physical fitness has likely heard that weights are for bulking up and cardio is for slimming down. Could it really be this simple? Well, yes and no. Many factors contribute to muscle growth and fat loss, but since this installment is about fat loss we will focus there.  I wrote about how we can best define fat loss in a previous post. That said, the goal of a reduction of size and weight will be achieved most fundamentally by burning more calories than you consume. There is NO way around this. In the most absolute terms a calorie deficit will lead to weight loss while a calorie surplus will lead to weight gain.  What is a bit more complex is how one goes about manipulating energy balance. Let’s dive into how your training modality impacts energy allocation, energy expenditure, and metabolic rate.

First up is how energy is stored. At a high level, the most basic storage vehicles for the calories you consume are either muscle and liver glycogen or fat cells. When we perform high intensity work (heavy lifting, jumping, sprinting etc) we deplete glycogen stores. Once those stores are depleted, our bodies will tap into fat stores to perform the work. Lower intensity work such as walking will rely on any energy available in the blood before tapping directly into fat stores.  You may have realized that according to this logic, if I want to burn the most fat then cardio is most efficient. In the sense of a pure capacity for burning fat this is true, but it does not tell the whole story.  You see, by depleting glycogen stores through weight training you create a priority for your body to replenish them.  So when you next consume excess calories, they must go to glycogen stores BEFORE any energy can be stored in fat cells. I think of this as “free” calories in the sense that they are calories that will not directly contribute toward your overall energy balance. For example, say you have a 500 calorie meal. If you are glycogen depleted and require 200 calories to refill those stores you will only have 300 calories available for fat storage. If you are not glycogen depleted then the entire 500 calories is made available for fat storage. The glycogen depleted person ends up with less of a surplus or more of a deficit which is more favorable for weight loss.

Energy allocation winner: Weights

Next up we have energy expenditure. Have you ever seen the “fat loss zone”  displayed on your favorite cardio equipment? It seems to suggest that anything under or above this won’t burn fat. Well that is not true. Regardless of your heart rate, if your body requires more energy than is readily available then it will begin to tap into fat stores. However, cardio has a distinct advantage here.  The short intense bursts of work required by weight training cannot be repeated in quick succession for long periods of time. What does this mean? It means that cardio allows for steady tapping of energy stores for a longer periods of time than can be leveraged with resistance training. Weight lifting is not terrible for burning fat, but it is extremely inefficient with regards to fatigue and total output. This makes medium to low-pace cardio the ideal training modality for losing fat.

Energy expenditure winner: Cardio

Last we have metabolic processes. I will be writing future posts to cover metabolism a little more thoroughly, but for now we just need to understand one thing with regards to weight loss. That one thing is simply that burning fat is a catabolic process meaning it is a breakdown of material (fat in this case) for the purpose of releasing energy. The metabolism in a broad sense is the totality of processes undertaken by the body to build, replicate, and destroy cells and other compounds. It includes all of the processes your body performs to keep you alive and moving. These processes require energy, and that energy comes from a combination of the calories you consume and the energy stores you accumulate. This is where “calories in, calories out” comes from. Anabolic (building) processes require energy while catabolic processes release energy. Maintaining processes and tissue require energy as well. That being said, the more muscle you aim to build and maintain through weight training, the more energy it costs you and the more fat you stand to burn. With cardio training, however, there is not only a lack of signal to build muscle but also a lack of signal to maintain muscle. In fact, without this stimulus your body will break down muscle tissue to some degree. A smaller person has a “slower” metabolism and a person with less muscle also has a slower metabolism. Put this together and you end up with someone who gets smaller but is unable to keep off the weight because the metabolism is now actually primed for fat gain and resistant to fat loss. The muscle produced and maintained through weight training gives it a solid advantage when it comes to losing fat.

Metabolic rate winner: Weights

So there you have it; a list of strengths and constraints for both training modalities. So what’s the overall take-away? Which modality is best for fat loss? Due to the boost in metabolism you get from muscle as well as it’s utilization of energy to replenish glycogen stores, if one modality is picked over the other it should be weight training. However, the fat-burning efficiency of cardio cannot be overstated. Because of this, a person who wants to maximize fat loss will benefit most by using both. I hope you found this helpful. Happy training and until next time.

-Chris