Cardio is often seen as the “fat loss tool”, while strength training is seen as the “muscle gain tool”. If you want to build muscle, lift weights. If you want to lose fat, do cardio. I’m here to tell you that strength training is more important for fat loss than cardio.
Yes, some people are only concerned with losing weight, regardless of whether that is fat, water, or muscle. But most people want to LOOK better (and feel better). So, the goal for most people, whether they know this or not, is to lose fat while maintaining or even gaining muscle. That is what gives the “toned” or “shredded” look everyone wants. Just losing weight, by losing fat and muscle, tends to leave you looking just smaller and sickly, and feeling weaker.
Beyond the superficial, maintaining and building muscle and strength helps you feel good and function well in daily life, especially as you age.
In order to maintain muscle as you are in a caloric deficit (which alone will lead to weight loss, but not necessarily fat loss), you need to be doing progressive strength training and eating enough protein. If you just eat in a caloric deficit and do a bunch of cardio, you’ll simply lose weight, and much of it will likely be muscle. Muscle is expensive for the body to maintain, so if it doesn’t need it, it will gladly get rid of it. Strength training and protein intake is your way of telling your body “I need that muscle!”.
Muscle burns about 6 calories per lb at rest. During activity it burns even more, though the amount will vary depending on the intensity of activity, type of activity (cardio vs strength training), etc.
Now let's ignore the potential extra calorie burn from using extra muscle for training, and lets say that in your first year of training you gain 10lbs of muscle (very possible for beginners). This extra 10lbs equals 60 extra calories burned each day. That may seem small, but the power is in the long term. 60 calories per day over a year equals 21,900 extra calories burned over a year. If your caloric intake remained consistent, that’s 6lbs lost over a year just by resting!
This is the same way that many people gain weight, called creeping weight gain. 5 years of being in a very small surplus and suddenly you realize you’ve gained 50lbs. In this case, it can lead to creeping weight loss. Now that you have 10lbs of muscle added, 5 years later and you’ve burned 30lbs of fat without even trying.
Now the effect can definitely be more extreme if you are more active, are purposefully trying to lose fat through a caloric deficit and exercise, and have gained more than 10lbs of muscle (think 20-60lbs of muscle over the course of several training years). And it can also be mitigated if your diet adjusts to increase calories by the same amount or more. But even then, you are able to maintain and lose weight without having to restrict food to such a large degree as before. I should probably note that gaining that much muscle does required periods of eating in a caloric surplus to gain weight. But doing that correctly leads to more muscle gain than fat, and fat is much easier to lose than muscle is to gain.
The above chart shows the effect that different interventions had on % bodyfat. (This data comes from a meta-analysis of several studies, not just one study).
It shows that adding just cardio does lead to a decrease in bodyfat% (likely due to the increased calorie expenditure putting subjects into a caloric deficit, even without restricting calories).
It also shows that adding just resistance training has the same effect, if not slightly more.
Unsurprisingly, the greatest decreases in bodyfat % come from a combination of energy restriction, high protein diet, and exercise.
You might be thinking now, “doesn’t cardio burn more total calories than strength training?”. It doesn't seem so. According to this study, the calorie burn per minute is about the same for running, cycling, and weightlifting. HRS (circuit training with weights) had the highest calorie burn.
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Yes, strength training is more important than cardio for fat loss for the above reasons, but cardio is still a great tool for fat loss. The problem strength training has is it's very fatiguing. You can do low intensity cardio for potentially hours, accumulating much more calories burned. Lower intensity cardio is a great way to burn lots of calories if you have lots of time, and higher intensity cardio is a great way to burn lots of calories if you don’t have as much time. The higher intensity you use though, the more fatigue and recovery cost you pay. By burning more calories, you can increase your caloric deficit, allowing you to lose fat faster, or not have to restrict your diet as much.
If you have just 30 minutes 3x / week, you should probably just focus on strength training, but if you have more time, cardio can be a good addition to your program.
At the end of the day, the #1 most important thing for weight loss is a caloric deficit. Anything after that is to optimize the ratio of fat loss vs muscle loss.
In order to do so, we want to prioritize, in order:
Now, what kind of cardio and how long is ideal? That's for another article. For now, if your goal is fat loss, start with a caloric deficit, make sure you're eating enough protein, and strength train! If you aren't losing weight and can't eat less, adding some cardio can tip the scales in your favor.
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