Why Cardio Is NOT The Best Way To Lose Weight

Want to lose fat? Then you need to get your butt on the treadmill. At least, that’s what most people assume—and why most weight-loss warriors aren’t getting the results they want from their workouts.

Consider this: When obese participants followed a diet and either a strength-training or cardio program for eight weeks, the two groups lost a similar amount of weight—but the strength trainers lost less fat-free mass (a.k.a. muscle) than the cardio-doers, according to research published in the American Journal of Clinical Nutrition. Meanwhile, when Harvard researchers followed 10,500 men over the course of 12 years, they found that strength training was better than cardio at warding off belly fat. (Cue the collective sigh of relief from cardio haters everywhere.)

Research reviews suggest that exercise programs on their own—without dietary changes—usually produce only modest weight loss over time, often on the order of a few kilograms. That’s it. All those hours on the treadmill, and you might only drop about 5 pounds. The takeaway? What you eat matters way more than how much you sweat.

We’re not saying you should cut cardio out of your life, but if strength training isn’t already a major part of your weight-loss plan—well, it needs to be.

Cardio vs. Strength Training

“People think to lose fat mass they need aerobic exercise and to forget about resistance training,” says Rania Mekary, Ph.D., a researcher with the Harvard T.H. Chan School of Public Health and lead author of the 12-year study.

On the surface, that assumption makes sense. After all, when you perform moderate-intensity cardio like running, biking, or swimming, the vast majority of your calories burned come from fat, she explains. (Hence why, when you’re cruising along at an easy pace on a cardio machine, it rewards you by telling you that you’re in the “fat-burning” zone.) Meanwhile, during resistance training, the bulk of your calories burned come from glycogen, stored carbs housed in your muscles and liver.

The first option seems far more advantageous for those trying to shed fat. That is, until you consider the fact that your muscle mass—which, when left to its own devices, decreases after age 30—is a key driver of your metabolism. And rather than building muscle, cardiovascular exercise can actually burn up some of it.

The Hidden Cost of Cardio-Only Approaches

Here’s something that might surprise you: when you lose weight through diet alone (or diet plus mostly-cardio training), a meaningful chunk of that weight loss can come from fat-free mass—not just fat. That’s a big deal, because losing muscle is like downsizing your body’s calorie-burning engine.

“Fat is the major energy source during aerobic training, but many people don’t realize that protein also contributes. And that protein comes from muscle,” Mekary says. “So if you are running, running, running, it can make you lose even more muscle than you would otherwise.”

The result: a slower and slower metabolism. That partially explains why, after many people lose weight, they tend to put it right back on. In fact, research from Columbia University shows that losing just 10 percent of your body weight significantly lowers your basal metabolic rate, the number of calories you burn just to stay alive.

This phenomenon—called metabolic adaptation—can be surprisingly persistent. Your body essentially “remembers” its previous weight and fights to get back there by slowing down how many calories you burn at rest. Some research suggests this slowdown can stick around for years, even if you regain some weight. It’s frustrating, but understanding it helps explain why so many people hit plateaus.

Related: 5 Myths About Your Metabolism—Busted

Why Strength Training Changes the Game

Meanwhile, strength training increases your metabolic rate in a big way. Over the short term, it causes just enough microscopic damage to your muscles that they have to work hard to recover—a process that requires a lot of energy (a.k.a. calories). Known as ‘excess post-exercise oxygen consumption’ (or EPOC), your metabolism can stay elevated for up to 72 hours after your strength training session, according to research published in the European Journal of Applied Physiology. You just don’t get that lasting boost with cardio, especially when it’s steady-state, Mekary says. Over the long term, by building the amount of muscle mass you have with strength training, you can increase your metabolism even further.

To put some numbers on it: after a couple months of consistent resistance training, research suggests your resting metabolism can tick up modestly—one more reason lifting makes maintenance feel less like a grind. Over the course of a year, that adds up without you having to do any extra work.

What’s more, strength training helps to dull the spikes in hunger-stimulating hormones that often come with weight loss, explains Spencer Nadolsky, D.O., a board-certified family and bariatric physician, diplomate of the American Board of Obesity Medicine, and author of The Fat Loss Prescription. That makes losing weight—and keeping it off—that much easier.

The 80/20 Rule You Need to Know

Here’s a reality check that might change how you approach your weight-loss journey: nutrition tends to drive most of your weight-loss results, while exercise plays a crucial supporting role—especially for keeping the weight off and protecting muscle. Think about that for a second—you simply cannot out-train a bad diet.

Running a mile burns about 100 calories. That’s roughly one banana or half a granola bar. Meanwhile, a single restaurant meal can easily pack 1,000+ calories. The math just doesn’t work in favor of cardio alone.

This doesn’t mean exercise is pointless—far from it. But it does mean that if you’re spending five hours a week on the treadmill while eating whatever you want, you’re probably not going to see the results you’re hoping for. The real magic happens when you combine smart nutrition with the right kind of exercise.

Better Together: How to Combine Cardio and Strength for Optimal Fat Loss

Still, for the best fat-loss results, you don’t want to ignore cardio altogether. “By combining anaerobic and aerobic exercise, you maintain muscle, burn more calories, and are able to burn both fat and glycogen,” says Mekary, noting that, according to her research, combination training is even better for fat loss compared to strength training alone. “It’s a win-win situation.”

While the best way to divide your workout routine depends in part on what you actually like to do (what does your schedule matter if you won’t stick to it?), Mekary recommends devoting about 70 percent of your workout time to strength training and 30 percent to cardio. If you hit the gym five days per week, that works out to roughly three strength days and two (slightly shorter) cardio days per week.

Scheduling Your Workouts for Maximum Results

“Ideally, you would schedule strength and cardio workouts on different days,” says Nadolsky, noting that performing cardio right before a strength workout can slightly inhibit muscle-building results. (Another study published in the European Journal of Applied Physiology found that men made comparable strength gains after 24 weeks regardless of whether they hit cardio or strength training first. But the guys who did cardio first initially had lower levels of testosterone—a marker of recovery and muscle-building potential—than those who hit the weights first.) It’s not a huge difference, but if you’re focusing on building muscle and can schedule your workouts like that, by all means, go for it.

Here’s a sample weekly split that works well for most people:

• Monday: Strength training (upper body)
• Tuesday: HIIT cardio (20-25 minutes)
• Wednesday: Strength training (lower body)
• Thursday: Rest or light activity
• Friday: Strength training (full body)
• Saturday: Moderate cardio or active recovery
• Sunday: Rest

Making the Most of Your Strength Sessions

Making the most of both your strength training and cardio sessions just takes some simple strategizing. During your strength workouts, focus on hitting as many muscle groups as possible by performing compound moves such as squats, deadlifts, thrusters, pull-ups, and bench presses.

These multi-joint exercises are your best friends for a few reasons:

• They burn more calories because they recruit more muscles
• They build functional strength that carries over to real life
• They’re more time-efficient than isolation exercises
• They trigger a bigger hormonal response that supports fat loss

If you’re newer to strength training, don’t let the barbell intimidate you. Bodyweight exercises, dumbbells, and resistance bands all count. The key is challenging your muscles progressively over time. And don’t forget to fuel those workouts with adequate protein—most research suggests aiming for about 1.2-1.6 grams per kilogram of body weight daily to help preserve and build muscle during weight loss.

The Case for HIIT

Spend the bulk of your cardio time on high-intensity intervals (HIIT) such as sprints on the treadmill, bike, or rowing machine. However, some moderate-intensity, steady-state can be good from time to time, too—especially when you feel like you need a little extra recovery from your lifting sessions and don’t want to go too hard with HIIT.

Here’s why HIIT deserves a spot in your routine:

• Time efficiency: A 20-minute HIIT session can deliver similar or better fat-loss results compared to 45-60 minutes of steady-state cardio
• Afterburn effect: HIIT can keep your metabolism elevated after you’re done—one reason it can punch above its weight in a short session
• Muscle preservation: Unlike long cardio sessions, HIIT is less likely to eat into your hard-earned muscle
• Fat oxidation: Some research suggests HIIT can quickly improve fat oxidation during exercise (one study found a jump of roughly a third after just a couple weeks), which is a nice bonus on top of the time savings.

A simple HIIT protocol to try: 30 seconds of all-out effort (think sprinting, burpees, or bike sprints), followed by 60-90 seconds of recovery. Repeat 8-10 times. Done in under 20 minutes, and you’ve checked off a seriously effective workout.

Don’t Forget About NEAT

One more thing worth mentioning: there’s a type of calorie burn that flies under the radar but can make a huge difference—NEAT, or non-exercise activity thermogenesis. This is all the movement you do outside of formal exercise: walking to your car, taking the stairs, fidgeting, standing while you work, even doing chores.

Here’s the wild part: the difference in NEAT between individuals can be as much as 2,000 calories per day. That’s enormous—and it’s something you can actually influence without adding another gym session to your week. Small habits like:

• Taking walking meetings
• Parking farther away
• Using a standing desk for part of your day
• Taking the stairs instead of the elevator

These might seem trivial, but they add up. Think of NEAT as the background music to your fat-loss efforts—it’s always playing, and turning up the volume can make a real difference.

The Bottom Line

At the end of the day, the most effective fat-loss strategy isn’t about choosing between cardio and strength training—it’s about using both strategically while prioritizing what you put on your plate. Strength training protects your metabolism and builds the muscle that keeps you burning calories around the clock. Strategic cardio (especially HIIT) boosts your cardiovascular health and adds to your calorie burn without eating into your muscle. And smart nutrition ties it all together.

So the next time someone tells you to just “do more cardio” to lose weight, you’ll know the full story. The treadmill has its place—it’s just not the throne.