Cardio or Weights: What's Better for Fat Loss?

By Aadam | March 16, 2020

Cardio or weights, which is better for fat loss? It’s a question that causes a lot of confusion. Some camps claim cardio is better and other camps will fervently tell you to avoid cardio and only lift weights. So which one is better? Let’s find out.


Every week I get dozens of emails from readers asking me all kinds of questions.

“Aadam, my friend said if I drink Diet Coke I’m basically poisoning myself–is my friend right?” (Your friend is wrong.)

Or “Aadam, my mum thinks creatine is a steroid and won’t buy it for me–what do I tell her?” (Get a job and buy your own damn creatine. Alternatively, send her this.)

And occasionally, “My girlfriend left me and I’m heartbroken and I’ve eaten my body weight in ice cream–HOW DO I GET HER BACK!?”

You know, typical fitness stuff. 

Among these typical-fitness-stuff questions, one that pops up frequently is “what’s better for fat loss: cardio or weights?” 

Now, when you’ve been doing this fitness thing for as long as I have you develop a sixth sense of sorts endowing you with the fantastical ability to see past the superficial and know what the person is really asking.

What these people are really asking is: “I want to know what burns the most fat–cardio or weights?”

Well, the answer is neither. Allow me to explain.

Cardio or weights for fat loss is the wrong question

Fat loss should be all about efficiency: You want to do the least amount of work possible while making the most amount of progress possible. Let’s call this Aadam’s Law Of Fat Loss Efficiency (or ALOFE for short).

While exercise has innumerable benefits and you certainly should be exercising (more on this later), using it for fat loss breaks my law of efficiency. 

Allow me to explain. 

This is based on the 3500 calorie rule that states a pound of fat contains 3500 calories and so, to lose a pound of fat you need to create a weekly deficit of 3500 calories or 500 calories per day. Ive explained why this is a bit simplistic here. But for the sake of this example, it works.

You can a) create this deficit via exercise, or b) create this deficit via food. 

Now, remember my law of efficiency (ALOFE)? Well, trying to burn 500 calories through exercise isn’t very efficient. 

For instance, let’s use the general rule of 100 calories burned per mile, you would have to run about 5 miles to burn 500 calories. Let’s assume you’re running an 8-minute mile, this would take you about 40 minutes. So a 40-minute run. Every day. I can think of at least 10 things I’d rather do, three of which involve inserting sharp objects into my body.

Weight training burns far fewer calories than cardio. The calories burned during a lifting session can range between ~70kcal–300kcal depending on a number of factors like experience level, the amount of weight lifted, training volume, load, the intensity and length of the session, exercise selection, and the length of the rest period between sets. 1 2 3 4 5 6 7 8 9

But, for the sake of this example let’s assume you burn ~300kcal per lifting session (you’re most definitely not burning this amount, but let’s pretend you are), you would need to weight train every single day at a very high intensity. Not only is this approach not conducive to muscle retention–a point I’ll return to later–but it also increases the chance of injury and overtraining. 

This ‘exercise for fat loss’ approach presents another problem many people struggle with: adherence.

Are you willing to engage in very intense exercise every day? Probably not. Especially if you’re starting out and are extremely unfit or, you know, have a life. 

On the other hand, it’s far easier to cut a few hundred calories by making small, yet attainable dietary changes. 

Here’s an example many of you can relate to. A Grande full-fat latte from Starbucks is 228 calories. 

Two lattes every day is 456 calories. 

If you swapped the full-fat version for the nonfat version, you cut the calories by over 50% (~260 calories). 

Even better, drink your coffee black–you know, how God intended–and add a tiny splash of milk and you’ll reduce the calories by a whopping 90% (~20 calories). 

I don’t know about you, but making small adjustments to my diet is way more appealing than trying to burn the same amount of calories through vigorous exercise every day. It also abides by my law of efficiency (ALOFE). 

At this point, if you’re someone who believed exercise was the crucial factor for fat loss you’re probably having a mini-breakdown questioning if your entire life up until this point has been a lie–uh, yes, probably. 

You’re probably also thinking “if I can lose fat just by eating less, why the hell should I exercise?”

I thought you’d never ask.

The role of exercise in fat loss

Ultimately, the goal of every sensible fat loss diet should be twofold: 

And while cardio has many benefits, it kinda sucks for muscle retention in a deficit. 

Bryner et al. put 20 people (17 women and three men) on an 800kcal/day liquid diet and split them into two groups:

After 12 weeks, both groups lost weight but…

Hunter et al. conducted a similar study in 2008. 

After 21 weeks, all three groups lost weight but…

…only the diet and resistance training group preserved lean mass. 

And finally, in 2015 Clark JE. published a systematic review and meta-analysis comparing the effectiveness of three treatments for weight loss:

The results showed that diet + resistance training or a combination of resistance training and cardio in combination with diet had a greater effect on improving body composition than diet alone or diet + cardio.

If you’re a regular Physiqonomics reader, this shouldn’t come as a surprise. By adequately loading your muscles and increasing this load over time, you provide a potent stimulus to your body that results in muscle gain.

In a calorie deficit, this same stimulus signals your body to hold on to muscle. Without the stimulus of weight training, the body doesn’t have a reason to preserve muscle mass. Cardio (alone) doesn’t provide the same stimulus that weight training does. 

Further, weight training has inherent muscle preserving effects. 

A 2014 paper found after five days of being in a calorie deficit, rates of muscle protein synthesis (MPS) dropped by 27%. Aa

When weight training was thrown into the mix, MPS was restored to levels seen when participants were in energy balance (i.e., maintenance intake). 

And when protein was added to weight training, the rates of MPS increased 34% above rates of energy balance.

Think about that: even in the absence of adequate protein, strength training alone was able to increase rates of MPS to the same extent as eating in energy balance. 

In agreement with this paper, a 2016 paper compared two different protein intakes–0.5g/lb or 1g/lb–in a pronounced calorie deficit (~40% below maintenance) in conjunction with strength and interval training. 

Unsurprisingly, the higher protein group gained lean mass. What is surprising is despite consuming protein way below the recommended intake, the low protein group preserved their lean mass. Aa

All of that is just a long-winded way of saying: weight training (in combination with adequate protein intake) preserves muscle mass in a calorie deficit while cardio (alone) doesn’t. 

But the importance of muscle retention extends beyond looking better 

Lean mass is strongly associated with your metabolic rate so it’s probably a good idea to preserve muscle so you don’t fuck up and enter Starvation Mode. Only joking, Starvation Mode is bullshit. What isn’t bullshit is preserving your muscle mass as you lose fat will help preserve your metabolic rate, attenuating any declines in metabolism. 

In addition, there’s evidence to suggest an increased loss of lean mass during a diet can increase the chances of weight regain due to increased appetite. 10

Why this happens isn’t yet fully understood, but one hypothesis is the Protein Leverage Hypothesis (PLH). 

The PLH states the body will increase appetite until its protein requirements are met. Because lean mass plays a crucial role in our survival if you begin losing lean mass your body will do everything it can to recoup the lost mass to keep you alive. The easiest way to do this is by ramping up hunger levels so you go looking for food. 

This doesn’t mean cardio’s bad

Well not entirely, anyway. 

The reason cardio’s gotten such a bad rap is because people abuse the hell out of it. 

I mean, if you’re eating in a calorie deficit, weight training multiple times per week, also running hundreds of miles per week, and hell, just throw in some CrossFit and weekly Zumba classes because fuck it why not? Is it any surprise you feel like shit and struggle to stick to your plan? That was rhetorical, the answer is no.

Think of cardio like an add-on. A strategic tool used in certain situations to augment fat loss. 

There may come a point in a diet when reducing food intake further can lead to adherence issues. By adding in some weekly cardio, you can continue eating adequate amounts of food while concomitantly increasing the deficit. 

Similarly, instead of creating the entire deficit from food, you may prefer a 50/50 split from cardio and diet. 

cardio-or-weights-50-50-split-diet-and-cardio

Something worth mentioning even though it’s not directly related to the topic at hand is the role of physical activity in weight maintenance. Losing fat is only a small part of everyone’s goal. The ultimate goal is to lose fat and keep it off for good. 

And while exercise alone isn’t very effective for fat loss, higher amounts of weekly physical activity is an important factor in weight maintenance. 11 12 13

The National Weight Control Registry–the largest database of individuals who have succeeded at long-term weight loss–has consistently found one of the key characteristics of weight maintainers is high levels of physical activity (averaging about an hour of moderate-intensity physical activity per day).

There are a number of reasons for this, but an idea that’s been gaining traction over the past few years is ‘energy flux’. 

At the end of a diet, you can approach weight maintenance in two ways:

cardio-or-weights-energy-flux-graph

“While both result in energy balance, in the face of an array of palatable food available in our current society, remaining in energy balance in a low flux, sedentary state seems improbable for most.” Researchers write in a 2017 paper. “Rather, maintaining a high flux state appears to be a more promising way to attenuate the weight loss-induced energy gap.” 14

Five years earlier, the Look Ahead Trial found higher levels of physical activity accompanied by higher food intake was associated with weight loss maintenance over a four-year period. 

These findings were supported by a 2016 study that showed low energy flux significantly predicted future fat gain. 

Theoretically, this makes sense. By increasing weekly physical activity (and thus energy expenditure) you can eat more food which automatically increases adherence. There’s also some evidence to suggest a high energy flux leads to reduced hunger which is a common issue at the end of a diet. 

In addition, there’s only so much weight training you can do before it becomes detrimental. Let alone the fact weight training alone doesn’t burn many calories. Cardio, on the other hand, can be implemented in myriad forms that complement your life like walking, sports, swimming, etc. and, compared to strength training, has a higher calorie expenditure. 

A combination of weight training and cardio programmed appropriately can be a great way to ramp up weekly physical activity (and energy expenditure).

As long as you keep the goal the goal and don’t abuse cardio, it can be programmed without any negative effects.

How to incorporate cardio  

How you decide to incorporate cardio (if you decide to at all) will depend on a number of factors like your personal preference, likes and dislikes, and what works best with your schedule. 

My personal approach to cardio for clients is:

  • Preferred: Daily walking; hitting a targeted number of steps or minutes
  • Optional (depending on the client): steady-state or HIIT 

My go-to ‘cardio’ is walking. Most people, no matter their fitness level, can walk with relative ease every day. Aa

A 30-minute run, for example, can be very difficult and unpleasant for someone who’s just starting out, and if they’re really overweight it can put a lot of undue stress on their knees. A 30-minute walk, on the other hand, is much easier and can even be enjoyable. 

Of course, walking, despite all its benefits, has one glaring drawback: time. 

Some people may not be able to walk the recommended 7-10k steps per day. In which case, other forms of cardio need to be considered. 

Steady-State Versus HIIT?

Ok, I’ve been waffling on for a bit too long and I really want to start wrapping this up. So, here’s a bullet-pointed list: 

  • If you’re short on time, HIIT can be a great way to get your cardio done in a time-efficient manner.
  • And because I know at least one person is going to mention something about HIIT being superior because of EPOC–it’s overblown.
  • If you’re deep into a cut and energy is low, HIIT can negatively affect energy levels, performance, and recovery so it should be programmed with that in mind.
  • Regardless of what you prefer (HIIT or steady-state), choose low-impact forms of cardio over high-impact. For example, the StairMaster, cycling, or elliptical would be preferable over activities like running or sprinting.

Alright, we’re do–WAIT! I have a few questions

Go on…

1. I enjoy running and don’t want to give it up. Can I run and lift weights? 

Yes. Just keep the goal the goal: do you want to lose fat? Then make weight training the priority and limit running to 1-2 sessions per week. 15

2. Will I lose muscle if I do both?

As long as you don’t abuse cardio, no. 

3. Can I do cardio and weights on the same day?

Cardio should be done on separate days from weight training, ideally leaving at least 24 hours between a lifting session and a cardio session. 15

4. But what if I have to do both in the same workout?

Uh, how about you don’t? I refuse to believe anyone is that busy they can’t separate the two. 

5. No but seriously, I am that busy–halp, please?

FINE. If you have to do cardio and weight training on the same day, then leaving at least six hours between the two sessions will prevent any declines in strength performance. For example, strength training in the morning and cardio in the evening or vice versa. 16

6. Should I do cardio or weights first?

If you have no choice but to do both cardio and weights in the same session, then you should do weight training first and cardio second.

7. Why am I not losing weight despite doing tons of exercise?

Motherfu–did you even read the article? Because you’re eating too fucking much.

8. Can I really lose fat just by eating in a deficit and lifting weights?

Yes.

Holy smokes we covered a lot. So here’s a quick summary:

  • Strength training is of the highest importance during a fat loss diet because it preserves muscle better than cardio. By preserving muscle mass, you’ll improve your body composition and preserve your metabolic rate.
  • Contrary to what your local meathead told you, cardio won’t automatically burn all your muscle off or lead to strength loss, just don’t abuse it.
  • Walking is going to be the most complementary to strength training as it’s both low impact and intensity and won’t interfere with your strength training.
  • If you enjoy traditional forms of cardio (like running) and want to continue doing it, then no more than 1-2 cardio sessions per week lasting between 20-40 mins.
  • HIIT (High-Intensity Interval Training) can be useful if you’re low on time.
  • Choosing low-impact cardio will be better than high-impact cardio (cycling or elliptical versus running; the same rule applies to interval training).