Strength Training for Fat Loss

Strength training isn’t often the first thing people think of when they’re trying to lose fat. But should it be? We’re all probably familiar with the common assumption that cardio “gets you lean” and strength training “gets you big”, which sounds like the exact opposite of the fat loss.

But can you actually lose weight by lifting? Is cardio or weights better for fat loss?

Let’s explore the age-old battle of cardio vs strength training.

Not All Movement is Created Equal

One of the (if not the) primary considerations for losing fat is maintaining an energy deficit over time, which can either be accomplished by reducing your total intake and/or increasing your total energy expenditure.

Increasing the total amount, frequency, and duration of physical activity is the most obvious way to increase this expenditure. When people find out about this, they jump to the conclusion that movement is movement, and they just have to “move more” in order to lose fat.

Newsflash: not all movement is created equal. Especially when it comes to how it influences fat loss.

There are two considerations that define every type of movement:

1. The amount of energy you burn while performing the movement
2. The long-term adaptations to consistently performing that movement

Let’s start with the easy one.

Let’s Get Physical

The amount of energy you burn doing any activity is going to be heavily based on the amount of time and intensity of the activity you choose to do. Here’s a table comparing the energy expenditure you’d experience from common forms of exercise.

(Note: Despite most people using “calories” as a measure of energy, kilocalories, or kcal, is the technically correct term and will be used for the remainder of the article.)

Time and intensity are inversely correlated, meaning the less intense an activity is, the longer you can do it, and vice versa. So while it would be awesome to cycle at 25+ mph for hours on end, I think that would break both the human body and the Laws of Physics. 

A major consideration when implementing exercise is that you will burn less energy doing any activity as you lose weight. This is why all of the kcal burn numbers in the diagram above are expressed per kilogram, per minute.

If someone weighs 220 lbs (100 kg), an hour of walking at 4.5 mph would burn 636 kcal. If that person lost 22 lbs (10 kg) and now weighs 198 lbs (90 kg), that same hour at the same speed would now burn 572 kcal.

This is part of the Catch-22 of using cardio as the only means of losing weight: you’re going to need to spend more and more time doing the activity just to burn a similar amount of energy and create the same magnitude of energy deficit.

“But Cardio Burns More Energy Than Weight Lifting”

When you’re trying to decide between cardio or weights for weight loss, you might dismiss the idea of diminishing returns because you simply think a higher total of kcal burned is all that matters. 

“So what if I’ll only burn 500 kcal when I’m 20 pounds lighter, I’ll still be expending more energy than if I was weight training!”

Well, remember the second consideration from earlier: the long-term adaptations to consistently performing that movement.

While it is true that cardio/endurance exercise burns more kcal than strength training, this is only true in the acute sense. Cardio has little to no effect on your resting metabolic rate, largely due to the fact that it doesn’t meaningfully stimulate hypertrophy (remember this for later). When you stop your cardio routine, any energy deficit you may have been creating will disappear.

This effect is compounded when you consider that energy expenditure is constrained to a degree. In a nutshell, you can’t simply keep doing physical activity for hours and hours every day and expect it to have an exactly linear, additive effect on your metabolism. While it’s true that energy expenditure is mostly additive, a recently published perspective suggests “some energy appears to ‘go missing’ and is currently unaccounted for.” This seems to be especially true when you’re in an energy deficit, which you likely will be in if you’re trying to lose fat.

This means that higher levels of activity at one point in the day will reduce energy expenditure at other points in the day. This often occurs subconsciously and takes the form of a reduction in Spontaneous Physical Activity (SPA) and Non-Exercise Activity Thermogenesis (NEAT).

As another strike against cardio, this compensation effect is typically only seen with pure low-intensity/aerobic activities, as little to no NEAT compensation has been found after strength training. It’s worth stating again: you’ll expend more energy in an acute sense with cardio, but the ramification that has across the rest of the day is more likely to hamper your long term fat loss, not increase it.

More Than Just The Burn

Instead of having an acute impact on metabolism like cardio, strength training has lasting effects on your metabolism for multiple reasons. Sure, you still stand to burn 100-200 kcal during your average weight training session, but when it comes to strength training for fat loss, consider the knock-on effects as the real “secret sauce.”

For starters, lean mass (muscle) is a metabolically expensive tissue, meaning your body requires more energy to maintain your lean mass than it does your fat mass. You can expend up to three times as many calories preserving a pound of muscle as you would a pound of fat. While the difference may seem trivial (6 kcal/lb vs 2 kcal/lb), this adds up quickly.

Validated formulas to estimate Resting Energy Expenditure (REE) like the Katch-McArdle Equation are anchored around lean mass measurements for this very reason: you simply burn more energy when you have more muscle, even at rest.

Bosselaers et al. demonstrated this effect perfectly in their 1994 study that pitted 10 strength trainees (classified in the study as “bodybuilders”) against 10 lean control subjects to examine how their energy expenditure differed across 24-hours. Even when sitting around doing nothing, the bodybuilders burned nearly 15% more kcal over the course of a day when compared to the control group that had a similar level of leanness. 

When comparing the two groups, the bodybuilders were carrying about 9 kg (20 lb) more fat-free mass than their lean counterparts on average. The obvious explanation here is that the bodybuilders were able to burn more kcal by simply carrying more muscle mass.

Of course, that new muscle didn’t just appear out of thin air; creating new lean tissue costs a lot of energy, too. Your metabolism increases to accommodate this higher rate of energy being expended as new tissue is created (anabolism).

To further validate strength training for fat loss, consider that it can also improve nutrient partitioning, increase glucose disposal, and improve insulin sensitivity. Strength training also significantly suppresses your appetite, to a much higher degree than endurance training does. Taken together, this means you’ll be less prone to overfeeding, and the nutrition that you do consume is more likely to be utilized as fuel as opposed to being stored as fat.

Weight Lifting for Weight Loss: The Verdict

When it comes to exclusively using strength training for weight loss, it has a whole lot going for it that simply can’t be said for cardio.

You burn less energy per unit of time in the acute sense than you would with cardio, but that’s far from the entire picture. Building and maintaining muscle creates a lasting positive effect on your metabolism, and cardio simply doesn’t generate nearly the same degree of hypertrophy as strength training does. Strength training also doesn’t suffer from constrained energy expenditure like cardio does, suppresses your appetite to a greater degree than cardio does, and improves the way your body utilizes nutrition to a greater degree than cardio does.

In fact, studies have found that whether you’re creating your energy deficit with less food or more cardio, you will lose the same amount of weight over time. This literally means that the hour you were about to spend on the treadmill can provide a similar effect on your energy balance as just leaving that other half of the sandwich on the table instead of eating it.

On the other hand, a 2021 meta-analysis found that starting a strength training routine reliably contributes to fat loss in healthy adults. More importantly, another 2015 meta-analysis found that strength training alone is more effective for fat loss in overweight adults on ad-libitum diets than either cardio alone or even a combination of strength training and cardio. In that same population (overweight adults, ad-lib diet), six to 12 months of cardio alone was ineffective at inducing weight loss.

Now, this is not to say targeted cardio sessions can’t be a useful add-on for healthy individuals with properly constructed diets. Cardio can still provide some additional kcal burn when used judiciously, and could be a safer alternative in some scenarios than further decreasing your intake in the name of losing more fat. Cardio can assist with weight loss and weight maintenance over time, so long as it’s used in a supplementary capacity.

But between cardio or weights for fat loss, the existing evidence heavily suggests that strength training will deliver much more reliable and sustainable results as your primary tool.

For more information like this, check out Menno’s Online PT Course, which details even more of the key differences between exercise modalities and how to optimize their use to achieve your desired goals.