Aerobic vs resistance training for fat loss and lean mass

Aerobic and resistance training can produce different results for fat loss and lean mass. Read the comparisons before choosing your exercise routine.

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Aerobic exercise can outperform resistance training for the weight of fat lost, yet show no advantage for body fat percentage. That apparent contradiction appears in a review comparing exercise programs in healthy adults.[2] The answer to “Which exercise helps me lose weight?” changes with the result you choose to measure. A scale, a body fat estimate and a measure of lean mass are answering different questions.

After getting home, do you make time for a walk or a strength session? A crowded calendar makes the choice feel urgent. But reducing abdominal fat and preserving muscle during weight loss are different aims. Before choosing an exercise, put your aim into words. Then ask whether the research measured that outcome, in people like you, against the alternative you are considering.

This article focuses on comparisons between exercise types: what they reduce, what they retain and how the studies organized the training. Resting metabolism and weight regain are covered separately in Strength training, metabolism and weight regain. Here, the useful starting point is more concrete: when time is limited, what does the evidence tell us about the role of aerobic exercise, resistance training and a combination of both?

Weight, fat mass and lean mass answer different questions

Losing body weight, losing the weight of fat and lowering body fat percentage are separate research outcomes. Fat-free mass is the amount of the body excluding fat; it should not be treated as a direct measurement of muscle alone. A review comparing aerobic, resistance and concurrent training treated fat mass and body fat percentage as its primary outcomes, while body weight and fat-free mass were separate secondary outcomes.[2] That distinction matters before we look at any winner.

The review brought together randomized controlled trials in metabolically healthy adults. In this kind of trial, participants are assigned to conditions by chance, allowing researchers to compare the results of the assigned programs. The systematic review included 36 studies and 1,564 participants. Of these, 31 studies supplied sufficient data for a meta-analysis pooling those trials to compare changes in body fat.[2] The exercise labels were shared across trials, but their participants and implementation were not identical.

In studies lasting at least 10 weeks, aerobic training reduced body weight by an average of 1.82 kg more than resistance training. The 95% confidence interval for the difference was −2.72 to −0.93 kg. Aerobic training also reduced fat mass by an average of 1.06 kg more, with a 95% confidence interval of −1.88 to −0.24 kg.[2] The intervals express uncertainty around the estimated average differences between the groups.

The 1.06 kg figure is therefore a comparison with resistance training. It does not mean that everyone who starts aerobic exercise will lose that amount of fat. Nor is it the average change from the aerobic group’s starting point.[2] Whenever a headline quotes a weight-loss number, look for the missing comparison: change from baseline, difference from doing nothing, or difference from another exercise program. Those are different statements, even when the unit is the same.

There was a trade-off in the same comparison. Aerobic training retained an average of 0.88 kg less fat-free mass than resistance training, with a 95% confidence interval of −1.73 to −0.03 kg. Meanwhile, changes in body fat percentage did not differ significantly between aerobic, resistance and concurrent training.[2] An advantage for the absolute weight of fat lost did not translate into a demonstrated advantage for the proportion of the body made up of fat.

An unchanged morning weight can make yesterday’s effort feel pointless. But these findings concern group averages across training interventions, not a verdict on an individual workout.[2] The broader interpretation of body composition is covered in Body weight and body fat as measures of progress. For this comparison, keep the outcomes separate: the exercise that produces the larger fall on the scale does not automatically produce the better result for every part of the body.

Aerobic exercise has a fat-loss advantage under some conditions

The average advantage for aerobic training needs its conditions attached. In the same review, studies shorter than 10 weeks found no significant differences between exercise types. When the workloads of aerobic, resistance and concurrent training were matched, changes in fat mass, body weight, body fat percentage and fat-free mass also did not differ significantly.[2] Duration and workload are part of the comparison, rather than background details that can be discarded once we know the exercise names.

This is relevant to an ordinary weekly schedule. If a walking session occupies a larger part of the evening than a strength session, the activities differ in both type and time. Comparing their names alone hides part of what you actually did. Likewise, switching activities after the first few sessions gives you little opportunity to consider results from longer interventions. A fair reading keeps the program and its duration together, without turning a study threshold into a promise about the date your body will change.

The review searched for comparative trials published from January 1980 to January 2023. Its subgroup analyses considered intervention duration, whether concurrent exercise took place on the same or different days, and whether workloads were matched.[2] These are several distinct questions inside the broad phrase “aerobic versus resistance training.” Thinking about your own plan in similar terms can make the choice clearer: which activity, how much of it, over what period, and alongside what else?

Resistance training also has evidence of fat reduction in its own right. A systematic review of 114 trials involving 4,184 participants with overweight or obesity found that resistance training alone reduced whole-body fat mass by an average of 1.0 kg relative to no-training controls. Body fat percentage fell by 1.6 percentage points. Lean mass increased by an average of 0.8 kg, with a 95% confidence interval of 0.6 to 1.0 kg.[6] Doing less well than another exercise on a particular outcome is different from having no effect compared with no exercise.

In that review, interventions combining resistance training with dietary energy restriction reduced fat mass by an average of 5.3 kg relative to groups receiving no intervention. The 95% confidence interval was −7.2 to −3.5 kg.[6] This larger figure belongs to the intervention as a whole, including its dietary component. Describing it as fat lost through strength training alone would remove a condition that was actually part of the treatment being tested.

A separate review in healthy adults also found benefits from full-body resistance training compared with no exercise. Fat mass fell by an average of 0.55 kg, with a 95% confidence interval of −0.75 to −0.34 kg, and body fat percentage fell by 1.46 percentage points.[7] These figures differ from those in the review of people with overweight or obesity, but the populations, selected trials and interventions also differ. They are not interchangeable estimates for the same person undertaking the same program.

The healthy-adult review included full-body resistance programs lasting at least 4 weeks. It gathered 58 studies, with 54 contributing to the meta-analysis. Measurement method was associated with differences in effects on fat mass and body fat percentage; sex was not.[7] Even the way an outcome is measured can help explain why results differ. Keep in mind that resistance training can reduce fat, while aerobic exercise reduced more under some study conditions.

Visceral-fat findings differ between reviews

“Belly fat” also needs a more precise question. Studies distinguish visceral fat from subcutaneous fat, and an older review in adults with overweight or obesity selected trials measuring visceral fat with CT or MRI imaging.[4] A change in how clothing fits, a change in body weight and a change in an imaging measurement of visceral fat are different pieces of information. They should not be exchanged for one another when interpreting an exercise result.

A 2012 review included 35 studies. Aerobic exercise reduced visceral fat compared with no-exercise controls, with a pooled effect size of −0.33 and a 95% confidence interval of −0.52 to −0.14. Resistance training did not show a statistically significant effect against controls. However, the 9 studies directly comparing aerobic with resistance training also found no statistically significant difference between the exercise types.[4] A significant result for one exercise and a nonsignificant result for another do not, by themselves, establish a significant difference between them.

A 2021 review examining exercise dose likewise found that aerobic exercise of at least moderate intensity reduced visceral fat, while resistance and combined training did not show statistically significant effects.[5] Yet a 2023 network meta-analysis of 84 randomized controlled trials and 4,836 participants reported visceral-fat reductions with aerobic exercise, resistance training and their combination.[1] A network meta-analysis uses direct comparisons and indirect comparisons through shared comparators. It brings a different set of evidence together from a simple head-to-head comparison.

The healthy-adult resistance-training review also reported a reduction in visceral fat: a standardized mean difference of −0.49, with a 95% confidence interval of −0.87 to −0.11.[7] A standardized mean difference expresses an effect after putting measurements on a common scale. The −0.49 is neither kilograms nor a percentage reduction. Reading it as either would give a numerical expectation that the study did not report.

There is also an unfavorable qualification in the 2023 network meta-analysis. Although resistance training showed a visceral-fat benefit, the authors described it as the least effective of the interventions compared.[1] If visceral fat is your main concern, keep both parts of that conclusion in mind. Evidence of improvement and evidence of a relatively smaller effect can coexist. Leaving out the latter would make the findings sound more supportive of resistance training than the authors’ conclusion was.

The 2012 review studied adults with overweight or obesity, whereas the healthy-adult resistance review selected a different population and different trials.[4][7] A newer publication does not automatically cancel every older result. Equally, an older conclusion should not become a reason to ignore later findings. First decide which outcome you want to understand, then look at the participants and comparison behind the estimate. This is especially useful when several articles use the same broad phrase, abdominal fat, for different measurements.

The 2023 analysis examined total body fat, waist circumference and subcutaneous fat as well as visceral fat. Improvements were reported for aerobic, resistance, combined and high-intensity interval training across these measures, but resistance training did not produce a statistically significant improvement in body weight.[1] The scale therefore omitted part of the information the researchers collected. Before choosing an exercise solely by its weight result, consider which changes you can assess through your existing measurements or health checks and which require a different kind of assessment.

Numbers: comparing exercise outcomes

At least 10 weeks of training: aerobic exercise reduced fat mass by an average of 1.06 kg more than resistance training; 95% confidence interval −1.88 to −0.24 kg.[2]

Fat-free mass retention: aerobic exercise retained an average of 0.88 kg less than resistance training in that comparison; 95% confidence interval −1.73 to −0.03 kg.[2]

Resistance training versus no training: the review including people with overweight or obesity reported an average 1.0 kg reduction in fat mass and a 0.8 kg increase in lean mass.[6]

Visceral fat across exercise types: a network analysis of 84 trials and 4,836 participants reported benefits from aerobic, resistance and combined training.[1]

Exercise overall and visceral fat: a pooled analysis in adults with overweight or obesity found an effect size of −0.28; 95% confidence interval −0.37 to −0.19.[20]