Putting Weights Back Into Weight Loss
Key findings: 60-second read
- Resistance training (RT) preserves fat-free mass during weight loss - RT increased FFM by 0.8-0.9 kg while diet-only and aerobic groups lost 1.1-2.8 kg of lean mass.
- RT produced the greatest fat mass reduction - men lost 8.9 kg of fat (vs 5.8 kg in diet-only); women lost 6.4 kg (vs 5.5 kg in diet-only).
- Only RT achieved true body recomposition - simultaneous fat loss and muscle gain, despite a ~500 kcal/day energy deficit.
- Fat-to-weight loss ratio was highest with RT - 1.1 kg of fat per kg lost vs 0.86 (aerobic) and 0.7 (diet-only), meaning higher quality weight loss.
- Abdominal circumference reduction correlated strongly with fat loss - r = 0.84, making it a useful clinical marker for visceral fat reduction.
Weight loss is not simply about the number on the scale. Anyone working in clinical practice has seen the patient who loses 10 kg but still feels weak, fatigued, and metabolically compromised. That is because what you lose matters as much as how much you lose.
A 2025 study published in the Journal of Exercise Science and Fitness examined this idea. Researchers followed 304 adults (183 men, 121 women) through a structured weight loss program, comparing three approaches: resistance training (RT), aerobic exercise (AR), and no exercise (NO), all combined with a calorie-restricted diet.
The findings challenge conventional thinking about weight loss and have direct implications for how physiotherapists, exercise physiologists, and clinicians should prescribe exercise during caloric restriction.
"Resistance training enhances weight-loss quality by maximising fat mass reduction while preserving or increasing fat-free mass. Incorporating RT into weight-loss programs may improve long-term weight maintenance and mitigate FFM loss."
On this page
Background: why weight loss quality matters
The global prevalence of people who are overweight and obese is projected to exceed 4 billion people by 2035, with no country reporting a decline in obesity rates. Dietary energy restriction remains the cornerstone of weight management, but it comes with a known cost: approximately 25% of weight lost during caloric restriction typically comes from fat-free mass (FFM), including skeletal muscle.
This is not merely an aesthetic concern. Skeletal muscle mass is the primary contributor to resting energy expenditure, plays a vital role in glucose metabolism, and its loss is a strong predictor of mortality. The age-related decline in muscle mass and strength, known as sarcopenia, is exacerbated by weight loss that fails to preserve lean tissue.
Central obesity, often assessed via abdominal circumference (ABC), is a stronger predictor of adverse metabolic outcomes than BMI, as it reflects visceral adipose tissue (VAT) accumulation. The study aimed to examine whether exercise modality could alter the composition of weight loss, shifting the proportion toward fat while preserving FFM.
Study design and methods
This retrospective cohort study included 304 adults (183 men, 121 women) aged 20-74 years with BMI ranging from 18.5 to 45 kg/m². Participants followed a hypocaloric diet designed to create an individualised energy deficit of approximately 500 kcal/day, calculated relative to each participant's measured resting metabolic rate (RMR) and total daily energy expenditure.
Protein intake was prescribed at 1.5 g/kg of total body weight per day, a relatively high target designed to support muscle protein synthesis during energy restriction. Participants self-selected one of three exercise regimens:
- NO group: no structured exercise
- AR group: aerobic exercise for 150-250 minutes per week at approximately 65% of maximal heart rate
- RT group: resistance training 2-3 times per week, including 7 upper-body and 2 lower-body exercises using weightlifting machines and free weights, with progressive overload
Body composition was assessed using dual-energy X-ray absorptiometry (DXA), the gold-standard method for quantifying fat mass (FM) and fat-free mass (FFM). Abdominal circumference was measured at the level of the umbilicus. Mean follow-up duration was 5.1 months ± 0.42 months.
Key inclusion criterion: Body fat reduction target of 24% for men and 31% for women, based on thresholds associated with prognostic outcomes in coronary heart disease and normal-weight obesity.
Protein intake: Standardised at 1.5 g/kg/day across all groups to reduce nutritional variability.
Energy deficit: Moderate 500 kcal/day deficit to minimise lean mass loss, as deficits exceeding this threshold impair muscle protein synthesis (12,13).
Results: men (n = 183)
Total weight loss was similar across all three groups, with no statistically significant differences:
- NO: -8.5 kg ± 3.2 kg
- AR: -9.0 kg ± 4.2 kg
- RT: -7.7 kg ± 4.2 kg
Despite comparable total weight loss, the composition of that weight loss differed dramatically.
Fat mass reduction
RT produced the greatest reduction in fat mass: -8.9 kg ± 4.1 kg, compared to -7.8 kg ± 3.2 kg in AR and -5.8 kg ± 2.5 kg in NO. The difference between RT and NO was highly significant (p < 0.001), as was the difference between RT and AR (p < 0.001). Even AR produced significantly greater fat loss than NO (p = 0.038).
Fat-free mass changes
This is where the separation between groups becomes most clinically meaningful. RT was the only modality associated with an increase in fat-free mass: +0.8 kg ± 5.0 kg. In contrast:
- AR: -1.1 kg ± 2.0 kg (FFM loss)
- NO: -2.8 kg ± 1.4 kg (FFM loss)
Bonferroni post-hoc tests showed RT differed significantly from both AR (p = 0.039) and NO (p = 0.006). The difference between AR and NO was not statistically significant.
Notably, only 14.6% of men in the RT group exhibited substantial FFM loss, whereas all men in the NO group lost FFM as part of their weight reduction.
Abdominal circumference reduction
ABC declined in all groups, with the greatest reduction in RT (-9.0 cm ± 3.7 cm), followed by AR (-8.0 cm ± 3.2 cm) and NO (-6.1 cm ± 2.4 cm). RT produced significantly greater reductions than both AR and NO (p < 0.001 for both comparisons).
| Measure | NO (n=17) | AR (n=44) | RT (n=122) | RT vs NO | RT vs AR |
|---|---|---|---|---|---|
| Weight change (kg) | -8.5 ± 3.2 | -9.0 ± 4.2 | -7.7 ± 4.2 | ns | ns |
| FFM change (kg) | -2.8 ± 1.4 | -1.1 ± 2.0 | +0.8 ± 5.0 | p = 0.006 | p = 0.039 |
| FM change (kg) | -5.8 ± 2.5 | -7.8 ± 3.2 | -8.9 ± 4.1 | p < 0.001 | p < 0.001 |
| ABC change (cm) | -6.1 ± 2.4 | -8.0 ± 3.2 | -9.0 ± 3.7 | p < 0.001 | p < 0.001 |
Results: women (n = 121)
The pattern in women was consistent with that observed in men, though with some differences in magnitude.
Total weight loss was similar across groups:
- NO: -7.13 kg ± 3.27 kg
- AR: -6.43 kg ± 3.53 kg
- RT: -5.42 kg ± 3.76 kg (no significant between-group differences)
Fat mass reduction
RT produced the greatest fat mass reduction: -6.36 kg ± 3.82 kg, compared to -5.47 kg ± 2.64 kg in NO and -4.10 kg ± 3.17 kg in AR. The difference between RT and NO was significant (p = 0.040).
Fat-free mass changes
RT was again the only modality associated with preservation and increase in FFM: +0.90 kg ± 1.24 kg. Both NO (-2.94 kg ± 1.40 kg) and AR (-0.37 kg ± 1.45 kg) experienced FFM loss. RT preserved FFM significantly more than both AR and NO (p < 0.001 for both comparisons). AR also preserved FFM significantly more than NO (p < 0.001).
Only 5.7% of women in the RT group exhibited substantial FFM loss, highlighting the protective effect of resistance training even more markedly in women.
Abdominal circumference reduction
ABC reductions were:
- RT: -7.50 cm ± 3.99 cm
- AR: -7.17 cm ± 3.46 cm
- NO: -6.00 cm ± 3.25 cm
RT produced significantly greater reductions than both NO (p < 0.001) and AR (p = 0.032).
"85% of RT participants gained lean body mass, and none lost 15% of body weight as FFM. By contrast, 50% of AR participants lost FFM."
Fat mass contribution to total weight loss
The proportion of weight loss attributed to fat mass differed across exercise modalities. This is perhaps the most clinically useful metric for understanding weight loss quality.
The FM-to-total weight loss ratio was:
- NO group: 0.7 ± 0.2 (for every 1 kg lost, 0.7 kg was fat, 0.3 kg was FFM)
- AR group: 0.86 ± 0.2 (for every 1 kg lost, 0.86 kg was fat, 0.14 kg was FFM)
- RT group: 1.1 ± 0.7 (for every 1 kg lost, 1.1 kg was fat, meaning FFM was gained overall)
The difference between RT and NO was highly significant (p = 0.0002), as was the difference between RT and AR (p = 0.0051).
This finding is remarkable: the RT group effectively lost more fat than total weight, indicating simultaneous fat loss and muscle gain (body recomposition) despite a sustained calorie deficit.
Abdominal circumference as a marker of high-quality weight loss
Central obesity is strongly associated with cardiometabolic risk, often more so than BMI. ABC serves as a practical marker of visceral adiposity, particularly in individuals with lower BMI where generalised obesity may not be apparent.
The study found a strong correlation between ABC reduction and FM loss (r = 0.84; p = 0.0001). Each kilogram of FM loss corresponded to approximately a 0.84 cm reduction in ABC. This finding suggests that ABC could serve as a practical, low-cost clinical marker for tracking the quality of weight loss, particularly in settings where DXA is not available.
"VAT is the most metabolically harmful fat depot and is closely linked to FM loss across various weight-loss interventions. Our findings reinforce that VAT reduction is primarily driven by FM loss rather than the method used to induce the deficit."
Discussion: why resistance training works
The study's findings align with known physiological mechanisms. Skeletal muscle mass is crucial for mobility, energy balance, and glucose metabolism. During energy restriction, muscle protein synthesis (MPS) is suppressed and anabolic signalling is reduced, making FFM preservation challenging.
Several factors likely contributed to the superior outcomes in the RT group:
Progressive overload
The RT protocol incorporated progressive overload, with participants increasing weights as they gained strength. This ensured a sustained muscle stimulus throughout the intervention period, counteracting the catabolic effects of energy restriction.
High protein intake
The standardised protein intake of 1.5 g/kg/day provided the necessary substrate for MPS. This is notably higher than typical population intake and aligns with current recommendations for individuals engaged in resistance training during energy restriction.
Body recomposition phenomenon
Simultaneous fat loss and muscle gain (body recomposition) is often considered difficult to achieve during energy restriction due to suppressed MPS. However, this study demonstrates that it is achievable with appropriate RT programming and protein intake, even in non-athletic populations with a mean age of 41 years (men) and 39.7 years (women).
Age-related anabolic resistance can limit hypertrophy, yet participants successfully preserved or gained FFM. This is clinically significant because sarcopenia and sarcopenic obesity are growing concerns in ageing populations.
Comparison with aerobic training
AR provided moderate FFM preservation compared to NO, but did not prevent FFM loss. This finding is consistent with the understanding that aerobic exercise, while beneficial for cardiovascular health and fat loss, does not provide the same muscle-preserving stimulus as resistance training during energy restriction.
Strengths and limitations
Strengths
- Large sample size (n=304) enhancing generalisability
- DXA for body composition (gold-standard method)
- Standardised protein intake (1.5 g/kg/day) reducing nutritional variability
- Individualised energy deficit based on measured RMR rather than estimated formulas
- High adherence rates supported by regular consultations
Limitations
- Self-selected exercise modality rather than randomisation, introducing potential selection bias and limiting causal inference
- Self-reported exercise adherence logs susceptible to recall bias and overreporting
- No control for sleep quality, stress, or other lifestyle factors known to influence body composition
- Variability in RT and AR training intensity represents a potential source of heterogeneity
- Retrospective design precludes definitive causal conclusions
Important caveat: The widely cited "quarter rule" (25% of weight loss from FFM) is, as the authors note, "at best an approximation with a limited mechanistic basis." This study demonstrates that RT substantially alters this expected composition.
Clinical implications for physiotherapists and clinicians
This study has several direct implications for physiotherapy:
1. Prescribe resistance training during weight loss interventions. The data are clear: RT preserves FFM while diet-only and aerobic-only approaches do not. For patients undergoing medically supervised weight loss, RT should be considered a core component rather than an optional addition.
2. Quality of weight loss matters more than quantity. Two patients may lose the same number of kilograms, but the patient who preserves or gains muscle will have better metabolic outcomes, higher resting energy expenditure, and improved long-term weight maintenance capacity.
3. Abdominal circumference is a useful clinical marker. The strong correlation between ABC reduction and FM loss (r = 0.84) supports using serial ABC measurements to track visceral fat reduction, particularly in settings without access to DXA.
4. Protein intake of 1.5 g/kg/day appears adequate. This target is achievable for most patients and, when combined with RT, supported FFM gains even during a 500 kcal/day deficit.
5. The benefits apply across sexes. While men lost more absolute fat mass, the pattern was consistent in women. RT was protective in both groups.
6. Progressive overload is essential. The RT protocol was not static; participants increased weights as they gained strength. Prescribing a fixed resistance program without progression is unlikely to produce the same results.
Conclusion
This study provides robust evidence that resistance training enhances weight-loss quality by maximising fat mass reduction while preserving or increasing fat-free mass. Total weight loss was comparable across groups, but the composition of that loss differed substantially. Only RT achieved true body recomposition, with simultaneous fat loss and muscle gain despite a sustained calorie deficit.
The findings reinforce that high-quality weight loss - maximising fat loss while maintaining muscle mass - should be the primary target of weight-loss programs to prevent sarcopenia, sarcopenic obesity, and normal-weight obesity, and to promote skeletal health, improve quality of life, and enhance glycaemic control and insulin sensitivity.
Given the well-established link between muscle loss, metabolic dysfunction, and mortality, integrating RT into weight-loss interventions is essential. Future research should focus on refining RT protocols to further enhance muscle retention and metabolic outcomes across diverse populations, including older adults and those with obesity-related comorbidities.
One key insight from this research
"Resistance training was the only exercise modality associated with an increase in fat-free mass during caloric restriction (+0.8-0.9 kg), while diet-only groups lost 2.8 kg (men) and 2.9 kg (women) of lean mass. The fat-to-weight loss ratio was highest with RT (1.1), meaning participants lost more fat than total weight through simultaneous muscle gain."
Frequently asked questions
Does this mean I should not do aerobic exercise during weight loss?
No. Aerobic exercise provided greater fat loss than diet alone and has well-established cardiovascular benefits. The study suggests that if the goal is to preserve muscle mass during weight loss, RT should be prioritised or added to aerobic training. The optimal approach may be combined training, though this was not directly tested in the study.
How much resistance training is needed?
The RT group performed resistance training 2-3 times per week, with 7 upper-body and 2 lower-body exercises using weightlifting machines and free weights. Progressive overload was emphasised, meaning participants increased weights as they gained strength. This volume appears sufficient to preserve and even increase FFM during a 500 kcal/day deficit.
Is the protein intake of 1.5 g/kg/day necessary?
The study standardised protein intake at this level across all groups. While it is difficult to isolate the independent effect of protein from RT, this intake likely supported the observed FFM gains. Current evidence suggests that individuals engaged in resistance training during energy restriction may benefit from protein intakes of 1.6-2.2 g/kg/day, so 1.5 g/kg/day represents a reasonable minimum target.
Can older adults achieve these results?
The study included participants up to age 74 years, with a mean age of 41 years in men and 39.7 years in women. Age-related anabolic resistance can limit hypertrophy, but participants successfully preserved or gained FFM. However, the study did not stratify results by age, so caution is warranted when extrapolating to older populations. That said, the principle that RT preserves FFM during weight loss likely holds across age groups, though the magnitude of effect may differ.
How does this apply to patients with obesity-related joint pain?
This is particularly relevant for physiotherapy practice. Patients with osteoarthritis or other joint conditions may find high-impact aerobic exercise challenging. RT can be performed in low-impact or seated positions while still providing the muscle-preserving stimulus needed during weight loss. The reduction in abdominal circumference (and likely visceral fat) also has direct metabolic benefits for this population.
As a physiotherapist, I see the effects of this delicate balance. Patients may lose significant weight but also strength, energy, and functional capacity. They may struggle to maintain their weight loss because their resting metabolic rate has dropped alongside their muscle mass.
This study reinforces what many in the field have suspected: resistance training is not just for bodybuilders or athletes. It is a fundamental tool for anyone undertaking weight loss, particularly those with metabolic health concerns, sarcopenic obesity, or age-related muscle loss.
If you are considering a weight loss program, or have lost weight in the past only to regain it, ask yourself: did your program include resistance training? If not, that may help explain why the results were not sustainable.
It's always best to work with a nutritionist or dietician to help support any individual weight loss program. Similarly, it may also help to work with a physiotherapist to develop the appropriate resistance training program fro you. If you would like to discuss your situation, I am here to help.
- Grant
Living With Persistent Pain?
If you're in pain, or it has lasted longer than expected, feels disproportionate to injury, or hasn't responded to standard treatment, you may benefit from a more holistic approach. Learn more about our physiotherapy services in Port Macquarie.
Want personalised guidance?
If you would like help making sense of your aches, pains, or ongoing symptoms, you can book with Grant either in Port Macquarie or via telehealth.
Disclaimer: This information is for educational purposes and does not replace individualised medical or exercise advice. Always consult a qualified health professional before starting a new exercise or dietary program. This blog post summarises a published research study (PMC12851882); the original source should be consulted for full methodological details. Individual responses to exercise and dietary interventions vary.
