Globally, more than one billion people are expected to be obese by 2030. Health professionals are deeply concerned by this statistic as obesity causes an increased risk of high blood pressure, insulin resistance, high blood lipids, heart disease, strokes, several types of cancer, lower quality of life, and a shorter lifespan. Exercise, dietary, and behavioural therapies that are provided in a non-stigmatised environment can effectively assist most individuals in losing fat mass while maintaining or increasing healthy lean mass. The distinction between aiming to lose fat mass rather than lean mass is important. Muscle and bone mass can also be reduced during weight loss phases. Maintaining lean mass while losing fat mass leads to a higher resting energy expenditure while keeping a smaller risk of hypertension and cardiovascular disease for individuals who otherwise are reaching the same body weight goal. Loss of muscle mass (sarcopenia) and bone mass (osteoporosis) impact particularly strongly on life span and quality of life in the elderly. Supported weight loss programs assisting lean mass maintenance, which will reduce frailty, are therefore particularly important for our aging population. 

One of the most effective strategies to increase or maintain lean mass while losing fat mass is resistance (strength) training. The most recent systematic reviews show that when resistance exercise is included with a calorie restriction across 12 to 48 weeks, it leads to an average of 5kg loss of fat mass. Resistance training alone, without calorie restriction, has shown a smaller reduction in fat mass. Despite being other exercise modalities to assist weight loss, aerobic exercises like walking, cycling, or swimming do NOT provide the protective effect of resistance training in maintaining or increasing lean mass. 

The subject of this blog is whether the moderators of the response to resistance training, including duration, frequency, number of sets per week (i.e., volume), and intensity, impact weight loss quality and quantity. I’ll summarise a recent review by Lopez et al. (2023) that should guide us to what levers to pull when including resistance training with a weight loss phase. 

• The authors systematically reviewed and analyzed whether the effects of resistance exercise on whole-body fat and lean mass are moderated by exercise dosage (i.e., intervention duration, weekly volume, and intensity) in overweight or obese adults. Age, body mass index (BMI), baseline values, and prescription of aerobic exercise and caloric restriction were also included and will be summarised briefly later. 
• Assessment methods across studies included skinfolds, dual-energy x-ray absorptiometry (DXA), and bioelectrical impedance (BIA) (which we can include with an ACE physical assessment). 
• Only randomised controlled trials evaluating the effects of resistance-based exercise programs combined or not with the nutritional intervention were included. 
• Exclusion criteria were as follows: 1) studies involving overweight/obese individuals with other chronic conditions such as type II diabetes or cancer; 2) studies involving overweight/obese participants enrolled in water-based resistance training as the only study intervention; 3) studies with interventions lasting less than four weeks; 4) studies comprising control groups receiving any active exercise or dietary interventions that constituted an intervention for body composition; and 5) studies written in a language other than English, Portuguese, or Spanish and 6) studies published after December 2020. 
• A total of 51 and 59 studies were included in the meta-analyses for assessing fat mass and lean mass changes in response to resistance exercise, respectively. 
• A total of 2537 participants with overweight/obesity participated in the included studies: 506 young adults (median age = 23.6 yr, BMI = 28.5 kg·m−2, body fat percentage = 32.9%) 901 middle-aged adults (median age = 44.5; BMI = 29.9 kg·m−2, and body fat percentage = 40.1%), and 1130 older adults (median age = 68.2 yr, BMI = 29.4 kg·m−2 and body fat percentage = 38.0%).  
• Intervention ranges included exercise program durations between 10-16 weeks, weekly frequency between 1-5 sessions per week, 45-99 sets of exercises per week, 12 to 60-minute sessions, and intensity set between 75 to 85% of 1RM. An example program from this data could include 5-10 exercises across at least three sessions where 3-4 sets are completed. 
• Caloric restriction, when used, ranged between 500 to 1500 calories per day. 
• There were three main findings.  

1. Improvements in fat mass were significant and occurred irrespective of resistance exercise duration, weekly volume, and peak intensity or accompanying aerobic exercise prescription in overweight or obese participants. However, caloric restriction alone was associated with reductions in whole-body lean mass. 

2. Sex and baseline levels of fat mass were significant moderators of resistance-based exercise effects on fat mass. Male participants with higher levels of fat mass experienced more significant reductions in this outcome. However, the authors state that the effect favouring males in this study is not consistent across other reviews they did not assess, so ladies, do stay optimistic about the fat loss process! 

3. Changes in lean mass after resistance exercise were significantly moderated by age, with more significant improvements observed in younger than middle-aged or older adults. 

This study strengthens evidence that resistance training during caloric restriction facilitates weight loss while increasing lean mass. Fortunately, for those who don’t like living in a gym or training excessively while hungry, more lifting did not seem better for maintaining lean mass during the weight loss phases. This makes sense when we reflect on current evidence of predictors of successful weight loss phases. Consistency across time while maintaining a calorie deficit strongly predicts a successful weight loss phase (Feig et al., 2017; Carpenter et al., 2022) despite perceptions of slow or no progress, diet fatigue, and environmental and social barriers. Lower amounts of exercise can improve adherence to long weight-loss phases. Just hit somewhere between the average of the parameters measured in this study, such as completing 3-4 sets of 5-10 exercises across at least three sessions per week. On average, your maintenance of lean mass should be successful when applying the simple but not easy principles of fat loss. More on optimising weight loss phases to come.  

Written by Tom Murphey, DPT. 

“Unfortunately for our community, scientific scaremongering is common, easy to believe, and hard to heal. Research is often messy, and strong stances or beliefs can be erroneous and dishonest. I aim to produce honest reviews of high-quality research to provide informed insight so you can make up your own mind on the science you value.” 

References. 

Carpenter, C. A., Eastman, A., & Ross, K. M. (2022). Consistency with and disengagement from self-monitoring of weight, dietary intake, and physical activity in a technology-based weight loss program: exploratory study. JMIR Formative Research, 6(2), e33603. 

Feig, E. H., & Lowe, M. R. (2017). Variability in weight change early in behavioral weight loss treatment: theoretical and clinical implications. Obesity, 25(9), 1509-1515. 

Lopez P, Radaelli R, Taaffe DR, Galvão DA, Newton RU, Nonemacher ER, Wendt VM, Bassanesi RN, Turella DJP, Rech A. Moderators of Resistance Training Effects in Overweight and Obese Adults: A Systematic Review and Meta-analysis. Med Sci Sports Exerc. 2022 Nov 1;54(11):1804-1816. doi: 10.1249/MSS.0000000000002984. Epub 2022 Aug 17. PMID: 35977113. https://journals.lww.com/acsm-msse/fulltext/2022/11000/moderators_of_resistance_training_effects_in.2.aspx