The Effects of Intermittent Fasting Combined with Resistance Training on Lean Body Mass: A Systematic Review of Human Studies

Abstract

Diets utilising intermittent fasting (IF) as a strategic method to manipulate body composition have recently grown in popularity, however, dietary practices involving fasting have also been followed for centuries for religious reasons (i.e., Ramadan). Regardless of the reasons for engaging in IF, the impacts on lean body mass (LBM) may be detrimental. Previous research has demonstrated that resistance training promotes LBM accrual, however, whether this still occurs during IF is unclear. Therefore, the objective of this review is to systematically analyse human studies investigating the effects of variations of IF combined with resistance training on changes in LBM in previously sedentary or trained (non-elite) individuals. Changes in body weight and fat mass, and protocol adherence were assessed as a secondary objective. This review followed the preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines. MEDLINE, CINAHL, PubMed and SportDiscus databases were searched for articles investigating IF, combined with resistance training that reported measures of body composition. Eight studies met the eligibility criteria. LBM was generally maintained, while one study reported a significant increase in LBM. Body fat mass or percentage was significantly reduced in five of eight studies. Results suggest that IF paired with resistance training generally maintains LBM, and can also promote fat loss. Future research should examine longer-term effects of various forms of IF combined with resistance training compared to traditional forms of energy restriction. Prospero registration CRD42018103867.

A Muscle-Centric Perspective on Intermittent Fasting: A Suboptimal Dietary Strategy for Supporting Muscle Protein Remodeling and Muscle Mass?

“…Many of the studies mentioned above prescribe variations of IF as the independent variable but do not explicitly control dietary intake ( 19 , 69 , 70 , 72 – 78 , 81 , 89 , 90 ) and/or physical activity ( 19 , 69 – 72 , 75 – 78 , 80 , 89 , 90 ), the latter of which is important to consider given that spontaneous physical activity may be modified by restricted eating ( 91 ) and can also influence the sensitivity of skeletal muscle to dietary AA ( 92 ). When IF is coupled with the potent anabolic stimulus of resistance exercise, a systematic review ( 93 ) observed no significant differences in FFM outcomes when compared to those resistance training with a normal diet. However, given the normal diet group also did not experience gains in FFM, as would be expected, the length (i.e., 4–8 weeks) of the included studies may also not have been adequate to reliably measure changes in FFM.…”

Fasting and Exercise in Oncology: Potential Synergism of Combined Interventions

“…The study demonstrated a significant increase in lean mass (1.0-1.4 kg) over the 8-week period for all groups compared to baseline with no between-group differences. All groups significantly increased their total energy intake during the intervention, which may have contributed to the significant increase in lean mass observed in contrast to other combined fasting and exercise studies that had an energy balance or deficit [40,68,69]. Moreover, this study was conducted in young, trained female participants and its applicability to the male, un-trained, and cancer populations is limited.…”

“…However, when food is not supplied, the body relies on processes of biosynthesis as well as stored glycogen, fats, and proteins as metabolic fuel substrates [38]. Therefore, the metabolic substrates, and their catabolic or anabolic pathways, differ in a fed state from a fasted state and is likely one of the key mechanisms responsible for many of the changes observed when undertaking fasting compared to a fed intervention [39,40]. In a fed state, the body predominantly utilizes glucose from the recently consumed meal as the primary source of fuel via glycolysis, oxidative phosphorylation, and carbohydrate oxidation [38,41,42].…”

“…As mentioned in Table 1, the practice of fasting exists in a variety of religions and cultures. While a few studies have utilized combined fasting and exercise interventions during Ramadan, the impacts of the combined intervention are not clear [40]. To our knowledge, there is a lack of investigations focusing on other types of religious fasting in combination with exercise in our literature search.…”

“…The impact of fasting and exercise interventions among cancer patients across the lifespan with particular focus on adolescent and young adults, and older cancer survivors warrants investigations [40,79]. The combined impact of exercise and fasting may be particularly impactful for these more vulnerable, understudied populations at high risk for poor cancer outcomes, premature aging, and exacerbated comorbidities [40].…”