Resistance training is a physical activity recommended for people of all ages and fitness levels and has many proven benefits. It builds muscle strength and mass, promotes bone health, increases mobility and improves overall quality of life. However, in order to progress and achieve the desired benefits, nutritional energy intake plays a key role. Indeed, an energy deficit (i.e. intake less than energy expenditure) is usually a limiting factor to produce anabolic hormones such as IGF-1 (Insulin-like Growth Factor-1) or growth hormone, which regulate protein metabolism. Protein synthesis is usually strongly affected by this deficit and this is accompanied by a loss of lean body mass. But what impact will a caloric deficit created through diet have on responses to strength training?
Numerous studies have attempted to analyse this issue, but taken individually, their statistical strength is generally low. Researchers from the University of Sport and Health Sciences in Munich, Germany conducted a meta-analysis of 59 studies involving 1495 people. More specifically, the researchers conducted two separate analyses. The first analysis included 7 randomised controlled studies (282 participants aged 60 ± 11 years) in which the control group trained without a caloric deficit, while the experimental group trained with a deficit. A second analysis included 25 studies that did not have a control group (training + caloric deficit or not) but were matched with 27 training studies with a control group (1213 participants aged 51 ± 16 years).
The training protocol had to last at least 3 weeks, with a minimum of 2 sessions per week, with body composition measurements performed via DEXA (Dual X-ray Absorption). Strength gains were measured via 1RM, 3RM or a voluntary maximal isometric contraction. Finally, the caloric deficit was estimated via the change in fat mass, the energy of which was estimated at approximately 9400 kcal per kilogram.
The main results of this study show that caloric deficit has a significant negative effect on lean body mass but none on muscle strength. Furthermore, this meta-analysis highlighted that a daily deficit of 500 kcal or less would not affect lean body mass.
Current research shows that an energy deficit directly affects IGF-1 production in a proportional way. A recent study showed that after only 3 days of energy deficit, IGF-1 stimulation following strength training was reduced. Furthermore, since protein synthesis is also affected by the energy balance, all these mechanisms explain the decrease in lean body mass despite training.
Strength gains were not affected by the presence or absence of a caloric deficit. Participants gained muscle strength despite reduced gains in lean body mass or even a loss. This suggests that these strength gains are independent of muscle hypertrophy and are instead due to neural adaptations or structural changes, typical of gains observed at the beginning of a resistance training program. It should be noted, however, that all but one of the studies recruited beginners. Indeed, strength gains were negatively impacted in the only study that was composed of experienced lifters.
This study has the merit of confirming what lifters had already understood: an energy deficit is not advantageous for muscle mass gain. And even if strength gain does not seem to be affected in this study, this is probably only valid for a beginner audience. It is often difficult for resistance-trained athletes to maintain a high level of strength during a caloric deficit phase. Another important point is that this meta-analysis indicates that up to -500 kcal per day, with resistance training, lean mass would not be affected.
In summary, people who want to gain muscle mass should avoid caloric deficit for too long a period, while those who want to lose weight should practice resistance training and maintain a caloric deficit to less than 500 kcal per day to limit the loss of lean mass.
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