Time-Restricted Eating and Resistance Training

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The combination of time-restricted eating (TRE) and resistance training (RT) has emerged as an extremely popular tool for improving body composition, fitness and health. After reading this piece, you will be completely up to date with the most recent research in the TRE and RT literature, and you will have several practical application tools to implement with your clientele.

Time-Restricted Eating and Cardiometabolic Health

Intermittent fasting (IF), which is broadly defined as an eating pattern during which individuals undergo prolonged periods of caloric restriction (> 12 hours), has recently emerged as a popular dietary strategy (Aragon & Schoenfeld, 2022). There are several applications of IF, including Ramadan, alternate-day fasting, modified alternate-day fasting, twice-weekly fasting and time-restricted eating (TRE) (Aragon & Schoenfeld, 2022). Of these IF options, TRE is arguably the easiest to adhere to because it simply requires an individual to eat their daily calories in a 4-10 hour ‘eating window’ followed by a 14-20 hour ‘fasting window’ (Gabel et al., 2021). As a result of the limited eating window TRE can induce unintentional caloric reduction (~350-500 kcal/day) (Gabel et al., 2021). Consuming fewer calories without trying to do so, explains why this dietary strategy can be extremely effective for fat loss (Santos, 2022).

Indeed, the TRE-stimulated fat loss contributes to a variety of improved cardiometabolic health markers such as reduced blood pressure, triglyceride levels, and oxidative stress (Gabel et al., 2021) in addition to improved markers of insulin sensitivity such as decreased glucose and insulin concentrations (Moro et al., 2021). Thus, TRE is an effective tool to manage caloric intake, decrease body fat, and improve cardiometabolic health.

Health and Fitness Outcomes of Resistance Training

Resistance training (RT) is commonly defined as a form of exercise where muscular force is applied to overcome a variety of external loads (e.g., barbells, dumbbells, and machines) (Currier et al., 2023). There are several well-known adaptations from RT, which include increased skeletal muscle hypertrophy, local muscular endurance, muscular strength, power, and overall physical performance (Currier et al., 2023). More recently, research has highlighted the lesser known health benefits of undertaking an RT program, such as decreased fat mass, blood glucose concentration, blood pressure, cancer risk, and fat mass, along with improved cognition and mitochondrial function (Abou-Sawan et al., 2023).

Taken together, these health benefits may explain the consistently reported inverse relationship between muscular strength and risk for all-cause mortality (Abou-Sawan, 2023). Moreover, for elderly lifters, the acquisition of greater muscle mass and strength improves quality of life and independence by increasing mobility and functional-task performance while reducing risk for falls (Abou-Sawan, 2023). It is therefore logical to conclude that RT is a powerful tool to improve fitness, health, and overall quality of life.             

Because TRE and RT each deliver a variety of benefits separately, it is reasonable to think that their combination would have a synergistic effect on health and fitness. Hence, the purpose of this column is to explore the combined effects of TRE + RT with a specific focus on body composition and muscular performance.

See also: Time-Restricted Eating and HIIT

How Does Time-Restricted Eating With Resistance Training Influence Body Composition?

Body recomposition, which is colloquially referred to as simultaneously building muscle and losing fat, has become a topic of interest in the world of exercise physiology (Barakat et al., 2020). Although it may be an oversimplification, when TRE and RT are combined in practice, individuals typically apply the former to help them lose fat, while the latter is most often applied to help build muscle (Ashtary-Larky et al., 2021). Because TRE consistently results in a negative energy balance (i.e., caloric deficit), it is more likely that the mechanical tension delivered by RT will help preserve muscle mass during the TRE diet (Keenan et al., 2020). This is an important concept, because we are all prone to shed muscle mass during caloric deficits because skeletal muscle is an energetically-expensive tissue to maintain. To quantify these potential changes to body composition, a recent meta-analysis concluded that when combined with RT, a variety of IF diets decreased body mass, body fat mass, and body fat percentage, while fat-free mass remained unaffected (i.e., it was preserved) (Ashtary-Larky et al., 2021). To make the findings more specific to TRE + RT, another recent systematic review concluded that lifters who combined both methods consistently decreased body mass and body fat percentage, while their fat-free mass did not change (which is a good thing!) (Kang et al., 2022). Therefore, based on available evidence, it seems like the combination of TRE + RT confers positive effects on body composition by decreasing fat mass and sustaining fat-free mass. For those aiming to increase (rather than merely sustain) fat-free mass, research suggests two effective methods to accomplish this:

1. Diet – maintain a relatively high protein intake (>1.6 g/kg/day) (Longland et al., 2016)
2. RT – perform ≥ 10 weekly sets per major muscle group per week (Schoenfeld et al., 2017)   

Will the Combination of Time-Restricted Eating and Resistance Training Blunt Strength Gains?

Elsewhere in the caloric restriction research, it has been demonstrated and discussed that greater caloric deficits impair strength acquisition from a RT program (Carlson et al., 2022; Garthe et al., 2011; Roth et al., 2022). It is therefore relevant to question if TRE + RT would result in blunted strength gains when compared to RT alone. Considering the previously mentioned systematic review by Kang et al. (2022), when all available research is analyzed together, subjects have consistently gained strength while following a TRE diet, and have not gained less than their non-TRE counterparts. In other words, TRE does not appear to negatively impact long-term strength gains. Below are highlights from specific research studies:

• After 8 weeks of training, Tinsley et al. (2017) reported that subjects who combined TRE + RT significantly improved their bench press 1-RM and leg press 1-RM.
• In a study that included all female subjects, Tinsley et al. (2019) demonstrated that 8 weeks of TRE + RT increased isometric and dynamic squat strength in addition to rate of force development (i.e., lower-body power).
• Despite being in a 25% caloric deficit, Stratton et al. (2020) concluded that 4 weeks of TRE + RT improved bench press 1-RM, leg press 1-RM, vertical jump height, and lower-body peak power.
• In the longest TRE + RT study to date, Moro et al. (2021) reported that despite significant decreases to body mass and muscle size, 12 months of TRE + RT increased bench press 1-RM and leg press 1-RM.

Perhaps the most intriguing aspect of the studies cited above is that despite the prospective caloric deficit, employing the combination of TRE + RT consistently led to similar outcomes as the ‘normal diet’ control groups. This suggests that your clients can make plentiful strength and power gains while adhering to a TRE diet.

See also: The Art and Science of Intermittent Fasting

Conclusion

In the absence of exercise interventions, TRE has emerged as an effective strategy to help clients achieve consistent caloric deficits. Over time, these TRE-driven caloric deficits culminate in fat loss, which contributes to several positive health outcomes, such as decreased blood pressure and increased insulin sensitivity. In a similar vein, RT has been combined with TRE to help sustain muscle mass and performance while fat loss occurs. According to available research, the combination of TRE + RT allows lifters to decrease body mass and fat mass without compromising their lean mass. Moreover, TRE + RT leads to positive strength and power gains that do not differ from the same RT program combined with a normal diet. Therefore, fitness professionals are encouraged to combine TRE + RT as an effective way to help their clients achieve their many health and fitness goals.