Key Points of Low Energy Availability and Protein Synthesis
- The study investigated the effects of low energy availability but high-protein diet combined with resistance exercise on muscle protein synthesis and various physiological markers in trained females.
- Participants in the low-calorie group experienced impairments in muscle protein synthesis, reductions in lean mass, nitrogen balance, thyroid hormone concentrations, and increased cortisol/insulin ratio. This suggests that not consuming enough calories to cover energy needs can have a negative impact on muscle health and growth.
- These findings suggest that low calories negatively affect skeletal muscle adaptations despite consuming high protein combined with resistance exercise and overall physiological function during exercise training in females.
Fitness competitors strive to maintain low body fat levels year-round and frequently follow reduced-calorie diets. Bodybuilders, especially natural male bodybuilders, often experience periods of low energy availability (LEA) during contest preparation. This is usually a result of aggressive energy restriction aimed at reducing body fat to extremely low levels to enhance muscle definition.
Prolonged LEA can lead to many negative health consequences such as, including weight loss, muscle loss, hormonal imbalances, loss of immunity, psychological problems, and cardiovascular issues. (Fagerberg, 2018) Increasing energy intake in combination with resistance training has been shown to promote muscle mass gains in male bodybuilders. (Ribeiro et al., 2019) Maintaining adequate energy availability is crucial for bodybuilders to get enough energy to support optimal performance and health.
A recent study sheds light on the potential negative impact of such dietary practices on muscle growth. Energy availability (EA) also plays a crucial role in muscle protein synthesis and overall muscle development. This article informs fitness competitors about the study’s findings and emphasizes the importance of considering energy availability when following reduced-calorie diets.
Low Energy Availability, Energy Expenditure, TRIAD, and its Impact on RED-S:
Energy availability (EA) is defined as the difference between energy intake (i.e., calories in) and exercise energy expenditure (i.e., calories burned) relative to lean muscle. (Loucks et al., 2011) Low-calorie intake is an important factor in athletic populations, particularly female athletes, as the reported prevalence of low energy availability (LEA) is high among them. (Loucks et al., 2011; Melin et al., 2015) This can lead to the Female Triad Syndrome, which is Energy deficiency, menstrual disturbances, and bone loss.
LEA can result from intentional or unintentional energy intake restrictions, increased energy expenditure due to training volume, or a combination of both. (Burke et al., 2018) Studies have shown that a frequently used threshold for LEA in females is ≤30 kcal · kg FFM · day (Loucks & Thuma, 2003) (Ihle & Loucks, 2004)).
The reported prevalence of LEA is high among athletic populations, particularly in female athletes, with reports of 31-60% in endurance sports (Melin et al., 2015), 53-58% in intermittent sports such as soccer, and 23-31% in power and strength-based sports. (Hoch et al., 2009)
Low Energy Availability and the Endocrine System
LEA can disrupt the endocrine system, affecting hormones such as leptin, thyroid hormones, growth hormone, insulin-like growth factor-1, cortisol, and the hypothalamic-pituitary-gonadal axis hormones. These hormonal disruptions can lead to reduced energy expenditure, changes in body composition (i.e., loss of muscle mass and body fat), and even psychological issues that persist even after recovery periods. (Areta et al., 2021)
In addition to hormonal disruptions, LEA can also have detrimental effects on bone health. Studies have shown an association between LEA and reduced bone mineral density (BMD) in athletes. (Hutson et al., 2021) This is particularly concerning as it increases the risk of stress fractures and other bone injuries, which can have long-term health implications and hinder athletic performance.
LEA can result in muscle loss, hormonal imbalances, decreased immune function, and negative psychological outcomes. (Chica-Latorre et al., 2022) Female bodybuilders are particularly at risk for Relative Energy Deficiency in Sport (RED-S), which is often preceded by low energy availability (Helms et al., 2019). Chronic low energy availability can lead to downregulation of physiological processes, including decreased resting metabolic rate and altered hormone levels. (Helms et al., 2019)
It is important for bodybuilders to carefully manage their energy intake during competition preparation to avoid the negative effects of LEA. Given these potential risks, bodybuilders and their coaches must be aware of the concept of EA and the dangers of LEA. Appropriate dietary strategies should be implemented to ensure adequate EA and prevent the negative effects of LEA.
Nutrition, Low Energy Availability (LEA), and Muscle Protein Synthesis
A low-calorie intake can lead to a decrease in muscle protein synthesis and an increase in muscle protein degradation, ultimately leading to muscle loss. In addition, low carbohydrate availability, which often accompanies LEA, can further impair muscle protein synthesis. (Pasiakos, 2023)
For example, following 10 days of a 20% energy deficit, resting mixed muscle fractional synthetic rate, a measure of muscle protein synthesis, was reduced in physically active adults. (Pasiakos et al., 2010) Another study demonstrated that resting myofibrillar muscle protein synthesis was reduced by 27% in resistance-trained males and females after five days with an EA of 30 kcal · kg FFM · day compared to 45 kcal · kg FFM · day. (Areta et al., 2014) However, a single bout of resistance exercise was found to restore myofibrillar protein synthesis levels, and adding protein supplementation increased protein synthesis rates above resting levels.
Several studies have explored the impact of low-calorie diets on muscle protein synthesis and overall muscle health. For instance, a study highlighted the importance of understanding the predictive relationship between acute muscle protein synthesis responses and subsequent muscle growth during resistance training. (Witard et al., 2022) It has been hypothesized that chronic adaptation with resistance training occurs through repeated periods of acute exercise-induced positive protein balance. (Mitchell et al., 2015)
Importance of Protein Intake and Resistance Exercise:
Protein intake plays a crucial role in muscle protein synthesis and preserving muscle mass during low-calorie diets and resistance exercise. The International Society of Sports Nutrition (ISSN) recommends a daily protein intake range of 1.4-2.0 g/kg (i.e., .6 – .8 grams per pound) of body weight, emphasizing the benefits of higher protein intakes for body composition. (Jäger et al., 2017)
Role of High Protein Intake in Preserving Muscle Mass
Studies have indicated that high protein intake is crucial for maintaining muscle mass during low-calorie diets and resistance exercise. Protein intake in the range of 1.6 g/kg/day (i.e., .7 grams per pound) has been suggested to optimize gains in muscle mass and strength during resistance exercise training. (Carbone et al., 2019)
To mitigate the negative effects of LEA on muscle protein synthesis, it is important to ensure adequate energy and nutrient intake, particularly protein and carbohydrates (Impey et al., 2016). Consuming leucine-rich protein before, during, and after exercise can help support muscle protein synthesis. (Impey et al., 2016) Additionally, resistance training effectively preserves muscle mass and stimulates muscle protein synthesis, even in the presence of LEA. (Murphy & Koehler, 2021)
New Study on Low Energy Availability but High Protein Diet on Muscle Protein Synthesis
It has been widely suggested that a high-protein diet with resistance exercise can prevent muscle loss while in a severe calorie deficit. In a randomized controlled trial, 30 trained females were divided into two groups:
a.) 10 days of LEA (25 kcal · kg FFM · day) or
b.) 10 days of optimal energy availability (OEA) (50 kcal · kg FFM · day).
Both groups followed a supervised exercise training program, including resistance and cardiovascular exercises. The exercise training program consisted of three 4-day training blocks, composed of heavy lower and upper body resistance exercise and moderate and high-intensity cardiovascular exercise on a bicycle ergometer.
On day six, the participants repeated the baseline tests after following an OEA diet for five days. Researchers matched the diets for protein intake, either at 2.2 g · kg lean mass · day or 1 gram of protein per pound of body weight, to limit negative effects.
They maintained a high carbohydrate intake relative to fat, especially on days when participants did cardiovascular exercise. Researchers measured muscle protein synthesis, body composition, resting metabolic rate, and blood biomarkers in the trained females before and after each exercise training intervention.
The females consumed about 2,400 calories on the higher-calorie day, whereas, on the low-calorie day, they consumed 1,349 calories. Despite the females consuming a high protein diet and performing resistance exercise, the study found that 10 days of LEA resulted in marked reductions in muscle protein synthesis compared to an adequate calorie diet. (Oxfeldt et al.) Reductions in lean mass, nitrogen balance, and hormonal markers such as androgen index and thyroid hormone concentrations accompanied this decline in muscle protein synthesis.
Lean mass decreased in the low energy availability (LEA) group by 0.4 kg from pre to post-intervention. The cortisol/insulin ratio also increased, suggesting an elevated muscle tissue breakdown. The author suggested that low calories produce less energy for protein synthesis, an energetically expensive process.
Implications for Fitness Competitors:
These findings have important implications for fitness competitors who follow reduced-calorie diets. Considering energy availability and its impact on muscle protein synthesis is crucial when striving for a lean physique. Prolonged LEA can impair muscle growth and development. This can be achieved by balancing energy intake with energy expenditure.
Additionally, athletes should focus on consuming adequate amounts of protein to support muscle protein synthesis and recovery. Carbohydrate intake should be prioritized, especially on days with cardiovascular exercise, to provide fuel for workouts. Resistance exercise should also be incorporated to stimulate muscle growth and strength. Overall, athletes should aim to maintain a balanced and nutritious diet to support their fitness goals.
While low-calorie diets can pose challenges to muscle protein synthesis and muscle mass preservation, high protein intake, and resistance exercise can mitigate these effects. Maintaining an optimal protein intake within the recommended range, combined with resistance exercise, is crucial for supporting muscle protein synthesis and preserving lean muscle mass.
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Does consuming more calories than needed for your body’s metabolic rate lead to increased muscle protein synthesis?
Research suggests that low energy availability can actually reduce muscle protein synthesis in trained individuals, particularly in females. However, a pilot study conducted on bodybuilders found that consuming more calories than needed after resistance training resulted in increased muscle mass (Ribeiro et al., 2019).