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Are You Sabotaging Your Muscle-Building Potential with Low Calories?

Beth Bradford

Jul 21, 2023

Research shows that even if you have enough protein, you still need enough calories to sustain your workouts.

In the days of intermittent fasting and keto diets, we’re often told to exercise in a fasted state. Of course, this isn’t new. Years ago, I remember reading countless articles about how you will burn more fat if you didn’t eat anything before you exercised. The logic was that the body would resort to fat stores rather than what you recently ate to fuel your workout. However, your body would have to be depleted of glycogen stores for it to do that.

Similarly, people who are trying to get stronger in their sport while also trying to shrink down to their “racing weight” will sacrifice too many calories despite heavy training. Sure, you might lose weight, but your body will break down in the process. You also might not be able to stay healthy in the long term.

A study published in The Journal of Physiology has shed new light on the effects of low energy availability (LEA) on muscle protein synthesis in female athletes. This research offers valuable insights into the potential consequences of energy restriction on skeletal muscle adaptations among female athletes.

The research team divided 30 trained females into two groups of 15. One group was subjected to LEA, consuming 25 kcal/kg of food per day, while the other group had optimal energy availability (OEA), consuming 50 kcal/kg of food mass per day. The amount of protein was consistent in both groups and based on each athlete’s lean body mass (amount of muscle). Athletes in both groups ate 2.2 grams of protein for each kilogram of lean body mass (I did the math–that’s about 97 grams of protein a day for me). 

The athletes were given prepared food during the experiment. Both groups undertook a supervised exercise training program for 10 days. 

The primary goal of the study was to quantify the rate of protein synthesis in two specific types of muscle proteins: myofibrillar and sarcoplasmic proteins. Myofibrillar proteins are responsible for the contraction and force generation in muscles, while sarcoplasmic proteins are involved in various functions like energy storage and metabolism. The researchers traced protein synthesis using deuterium oxide, a form of water that contains a larger-than-normal amount of the hydrogen isotope deuterium. 

The women’s exercise program consisted of three 4-day training blocks with no rest days. Day 1 was moderate-intensity indoor cycling for 45 to 60 minutes. Day 3 consisted of a high-intensity training session on the bike (6-10 hard intervals for two minutes followed by one minute rest) plus upper body weight training (4 exercises). Days 2 and 4 were lower-body strength training (4 exercises). 

A low-calorie diet leads to poor muscle synthesis

Despite high dietary protein intake and resistance exercise, LEA led to significant reductions in both myofibrillar and sarcoplasmic muscle protein synthesis compared to OEA. This suggests that when energy availability is low, you hinder your body's ability to build and repair muscle protein, even when you consume more protein intake is high and you lift weights.

Accompanying these changes in muscle protein synthesis, several other physiological alterations were observed in the LEA group. The LEA group saw a 3-pound weight reduction and lost both fat and muscle. The OEA group’s weight was the same even though they gained muscle. Resting metabolic rate and thyroid hormones in the LEA group decreased even though they remained the same in the OEA group. These findings suggest that beyond the effects on muscle protein synthesis, LEA may have broader implications on overall body composition, metabolic health, and hormonal balance.

The implications of this study are particularly significant for athletes, trainers, and health professionals working with female athletes. The findings highlight the potential risks associated with energy restriction, particularly about muscle development and overall health. Importantly, the study indicates that even high dietary protein intake and resistance exercise may not be sufficient to counteract the adverse effects of LEA on muscle protein synthesis.

However, it's important to note that the study has certain limitations. For example, the sample size was relatively small, and the study’s duration was short. Therefore, further research is required to validate these findings and to explore the long-term implications of LEA on muscle protein synthesis and overall health in female athletes.

In conclusion, this research contributes significantly to our understanding of the impact of energy availability on muscle protein synthesis. It underscores the importance of adequate energy intake for optimal muscle development, particularly among trained females. As we continue to explore this complex interplay, one thing is becoming increasingly clear - nutrition and energy availability play a crucial role in athletic performance, health, and well-being. 

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