Not eating enough calories impacts overall health, workout performance, and recovery.
Athletes who undereat, particularly those focused onΒ building strength and muscle, face significant risks.Β
OnΒ Sept.Β 8, 2024, theΒ ultra-marathonerΒ and seven-timeΒ CrossFit GamesΒ athlete discussed the perils of undereating and its impact on muscle and strength gains.
[Related: 9 Types of Diets β How They Work and Pros & Cons]
What Happens When One Undereats?
OβConnell emphasizes that eating less deprives the body of essential nutrients necessary for optimal functioning, including building and repairing muscle tissues. Undereating can result in energy deficiency, where the body lacks sufficient calories to support muscle growth.
Rather than building muscle, the body may begin to lose muscle mass, also known asΒ muscle atrophy. This occurs because, without adequate diet fuel, the body breaks down muscle tissue to meet its energy needs.
The Role of Proteins in Muscle Growth
Protein is crucial for muscle growth and repair, particularly during workouts. The body struggles to repair damaged muscles without sufficient protein intake, ultimately hindering muscle growth.Β (1)
Small tears occur in theΒ muscle fibers. Protein providesΒ amino acidsΒ to repair these tears, building stronger muscles.
The Role of Carbohydrates & Fats in Muscle Growth
Many often neglect carbohydrates and fats due to the predominant focus on protein. OβConnell explains that carbohydrates are a primary energy source, particularly duringΒ high-intensity workouts.
If you donβt consume enough carbs,Β glycogenΒ stores deplete, leading to fatigue and reduced workout performanceβ¦you wonβt be able to lift as heavy or train as intensely.
Healthy fatsΒ andΒ testosteroneΒ are crucial for hormone production and muscle growth.Β (2) Fats offer a slow-burning energy source essential for maintaining energy levels throughout daily activities and workouts. Research indicates that athletes who consume a balanced intake of carbohydrates and fats tend to perform better.Β (3)Β
OβConnellβsΒ ThoughtsΒ on Building Muscle & Losing Fat
Focus onΒ fat lossΒ or muscle gain rather than both simultaneously. To effectively build muscle, itβs likely better to maintain a slightΒ caloric surplus, which provides the energy necessary for muscle growth.


Conversely, if the goal is fat loss, gaining muscle mass can become challenging while in aΒ caloric deficit.
Losing fat while gaining muscle is possible, but itβs most effective inΒ beginners. Cycle betweenΒ bulking β caloric surplus for muscle gain β andΒ cutting β your caloric deficit.
Consequences of Relative Energy Deficiency (RED)
Relative energy deficiency (RED) occurs due to chronic under-eating and can lead to a wide range of associated issues, including:
βTo prevent this,Β listen to the body and eat enough to meet the bodyβs needs,β OβConnell recommends.Β
Signs & Symptoms of RED
- Constant fatigue
- Lack of proper sleep
- No mass and strength gains
- Frequent illness
- LowΒ blood sugar, causing mood swings
- Anemia
- Difficulty concentrating
- Muscle soreness
Adjusting Diet for Optimal Muscle Growth
Before adjusting a diet for muscle growth, understand total daily energy expenditure (TDEE) β the energy consumed in a day. Once aware, OβConnell recommends the following steps:
- Consume enough calories for daily activities and workouts
- Focus on nutrient-dense foods that provide the essentialΒ macronutrients
- Always be in a slight calorie surplus
- Pay attention to the meal timing
Building muscle relies onΒ workouts and proper nutrition.
Under-eating can sabotage progress, no matter how hard you train. Muscles need nutrients to repair and grow. Prioritize diet as much as workouts to see the best results.
References
- Cava, E., Yeat, N. C., & Mittendorfer, B. (2017). Preserving Healthy Muscle during Weight Loss. Advances in nutrition (Bethesda, Md.), 8(3), 511β519.Β https://doi.org/10.3945/an.116.014506
- Griggs, R. C., Kingston, W., Jozefowicz, R. F., Herr, B. E., Forbes, G., & Halliday, D. (1989). Effect of testosterone on muscle mass and muscle protein synthesis. Journal of applied physiology (Bethesda, Md. : 1985), 66(1), 498β503.Β https://doi.org/10.1152/jappl.1989.66.1.498Β
- Kanter M. (2018). High-Quality Carbohydrates and Physical Performance: Expert Panel Report. Nutrition today, 53(1), 35β39.Β https://doi.org/10.1097/NT.0000000000000238
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