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Does Intermittent Fasting Make You Lose Muscle Mass?

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Does Intermittent Fasting Make You Lose Muscle Mass

Intermittent fasting is well-known for weight loss and overall health, and it is praised for its simplicity and potential benefits.

However, the question remains: does intermittent fasting make you lose muscle mass? This is particularly critical for those focused on maintaining lean mass or building muscle while reducing fat.

In this article, we will learn whether intermittent fasting causes muscle loss, how it affects muscle loss, and what you can do to preserve your hard-earned muscle while benefiting from this eating strategy. Let’s look into the facts and myths surrounding intermittent fasting and muscle maintenance.

What Is Intermittent Fasting?

Intermittent fasting, also known as IF, is an eating pattern that cycles between periods of eating and fasting. It doesn’t dictate what foods to eat but when to eat them. This approach focuses on timing rather than specific food restrictions, and it has gained popularity due to its potential health benefits, such as weight loss, improved metabolism, and increased longevity1.

There are several common methods of intermittent fasting, each differing in the timing of fasting and eating windows, which can influence its effects:

  • 16/8 Method (Leangains protocol): You fast for 16 hours and restrict your eating to an 8-hour window, typically by skipping breakfast and eating between noon and 8 pm.
  • 5:2 Diet: You eat normally five days a week, then restrict calories to 500-600 on the other two days.
  • Eat-Stop-Eat: This involves fasting for 24 hours once or twice a week. For example, you might fast from dinner one day to dinner the next day.
  • Alternate-Day Fasting: You alternate between days of normal eating and days where you fast or eat very few calories, such as 500 calories.
  • Warrior Diet: You eat small amounts of raw fruits and vegetables during the day and have one large meal at night, following a 20-hour fasting period and a 4-hour eating window.

Benefits of Intermittent Fasting

  • Weight Loss and Fat Loss: Intermittent fasting can lead to a caloric deficit and increase the body’s fat-burning ability2.
  • Improved Metabolic Health: IF can lower blood sugar, insulin resistance, and cholesterol levels3.
  • Cell Repair and Longevity: Fasting triggers autophagy. This process helps the body clean out damaged cells, contributing to longevity and reducing the risk of diseases like cancer and Alzheimer’s4.

What Is Muscle Mass?

Muscle mass refers to the total weight of muscles in the body, including skeletal muscles, smooth muscles (like those in the digestive system), and cardiac muscle (the heart). When people talk about increasing muscle mass, they generally refer to increasing the size and weight of skeletal muscles—the muscles attached to bones responsible for movement and physical strength5.

Key Components of Muscle Mass

  • Skeletal Muscle: Most people aim to build this type of muscle through exercise. It’s under voluntary control, meaning you can actively contract and relax these muscles to move. Examples include muscles like the biceps, quadriceps, and deltoids6.
  • Smooth Muscle: Found in the walls of internal organs such as the stomach, intestines, and blood vessels, smooth muscle functions involuntarily to help digestion and circulation. Although it is not what people typically aim to build during strength training, it still contributes to overall muscle mass7.
  • Cardiac Muscle: The heart’s muscle, the myocardium, pumps blood throughout the body. Like smooth muscle, cardiac muscle is not under voluntary control but contributes to the body’s overall muscle mass8.

How is Muscle Mass Measured?

Muscle mass can be estimated from body mass using several methods, such as:

  • Body Composition Scales: These scales use bioelectrical impedance to estimate the proportion of muscle mass in your body9.
  • DEXA (Dual-Energy X-ray Absorptiometry) Scans: This is a more precise method that measures body composition, including bone density, fat mass, and lean muscle mass10.
  • Skinfold Calipers: These are used to measure body fat percentage, and from that, muscle mass can be estimated, although it’s less accurate than other methods11.

Factors That Influence Muscle Mass

Several factors play a role in determining your muscle mass:

  • Genetics: Genetics can influence your potential for building muscle and how easily you gain or lose muscle mass12.
  • Age: Muscle mass typically peaks in the 20s and declines after age 30 due to sarcopenia. However, exercise and proper nutrition can slow this process13.
  • Gender: Men generally have more muscle mass than women due to higher levels of testosterone, a hormone that supports muscle growth14.
  • Diet: A diet rich in protein and adequate calories is crucial for muscle growth and maintenance.
  • Exercise: Strength training exercises like weightlifting or resistance training are the most effective ways to build muscle mass.

Why is Muscle Mass Important?

  1. Physical Strength: More muscle mass generally means more strength and better physical performance15.
  2. Metabolism: Muscle is more metabolically active than fat, meaning it burns more calories at rest, aiding weight management16.
  3. Bone Health: Muscle mass supports bone density and strength, reducing the risk of osteoporosis and fractures17.
  4. Overall Health: Higher levels of muscle mass are associated with better insulin sensitivity, cardiovascular health, and reduced risk of chronic conditions3.

Does Intermittent Fasting Make You Lose Muscle Mass?

Intermittent fasting can lead to muscle loss if a normal diet is not approached correctly, but it doesn’t necessarily result in muscle loss if certain factors are managed well. Here’s how IF interacts with muscle mass and how to avoid muscle breakdown during fasting periods:

How Intermittent Fasting Could Lead to Muscle Loss

  1. Caloric Deficit: If you eat fewer calories than your body needs to maintain weight over an extended period, your body may turn to muscle tissue as an energy source, especially if your protein intake is insufficient18.
  2. Prolonged Fasting Periods: During long fasting windows, the body could break down muscle tissue to use the amino acids for fuel or other bodily functions. This can occur if your overall protein intake is low or you need to engage in muscle-preserving activities like strength training19.
  3. Inadequate Protein Intake: During fasting, if you’re not consuming enough protein during your eating windows, it could lead to muscle protein breakdown exceeding synthesis, causing muscle loss over time20.

How to Preserve Muscle Mass While Doing Intermittent Fasting

  1. Adequate Protein Consumption
    • During your eating windows, prioritize high-protein meals to ensure your body has enough amino acids for muscle maintenance and repair. Aim for about 1.6–2.2 grams of protein per kilogram of body weight (0.7–1.0 grams per pound) daily, which helps offset muscle loss21.
  2. Strength Training
    • Engage in resistance training at least 2-3 times per week. Lifting weights or doing bodyweight exercises stimulates muscle protein synthesis, helping to preserve or even build muscle during intermittent fasting.
    • Exercising in a fasted state (like doing weight training before your first meal) is effective for some, but it’s essential to refuel adequately after exercise to promote recovery.
  3. Time Your Protein Intake
    • Distribute protein evenly across your eating windows. For example, if you’re doing the 16/8 method, eat protein every meal within 8 hours to stimulate muscle protein synthesis22.
    • Some people may also benefit from supplementing with protein or branched-chain amino acids (BCAAs) before or after workouts to enhance muscle recovery and prevent breakdown, mainly if working out fasted22.
  4. Avoid Extreme Caloric Deficits
    • A moderate calorie deficit (10-20% below your maintenance level) can promote fat loss while minimizing muscle loss. Extreme caloric restriction often leads to muscle breakdown as the body struggles to meet its energy needs23.
    • Ensure you consume enough calories during your eating windows, especially when combining fasting with exercise23.
  5. Eat Post-Workout
    • Consuming a protein-rich meal after exercise helps to maximize recovery and muscle protein synthesis, which is particularly important if you’re fasting during part of the day.
  6. Shorter Fasting Windows
    • Some people find that shorter fasting windows (e.g., the 16/8 method) are more sustainable for preserving muscle mass than longer fasts like the 24-hour fasts in Eat-Stop-Eat, where muscle breakdown could increase.

Summary

Intermittent fasting is popular for weight loss and health benefits, but many worry about its impact on muscle mass.

Intermittent fasting involves cycling between eating and fasting periods without restricting specific foods. While it can potentially lead to muscle loss, especially if combined with low protein intake or extended fasting periods, this isn’t a guaranteed outcome.

Muscle loss can be minimized or even avoided with a proper approach—such as eating adequate protein, engaging in regular strength training, avoiding extreme calorie deficits, and using shorter fasting windows. By doing all this, you can make intermittent fasting work for you, supporting both fat reduction and muscle maintenance.

Citations

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2 Kim JY. Optimal Diet Strategies for Weight Loss and Weight Loss Maintenance. J Obes Metab Syndr. 2021 Mar 30;30(1):20-31. doi: 10.7570/jomes20065. PMID: 33107442; PMCID: PMC8017325.

3 Freeman AM, Acevedo LA, Pennings N. Insulin Resistance. [Updated 2023 Aug 17]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK507839/

4 Shabkhizan R, Haiaty S, Moslehian MS, Bazmani A, Sadeghsoltani F, Saghaei Bagheri H, Rahbarghazi R, Sakhinia E. The Beneficial and Adverse Effects of Autophagic Response to Caloric Restriction and Fasting. Adv Nutr. 2023 Sep;14(5):1211-1225. doi: 10.1016/j.advnut.2023.07.006. Epub 2023 Jul 30. PMID: 37527766; PMCID: PMC10509423.

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6 McCuller C, Jessu R, Callahan AL. Physiology, Skeletal Muscle. [Updated 2023 Jul 30]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK537139/

7 Hafen BB, Shook M, Burns B. Anatomy, Smooth Muscle. [Updated 2023 Jul 17]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK532857/

8 Ripa R, George T, Shumway KR, et al. Physiology, Cardiac Muscle. [Updated 2023 Jul 30]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK572070/

9 Duren DL, Sherwood RJ, Czerwinski SA, Lee M, Choh AC, Siervogel RM, Cameron Chumlea W. Body composition methods: comparisons and interpretation. J Diabetes Sci Technol. 2008 Nov;2(6):1139-46. doi: 10.1177/193229680800200623. PMID: 19885303; PMCID: PMC2769821.

10 Shepherd JA, Ng BK, Sommer MJ, Heymsfield SB. Body composition by DXA. Bone. 2017 Nov;104:101-105. doi: 10.1016/j.bone.2017.06.010. Epub 2017 Jun 16. PMID: 28625918; PMCID: PMC5659281.

11 Institute of Medicine (US) Committee on Military Nutrition Research; Marriott BM, Grumstrup-Scott J, editors. Body Composition and Physical Performance: Applications For the Military Services. Washington (DC): National Academies Press (US); 1990. 14, Body Composition Measurement: Accuracy, Validity, and Comparability. Available from: https://www.ncbi.nlm.nih.gov/books/NBK235949/

12 Roth SM. Genetic aspects of skeletal muscle strength and mass with relevance to sarcopenia. Bonekey Rep. 2012 Apr 4;1:58. doi: 10.1038/bonekey.2012.58. PMID: 27127623; PMCID: PMC4816288.

13 Volpi E, Nazemi R, Fujita S. Muscle tissue changes with aging. Curr Opin Clin Nutr Metab Care. 2004 Jul;7(4):405-10. doi: 10.1097/01.mco.0000134362.76653.b2. PMID: 15192443; PMCID: PMC2804956.

14 Nassar GN, Leslie SW. Physiology, Testosterone. [Updated 2023 Jan 2]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK526128/

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