Weekly body weight losses between 0.5-1% have been suggested as optimal; however, this depends on the amount of body fat starting the diet to determine the appropriate deficit.



  • The best diet to lose fat should consist of high protein, resistance exercise, and calorie tracking.
  • Diets with greater than 40% calorie reduction is associated with losses in lean mass despite high protein.
  • A gradual reduction in calories is the best practice to not lose muscle while dieting.
  • Losing muscle while dieting is determined by how lean you are starting a diet.


The magnitude of lean muscle loss (i.e., muscle catabolism) during a diet depends on the severity and duration of calorie restriction. Changes in muscle mass loss are the balance between muscle protein synthesis (MPS) (i.e., breaking down muscle) and muscle tissue breakdown (MPB) (i.e., build muscle).

In a severe calorie deficit with rapid weight loss, a catabolic state occurs, and there is a significant increase in protein breakdown relative to the rate of protein synthesis. The goal of a successful diet is to create a calorie deficit and lose fat but retain as much muscle as possible. Most people think it takes 3,500 calories to burn one pound of fat. This is not true, but if you want to read the full story, check out this article.


One of the common questions in the fitness and health community is how to prevent muscle loss when fasting/how to prevent muscle loss during intermittent fasting. Loss of lean body mass often occurs with calorie restriction, but strength training several times a week can prevent most muscle loss, but not all.

Amino acids (AA) serve as the building blocks of protein, and the body cannot store them like it does with fats and carbohydrates. We categorize 20 amino acids into essential and non-essential amino acids. When the body doesn’t have enough calories, it uses muscle protein as the only source of essential amino acids (EAA) for the rest of the body due to the inability to store AAs.
If amino acid concentrations drop because of a long-term energy deficit, the body increases the muscle protein breakdown (MPB) rate to keep blood amino acid levels stable until someone consumes food or protein.(1)


Weight loss during the first weeks of caloric restriction is largely attributed to glycogen, protein, and fluid changes. Long-term weight loss is mainly attributed to changes in body composition (i.e., fat mass and varying degrees of loss of lean mass).(2)

Most studies examining severe caloric restriction losses have found that caloric deficits greater than >40% result in losses in lean body mass (LBM). When energy deficits are above 40%, high protein intakes do not appear to restore muscle protein synthesis to levels observed during energy balance. The art of losing body fat is to do so without losing muscle.

Studies on the Best Diet to Lose Fat

In a study of elite track athletes, those with the lowest initial body fat starting a diet had the greatest lean mass losses. They found that a daily caloric restriction of 740 calories or a 24% daily caloric restriction with a high protein diet reduced fat and preserved lean mass.(3) Severe calorie-restricted diets with greater than 1000 calorie deficits per day can lead to reduced anabolic hormones and greater losses in lean mass.

Weekly body weight losses between 0.5-1% have been suggested as optimal; however, this depends on the amount of body fat starting the diet to determine the appropriate deficit. In a recent meta-analysis on the impact of lean mass gains and energy deficits, a deficit of 500 kcal per day was the threshold for reducing lean mass gains.

For every 100-kcal deficit above the 500-kcal deficit, the increases in lean mass were further reduced. The author recommended that individuals looking to gain muscle/maintain lean mass during resistance training should not reduce calories greater than 500 calories per day.(4)


In sports, maintaining lean muscle mass during calorie restriction is essential for athletic performance and success. Weight training is essential for preserving lean mass during caloric restriction while a steady loss of body fat percentage. Aerobic exercise is less successful in preserving lean mass than strength training workouts. (5)

In a study of young college students who were told not to perform resistance exercise and were assigned to a high protein diet plus calorie restriction, they lost muscle despite performing their normal activities. They were allowed to complete their normal activities, including a wide range of sports: gymnastics, bouldering, climbing, soccer, spikeball, bicycling, jogging, table tennis, swimming, volleyball, basketball, boxing, dancing, and paddle boarding.

At the end of six weeks, the subjects in the high protein and calorie restriction plus the normal activities lost -1.49 kg or 3.3 pounds of lean mass. The author concluded, “high protein moderate energy restriction is likely not able to prevent lean mass loss in college students in the absence of resistance training.”


Exercise is such a powerful method of preserving lean mass that even low-intensity exercise can preserve muscle mass during severe caloric restriction (i.e., lose weight). Researchers examined how a severe calorie restriction would be impacted by low-intensity exercise while consuming a protein supplement.

Ok, are you ready for the exercise protocol? They started with low-intensity one-arm cycling for 45 minutes until fatigue. The other arms served as a control for the experiment.

After this, they walked for 22 miles (~ 8 hours)!! They did this for four days!!

Amazingly, the arms that performed low-intensity cycling with severe calorie restriction attenuated the loss of muscle mass by 29% in the exercise arm compared to the control group arm that was not exercised.

They then compared the control arm (i.e., no exercise) to the loss of lean muscle mass in the legs. Compared to the control arm that did not exercise, 8 hours of walking reduced the loss of lean leg mass by 57%, indicating that the longer exercise had a more protective effect. Unsurprisingly, the added protein supplement had no effect on sparing lean mass with such a severe caloric deficit.(6)

These are extreme calorie restriction studies, but it emphasizes that even a high-protein diet cannot retain muscle if the daily calorie reduction is too large. However, it shows that exercise has a protective effect on preserving muscle in a caloric restriction.


  • Caloric restriction of more than 40% causes losses in lean mass, even with high protein intake.
  • Your initial level of leanness determines the losses in lean muscle mass when you start a diet.
  • Experts suggest a range of weekly body weight losses between 0.5-1%. However, the appropriate deficit varies based on the amount of body fat you have when you begin your diet.


1.         Church DD, Gwin JA, Wolfe RR, Pasiakos SM, Ferrando AA. Mitigation of Muscle Loss in Stressed Physiology: Military Relevance. Nutrients. 2019;11(8):1703.

2.         Weinheimer EM, Sands LP, Campbell WW. A systematic review of the separate and combined effects of energy restriction and exercise on fat-free mass in middle-aged and older adults: implications for sarcopenic obesity. Nutrition Reviews. 2010;68(7):375-88.

3.         Huovinen HT, Hulmi JJ, Isolehto J, Kyröläinen H, Puurtinen R, Karila T, et al. Body composition and power performance improved after weight reduction in male athletes without hampering hormonal balance. J Strength Cond Res. 2015;29(1):29-36.

4.         Murphy C, Koehler K. Energy Deficiency Impairs Resistance Training Gains in Lean Mass but not Strength: A Meta‐Analysis and Meta‐Regression. Scandinavian Journal of Medicine & Science in Sports. 2022;32.

5.         Beavers KM, Ambrosius WT, Rejeski WJ, Burdette JH, Walkup MP, Sheedy JL, et al. Effect of Exercise Type During Intentional Weight Loss on Body Composition in Older Adults with Obesity. Obesity. 2017;25(11):1823-9.

6.         Calbet JAL, Ponce-González JG, Calle-Herrero JdL, Perez-Suarez I, Martin-Rincon M, Santana A, et al. Exercise Preserves Lean Mass and Performance during Severe Energy Deficit: The Role of Exercise Volume and Dietary Protein Content. Frontiers in Physiology. 2017;8.

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