How to Lose Fat and Build Lean Muscle Mass on a Caloric Restriction Diet
Caloric restriction is the most well-studied form of intermittent fasting. I talked about how to approach caloric restriction and how it impacts disease and longevity in my previous post. Many people practice caloric restriction to lose fat, but they find themselves losing lean muscle mass in the process. It’s a no-brainer that if you eat less, you’ll eventually lose weight. Several studies have shown that weight loss is possible and sustainable on a caloric restriction diet without negatively impacting the quality of life. 1,2

Figure 1. Some of the benefits associated with weight loss. Copyright © 2020 Fit With Heba, All rights reserved.
Weight loss is associated with better health outcomes including improvements in cognitive function, insulin sensitivity, blood pressure, stress, total cholesterol, LDL cholesterol and much more.3,4
Despite all the benefits associated with weight loss and caloric restriction, we can’t spot target fat, so we’ll inevitably lose muscle mass in the process. For a while, it became the norm that if you wanted to lose fat, you had to sacrifice your muscle in the process. Thanks to modern science and research, we can throw away that mentality and focus on the ways we can simultaneously lose weight and maintain muscle throughout caloric restriction. Before that, we must understand why losing muscle is a bad idea in the first place.
Whether you are looking to lose weight, gain muscle, or just focus on your overall health, this 6-week customized meal plan will get you the results you want.
Why is Muscle Important?
Muscle plays a central role in protein metabolism by serving as the main supplier of amino acids which come from broken down protein from our food. Blood amino acid supply is important because these amino acids get integrated into essential organs and tissues when needed. During fasting, starvation, or low caloric intake, blood amino acid supply is low, so muscles supply the amino acids needed to maintain protein synthesis in essential organs and tissues.5,6 Additionally, muscle amino acids serve as precursors for plasma glucose synthesis during fasting.

Figure 2. Muscle protein gets broken down during fasting and caloric restriction to provide amino acids to vital organs and tissues for protein synthesis. Copyright © 2020 Fit With Heba, All rights reserved.
Altered muscle metabolism plays an important role in the initiation and prevention of many common conditions and chronic diseases. Muscle mass is also very important for recovery from critical illness or severe trauma. Additionally, muscle strength and function are central to the recovery process.
During stressed states such as cancer and traumatic injury, the body uses more amino acids from muscle protein breakdown than during starvation.7 Individuals with low muscle mass respond poorly to stress and recover more slowly. For example, survival from a severe burn is lowest in individuals with reduced lean body mass.8,9 Muscle mass can also predict the recurrence of many diseases. For example, studies have shown that in cancer patients, a decrease in muscle protein supply increases the recurrence of cancer and decreases the survival rate.10 This is not to say this is strictly due to lean muscle mass. Individuals who accumulate lean muscle mass tend to lead healthier lifestyles, exercise more, and eat properly in comparison to the average person. All of these factors can positively impact injury recovery and survival rates.
How Diet Can Offset Muscle Mass Due to Caloric Restriction
The loss of muscle mass can occur during weight loss and can have several harmful consequences as I’ve already mentioned. These consequences may lessen or negate some of the benefits of weight loss in the long run.
Protein seems to be the most important macronutrient during times of caloric restriction to replenish muscle protein. Higher protein intake during periods of caloric restriction has been shown to help offset the lean muscle mass loss that is typically associated with higher carbohydrate diets.11 After protein ingestion, amino acids stimulate increased rates of muscle protein synthesis and suppress muscle protein breakdown for several hours.12 This process promotes lean muscle accumulation and prevents lean muscle loss over time.
Because muscle protein is being used up during fasting or caloric restriction, all the amino acids that come from food intake gets incorporated into muscle protein to replete what was lost. Under normal conditions, the protein supplied to the muscles during a feeding window should cancel out the loss of muscle protein in the fasting state.
How Resistance Training Can Offset Muscle Loss Due to Caloric Restriction
Remember autophagy from my last blog post about caloric restriction? It is responsible for getting rid of the damaged parts to stimulate the recovery and function of muscle.13,14,15 Muscle can be easily damaged following physical activity, malnutrition, and aging. Autophagy is increased during fasting, atrophy, and exercise, and impairment in autophagy results in the accumulation of dysfunctional proteins. 16,17,18,19
So far, we know that caloric restriction increases autophagy which in turn helps in muscle mass recovery, building, and maintenance. Turns out, resistance training (RT) in combination with enough protein is also a great addition to a caloric restriction regime to increase autophagy and muscle building.

Figure 3. Resistance training with adequate amounts of protein is shown to offset muscle loss during fasting and caloric restriction. Copyright © 2020 Fit With Heba, All rights reserved.
One study found that a calorically restrictive diet composed of 55% carbohydrate, 15% protein, and 30% fat combined with 3 days RT per week for 12 and 24 weeks was able to prevent almost 100% muscle loss in obese elderly people.20. Another study found that with caloric restriction, consumption of a diet containing 2.4g protein/kg body weight/day was more effective than consumption of a diet containing 1.2g protein/kg body weight/day in promoting increases in lean muscle mass and loss of fat mass when combined with a high volume of resistance and anaerobic exercise in men.21 Studies on women are limited, considering men are more likely to practice RT. Despite this, there is no reason not to believe that RT would not work for women.
Conclusion
While we once thought that it was almost impossible to build or even maintain muscle mass on a caloric restriction diet, we now know that there are several ways to not only maintain but also gain lean muscle mass while simultaneously losing weight. Caloric restriction will increase autophagy, leading to several health benefits. With enough protein and resistance training, fat loss along with muscle building is very possible. We shouldn’t only want to build muscle to look good, but we should also want to build it to remain healthy and make sure that we can deal with stress, injury, and disease to recover quicker.
References
- Rochon J, Bales CW, Ravussin E, et al. Design and conduct of the CALERIE study: Comprehensive Assessment of the Long-term Effects of Reducing Intake of Energy. Journals Gerontol – Ser A Biol Sci Med Sci. 2011.
- Redman LM, Heilbronn LK, Martin CK, Alfonso A, Smith SR, Ravussin E. Effect of calorie restriction with or without exercise on body composition and fat distribution. J Clin Endocrinol Metab. 2007.
- Ganesan K, Habboush Y, Sultan S. Intermittent Fasting: The Choice for a Healthier Lifestyle. Cureus. 2018.
- Veronese N, Facchini S, Stubbs B, et al. Weight loss is associated with improvements in cognitive function among overweight and obese people: A systematic review and meta-analysis. Neurosci Biobehav Rev. 2017.
- DeCherney A, Berkowitz G. Starvation in Man. N Engl J Med. 1982.
- Felig P, Owen OE, Wahren J, Cahill GF. Amino acid metabolism during prolonged starvation. J Clin Invest. 1969.
- Biolo G, Declan Fleming RY, Maggi SP, Nguyen TT, Herndon DN, Wolfe RR. Inverse regulation of protein turnover and amino acid transport in skeletal muscle of hypercatabolic patients. J Clin Endocrinol Metab. 2002.
- Pereira CT, Barrow RE, Sterns AM, et al. Age-dependent differences in survival after severe burns: A unicentric review of 1,674 patients and 179 autopsies over 15 years. J Am Coll Surg. 2006.
- Zhang X jun, Chinkes DL, Cox RA, Wolfe RR. The Flow Phase of Wound Metabolism Is Characterized by Stimulated Protein Synthesis Rather Than Cell Proliferation. J Surg Res. 2006.
- KADAR L, ALBERTSSON M, AREBERG J, LANDBERG T, MATTSSON S. The Prognostic Value of Body Protein in Patients with Lung Cancer. Ann N Y Acad Sci. 2006.
- Krieger JW, Sitren HS, Daniels MJ, Langkamp-Henken B. Effects of variation in protein and carbohydrate intake on body mass and composition during energy restriction: A meta-regression. Am J Clin Nutr. 2006.
- Churchward-Venne TA, Murphy CH, Longland TM, Phillips SM. Role of protein and amino acids in promoting lean mass accretion with resistance exercise and attenuating lean mass loss during energy deficit in humans. Amino Acids. 2013.
- Bonaldo P, Sandri M. Cellular and molecular mechanisms of muscle atrophy. DMM Dis Model Mech. 2013.
- Sandri M. Autophagy in skeletal muscle. FEBS Lett. 2010.
- Sandri M. Protein breakdown in muscle wasting: Role of autophagy-lysosome and ubiquitin-proteasome. Int J Biochem Cell Biol. 2013.
- O’Leary MFN, Vainshtein A, Carter HN, Zhang Y, Hood DA. Denervation-induced mitochondrial dysfunction and autophagy in skeletal muscle of apoptosis-deficient animals. Am J Physiol – Cell Physiol. 2012.
- Mammucari C, Milan G, Romanello V, et al. FoxO3 Controls Autophagy in Skeletal Muscle In Vivo. Cell Metab. 2007.
- Grumati P, Coletto L, Schiavinato A, et al. Physical exercise stimulates autophagy in normal skeletal muscles but is detrimental for collagen VI-deficient muscles. Autophagy. 2011.
- Vainshtein A, Grumati P, Sandri M, Bonaldo P. Skeletal muscle, autophagy, and physical activity: The ménage à trois of metabolic regulation in health and disease. J Mol Med. 2014.
- Sardeli A V., Komatsu TR, Mori MA, Gáspari AF, Chacon-Mikahil MPT. Resistance training prevents muscle loss induced by caloric restriction in obese elderly individuals: A systematic review and meta-analysis. Nutrients. 2018.
- Longland TM, Oikawa SY, Mitchell CJ, Devries MC, Phillips SM. High protein exercise caloric restriction promotes greater lean mass gain and fat mass loss. Am J Clin Nutr. 2016.
Hi
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Wow!!! Amazing to learn so much from you!! Love it. Thank you
You’re more than welcome! Glad you loved it.
Great article! Now I feel less bad for (deliberately) neglecting cardio😅 I didn’t think it was possible to do so but even if it was, i thought it would be too complicated. But thanks to your article and the studies you provided, it doesn’t only seem possible but doable as well. This was nice read like your previous articlr! I can’t wait for what you have in store next 🙂
P.S you deserve kudos for providing your own diagrams and pictures. It shows how much effort you put into making people hear AND see how these mechanisms work in the body!
Well, the unfortunate news is that we all should still do cardio occasionally for our cardiovascular health 😅 I know it’s the worst thing ever. I’m glad you liked the article and that it was helpful! Thank you so much for the support and there will definitely be more content coming out soon!
Hi!
I really enjoyed this article, very informative with great sources.
Thanks for taking the time to do this for us!
From my understanding, we are able to lose fat by upping our protein intake while being on a caloric deficit.
Also, do we have to implement cardio in our workout routine to lose weight? I know cardio is great for the heart but everyone says you have to do it to lose fat.
Hi Emely,
I’m glad you enjoyed the article! The focus on protein here is not about losing fat but it’s about gaining and maintaining muscle mass if you are trying to lose fat. Before I answer your question, I want to emphasize that just because protein is the focus, it doesn’t mean you should neglect your healthy fats because those are important for hormonal and metabolism regulation which will fluctuate as you lose weight. Your diet is all about balance.
To lose fat, you have to be in a caloric deficit. There is no doubt about that. The first weight-loss method is being in a caloric deficit by simply decreasing the calories you consume. At the end of the day, it all comes down to the overall calories you’re consuming. They have to be below your maintenance level calories. How you decide to be in a caloric deficit is up to you.
The second weight-loss method includes exercising more so that the calories you burn put you in an overall deficit. The problem with losing weight is that people don’t always understand how to approach it properly so they lose a lot of muscle in the process. Ideally, you want to combine both a caloric deficit with resistance training to lose fat efficiently while maintaining/building muscle. You don’t have to eat a lot of protein to lose fat. The protein is important for the muscle.
Goal 1: Lose fat while maintaining/building muscle
-Need to be in an overall caloric deficit
-Need to focus on protein
-Need to perform high volume resistance training
-Cardio not required
Here, combining cardio with resistance training might put you in a drastic caloric deficit and that can be detrimental to your muscles.
Goal 2: Lose fat and not care about muscle or anything else
-Need to be in an overall caloric deficit
-Focus on protein is not essential
-No exercise is necessary
-Muscle loss is guaranteed
In this scenario, even though you don’t need to do cardio, its a good idea to add it because it’ll make you lose weight quicker.
Let’s say you need to eat 1500 calories to lose weight. Would you rather not exercise at all and just eat 1500 calories or would you rather eat 1800 calories and exercise to burn 300 calories? That is up to you. Personally I would rather eat more and enjoy myself while burning off the calories through exercise. This makes it easier to maintain muscle mass which we all know is important.
Cardio is so important for your cardiovascular health whether you are trying to lose weight or not. It’s not necessary for weight loss but it is for your overall health. Weight loss is easier if you’re healthier.
Everyone is different so you have to find what works best for you. I would consider adding HIIT sessions every now and then just for your health and find a balance with how much you can work out and how much you can eat to achieve the ideal weight loss.
I hope this helps!
Heba! I finally got around to reading your blog and I appreciate your hard work, effort and research! You’re definitely good at what you do. Thanks for this article and I look forward to more!
Hi Nimrah! Thank you so much for taking the time to read them and I’m glad they’re helpful! There will be plenty more to come.
Nice Article. Thank you for sharing.
You’re more than welcome! Thank you for taking the time to read it!
Really interesting ideas, thanks for sharing this.
Thanks for sharing much information! It helps a lot.