Many people want to lose weight, but what they mean is that they want to lose fat. Unfortunately, most calorie-restricted diets result in muscle loss. Intermittent fasting is an excellent method to lose fat while preserving muscles.
There are many strategies you can try to lose some unwanted fat. For example, maybe you or a friend have tried a popular diet like Whole 30 or Paleo…or maybe this is the first time you’ve decided to try a diet.
Either way, looking for the most effective diet that’s the easiest to turn into a habit is HARD! There are so many articles, websites, books, etc. written on this exact topic. Some are rooted in science and some…well, aren’t scientifically-founded.
One dietary strategy that has become popular recently is intermittent fasting. One of the reasons why intermittent fasting has become popular is because it works!
In this article, we’re going to explain how intermittent fasting is an effective dietary strategy for fat loss.
Many of us say we want to lose some weight but what most of us mean is that we want to lose fat. And yes, there’s a big difference.
Losing weight simply means that the number you see on the scale has gotten smaller. What that number doesn’t tell you is what you’ve lost. Losing weight can oftentimes be misleading because it can be a result of losing body water or muscle mass.
Losing body water happens all of the time. For example, you lose body water when you perspire or urinate. This can affect your weight but once you rehydrate, your weight will go back to where it was.
Many people lose muscle mass when one a diet. This isn’t an ideal situation because muscles burn a lot of energy. This means that losing muscle mass will decrease the amount of calories you burn each day. Over time, this can lead to you eating more than you burn, which leads to an increase in body fat.
Losing fat means exactly what it suggests – decreasing your body fat percentage. No matter what weight loss strategy you are using, losing fat mass should be the goal.
The most common strategy to lose weight (or fat) is restricting calories. Unfortunately, long-term caloric restriction can cause a lot of undesirable side effects including weight-loss plateaus, fat regain when eating normally again, changes to hormonal pathways, decreased bone density, and loss of muscle mass (1, 2, 3, 4).
This doesn’t sound good, does it?
Now that we’ve discussed some of the cons to caloric restriction, you’re probably wondering if intermittent fasting is a good strategy that won’t cause some of those undesirable side effects we just mentioned. And the short answer is yes, it definitely can be a better option!
For starters, intermittent fasting has been shown time and time again to help better your health. It can decrease the risk of cardiovascular disease, insulin resistance, decrease inflammation, and more (5, 6, 7, 8, 9).
The reason fasting may be a superior choice to caloric restriction for fat loss is because intermittent fasting helps you become more “metabolically flexible” or “metabolically efficient.” What does this mean? The term “metabolic flexibility” is just a fancy way of saying that your body is more efficient at using your fat stores for fuel as opposed to your stored sugar.
In order to achieve this, you have to train your body. The best way to train your body is to fast for a certain period of time (12+ hours) so that your body loses most of its stored sugar (glycogen). When this occurs, your body will turn to its fat stores for energy.
Some scientists refer to this shift as “flipping the metabolic switch”(10). After doing this for a while, your body becomes better trained at using certain metabolic pathways to use fat for fuel…ones that your body may not be using much right now. When your body is better trained for using more fat throughout the day-that’s when you’re more metabolically flexible.
When you teach your body to use more stored fat for fuel, you are really training it to make use of your fat stores. This means that your body will be using more fat for energy no matter what you’re doing – watching TV, walking, exercising, etc.
People who are more metabolically flexible tend to be leaner individuals with lower body fat percentages (11, 12). Metabolic flexibility also appears to be something that your body can sustain long-term, meaning that it won’t just go away if you decide to stop intermittent fasting.
Training your body to be more metabolically flexible has been shown to be not only effective for weight loss but studies show that people who are more metabolically flexible are at a lower risk of developing certain diseases (13, 14).
Scientists believe that this is part of the reason why your body may not lose muscle mass while fasting. Your muscles also have some stored fat and this fat can be used for energy by your muscles if you’re exercising and/or moving around. If your body isn’t well-trained to use fat, your body can and will break down your muscles for energy, if needed (10, 15).
Another reason why your body may not lose muscle mass while fasting is because fasting increases the levels of human growth hormone. This hormone also helps your body burn more fat while preserving muscle mass (16, 17).
Weight loss isn’t the same as fat loss. Losing fat while maintaining muscle mass should be the goal when starting a new diet.
You might be interested in reading our other articles about fasting and loose skin, as well as how to get rid of face fat with intermittent fasting, fasting and cellulite or stress as a reason for weight loss.
1. Pettersson S, Pipping Ekström M, Berg CM. The food and weight combat. A problematic fight for the elite combat sports athlete. Appetite. Academic Press; 2012;59:234–42.
2. Koehler K, Hoerner NR, Gibbs JC, Zinner C, Braun H, De Souza MJ, Schaenzer W. Low energy availability in exercising men is associated with reduced leptin and insulin but not with changes in other metabolic hormones. J Sports Sci [Internet]. Routledge; 2016 [cited 2020 Jul 29];34:1921–9. Available from: https://pubmed.ncbi.nlm.nih.gov/26852783/
3. Redman LM, Ravussin E. Caloric restriction in humans: Impact on physiological, psychological, and behavioral outcomes [Internet]. Antioxidants and Redox Signaling. Mary Ann Liebert, Inc.; 2011 [cited 2020 Aug 16]. p. 275–87. Available from: /pmc/articles/PMC3014770/?report=abstract
4. Benton D, Young HA. Reducing Calorie Intake May Not Help You Lose Body Weight. Perspect Psychol Sci [Internet]. SAGE Publications Inc.; 2017 [cited 2020 Jul 28];12:703–14. Available from: /pmc/articles/PMC5639963/?report=abstract
5. Mattson MP, Longo VD, Harvie M. Impact of intermittent fasting on health and disease processes. Ageing Research Reviews. Elsevier Ireland Ltd; 2017. p. 46–58.
6. Malinowski B, Zalewska K, Węsierska A, Sokołowska MM, Socha M, Liczner G, Pawlak-Osińska K, Wiciński M. Intermittent fasting in cardiovascular disorders—an overview. Nutrients. MDPI AG; 2019.
7. Hutchison AT, Regmi P, Manoogian ENC, Fleischer JG, Wittert GA, Panda S, Heilbronn LK. Time‐Restricted Feeding Improves Glucose Tolerance in Men at Risk for Type 2 Diabetes: A Randomized Crossover Trial. Obesity [Internet]. Blackwell Publishing Inc.; 2019 [cited 2020 May 21];27:oby.22449. Available from: https://onlinelibrary.wiley.com/doi/abs/10.1002/oby.22449
8. Paoli A, Tinsley G, Bianco A, Moro T. The influence of meal frequency and timing on health in humans: The role of fasting. Nutrients. MDPI AG; 2019.
9. Longo VD, Mattson MP. Fasting: Molecular mechanisms and clinical applications. Cell Metabolism. NIH Public Access; 2014. p. 181–92.
10. Anton SD, Moehl K, Donahoo WT, Marosi K, Lee SA, Mainous AG, Leeuwenburgh C, Mattson MP. Flipping the Metabolic Switch: Understanding and Applying the Health Benefits of Fasting. Obesity. Blackwell Publishing Inc.; 2018. p. 254–68.
11. Astrup A. Obesity and metabolic efficiency. CIBA Found Symp [Internet]. Ciba Found Symp; 1996 [cited 2021 May 27];201:159–73. Available from: https://pubmed.ncbi.nlm.nih.gov/9017280/
12. Galgani J, Ravussin E. Energy metabolism, fuel selection and body weight regulation [Internet]. International Journal of Obesity. NIH Public Access; 2008 [cited 2021 May 27]. p. S109. Available from: /pmc/articles/PMC2897177/
13. Goodpaster BH, Sparks LM. Metabolic Flexibility in Health and Disease. Cell Metabolism. Cell Press; 2017. p. 1027–36.
14. Smith RL, Soeters MR, Wüst RCI, Houtkooper RH. Metabolic flexibility as an adaptation to energy resources and requirements in health and disease [Internet]. Endocrine Reviews. Oxford University Press; 2018 [cited 2021 May 27]. p. 489–517. Available from: /pmc/articles/PMC6093334/
15. Muoio DM, Way JM, Tanner CJ, Winegar DA, Kliewer SA, Houmard JA, Kraus WE, Lynis Dohm G. Peroxisome proliferator-activated receptor-α regulates fatty acid utilization in primary human skeletal muscle cells. Diabetes. American Diabetes Association Inc.; 2002;51:901–9.
16. Aksungar FB, Sarikaya M, Coskun A, Serteser M, Unsal I. Comparison of intermittent fasting versus caloric restriction in obese subjects: A two year follow-up. J Nutr Heal Aging [Internet]. Springer-Verlag France; 2017 [cited 2021 May 27];21:681–5. Available from: https://pubmed.ncbi.nlm.nih.gov/28537332/
17. Moller L, Dalman L, Norrelund H, Billestrup N, Frystyk J, Moller N, Jorgensen JOL. Impact of fasting on growth hormone signaling and action in muscle and fat. J Clin Endocrinol Metab [Internet]. Endocrine Society; 2009 [cited 2021 Jun 2];94:965–72. Available from: https://pubmed.ncbi.nlm.nih.gov/19066303/
Intermittent fasting windows differ in length and timing. Read on to learn about how to find the right fasting window.