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Can Losing Weight Ruin Your Metabolism?

Elisa - Jenny Craig

Ask an RD: Dietitian Janet Nash shares the role metabolism plays in weight loss.

A common concern I hear during weight loss is “will losing weight ruin my metabolism?” The concern typically stems from past yo-yo dieting or that getting to a lower weight will make weight maintenance more difficult. Wouldn’t it be great if we could somehow lose the weight without jeopardizing our metabolism?


When we lose weight, we lose two different types: fat and lean mass. However, both are not created equal. Lean body mass includes muscle and other parts of the body that don’t contain fat. It’s estimated that approximately 14-23% of weight loss comprises of lean body mass1,which is mass you want to keep.  As a result, this lowers the rate at which metabolism burns fuel because muscle tissue is more active than fat and requires more calories to maintain. Is it possible to combat this cycle and burn fat and preserve lean mass?

Flipping the Switch - Burn Fat and Preserve Muscle

shutterstock_Clock_Eating_Web_500.jpgAccording to the journal, Obesity2, it is possible to maintain muscle while reducing fat. In the study, researchers concluded that Intermittent Fasting (IF), a weight loss strategy focusing on a specific eating time-frame, followed by a period of non-consumption, prompts the body to burn fat instead of glucose. This process helps preserve essential protein which makes up the body’s muscles and non-fat tissues while reducing unwanted fat.

There are different approaches to Intermittent Fasting. One method, called Time- Restricted Feeding (TRF), limits food consumption to 12 hours or less, followed by a period of abstaining from nourishment for 12 hours or more. By not putting any calories into the body for this designated time, we can “flip the switch” and go from burning glucose to burning fat for fuel. 

However, for this process to work, calories should not be consumed in any form (besides water and calorie free drinks) so that there can be a depletion of sugar that is naturally stored in the liver. When the body runs out of sugar, it will target another fuel source – fat.  This shift from burning glucose to fat naturally decreases fat stores and preserves muscle mass and function.  Furthermore, this method used in conjunction with a successful weight loss program, such as Jenny Craig’s Rapid Results, has been proven to be more effective than simply cutting calories (3).

More Benefits Than Weight Loss

In addition to fat loss and lean mass preservation, studies have revealed Intermittent Fasting has many other benefits.  First, the process promotes not only fat loss but specifically targets abdominal fat, which studies have shown to be a key component in reducing the risk of developing diabetes4. Individuals may also see improvements in blood pressure, cholesterol and triglycerides levels, all of which help decrease the risk for cardiovascular disease5. Improved mood, immune and mental functions have also been reported4,6. You can even experience better appetite control with less hunger and cravings7.  

Putting the Pieces Together

shutterstock_Sleep_Web_500.jpgWeight loss can be a puzzle with many pieces, and often, can be challenging to fit together.  By incorporating Intermittent Fasting into your routine, you can simplify your weight loss plan by focusing on when you eat.  You can then shift your attention to other things such as relaxation, getting active and sleep, all of which are important for your overall health. And another bonus, sleep is part of the non-nourishment timeframe, so that should be about 8 of the 12 hours a day for your body to repair and rejuvenate.

To ensure results, it helps to have a structured meal plan that includes portion-controlled servings and snacks.  With a strategy in place, you won’t need to worry about which foods to eat during the day. Make sure to schedule the time to exercise and incorporate resistance training which can further aide in lean body mass retention8 and metabolism maintenance.

If you lead a busy lifestyle and don’t know what to eat, or need some guidance, let Jenny Craig help you with their new Rapid ResultsTM program which incorporates Time-Restricted Feeding (TRF) in an easy-to-follow plan:


  •          Eat 6 times a day during the 12-hour nourishment period
  •          Take a break during the 12-hour rejuvenation period
  •          Premium menu including perfectly-portioned meals and snacks
  •          Personal consultant to help you incorporate exercise as well as other healthy lifestyle habits
  •          Customized plan that works best for your lifestyle

Contact us for a free appointment to learn more.


1.       Chaston, TB. Et al. “Changes in fat-free mass during significant weight loss: a systematic review.” Int J Obes (Lond), vol. 31, no. 5, 31 Oct. 2006, pp. 743–750., doi:10.1038/sj.ijo.0803483.

2.       Anton, Stephen D., et al. “Flipping the Metabolic Switch: Understanding and Applying the Health Benefits of Fasting.”  Obesity, vol. 26, no. 2, 31 Oct. 2017, pp. 254–268., doi:10.1002/oby.22065.

3.       https://www.mensfitness.com/weight-loss/burn-fat-fast/why-intermittent-fasting-may-be-best-diet-plan

4.       Chaix, Amandine, et al. "Time-Restricted Feeding Is a Preventative and Therapeutic Intervention against Diverse Nutritional Challenges." Cell Metabolism, vol. 20, no. 6, 2 Dec. 2014, pp. 991–1005., doi:10.1016/j.cmet.2014.11.001.

5.       Scheer, Frank A. J. L. et al. “Adverse Metabolic and Cardiovascular Consequences of Circadian Misalignment.” Proceedings of the National Academy of Sciences of the United States of America, vol. 106, no. 11 (2009): pp. 4453–4458., doi:10.1073/pnas.0808180106

6.       Vasconcelos, Andrea R, et al. “Intermittent fasting attenuates lipopolysaccharide-induced neuroinflammation and memory impairment.” Journal of Neuroinflammation, vol. 11, no. 1, 6 May 2014, pg. 85., doi:10.1186/1742-2094-11-85.

7.       Peterson, C. Pennington Biomedical Research Center. “Time-Restricted Feeding Increases Fat Oxidation and Reduces Swings in Appetite Levels in Humans.” Oral abstract presentation at: The Obesity Society Annual Meeting at ObesityWeekSM 2016; October 31 – November 4, 2016. www.obesityweek.com.

8.       Campbell, Wayne W, et al. “Resistance Training Preserves Fat-Free Mass Without Impacting Changes in Protein Metabolism After Weight Loss in Older Women.” Obesity (Silver Spring, Md.), vol, 17, no. 7., 26 Feb. 2009, pp. 1332-1339., doi:10.1038/oby.2009.2.


Edited by Elisa - Jenny Craig

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