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Metabolism 101: Our R.D. Debunks 5 Metabolism Myths

By Stephanie E - Jenny Craig

Reviewed by Briana Rodriquez, R.D.


We all have that one friend. That friend who credits their fast metabolism for their ability to eat whatever they like, without seeming to gain a pound. For others, a seemingly “slow” metabolism might feel like a barrier to weight loss.


Many people are quick to attribute their metabolism to a whole host of things, from their weight to their appetite. But what’s the truth about your metabolism, and is there anything you can do to make it work in your favor?


Jenny Craig’s Registered Dietitian Nutritionist, Briana Rodriquez, sat down with us to discuss common metabolism myths, facts, and what you can do to support healthy weight loss, no matter what “type” of metabolism you may have.

What is your metabolism?

Before we get into metabolism myths, here’s what your metabolism is — and isn’t.


“Your metabolism isn’t like a muscle you can choose to strengthen — it’s a complex set of chemical reactions that take place in each of your body’s cells,” says Rodriquez.1


Your metabolism turns the food you eat into the energy that helps keep you going. It’s constantly running — even when you’re asleep, she explains. Rodriquez continues, “You can support your metabolism by eating healthy foods and including regular physical activity into your routine.”


The terms “resting metabolic rate” (RMR) and “basal metabolic rate” (BMR or BEE, basal energy expenditure) are often used interchangeably, but they have slight differences. RMR is the number of calories your body burns while at rest. BMR is an estimation of the minimum number of calories your body needs to do basic functions, like breathing, while it’s at rest.


Finding out your exact RMR can only be done in lab, but it’s possible to calculate your BMR. This calculation shouldn’t be used to determine how many calories you should eat a day, because you’ll need to factor in other components of your lifestyle such as activity level and health goals — but it can give you an idea of how much energy your body needs to perform essential functions.


Although online tools and equations may not be extremely accurate, they can give you a rough estimate. According to Ace Fitness, the Mifflin-St Jeor Equation is one way to measure your BMR:2

  • Men: 9.99 x weight (in kilograms) + 6.25 x height (in centimeters) – 4.92 x age + 5
  • Women: 9.99 x weight (in kilograms) + 6.25 x height (in centimeters) – 4.92 x age – 161


Knowing your BMR may help you get a better understanding of your metabolism — but it’s just one piece of the weight loss puzzle. To lose weight effectively, you’ll want to find a weight loss program that takes your lifestyle, eating habits and potentially your genetics into account to create a plan that works best for you.


Now that we’ve discussed what metabolism is, let’s explore the top metabolism myths and facts.  

Metabolism Myth #1: After 30, your metabolism goes downhill.

Photo by ljubaphoto on iStock

Metabolism_101_Myth1_Photo by ljubaphoto on iStock.jpgIf you’ve ever heard someone blame their age on their slowing metabolism, there may be some truth to it. Your metabolism doesn’t stay the same forever; it changes throughout your life. But the good news is, your metabolism isn’t like a switch that suddenly turns off when you reach a certain age! Research suggests changes to your metabolism usually happen slowly over time.


One study found that participants’ physical activity level and the total amount of energy they expended gradually declined throughout their adult lives.3 Participants’ total energy expenditure dropped by about 150 calories per decade.


A person’s metabolism might not be the only thing causing weight gain. Less than 5% of adults take part in 30 minutes of physical activity per day, the Department of Health & Human Services (HHS) reports.4 Too little exercise combined with an excess of calories from saturated fat, refined grains and sodium, common in a typical American diet, may make gaining weight difficult to avoid.



Try this: To help maintain your metabolism, build muscle mass by engaging in strength training. You can try body weight exercises, like push-ups and planks, or using gym equipment to add difficulty. Realistically, says Rodriquez, increasing your muscle mass may create a small change in the number of calories your body can burn while at rest. The biggest benefit of increasing your muscle mass? Being able to do more physical activity than you could before. Building your muscles allows you to do more intense exercise, which can burn more calories than low-intensity exercise. 

Metabolism Myth #2: “Slim” people naturally have better metabolisms.

Looks can be deceiving. Even if people appear to be in shape, that doesn’t mean they have a “fast” metabolism. A person with more lean mass (bone, connective tissue and muscle) burns more calories than someone with less lean mass.5 Consider an athlete and a non-athlete who weigh the same — the athlete is more active and will burn significantly more calories, while the non-athlete is likely less active and may have more body fat.



Try this: If weight loss is your goal, developing healthy lifestyle habits will put you on the path to success. No matter your body type or weight, everyone can benefit from eating nutritious meals, following the appropriate portion sizes, and taking part in physical activity, Rodriquez says.

Metabolism Myth #3: Skipping meals can jump-start metabolism.

Photo by Engin Akyurt on Pexels
Metabolism101_Myth3_Photo by Engin Akyurt on Pexels (1).jpg

Without the right nutrients, your metabolism can’t function at its best, and your body may start feeling the adverse effects. Skipping meals may affect your health in many ways, including having low energy, or even gaining weight, says Rodriquez.


“If you skip breakfast, you might be so hungry at lunch that you accidentally overeat,” she explains. “Avoid getting into a cycle of meal skipping and potentially overeating by spreading your meals out over the course of the day. Healthy snacks can also help curb hunger pangs without disrupting your weight loss.”  


Fueling your body with healthy meals helps to keep everything running smoothly, so don’t skip meals — enjoy them!



Try this: Take time to eat breakfast — it may help to support your weight loss and your body’s natural circadian rhythms. If you’re following Jenny Craig, we do all the hard work for you, so you won’t need to calculate your BMR or even count calories. With Jenny Craig, you’ll eat six times each day — three meals and three snacks — perfectly portioned to help support your goals.


Metabolism Myth #4: Skimping on sleep won’t affect metabolism.

Photo by monkeybusinessimages on iStock

sleep-metabolismIf you haven’t been getting enough sleep, your metabolism might be struggling to keep up. Over 35% of American adults sleep less than seven hours each day — and that’s the bare minimum that the American Sleep Association recommends.6

Losing sleep can affect your RMR and your weight loss — but not in a good way. One study found that adults who were restricted to four hours of sleep per night, for five nights, gained over 2 lbs. in five days and consumed more calories per day (they consumed more calories from fat and less calories from protein) compared to a control group that slept normally.7


Your metabolism and sleep habits are also influenced by a variety of hormones, including leptin (which suppresses appetite) and ghrelin (which promotes appetite). In a separate study, researchers noted that men who experienced sleep deprivation two nights in a row showed reduced levels of leptin, increased levels of ghrelin, and an increase in self-reported hunger.8



Try this: Instead of struggling through another sleepless night, try these sleep hygiene tips. Getting a good night’s rest comes with a number of health benefits — appetite management, and a lowered risk for high blood pressure and heart disease — so it’s important to get your shut-eye.

Metabolism Myth #5: A slower metabolism means you won’t be able to lose weight.

If you’ve started to follow a DNA-based weight loss program, like Jenny Craig’s DNA Decoder Plan, you’ll learn more about your metabolism and how it works. (This is how your DNA may impact your weight loss.)


Update: We have paused our weight loss insights plan for now. In the meantime, stay healthy and check out our new meal delivery options.


Research suggests a handful of genes are associated with RMR and may shed light on how responsive a person’s metabolism is to diet and exercise.9-12 While a “below average” RMR result may seem disappointing at first, it doesn’t have to derail your weight loss efforts. With your DNA results, you’ll have the knowledge you need to move your weight loss in the right direction.


Your RMR is only one part of your metabolism — the energy that your body uses during physical activity is another.


“There are plenty of healthy activities you can do to support your metabolism,” Rodriquez says. “Exercising regularly will encourage your body to use more energy, which is great for weight loss.”



Try this: To fit more activity into your day, start by making small changes, like parking farther away from your work building, local mall or grocery store. Give different types of exercise for beginners a shot, or even try a new workout class to change things up.


Your metabolism is a complex process and can be thrown off track under certain circumstances. As a result, there’s a ton of metabolism misinformation out there. Use these myths and truths as tools to make lifestyle changes to support a healthy metabolism!


Want to support your metabolism with healthy meals delivered to your doorstep? Get Jenny Craig delivered today.




[1] https://www.britannica.com/science/metabolism

[2] https://www.acefitness.org/certifiednewsarticle/2882/resting-metabolic-rate-best-ways-to-measure-it-and/

[3] https://www.cambridge.org/core/journals/public-health-nutrition/article/energy-requirements-and-aging/E11815CE5C6E12FC1A7D914E42F5F9FD

[4] https://www.hhs.gov/fitness/resource-center/facts-and-statistics/index.html

[5] https://www.cnn.com/2019/03/07/health/skinny-metabolism-food-drayer/index.html

[6] https://www.sleepassociation.org/about-sleep/sleep-statistics/

[7] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4701627/

[8] https://annals.org/aim/article-abstract/717987/brief-communication-sleep-curtailment-healthy-young-men-associated-decreased-leptin

[9] https://www.ncbi.nlm.nih.gov/pubmed/12006639

[10] https://www.ncbi.nlm.nih.gov/pubmed/16231024

[11] https://www.ncbi.nlm.nih.gov/pubmed/17158439

[12] https://www.ncbi.nlm.nih.gov/pubmed/24335056

Stephanie Eng-Aponte

bio-photo-stephanie.jpgStephanie Eng-Aponte is a copywriter for Jenny Craig and has written for the health and wellness, tech, and environmental industries. Stephanie graduated from Rutgers University with a Bachelor of Arts degree in Journalism and Media Studies. They employ an “eat first, write later” approach to food blogging and enjoy the occasional Oxford comma. Outside of writing, you can find them photographing a muttley crew of rescue pups, brewing kombucha, or exploring San Diego.


Favorite healthy snack: green apple slices with sunflower butter




Reviewed by Briana Rodriquez, RDN


bio-photo-briana.pngBriana is a Registered Dietitian Nutritionist and Certified Personal Trainer for Jenny Craig, based in Carlsbad, California. She is passionate about utilizing food as functional and preventative medicine. Guided by a simplistic and optimistic approach, Briana’s philosophy is to help people improve their health and achieve their goals through the development of sustainable habits to live a healthy life. In her free time, you can find her strength training, indoor cycling, coffee tasting, and at local eateries with her husband and two dogs.


Favorite healthy snack: peanut butter with celery alongside a grapefruit-flavored sparkling water (so refreshing!)



This article is based on scientific research and/or other scientific articles and was written by an experienced health and lifestyle contributor and fact-checked by Briana Rodriquez, RDN, Registered Dietitian Nutritionist at Jenny Craig. 


Our goal at Jenny Craig is to provide the most up-to-date and objective information on health-related topics, so our readers can make informed decisions based on factual content. All articles undergo an extensive review process, and depending on topic, are reviewed by a Registered Dietitian Nutritionist (RDN) or Nutritionist, to ensure accuracy.


This article contains trusted sources including scientific, peer-reviewed papers. All references are hyperlinked at the end of the article to take readers directly to the source.


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