Are you looking to optimize your weight loss journey and understand your body's unique energy needs? Do you wonder if losing weight damages your metabolism, or if there's a way to lose weight and keep it off without constant hunger? Understanding your Resting Metabolic Rate (RMR) is a crucial step in achieving sustainable weight management.
What is Resting Metabolic Rate (RMR)?
Metabolism refers to the bodily processes needed to maintain life. Your resting metabolic rate is the total number of calories burned when your body is completely at rest, supporting essential functions like breathing, circulating blood, organ functions, and basic neurological functions. RMR, often referred to as resting energy expenditure (REE), is typically defined as the energy expended by the body in a resting state. This encompasses the energy expenditure while the individual is awake, in a post-absorptive and thermoneutral condition and has refrained from exercise for approximately 12 h.
Your RMR accounts for about 60-75% of the total calories you burn each day. Therefore, understanding your RMR can provide valuable insights into how many calories you should consume and burn for effective weight loss. The remaining percentage comes from physical activity (exercise or non-exercise movement) and the thermic effect of food (the energy required to digest and process food).
The Importance of RMR in Nutrition and Weight Loss
The relationship between your RMR and weight loss is simple: the higher your metabolic rate, the more calories you burn at rest, leading to more significant weight loss. Conversely, a lower metabolic rate means fewer calories burned at rest, making it harder to lose weight. This explains why some people can eat a lot without gaining weight while others struggle with shedding pounds despite strict diets. It all comes down to their individual metabolic rates.
Knowing how many calories your body needs just for basic functions can help you plan your diet more effectively. If you consume fewer calories than your RMR requires, you may not provide enough fuel for these essential bodily functions. This could lead to fatigue, nutrient deficiencies, a weakened immune system, and other health problems over time.
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Factors Influencing Resting Metabolic Rate
Several factors can affect your RMR. These include:
- Age: RMR decreases with age. Basal metabolism has been observed to decrease by 1-2% per decade from the age of 20 to 75 years, with this aging process often accompanied by the substitution of muscle mass with an increase in fat mass (FM).
- Gender: Men generally have higher RMR due to more muscle mass. RMR tends to be higher in men compared to women probably because of the higher proportion of fat-free mass (FFM) in the former.
- Genetics: Genetics and epigenetics can also play a significant role.
- Body Size and Composition: More muscle mass increases RMR. FFM serves as the primary determinant of resting energy expenditure.
- Temperature: Cold weather can increase RMR as the body works harder to maintain normal temperature.
- Nutritional Status: Consuming protein-rich foods can increase your metabolism because they require more energy for digestion compared to fats or carbohydrates.
- Hormones: Fluctuations in hormone secretion levels, including leptin, ghrelin, glucagon-like peptide-1 (GLP-1), and cholecystokinin (CCK) can influence RMR.
- Energy Restriction: An additional factor that influences RMR is the implementation of energy restriction, as observed in weight loss interventions through reduced energy intake. This practice, named metabolic adaptation, leads to a decrease in RMR as a biological response to energy restriction and may elucidate the difficulty in properly calculating patient’s energy needs, as well as maintaining weight loss associated with low-calorie diets.
Measuring Resting Metabolic Rate
Accurate measurement of RMR is essential in clinical practice for better clinical decision-making and the selection of optimal therapeutic approaches. However, this process, which is performed via direct or indirect calorimetry, often requires skilled technicians and sophisticated methodologies, which can be costly and difficult to carry out. Due to these challenges, RMR measurement is often impractical in many clinical and community settings.
There are several ways to estimate or measure your RMR:
- Prediction Equations: RMR prediction equations utilize easily obtainable variables such as age, height, and body weight. Unfortunately, these equations only explain between 50% to 75% of the variability in RMR. There is ongoing debate regarding the validity of these equations, as they may not accurately estimate caloric needs, given their application in significantly different populations and conditions than they were originally intended for.
- Indirect Calorimetry: Indirect calorimetry stands as the gold standard for assessing RMR in clinical settings. This method relies on measuring the intake of oxygen and the release of carbon dioxide, which are then used to compute the respiratory exchange ratio (RER), calculated as the ratio of carbon dioxide production (VCO2) to oxygen consumption (VO2).
- Portable Devices: Portable devices designed to evaluate RMR have been created for practical use in office and clinic environments and have undergone validation in adult populations. While a conventional indirect calorimeter assesses an individual’s expired gas volume and the proportions of CO2 and O2, thus estimating RMR, smaller portable versions lack a CO2 sensor. Instead, they measure O2 consumption, operating on the assumption that CO2 production approximately equals 85% of O2 consumption.
RMR Testing: What to Expect
RMR testing measures the number of calories your body burns at rest to maintain essential functions like breathing, circulation, and cellular repair. A typical RMR test takes 15-20 minutes. The operator puts the participant’s information into the RMR machine and the participant relaxes in a chair and breaths into a tube that is connected to the RMR machine for 10 minutes. It’s recommended to test your RMR every 3-6 months, especially if your weight, activity level, or health goals change.
The "Biggest Loser" Study and Metabolic Adaptation
Amidst the optimism that the TV show "The Biggest Loser" has spread for years by transforming lives through weight loss, the study of "Biggest Loser" participants revealed what many could have already guessed: The majority of them were unable to keep off most of the weight they lost on the show. This is certainly the case for most people who have ever embarked on a journey to shed unwanted weight.
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The study, “Persistent metabolic adaptation 6 years after ‘The Biggest Loser’ competition,” measured changes in both body composition and resting metabolic rate over time for 14 game show participants. These individuals had lost an average of 128 pounds by the end of that season’s show, yet just six years later they regained an average of 90 pounds, reported Runner’s World magazine in a follow-up article to the study.
When a person loses weight, the decline in his or her resting metabolic rate (RMR) is “often greater than would be expected based on the measured changes in body composition,” according to the study’s authors. This decline in RMR that follows a drop in body weight is what they refer to as metabolic adaptation. To maintain weight loss, individuals must consume a significantly lower number of calories per day due to the fact that RMR accounts for close to 70% of calorie burn, reported Runner’s World.
This metabolic adaptation is also referred to as the “metabolic penalty” or “fat memory” that postulates that the RMR drops and stays lower as long as the weight is kept off. As Gomer explained, though there is a modest slowdown in metabolic rate following weight loss, the so-called “metabolic penalty” is not the main reason most people end up regaining lost weight. Furthermore, people tend to gain back the weight they lost largely because they are much hungrier and tend to eat more.
However, as Pritikin’s Director of Nutrition and educator Kimberly Gomer, pointed out, the results of this study are quite extreme and an outlier compared to all other previous research on the topic.
Overcoming Metabolic Adaptation
True, research has proven over and over that crash diets don’t work. “We know biologically the main reason people tend to regain weight after following a calorie-restricted diet coupled with increased activity has less to do with some metabolic adaptation and more to do with the fact that people are smaller, and smaller people simply need less food to maintain their smaller body size,” he explained.
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More importantly, “the main reason people regain weight after a crash diet and exercise program is that they are very hungry, and this increased hunger is what drives them to eat more and regain weight. That’s why at the Pritikin Longevity Center in Miami, there is no crash diet or extreme exercise program put into place. From day one, guests learn that counting calories and using intellectual will to fight increased hunger is not the answer. Instead of counting or restricting calories, the focus is on what foods promote obesity and what foods promote a healthier body weight.
Instead of being consumed with counting calories, the focus should be on food - food choices that fill us up. Natural, whole foods that have a low calorie density are one key strategy for not only losing excess weight without being hungrier, but also keeping it off in the long run. We need foods that are big and filling, but are not big in calorie density. Natural, whole foods with a low to moderate calorie density are the cornerstone of the Pritikin Eating Plan. These healthier food choices help people feel satiated on far fewer calories.
Strategies to Improve Your RMR
Here are some strategies to improve your RMR:
- Build Muscle Mass: Building lean body mass is another effective method for boosting RMR. The ability to preserve muscle mass or even better, build muscle mass can help preserve our age-related losses. Even a small gain of 2-to-4 pounds of muscle mass can provide a 7-to-8% boost in metabolism, which can add approximately 90-to-110 kcal to TDEE per day or 9-to-11 lbs.
- Eat Protein-Rich Foods: Consuming protein-rich foods can increase your metabolism because they require more energy for digestion compared to fats or carbohydrates.
- Focus on Whole Foods: Instead of counting or restricting calories, the focus is on what foods promote obesity and what foods promote a healthier body weight. Natural, whole foods that have a low calorie density are one key strategy for not only losing excess weight without being hungrier, but also keeping it off in the long run.
- Avoid Crash Diets: From day one, guests learn that counting calories and using intellectual will to fight increased hunger is not the answer.
The Role of Circadian Rhythms
Circadian rhythms are the 24-hour cycles that regulate our biology. These rhythms help organize our physiological processes in response to light and dark. Disrupting these rhythms can lead to poor sleep quality, which impacts both physical and mental health. Misaligned circadian rhythms can contribute to chronic health issues such as obesity, diabetes, cardiovascular diseases, and weakened immune function.