Trying to lose weight can feel like an uphill battle. You track calories and exercise, but results are slow. Metabolic testing offers a scientific approach to understanding your body's unique energy needs, paving the way for personalized and effective weight management. This article provides a comprehensive overview of metabolic testing and how it can be used to personalize weight control programs.
Understanding Metabolism and Energy Balance
Our metabolism is the engine that converts food into fuel, dictating how our bodies burn calories and manage weight. Many factors influence metabolism, including age, genetics, weight, body composition, and hormones. Resting metabolic rate (RMR) defines the calorie value required by our body to function at rest and makes up 70 percent of our metabolism.
A good way to understand the body’s metabolism is to think about it as fuel efficiency, just like a car. Energy Balance is the relationship between energy intake (eating) and energy expenditure (metabolic rate).
- Positive energy balance: When energy intake is more than energy expenditure.
- Negative energy balance: When energy intake is less than energy expenditure.
- Neutral energy balance: When energy intake is equal to energy expenditure.
Obesity results from a positive energy balance, where calorie consumption exceeds expenditure. The main goal of obesity treatment is to shift a person from a positive to a negative energy balance. While this principle leads to weight loss, individual responses to diet and exercise vary widely.
What is Resting Metabolic Rate (RMR)?
Metabolic rate measures how quickly your body expends energy or your "caloric burn rate". RMR measures the calories your body needs to sustain function while at rest, and knowing your individual RMR provides a clear picture of your energy balance needs. PEAK measures RMR with gas analysis through indirect calorimetry. This non-invasive test takes only 10 minutes. The operator inputs the participant’s information into the RMR machine, and the participant relaxes in a chair, breathing into a tube connected to the machine.
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Factors Affecting Metabolism
Several factors influence an individual's metabolic rate:
- Age: Metabolism naturally slows down with age.
- Genetics: Genetic predisposition plays a role in metabolic rate.
- Weight: Heavier individuals generally have higher RMRs.
- Body Composition: Muscle mass is metabolically active, so individuals with more muscle tend to have higher RMRs.
- Hormones: Hormones significantly impact metabolism.
It’s equally important to make changes to factors such as sleep, stress and body composition. Incorporating strength training into your routine will promote the growth of muscle mass.
How Metabolic Testing Works
Metabolic testing evaluates the rate at which a person burns calories as energy and uses oxygen. Most forms of metabolic testing start with RMR testing, also known as basal metabolic rate testing. Even if you don’t realize it, you are constantly expending calories. The rate of calories that your body burns to perform all these functions is the basal or resting metabolic rate.
Types of Metabolic Tests
Resting Metabolic Rate (RMR) Test: The basis for any metabolic evaluation, the Resting Metabolic Rate (RMR) test estimates the number of calories burned at rest to determine baseline caloric needs. This test is simple, painless, and takes 10-15 minutes. You'll breathe into a tube while comfortably resting in a private room.
At Iowa Weight Loss Specialists, they use metabolic testing known as indirect calorimetry, which measures your body's Resting Energy Expenditure (REE) or Basic Metabolic Rate (BMR).
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The MedGem® is a medical device that measures your resting metabolic rate. Using the MedGem, patients breathe through a mouthpiece that measures their oxygen intake. This predicts the amount of oxygen cells are using to produce energy. That energy is actually the calories needed to maintain a certain weight.
Exercise Metabolism Test: The Exercise Metabolism looks at your response to increasing intensity of aerobic exercise. It is a great way to establish your Zone 2 intensity, as well as metabolic efficiency and maximal fat oxidation (FatMAX), to determine how much fat and how much carbohydrate are being utilized during exercise. The test measures how many calories you actually burn at different exercise intensities. This will allow for a more accurate determination of total caloric expenditure during exercise.
Metabolic Efficiency Test: The metabolic efficiency tests combines oxygen consumption and lactate measurements to give you valuable insight into your endurance capacity. The ultimate test for the endurance athlete, whether you are an Ironman triathlete, ultra runner, long distance cyclist or other long distance endeavor or simply want an even more rigorous assessment of your Zone 2 for health. The test looks specifically at low to moderate effort levels, pinpointing you aerobic or economy threshold to dial in endurance training and competition paces, as well as your metabolic efficiency (fat utilization). The test will also measure your maximal fat oxidation rate (FatMAX) and help guide your fueling needs (carbohydrate replenishment).
VO2 Max Test: A VO2 max test, also known as the anaerobic capacity test, measures the amount of oxygen that you use when exercising. The V02 test can help you understand when and how your body uses oxygen based on the intensity level of a given physical activity and can help estimate the number of calories that you use when exercising.
Lactate Threshold Test: As you exercise, your muscles produce lactic acid. The lactate threshold refers to the point when you have too much lactic acid buildup in your muscle mass. This test is typically reserved for professional athletes.
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At-Home Metabolism Tests: At-home tests, like the Everlywell Metabolism Test, measure the levels of certain metabolic hormones that influence your metabolism. Note that this is different from a typical metabolic rate test. At-home metabolism tests are hormone tests that don’t measure your metabolic rate or look at how your body uses calories.
Preparing for a Metabolic Test
To ensure accurate results, it’s essential to follow pre-test guidelines. Generally, these include:
- Fasting: Fast for at least four to five hours before the test.
- Avoid Stimulants: Avoid caffeine or cold medications.
- Refrain from Exercise: Avoid exercise for at least four hours prior.
- No Smoking: Refrain from smoking.
The Metabolic Testing Procedure
During the most common RMR test, you will relax in a chair and breathe into a tube or wear a mask for about 10-15 minutes. The machine analyzes the air you breathe in and out to measure oxygen consumption and carbon dioxide production. This data helps determine your RMR, indicating the number of calories your body burns at rest.
When your body burns food for fuel, it requires oxygen and produces carbon dioxide.
Using Metabolic Testing for Personalized Weight Loss
Metabolic testing provides valuable information for creating personalized weight loss plans. Here's how:
- Setting Calorie Goals: Research suggests that measuring metabolic rate can be used to set calorie goals for weight loss and maintenance. Once your test is completed, your target caloric zones are calculated. This determines the maximum calories you can eat while still losing weight. In other words, you'll learn how to eat for your metabolism!
- Optimizing Macronutrient Composition: Respiratory quotient (RQ) can guide macronutrient composition of the diet and maximize fat loss. The energy source that a person uses can be measured by assessing a person's respiratory quotient (RQ). This, in combination with measuring urinary nitrogen and stable isotopes, can be used to establish whether a person is burning fat, protein, or stored carbohydrates.
- Personalizing Behavioral Weight Loss Programs: Incorporating metabolic measures can personalize behavioral weight loss programs.
Resting Metabolic Rate (RMR) and Calorie Goals
An important part of energy balance is knowing how much energy (calories) an individual is expending to know what their initial calorie intake goal should be. This determination is based primarily on two factors: their resting metabolic rate (RMR) and how many calories they burn during movement/activity. Both can be directly measured. Knowing your individual RMR, the estimation of energy balance for your needs becomes a clear picture.
Thermic Effect of Food (TEF)
The digestion of food requires energy, which is generally 10% of the energy a person consumes. This is called the thermic effect of food (TEF), which we will be discussing as a way to personalize diets and integrate this information into the energy balance equation.
The thermic effect of food (TEF) differs based on the macronutrient content of the food. For example, the thermic effect of energy from fat is between 2% and 5% of the energy consumed, the thermic effect of carbohydrates is between 5% and 15%, while protein takes more energy to break down and digest, with changes in thermic effect of food by 20%-30%.
Respiratory Quotient (RQ) and Fuel Utilization
The goal of any diet program is to reduce body weight by burning fat. The energy source that a person uses can be measured by assessing a person's respiratory quotient (RQ). This, in combination with measuring urinary nitrogen and stable isotopes, can be used to establish whether a person is burning fat, protein, or stored carbohydrates.
Metabolic Flexibility
Metabolic flexibility refers to shifts in fuel oxidation when metabolic needs change, such as during a fast, diet, or exercise program. Individual differences in metabolic flexibility to fasting, diet, or exercise programs, determine which type of fuel a person is using and whether they are prioritizing fat when trying to lose weight.
The Role of Exercise
All exercises are not equal in terms of their influence on energy expenditure and weight loss. In general, aerobic exercise will burn more calories than resistance exercise, which can burn more calories per minute than stretching/flexibility exercise. The duration of these types of exercises can differ greatly, as well as changes in body composition as a function of the different types of exercise. The intensity of the exercise is important, and some people will benefit from high‐intensity interval training, in which people alternate very high intensity intervals with rest of low intensity intervals in comparison to longer periods of moderate intensity exercise.
Why Metabolic Testing Matters
Metabolic testing is not only more scientific, but also significantly more accurate. “That formula doesn't consider what’s happening, metabolically, inside the body - like muscle mass versus fat mass,” Urse explains. “As long as patients follow their meal plan and do the exercise, they will accomplish the desired results.
Addressing Individual Differences
There are large individual differences in weight loss and maintenance. Metabolic testing can provide phenotypical information that can be used to personalize treatment so that people remain in negative energy balance during weight loss and remain in energy balance during maintenance.
Adapting to Changes During Weight Loss
As people lose weight, their resting metabolic rate decreases to a greater extent than their weight or fat‐free mass. When and if people reach a desired weight, and their metabolic rate has stabilized, they will need a different dietary and activity prescription, which is seldom quantified in terms of what their body needs to maintain weight.