Your Quick Guide to Metabolism

What is Metabolism and How Can We Measure it?

Metabolism is the process by which your body converts what you eat and drink into energy. This process runs all day to keep your body moving whether you are resting or active.  

Your basal metabolic rate is the amount of calories that your body burns to perform its most basic life sustaining functions such as breathing, controlling your body temperature, and blood circulation.  Similarly and sometimes used interchangeably is your resting metabolic rate which is the amount of calories your body burns when it’s at rest. There are many different factors that can affect this resting metabolic rate such as your body size and composition, your sex, and your age. 

There are three other factors that also determine how many calories you burn in a day: 

Thermic Effect of Food (TEF): This is the  increase in metabolic rate that occurs after a meal. It involves the energy required to digest, absorb, transport and store the food you consume. It takes about 10% of the calories you are consuming to assist with TEF. There is a lot of research evaluating how certain food types and meal sizes can effect TEF and how it is linked to unhealthy weight gain and obesity. There are many foods that actually increase the TEF, which means they require more energy to digest them, and thus burn more calories. Here is a great list by Medical News Today on foods that I recommend to all my patients when embarking on a healthier lifestyle: 10 best foods to boost metabolism. 

Energy burning during physical activity: this includes the calories burned during exercise. This can be very variable for any individual.  

Did you know that you can burn calories through your everyday activities like typing, walking around your office, or fidgeting? This is called Non Exercise Activity Thermogenesis (NEAT): energy burned doing normal day to day activities. Boosting NEAT is one of the easiest ways to burn more calories throughout the day and thus boost “metabolism”. NEAT encompasses the expenditure of energy that is secondary to movement beyond purposeful exercise and resistance training activities. Activities that promote NEAT include a series of continuous and vital movements with postural changes that do not involve moderate- to vigorous-intensity exercise and occur at a trivial or low energy workload on a daily basis for minutes to hours. Sitting for prolonged periods of time has been shown to lead to weight gain. Sitting time is also independently associated with an increased risk of diabetes. A Canadian study showed a dose-response relationship between sitting time and mortality from all causes and cardiovascular disease, independent of leisure-time physical activity. Therefore, physical activity does not counteract the negative effects of prolonged sitting. The pandemic with “work from home” orders has certainly increased the sitting and TV time for many. I encourage all of my patients, no matter their physical activity level, to be mindful of their sitting time during the day. Set alarms to stand and walk around your office every hour, invest in a standing desk to help promote standing intermittently while working, stretch your legs, do light sitting and standing exercises on your chair, and take an afternoon break to walk outside to help promote your NEAT!

Take a look at my research tab for links to the studies I mentioned above.

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Easy ways to increase your NEAT:

• Park farther away from entrances

• Take the stairs instead of the elevators/escalator 

• Stand instead of sit 

• Don’t stay seated for long periods of time 

• Set a daily step goal 

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The amount of energy needed to carry out all of these physical functions is known as Energy Expenditure (EE).

What affects your Basal Metabolic Rate?  One of the biggest factors that affects your EE is your lean body mass (LBM)  which is all your body’s components (muscle, bone, ligaments, tendons, and organs) except fat. Your LBM accounts for about 70% of your BMR, with the remaining contributors  being age, sex, fat mass, and genetics. There are also certain endocrinological (hormonal) disorders that can decrease your basal metabolic rate such as hypothyroidism (low thyroid hormone), polycystic ovarian syndrome (PCOS - alteration in hormones that can affect women leading to insulin resistance, weight gain, and menstrual irregularities) and hypogonadism (low testosterone levels in men).  In addition to aerobic (cardio) exercise, it is important for all people of any age to incorporate some form of strength training at least two times a week. It not only helps keep your bones strong, but helps build that lean body mass. One study that was published in 2018, showed that women that performed resistance training for 6 weeks had a significant increase in BMR for up to 48 hours after their training session! (Sign me up for strength training please ! ) 

How can you assess your metabolism? 
Assessing your actual metabolic rate is a little bit tricky and it is hard to get accurate readings.  The “gold standard” meaning the best known scientific way to measure your metabolic rate is with an indirect calorimeter.  It’s a bit of a complicated process. But the gist is this - Carbon based nutrients convert to Carbon Dioxide (CO2), H2O and heat in the presence of O2. By way of a very complicated equation an indirect calorimeter is a device that measures the amount of oxygen that is inspired and carbon dioxide released by the body and your Energy Expenditure is then calculated. Unfortunately, not many outpatient clinics have access to an indirect calorimeter. They are usually used in research centers, or in intensive care units for ventilated patients. If you want to learn more about the nitty gritty of indirect calorimeter- click here. 

A way that is more readily available is through a Bio Impedance Analysis. A BIA scale is not as accurate as an indirect calorimeter but it is still a reliable method of getting a ballpark idea of what your body composition is at and thus your Metabolic Rate. I use one at my clinic for all my new patients.  The scale uses electrodes which submit a low level electrical current through your body (you do not feel this current). The current assesses the resistance of that current flowing through muscle, bones, water, and fat. This allows the scale to determine your percent body fat, total body water, your fat mass and fat free mass, and the more advanced scales can even give a segmental analysis of your fat percentage. This analysis breaks down each body area and it’s percent body fat, and also gives an assessment of visceral body fat, which is the inflammatory fat that surrounds organs and is a high risk factor for metabolic disease. There are different calibers of BIA scales- the most accurate results are likely with the newer models of Inbody, Tanita, or Seca.  Many physical therapy, sports centers, and weight management doctors have access to these scales. 

What are other ways to assess your metabolism without getting actual measurements through a scale or calorimeter? 
Making sure you are burning and using adequate fuel throughout the day can certainly manifest itself in your overall sense of energy. If you are feeling constantly tired, fatigued, or hungry, or have a very strong sweet tooth. If you are not physically active, or gaining weight especially in your mid section. If you smoke or drink excessive alcohol. These can all be signs of a low metabolic rate which can be early signs of metabolic disease. 

If you are experiencing any of these symptoms I urge you to talk to your doctor about it! Metabolic health is the key to living a long life without chronic disease. 

Stay tuned for my next blog post where I will go into more details of Achieving Metabolic Health!

Leave Comments below & Remember to take a look at my Research Tab for more detailed background information on understanding Metabolism.

Best in Health,

Your Friendly Metabolic Doc