When many people think of energy, they equate it to how alert they are throughout the day or the level of intensity they were able to complete their workout in, but what many people forget about is the massive amount of energy your body uses to sustain involuntary functions. How inconvenient would it be for you to sit there telling your heart to beat, your lungs to breathe, your stomach to digest—it would consume your life. Luckily we do not have to do that, but the number of calories you burn daily by those involuntary functions really adds up, and the energy needed to sustain a number of physiological functions at rest is known as your basal metabolism. Your Basal Metabolic Rate (BMR) is the rate of energy for this metabolism. Our BMR’s are not static, and in fact, are quite the contrary. It is highly variable and dependent upon a number factors including: your physical and emotional health status, age, gender, physical activity levels, and supplements or medications you may be consuming daily. You may be asking yourself why this topic is important, but understanding your metabolism and how it physiologically functions will provide you with a proper understanding of how to correctly and efficiently make modifications to your own nutrition.
Let’s look at some factors which affect your BMR:
Current Body Composition
BMR is highly dependent upon your current body composition. The more lean body tissue your frame has, the higher your metabolic capacity will be because lean body tissue is more metabolic. Muscles are high maintenance tissues that require more calories even while at rest to sustain itself. Therefore, over time if you increase lean muscle tissue in your body, you have the potential to increase your BMR.
Age
Most will tell you that as you age and get older your metabolic rate drops drastically. You’ve heard all the old timers before try to justify this argument, right? “I used to have a high metabolism until I turned “X” age and it all went downhill from there” or “If you keep eating like that, you’re going to end up looking like me”. This is true to a certain extent, but not at the simplicity that people think. A more plausible explanation is that changes in our hormones and endocrine function occur as we age, and we tend to lose lean body tissue. More often than not, the decline in BMR as we age is more so a result of a decrease in overall physical activity, which ultimately yields a decrease in lean body tissue. As we get older we tend to start prioritizing our lives—our careers get in the way, we get married, have kids, take our kids places—and then suddenly all other things around us take precedent over our own health, where, in this case our metabolic health sort of takes a back seat, and going to the gym to throw some weights around isn’t as important.
Physical activity levels
In regards to physical activity, it has been found that participating in more anaerobic training can have a longer impact on the metabolism than aerobic style training. However, as with most things that pertain to the human body, there is no set mathematical formula that works for each person to raise their BMR . Anaerobic training will providing the training stimulus by which you can accrue lean body tissue, you won’t get this from traditional aerobic work, especially if it’s of the moderate to low variety type. Remember, the more lean body tissue you have, the greater your potential for a higher BMR. Not to mention, if you keep a high intensity during exercise, it will positively affect EPOC levels. This will cause temporary increases in your BMR following exercise.
Mental/ and Physical Health Status
A high level of stress and anxiety can cause an increase in your BMR, but will also likely cause a rise in cortisol levels (catabolic stress hormone). Easier said than done, but its best to avoid this type of stress and focus on the type of external stress that will only benefit you, i.e. Exercise. Anaerobic and aerobic exercise are both forms of external stress that ultimately yield an adaptation response, either an increase in muscular strength/hypertrophy or increase in cardiovascular conditioning, pending your goals.
The effects of foreign pathogens on our immune systems can also have implications on our BMR, such as when we have a fever, we will typically see a rise in BMR as our body uses more resources to fight off infection.
Gender
Studies done and published in the Journals of Applied Physiology showed men generally have higher resting metabolic rates than women. This is most likely due to the fact that men typically have more muscle mass. Another item to consider in tune to aging and gender differences has to do with regards to women and menopause. When the ovaries suddenly stop producing estrogen, they experience a disruption in their entire endocrine function, which leads to diminished muscle and bone mass. This in turn will further lower metabolic rates.
Supplements
Increasing BMRs is possible through the usage of certain supplements. Fat burners, pre-workouts, energy aids/drinks, coffee or other caffeine containing substances or compounds affect the sympathetic nervous system. The sympathetic nervous system then increases the BMR to accommodate for these products. This is also true for certain medications which may have stimulant type effects. Another factor to consider is nicotine, as this highly addictive compound is also a stimulant.
Current Dietary Demands
The types of food you are consuming, nutrient timing (to a certain degree), and current energy requirements will also affect your basal metabolic rate. If you are someone, for example, who is in prep for a physique competition and have been dieting for some time, your metabolic rate will be drastically different than what it was at the start of prep. For one, no matter how well planned your prep and how well methodical your planned weekly rate of loss is, you will still lose lean body tissue, i.e. muscle mass to a certain degree. Again this rate of loss is highly dependent upon those previously aforementioned variables along with the type of training you’re implementing.
Don’t forget, your metabolism is highly variable and highly adaptive and metabolic compensation must be taken into account when discussing caloric restrictions. If you’ve read any current nutrition based article or watch most YouTube videos on the topic, you’ll hear the phrase “metabolic adaptation” thrown around. Progressive restrictive modifications to our diets will overtime yield a slowing metabolism to a certain degree known as adaptive thermogenesis.
Also, let’s not forget the individual composition of your dietary needs. Diets higher in protein will likely have a higher associated BMR due to the thermic effect of protein, as compared to the other macronutrients. The thermic effect of each macronutrient is also often greater when you consume larger potions in one sitting, rather than spacing out over the course of the day. An interesting side note on the topic of the thermic effect of food, is that it is hypothesized in research that this effect is reduced in populations who are overweight or obese, which has been postulated in their efficient storage of fat. In general fasting or severely calorie restricted, low carbohydrate diets or being in a general malnourished state will lead to lower BMR levels.
Endocrine System
The overall function of our endocrine system will affect our basal metabolic rates. For example, thyroxin, a thyroid hormone, functions in regulating our BMR. Leptin levels will also affect our basal metabolic rates. Hormones are incredibly important and play a major role in chemical reactions throughout our bodies by either slowing down or speeding up reactions. For women, certain premenstrual hormones will also increase BMR, and once in the various stages of pregnancy, BMR remains slightly higher as well.
Conclusion
To conclude, there are many factors that contribute to and affect BMR. Some changes such as age, endocrine function, and body composition will inevitably change over time, but the rate at which they affect the BMR is highly variable due to supplements, mental health, nutrition, and exercise level. If you have any further questions on how any of these factors relate to your personal BMR or how to improve your BMR, do not hesitate to reach out to me.
Disclaimer
All programs and articles provided are intellectual property of James Shmagranoff. No copies or redistribution of these is allowed without express permission from James Shmagranoff. James Shmagranoff is not a doctor and nothing contained within this article is to be taken as medical advice. Always follow the directions of your medical practitioner.
Sources
F.X. Pi-Sunyer, Overnutrition and undernutrition as modifiers of metabolic processes in disease states, American Journal of Clinical Nutrition 72(2000);533S-537S.
J.T.Lemmer and coauthors, Effect of strength training on resting metabolic rate and physical activity: Age and gender comparisons. Medicine and Science in Sports and Exercise 33 (2001): 532-541.
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