Basal metabolic rate (BMR), and the resting metabolic rate (RMR) are medical tests used extensively in the last century but has been all but forgotten by modern medicine. However they are still important in this era despite the marked advance of other technology. These are useful in many nutritional problems but it is particularly helpful in weight loss and thyroid disease. They cost $50, take 15 minutes and are done in the doctors office These measurements are the amount of energy used resting after fasting done at room temperature.. The release of energy in this state is sufficient only for the functioning of the vital organs, such as the heart, brain and liver. They decrease with age and loss of muscle and altered by hormones, drugs and diseases.
Cardiovascular fitness has been shown in the 1990s not to correlate with BMR and RMR, when fat-free body mass was adjusted. New research has shown aerobic exercise does not increase resting energy consumption. But stress levels can. BMR and RMR are measured by gas analysis through by direct calorimetry with devices such as the Reevue but a poor estimation can be acquired through an equations using age, sex, height, and weight.
Whether we gain or loose weight is dependent on our food consumption and energy expenditure. About 70% of a human's total energy outlay is due to the basal life processes of our vital organs. About 20% of one's energy expense comes from physical activity and another 10% from digestive and caloric heat processes. These mechanisms are referred to as Thermogenesis which comes from shivering and the volume of innate and genetic brown fat endowed to the individual. Life requires an intake of oxygen along with coenzymes (vitamins and minerals) to metabolize food. Anaerobic such as resistance training, but not aerobic builds additional muscle mass, which is fat free mass. Additional fat free mass will lead to a higher resting metabolic rate.
The regular Aerobic exercise is beneficial for cardiovascular reasons as well as direct calorie burning. Recent studies indicate that heavy endurance exercise increases resting metabolism. But light cardiovascular training has not the same effect. Continuous moderate exercise such as jogging or doing many light weight repetitions does consume calories, but not an “after burn”. On the other hand Aerobic Interval Training (AIT) or Progressively Accelerated Cardiovascular Exercise (PACE) not only consumed calories but also gives a significant after burn by increasing the BMR and RMR for 72 hours. This is why I recommend Burst Training (pushing to temporary respiratory fatigue)when doing aerobics. For example, when jogging, periodically run so fast that one is unable to do more than a minute because of extreme shortness of breath. This pushes past the aerobic state into an anaerobic one with an oxygen debt! This then resets the metabolic rate to a higher level. Doing a RMR/BMR not only predicts who will be overweight (obesity), but what how much one needs to do to loose that fat. For example there are ways to increase thermogenesis such as cosumption of bitter orange, ginger, capacisin, ephedra, guarana, and caffeine.
BMR/RMR is very helpful in diagnosing thyroid disease. In an overactive thyroid it is high and low in hypothyroidism, which has several varieties. A Secondary in which the pituitary is at fault and two Primaries which are Type I Hypothyroidism in which there is suboptimal Thyroxin production, but even more common is the Type II in which there is enough Thyroid Hormone, but the cellular receptors are blunted. The cell is less metabolically active despite adequate amounts of Thyroxin in the blood. With Type I the T4, and T3 are low and the Pituitary tries to stimulate the Thyroid by making more TSH that therefore is higher than normal. With Type II like in Type II Diabetes in which there is enough insulin but the cells are resistant to the effects of the hormone all these blood tests are normal. It is almost impossible to diagnose Type II Hypothyroidism for certain and to properly treat it without these test of metabolism, the BMR/RMR. In this day and age when we ingest so many hormone receptor disrupters in our pollutants (pesticides, plastic molecules etc) in our food and drink, no wonder why we are having an epidemic of Type II Hypothyroid that we physicians ignore. If you are having trouble losing weight or have symptoms of low thyroid such as fatigue, cold intolerance and yet have normal thyroid tests, get a RMR. You deserve to be fixed.