Variables that Affect Your Basal Metabolic Rate (BMR)

There are a number of different factors that can make an individual overweight, such as genetics and the obvious components of diet and exercise. While no one factor is a definitive indicator of the cause of weight gain, one such measure has been growing in popularity in recent years. This measure is known as your basal metabolic rate, or BMR.

Basal metabolic rate essentially refers to the amount of energy that your body expends when at rest in a neutrally temperate environment. It is also necessary for the digestive system to be inactive, which requires at least a 12-hour fast.

Your sympathetic nervous system, essentially your fight or flight system, must be inactive as well. When all of these elements are in place, your Basal Metabolic Rate refers to the amount of energy, in calories, that your body expends when simply running the necessary mechanisms within your body. This primarily refers to the amount of energy required for your vital organs and various systems to function properly.

Knowing your BMR is important for a variety of different reasons. For instance, the higher your BMR, the more calories you burn on a daily basis. Thus, individuals with a higher BMR tend to be better aligned with their target weight when compared to individuals with a lower BMR. BMR has been cited as one of the major genetic components that cause obesity. While BMR itself cannot cause obesity, it can place an individual at a much higher risk of becoming obese during their lifetime. Several recent studies have found a possible connection between an individual's BMR and their expected lifespan, though this research is still considered inconclusive.

There are several variables that can affect an individual's BMR. These variables include the types of foods and beverages consumed, illnesses, external temperature, amount of physical activity and stress level. For instance, individuals that live in colder climates are often reported as having higher BMRs on average. The reason for their higher BMR level is the fact that their physical body is required to expend more energy in order to maintain a constant body temperature. Several additional variables that have been medically proven to affect an individual's BMR are as follows:

• Genetics - Some individuals are born with a higher metabolism, while others have a lower metabolism. 

• Gender - In general, men have a higher density of lean muscle mass and a lower body fat percentage. Because of this, men tend to have higher BMRs.

• Age - An individual's BMR reduces as they age. After the age of 20, an individual's BMR decreases by approximately 2%, per decade.



• Weight - The heavier the individual, the higher their BMR. For instance, the BMR of an obese women is 25% higher than the BMRs of thin women.

• Body Surface Area - The body surface area variable is related to an individual's height and weight. The larger an individual's body surface area, the higher their Basal Metabolic Rate. For instance, when comparing a tall individual to a short individual of the same weight where they both follow a calorie-controlled diet to maintain the weight of the taller individual, the shorter individual will most likely gain up to 15 pounds per year.

• Body Fat Percentage - The lower an individual's body fat percentage, the higher their BMR. This is one reason why men typically have a BMR that is 10-15% higher than that of women.

• Diet - Starvation diets typically reduce an individual's BMR by as much as 30%. Low-calorie, restrictive weight loss diets can cause an individual's BMR to decrease by as much as 20%. This is why most individuals find it difficult to lose the last 5 to 20 pounds of weight. 

• Body Temperature - The BMR of an individual increases approximately 7% for every increase of 1.36 degrees fahrenheit in the internal temperature of their body. The internal chemical reactions that take place within the body actually occur more quickly at higher temperatures.

• External Temperature - The external temperature of the body also has the ability to affect an individual's BMR. Exposure to cold temperatures causes an individual's BMR to increase, due to the fact that the body must provide additional heat to maintain its optimal internal temperature. Likewise, prolonged exposure to heat can raise an individual's BMR as the body must expend energy to prevent its internal temperature from rising.

• Glands - Thyroxin (produced via the thyroid gland) is one of the primary BMR regulators. The higher the level of thyroxin production, the higher the BMR. Thyrotoxicosis, a condition in which too much thyroxin is produced, can cause an individual's BMR to double. On the other hand, Myxoedema, a condition in which too little thyroxin is produced, can cause an individual's BMR to decrease to 30% to 40% below their normal level. Adrenaline, to a lesser degree, can also increase an individual's BMR.

• Exercise - Physical exercise is not only responsible for burning calories, but also for increasing an individual's BMR due to the additional lean muscle mass that is created as a result of exercise. Lean muscle tissue is much more metabolically demanding than fat tissue, so an individual will burn more calories even while sleeping.  

Long-Term Changes

While the aforementioned reasons for changes in one’s BMR are mostly due to temporary external variations, there are a few variables that can produce long-term changes in an individual's personal BMR. One such variable is menopause, which can either increase or decrease an individual's BMR due to the hormonal changes that are occurring in the body. Weight training, as opposed to aerobic training, has also been cited as a mechanism that can increase a person's long-term BMR. On the other hand, medical studies have conclusively determined that as the human body ages, the BMR of a person decreases. This fact, as depicted in Table #1, coupled with the probability that as an individual ages their level of physical activity will decrease, answers the question as to why human beings tend to gain weight as they age.

This section of our website is designed to provide information that is focused on a variety of topics related to an individual's BMR and how it pertains to body weight, methods for calculating an individual's personal BMR, and dietary and physical activity approaches that will facilitate a synergistic weight loss strategy. In addition, our weight loss section includes discussions related to caloric intake approaches, setting weight loss goals, dietary approaches to weight loss, specific weight loss programs, general and targeted weight loss fitness routines, and weight loss strategies.