Understanding your calorie needs is a key step in your journey to effectively manage your weight, and the first thing you need to pay attention to is your Basal Metabolic Rate (BMR). In this article we cover everything you need to know about BMR, so read on

What is Basal Metabolic Rate (BMR)

BMR is the minimum number of calories our body needs to perform life-sustaining functions such as breathing, blood circulation, brain activity, cell production and so forth. On average, these basic functions account for 60-75% of our total daily energy expenditure (TDEE). Note that BMR only indicates the calories you burn while at rest (minimal to no movement) and doesn’t account for the calories you expend going about your daily life, such as walking, doing house chores etc. In order to determine how many calories you burn in a typical day that take into account your activity level, you will need to calculate your TDEE.

Why is BMR important?

BMR is not a fixed number and can vary between individuals (more on this below). A baseline estimate of your minimum calorie needs (BMR) is therefore an important starting point that will allow you to take a customized approach towards your goals.

 Regardless of you want to achieve (weight loss, weight gain, weight maintenance, muscle building), your BMR can act as a reference point from which you can manipulate your calorie intake that matches your goals. 

Consistently eating too few calories than your body needs can have a diminishing effect on your metabolism, and getting an idea of your BMR will help you to take a safe and healthy approach towards your diet and fitness goals.

Factors that affect your BMR

Amongst others, individual characteristics such as age, sex, body composition, and diet history have an impact on the rate at which we expend energy. 

Age: The rate at which we burn calories starts to decline as we age due to, amongst others, loss of muscle mass, reduced activity, and hormonal changes. By contrast, young people require a constant supply of energy to maintain a steady growth, as a result tend to burn calories at a higher rate .

Sex: Men tend to have higher BMR than women as they typically have more muscle mass, therefore burn more energy at rest than do women.

 Body composition: Muscle tissue requires more energy to maintain than fat tissue. So, people with high lean body mass (specially muscle mass) tend to burn more calories at rest than people with higher body fat.

Diet history: People who heavily restrict their calorie intake, through extreme dieting for example, may have slower metabolism (decreased BMR) than people who maintain regular (or close to regular) calorie intake.

How do you determine your BMR?

 Laboratory testing gives you the most accurate reading of your BMR, however it is not necessary, nor practical, as there are are readily available tools that you can use to get a fair estimate.

  • You can use a formula like the Harris-Benedict Equation below, all you need to do is insert your weight, height, and age to establish your BMR.
    • Men: 88.362 + (13.397 × weight in kg) + (4.799 × height in cm) – (5.677 × age in years)
    • Women: 447.593 + (9.247 × weight in kg) + (3.098 × height in cm) – (4.330 × age in years)
  • Using  an online calculator, such as this one, is the easiest way to get an estimate of your BMR. You simply need to enter your weight, height, and age when prompted.

Should I eat below my BMR to lose weight?

 It is generally advised that the average calorie intake should not drop below 1200 (for adult female) and below 1800 (for adult male).  It is therefore best to consider the following factors before following a program that heavily restricts your calorie intake (especially if your BMR hover around the above numbers)

Slowed metabolism: Eating below your minimum calorie needs for prolonged period will likely cause your metabolism to slow down. This is because your body raises its defense mechanism for its survival and starts to conserve energy (store fat) by lowering the rate at which you burn calories (metabolic adaptation).

Loss of muscle mass: Excessive calorie deficit over a long period will also put you at risk of accelerated muscle loss (up to 40% of total weight loss) as your body resort to tearing down muscle tissue to use for energy. This will have an effect on the speed at which you burn calories while at rest.

What does this mean for weight loss?  The calorie deficit you had originally created may no longer be viable as your BMR has now declined . To lose weight, you may need to cut your calories even further, which can lead to more muscle loss and even slower metabolism. Eventually, progressively larger reductions in calorie intake may start to compromise your health as other problems such as nutrient deficiencies, hormone irregularities, fatigue, and cognitive decline may follow.

Eating below your BMR isn’t necessarily bad, if done for short length of time, we all do it time to time. However, it is worth baring in mind that consistently eating below the calories your body needs to function optimally may come with unintended consequences. And this may impact not only your weight management goals but also your overall health.

How can I increase my BMR?

There are certain biological features that we cannot change, such as our age and sex, both of which can impact the rate at which we burn calories. However, building muscle, ensuring adequate protein intake and getting sufficient sleep are the most important (evidence-based) measures you can take towards increasing your BMR. Let’s look at these in turn.

Train to build muscle: As mentioned before, having more muscle mass can elevate the calories you burn at rest. Making strength training a part of your lifestyle will not only increase your BMR, but also allow you to lead an active lifestyle which in turn increases your overall calorie burn. Research shows that incorporating weight training, even few times a week, can also offset the muscle loss that comes with getting older, and help you avoid the BMR reduction associated with rapid weight loss. There are many ways you can perform strength training, including body weight exercises (such as squats, planks, pull ups, push ups), using free weights (dumbbells, kettlebells, barbells), resistance bands, as well as weight machines in a gym.

Increase your protein intake:  Aiming for a higher protein intake in your diet, among other benefits, will help give your metabolism a major boost. How? First, protein has a relatively higher thermic Effect of Food (TEF), this means your body expends substantially more energy to digest and metabolize protein (20-30% of total intake) than it does for fats (0-5%) or carbs (5-15%). Second, protein is the most satiating (feeling fuller for longer) macronutrient than fats and carbs (mainly due to its TEF), and improving your intake may help you maintain your BMR even while eating at calorie deficit. Third, eating adequate protein (1.2-1.6g per kg), combined with resistance training), is the foundation to muscle building and maintenance of lean body mass, both of which stand to improve your BMR. 

Maintain adequate sleep: The vital importance of getting a good night sleep can’t be overstated, and you should maintain a regular sleep schedule with the aim to get uninterrupted 7-8 hours of sleep.

Lack of sufficient and quality sleep can have wide ranging impact that can affect, among others, your ability to maintain optimal metabolic rate. It can alter your hormones, leading to elevated gherlin and cortisol levels (responsible for appetite increase), and a decrease in the circulating levels of  leptin (responsible for regulating hunger). 

Although more research is needed,  sleep deprivation is also believed to result in metabolic adaptation in a similar way excessive calorie restriction and physical inactivity would, leading to lowered BMR.  Reduced quality (and quantity) of sleep may also put you in an elevated risk for muscle mass reduction, which, as we have seen throughout this article, is a primary contributor to decreased BMR.  

References

Connolly, J., Romano, T., Patruno, M. (1999). Effects of dieting and exercise on resting metabolic rate and implications for weight management, Family Practice, 16 (2), 196–201 

Johannsen, D., Knuth, ND., Huizenga, R.,  Rood JC., Ravussin E., Hall KD. (2012). Metabolic slowing with massive weight loss despite preservation of fat-free mass. J Clin Endocrinol Metab. 97(7), 2489-96.

McCarthy D., Berg A. (2021). Weight Loss Strategies and the Risk of Skeletal Muscle Mass Loss. Nutrients. 13(7), 2473.

Ravn, A. M., Gregersen, N. T., Christensen, R., Rasmussen, L. G., Hels, O., Belza, A., Raben, A., Larsen, T. M., Toubro, S., & Astrup, A. (2013). Thermic effect of a meal and appetite in adults: an individual participant data meta-analysis of meal-test trials. Food & nutrition research, 57, 10.3402/fnr.v57i0.19676

Johnston CS., Day CS., Swan PD. ( 2002). Postprandial thermogenesis is increased 100% on a high-protein, low-fat diet versus a high-carbohydrate, low-fat diet in healthy, young women. J Am Coll Nutr. 21(1), 55-61

Leidy, H. J., Clifton, P. M., Astrup, A., Wycherley, T. P., Westerterp-Plantenga, M. S., Luscombe-Marsh, N. D., Woods, S. C., & Mattes, R. D. (2015). The role of protein in weight loss and maintenance. The American journal of clinical nutrition, 101(6), 1320S–1329S.

Schmid, S. M., Hallschmid, M., Jauch-Chara, K., Born, J., & Schultes, B. (2008). A single night of sleep deprivation increases ghrelin levels and feelings of hunger in normal-weight healthy men. Journal of sleep research, 17(3), 331–334

Penev P. D. (2012). Update on energy homeostasis and insufficient sleep. The Journal of clinical endocrinology and metabolism, 97(6), 1792–1801. 

Hanna Haile is a Registered Associate Nutritionist with specialty in global public health nutrition and health promotion. Hanna is the Founder of Heritage Nutrition and  provides culturally-inclusive guidance to people from diverse backgrounds. Her work revolves around helping clients realise their nutritional and health goals through a set of evidence-based dietary and lifestyle strategies. Hanna is also a health & Nutrition writer and Published Author in Journal of World Public Health Nutrition. 

 

Disclaimer: This article is not, nor does it try to be, a substitute to the advice of your medical care. You should follow the treatment and recommendations of your doctor and specific dietician at all times. Please check out our full disclaimer on our website here