On the other hand, RMR is the energy required by an animal to stay alive without activity, and it is only precise enough for practical purposes. It is only one of the main contributing components of energy expenditure- albeit a significant one, at 70%.
As RMR is a minimum threshold, the actual metabolic rate and demands will generally be quite a bit higher.
What goes into a resting metabolic rate?
For the majority of people (barring medical or physical abnormalities, such as hypothyroidism) RMR can be calculated from a few variables. These are:
- Lean (fat-free) body mass
For most of us, therefore, a resting metabolic rate calculator will be perfect for determining our own individual RMRs.
What can affect resting metabolic rate?
There will also be a few different things that can affect metabolic rate, showing that RMR is by no means fixed for anyone. These include:
- Your age: RMR decreases over time, as you age. This is a key reason behind common later life weight gain.
- Muscle mass: the higher your lean body mass, the higher your RMR, as muscle increases your metabolic rate.
- Genetics: there will be a significant genetic factor at work, meaning that RMR will only be best guess. Somebody more genetically predisposed towards burning energy will have a higher RMR than somebody who is not, regardless of biometric data.
- Climate and environment: cold weather can increase RMR, mostly through lifestyle factors. It is generally more energy demanding to move around in colder climates.
- Nutrient intake schedule: Generally, smaller, more regular meals will lead to a slight increase in RMR.
- Pregnancy: pregnancy will raise your RMR- you are eating for two, after all.
RMR will generally fall if you lose muscle. Losing fat alone, whilst maintaining or even increasing lean body mass, will not result in a lowered RMR. The best way to lose fat whilst retaining lean body mass (muscle) is to follow a moderate caloric deficit whilst engaging in resistance training and keeping protein intake high.
Crash diets, in which people lose several pounds or kilograms of bodyweight per week, are counterintuitive because of their effect on RMR. They will typically lower lean body mass (muscle mass) as well as body fat, meaning that resting metabolic rates fall. The body’s ability to process energy is therefore compromised and its ability to keep weight off- and stay healthy and structurally sound- is deeply impaired.
Digestive health, contrary to some popular opinion, has little to no bearing on RMR. RMR will not grow less efficient due to changing food intake, increasing fibre intake, or performing any of the other common hacks involved in improving digestion (though they are still worth doing for the sake of overall health). No more energy will be burned by an improved digestive system.
Finally, though genetics do form an important variable in determining RMR, their actual impact is low. Yes, it is true that genetics will alter somebody’s RMR, but research suggests the rate of variance is very low.
Knowing your RMR can mean the difference between success and failure with any dietary, health or fitness goal in mind. Knowing your body’s needs, requirements, and limitations with regards energy metabolism, will help you to keep yourself healthy and well-nourished, without allowing body fat reserves to grow too high. In short, you will be able to structure an appropriate, healthy, balanced diet when you know what your body requires, which will lead to significantly greater long-term health and wellbeing for most people.