A surprisingly common complaint in the fitness industry is having a ‘slow’ metabolism. It’s used as a reason (or excuse, depending how you look at it) that prevents an individual from losing weight. But what is a slow metabolism? How does your metabolic rate affect your weight? How can you boost your metabolism? In this article we’re going to cover all things metabolism, to teach you how you can use resistance training as a tool to promote healthy and optimal metabolic function.
What is your metabolic rate?
When you eat and drink, your body has to process the energy and nutrients that the food contains in order to send them to where they need to be in the body to fulfill their specific function. The biochemical process of breaking down food, absorbing, transporting nutrients and storing calories is known as your metabolism. During the metabolic process, food is broken down, combined with oxygen and released into the bloodstream to be used, transported or stored.
Your metabolism isn’t an organ or a muscle, it’s a number of complex chemical processes that all contribute to how you use the calories you consume in your diet. Your metabolism is constantly working to provide the necessary fuel for your major organs — particularly the brain, heart, liver and kidneys — to ensure that they have the energy to keep fulfilling their functions in the body. As well as maintaining your vital organs, your metabolism also impacts other biological processes like the digestive system and lymphatic drainage. Everything is connected — and the metabolism is the fuel that keeps the engine running!
When you don’t have enough circulating energy and nutrients, it is the job of your metabolism to break down stored energy (stored in the form of triglycerides in adipose tissue and glycogen in the muscles). Similarly, when you eat more than you need to use, your metabolism helps these calories to be stored for later use.
Your metabolic rate refers to the rate at which you burn energy. Your basal metabolic rate (BMR) is the rate at which you burn energy at rest; burning the minimum amount of energy to perform the basic functions to sustain life like:
- Nutrient metabolism
- Cell production
Your basal metabolic rate contributes to roughly 70 percent of the total amount of calories a day you need to consume to sustain your energy levels, daily activities and basic biological functions. The total number of calories you need to consume per day is known as your total daily energy expenditure (TDEE), aside from your BMR, the remaining 30 percent that contributes to your total energy requirements includes:
- Non-exercise activity thermogenesis (NEAT) which includes walking, fidgeting, hand gestures and any activity that is not exercise based, and makes up 15 percent of your TDEE
- The thermic effect of food (TEF) which is the calories burnt from digesting the food you have consumed throughout the day, accounting for 10 percent of your TDEE
- Exercise activity thermogenesis (EAT) which is the amount of calories burnt during exercise, accounting for only 5 percent of your TDEE.
As shown in a study published in The American Journal of Clinical Nutrition, your metabolic rate is influenced by a number of variables including your:
- Activity level
- Body fat percentage
- Muscle mass percentage
- General health
Thus, your metabolism is a highly complex and personalized biochemical system — no two people will have the same metabolic rate.
How does your metabolic rate affect you?
Following on from the above, each person has a different metabolic rate depending on the above variables. If you are healthy and not diagnosed with any chronic health conditions, the likelihood is that you are metabolically healthy. A healthy metabolism is preferred, as it will help you to maintain a healthy body weight and use energy efficiently. A fast metabolism (hyperthyroidism) will burn through energy quickly, causing you to lose weight, while a slow one (hypothyroidism) will promote energy storage, causing you to gain weight. However, despite being a popular excuse, a slow metabolism is actually rare.
How to affect your metabolic rate?
One of the variables that affects your metabolic rate most notably is your activity level and physique. While you can’t change some variables like your height, you can change your weight, muscle mass, fat mass and activity level — all key contributors to your metabolic rate. One of the only scientifically proven ways to boost your metabolism is resistance training, to influence the effect of the aforementioned variables.
In Layman’s terms: if you want to become more metabolically efficient — i.e. burn calories, reduce fat storage, transport energy effectively — you need to start resistance training.
How does resistance training increase your metabolic rate?
Studies show that resistance training will help to promote metabolic health and efficiency by helping you:
- Build muscle mass — the more muscle mass you have, the more energy needed to maintain the muscle while at rest, increasing your BMR
- Lose excess fat — while this does slow down your metabolic rate because you are lighter and thus require less calories, you become more metabolically efficient because your body is metabolizing fat stores and restoring regularly.
- Increase your BMR — aside from building muscle mass to increase your BMR, when you regularly exercise, your body needs to repair damaged muscle tissue, replenish glycogen stores and modulate inflammation and toxins caused by exercise — these processes all require energy, increasing your BMR.
- Increase your NEAT — when you are more active you are engaging in more NEAT, like walking around the gym.
- Increase your EAT — while your exercise activity has a minimal effect on your metabolism (contributing to only 5 percent of your TDEE), ensuring you are doing intense resistance training will help give your metabolism the boost it needs.
If you want to maintain a healthy metabolism, there are some types of resistance training that are superior:
High intensity interval training (HIIT)
HIIT involves working at maximum capacity for between 15 to 45 seconds — followed by a short, sometimes active, rest period. This is then repeated for 10 to 15 minutes. When you do HIIT you create an oxygen deficit known as excess post-oxygen consumption (EPOC), which causes an increase in your metabolic rate.
A study that examined the effects of a six minute HIIT section found that the participants burnt up to 112 calories in the six minute workout. But due to the elevated metabolic rate, continued burning more calories over the next 24 hours, resulting in 457 calories burnt in total from this one six minute workout.
Lifting weights helps you to build muscle mass and lose fat, which both promote metabolic efficiency. A study found that after a 24 week clinical trial, the participants that did weight lifting saw a 9 percent increase in their basal metabolic rate.
As you can see, when you look at exercise in isolation, its affect on your metabolic rate is minimal, contributing to only 5 percent of your total energy expenditure. However, when you look at the bigger picture, you see that exercise — specifically resistance training — plays a big role in your metabolism. This is because of how it influences your body composition and activity levels, ultimately increasing how many calories you burn at rest and how efficiently you metabolize the energy consumed.