This word “metabolism” is thrown around a lot these days. We say kids have a fast metabolism when they run around all day and need feeding every couple of hours. We presume our metabolism slows down as we age and become more tired. Apparently if we eat too much or too little it might slow our metabolism down. People often say they have a slow metabolism as a reason for putting on weight easily. Confusing, right!
So what is metabolism and is mine slow?
Well technically “metabolism” is the word to describe all of the biochemical reactions in your body that keep you alive. It’s how you take in nutrients from food, oxygen from air and use them to fuel everything you do.
Your body has an incredible ability to grow, heal, and generally stay alive. And without this amazing biochemistry you would not be possible.
Metabolism includes how the cells in your body:
- Allow activities you can physically control (e.g. moving your arms & legs).
- Allow activities you can’t control (e.g. heart beat, wound healing, processing of nutrients & toxins).
- Allow storage of excess energy from food for later.
When you put all of these metabolism processes together you can imagine that some might work too quickly, too slowly, or just right.
Which brings us to the “metabolic rate”.
There are a couple of different ways to measure metabolic rate. One is the “resting metabolic rate” (RMR) which is how much energy your body uses when you’re not being physically active.
The other is the “total daily energy expenditure” (TDEE) which measures both the resting metabolic rate as well as the energy used for “work” (e.g. exercise) throughout a 24-hour period.
This is how fast your metabolism works and is measured in calories (yup, those calories!).
The calories you get when you eat food will be used in one of three places:
- Work (i.e. exercise and other activity).
- Heat (i.e. from all those biochemical reactions).
- Storage (i.e. extra leftover “unburned” calories stored as fat).
As you can imagine the more calories you burn as work or by creating heat the easier it is to lose weight and keep it off because there will be fewer “leftover” calories to store for later. But don’t worry – we know that metabolic rate is much more complicated than the old adage “calories in calories out”! In fact it’s so complicated I’m going to list a few of the common things that can slow it down.
What affects your metabolism?
In a nutshell: a lot!
Examples of common reasons why your metabolism can slow down:
- low thyroid hormone
- your history of dieting
- your size and body composition
- your activity level
- lack of sleep
- the type of food you eat
We’ll briefly touch on each one below and I promise to give you better advice than just to “eat less and exercise more”.
The first thing you may think of is your thyroid. This gland at the front of your throat releases hormones to tell your body to “speed up” your metabolism. Of course, the more thyroid hormone there is the faster things will work and the more calories you’ll burn.
Low thyroid hormones
Your thyroid is the master controller of your metabolism. When it produces fewer hormones your metabolism slows down. The thyroid hormones (T3 & T4) tell the cells in your body when to use more energy and become more metabolically active. Ideally it should work to keep your metabolism just right. But there are several things that can affect it and throw it off course. Things like autoimmune diseases and mineral deficiencies (e.g. iodine or selenium) for example.
Tip: Talk with your doctor about having your thyroid hormones tested.
But that’s not the only thing that affects your metabolic rate.
Your history of dieting
When people lose weight their metabolic rate often slows down. This is because the body senses that food may be scarce and adapts by trying to continue with all the necessary life functions and do it all with less food.
While dieting can lead to a reduction in amount of fat it unfortunately can also lead to a reduction in the amount of muscle you have. As you know more muscle means faster resting metabolic rate.
Tip: Make sure you’re eating enough food to fuel your body without overdoing it.
Your size and body composition
In general, larger people have faster metabolic rates. This is because it takes more energy to fuel a larger body than a smaller one.
However, you already know that gaining weight is rarely the best strategy for increasing your metabolism. Larger people have higher metabolic rates; but your body composition is crucial!
As you can imagine muscles that actively move and do work need more energy than fat does. So the more lean muscle mass you have the more energy your body will burn and the higher your metabolic rate will be. Even when you’re not working out.
This is exactly why weight training is often recommended as a part of a weight loss programme. Because you want muscles to be burning those calories for you.
When people lose weight their metabolic rate often slows down which you don’t want to happen. So you definitely want to offset that with maintaining, or even increasing your muscle mass as you lose weight.
Aerobic exercise also temporarily increases your metabolic rate. Your muscles are burning fuel to move so they’re doing “work”.
Tip: Do some weight training to help increase your muscle mass.
Which leads us to…
Your activity level
Aerobic exercise temporarily increases your metabolic rate. Your muscles are burning fuel to move and do “work” and you can tell because you’re also getting hotter.
Even little things can add up. Walking a bit further than you usually do, using a standing desk instead of sitting all day, or taking the stairs instead of the elevator can all contribute to more activity in your day.
Tip: Incorporate movement into your day. Also, exercise regularly.
Lack of sleep
There is plenty of research that shows the influence that sleep has on your metabolic rate. The general consensus is to get 7-9 hours of sleep every night.
Tip: Try to create a routine that allows at least 7 hours of sleep every night. If you are interested in learning more tips for improving your sleep, check out our article on Coronasomnia here
Finally, The type of food you eat also affects your metabolism!
Your body actually burns calories when it is absorbing, digesting, and metabolising your food. This is called the “thermic effect of food” (TEF).
You can use it to your advantage when you understand how your body metabolises foods differently.
Fats, for example increase your TEF by 0-3%; carbs increase it by 5-10%, and protein increases it by 15-30%. By trading some of your fat or carbs for lean protein you can slightly increase your metabolic rate.
Another bonus of protein is that your muscles need it to grow. By working them out and feeding them what they need they will help you to lose weight and keep it off. At the bottom of this article we have included a great recipe for lemon roasted chicken breasts that will fill your protein need!
This is just the tip of the iceberg when it comes to metabolism and how so many different things can work to increase (or decrease) your metabolic rate.
Recipe (Lean Protein): Lemon Herb Roasted Chicken Breasts
2 lemons, sliced
1 tablespoon rosemary
1 tablespoon thyme
2 cloves garlic, thinly sliced
4 chicken breasts (boneless, skinless)
dash salt & pepper
1 tablespoon extra virgin olive old
Preheat oven to 220 C/180 C Fan. Layer ½ of the lemon slices on the bottom of a baking dish. Sprinkle with ½ of the herbs and ½ of the sliced garlic.
Place the chicken breasts on top and sprinkle with salt & pepper. Place remaining lemon, herbs and garlic on top of the chicken. Drizzle with olive oil. Cover with a lid or foil.
Bake for 45 minutes until chicken is cooked through. If you want the chicken to be a bit more “roasty” then remove the lid/foil and bake for another few minutes (watching carefully not to burn it).
Serve & enjoy!
Tip: You can add a leftover sliced chicken breast to your salad for lunch the next day!