Many people claim that they cannot lose weight because they have a slow metabolism and are constantly looking for ways to boost their metabolism. A lot of these people do not truly understand the term metabolism. According to Wikipedia:
“Metabolism is a set of chemical reactions that occur in living organisms in order to maintain life”
In humans the food we eat fuels these chemical reactions. So when people refer to a fast or slow metabolism they are generally referring to the average amount of calories their body burns in a day. There are three main factors that affect your metabolism:
1) BASAL METABOLIC RATE (BMR):- This is the amount of energy you use to perform the basic functions that keep you alive e.g. if you lied in bed all day and burned 1000 calories then your BMR would be 1000 calories per day. You can roughly estimate your BMR by multiplying your weight in pounds by 14 if you are male and by 12 if you are female e.g. if you are male and weigh 150lbs your BMR will be about 2100 calories. You can also use this BMR calculator. BMR has the biggest influence on your metabolism and normally accounts for 60% to 65% of the calories you consume. Your BMR is largely down to genetics but there are a number of things that can affect it:
- Building muscle:- This can increase your BMR as muscle requires more calories to maintain than fat.
- Dehydration:- This can contribute towards a low BMR as it prevents your body from performing a number of basic functions.
- Illness:- Illness can significantly affect the way your body works and therefore influence your BMR. Thyroid conditions in particular can have a major influence over your BMR.
- Supplements:- Certain supplements can slightly influence your BMR.
- Vitamin or Mineral Deficiency:- This can reduce your BMR if it stops your body from performing basic functions properly.
- Weather:- This has an impact on your BMR because your body will have to use extra calories to warm you up or cool you down depending what the weather is like outside.
2) PHYSICAL ACTIVITY:- Certain people are more active than others. More active people will burn more calories through physical activity than less active people. This has the second largest influence on your metabolism using between 25% and 30% of the calories you consume.
The amount of physical activity you do each day is something that you can directly influence. If you drive to work, sit at a desk all day, drive back home, watch TV, go to bed and repeat then you are not going to burn many calories through physical activity. However, if you make physical activity part of your lifestyle and do a little bit of activity each day it can quickly add up to a lot of calories burned.
3) THERMIC EFFECT OF FOOD:- Food cannot digest itself. This process requires calories too. Digestions has the third largest influence on your metabolism and uses around 10% of the calories you consume. You cannot hugely increase the amount of calories you burn through the foods you eat. However, certain foods do have a better thermic effect than others:
- Fibre:- Complex carbohydrates that are high in fibre such as fruits, vegetables and whole grains burn more calories during digestion than simple carbohydrates such as white bread, white pasta and sugary foods.
- Protein:- Protein is thought to burn two to three times the amount of calories that carbohydrates and fats do during digestion. Furthermore, according to a study from McArdle et. al (1986)  when eating a meal that consists of pure protein up to 25% of the calories consumed can be used during digestion and absorption.
- Spicy Foods:- Spicy foods can temporarily increase the amount of calories you burn. This is because certain spices are thought to stimulate fat burning. On top of this spicy foods temporarily raise your body’s temperature after you eat them meaning you burn more calories.
So there you have it. There are three main things that affect your metabolism; your BMR, your physical activity and the thermic effect of the foods that you eat. Although you can have some influence over your metabolism and increase the amount of calories you burn each day there is no magic way to drastically increase your metabolism (unless you do A LOT of exercise every day). What you eat and how much you eat has a much larger influence over how much weight you gain or lose. To maintain or lose weight:
“The Calories you Consume = BMR + Physical Activity + Thermic Effect of Food”
Good luck with your fitness goals!