WHAT IS THERMOGENESIS
Thermogenesis means the generation of heat, and it is what is keeping you alive right now. A lot of people are aware of thermogenesis, but many think that it applies solely to your metabolism. Whilst they’re not wrong – thermogenesis directly affects your metabolism, there’s a lot more to it than that.
The first thing you should understand is that your body can only withstand a drop in body temperature of 10 degrees, and a rise in temperature of 5 degrees. That really isn’t much is it? Luckily your Hypothalamus has you covered.
The Hypothalamus is situated in the centre of your brain and is responsible for a process known as thermoregulation (finding a temperature balance). When you are very cold your Hypothalamus (or more accurately the primary motor centre that is found within the Hypothalamus) can cause your muscles to shiver. This can increase your metabolism five-fold and will raise your body temperature.
On the other hand, if you begin to get too hot, either from the weather or from aerobic/anaerobic exercise your Hypothalamus will cause you to begin to sweat. This will lower your body temperature. Both of these are examples of thermoregulation.
The purpose of thermoregulation is to keep your body temperature at the perfect balance, this is known as Homeostasis. Thermoregulation is one control for Homeostasis but it is not the only one, the body also regulates blood glucose, calcium levels, the partial pressure of o2 and Co2, blood pressure etc ….
There are three factors that make up your metabolism, these are: Your Resting Metabolic Rate (RMR), the Thermic Effect of Food (TEF), and the Thermic Effect of Exercise (TEE). Add all of these together and you will have an idea of how many calories you are using each day. Your RMR is responsible for between 60 and 75% of your daily calories burned, whilst your TEF is 10% and your TEE is between 15 and 30% (depending on how active you are).
When people talk about exercises or foods that can boost your metabolism, a lot of people think that this means that they boost it for life… that your metabolism is like a savings account that you add money to. But these exercises and foods will only temporarily boost your TEF and TEE and as you can see, they only make up 25-40% of your calories per day.
Making long term changes to your metabolism is something that is difficult to do, but it is what is responsible for long term weight maintenance (after you have lost the initial weight). Temperature can also affect your daily calories burned as we saw at the beginning of this article.
THE THERMIC EFFECT OF FOOD
If you’ve spent any time looking at the facebook wall of someone who has recently started exercising then you’ve probably seen a comparison picture of the calories in a Snickers bar, and the amount of exercise that it would take to burn it off. Well here’s some good news, the comparison is way off. Sure there are 223 calories in a Snickers bar, and walking for 10,000 steps burns 223 calories, but it’s nowhere near as simple as that.
For starters, as we’ve already mentioned; your RMR is responsible for 60-75% of the calories that you burn daily. Secondly, due to something called NEAT (which we will go into in a bit) the majority of your calories burned by your activity levels don’t actually involve exercise.
But most importantly of all, you burn calories eating! The act of consuming and digesting that snickers bar would actually burn calories, not many (don’t let people start telling you that negative calorie foods are a thing) but enough to change the equation.
As you know all foods are made up of three main macronutrients: protein, fat, and carbohydrates (we won’t be looking at alcohol though it is technically the fourth macro). Each macronutrient has a different thermic effect.
Protein has the highest  with 25-30% of the calories consumed being used to digest it, this is because protein is the hardest macro to break down meaning the body has to spend more energy doing so. Carbohydrates and fats both have a thermic effect of around 5-15% .
So for the sake of argument let’s say that fat is 10%, carbohydrates are 10%, and protein is 25%. The Snickers bar is 223 calories (11g fat, 3g protein, 28g carbohydrates). The 11g of fat equals 99 calories (fat is 9 calories per gram), the 3g of protein is 12 calories (protein is 4 calories per gram), and the 28g of carbohydrates are 112 calories (carbs are also 4 calories per gram).
So let’s take away 10% of the fat (9.9 calories), 25% of the protein (3 calories), and 10% of the carbohydrates (11.2 calories). This comes to 24.1 calories, meaning that you don’t need to work off 223 calories – you have to work off 198.9 calories. Remember, this is the low end of the scale. We could have done this equation with 15% for fats and carbohydrates, and 30% for protein.
Obviously if you ate one Snickers bar and didn’t perform any form of exercise, then you would gain weight. But even if you consider yourself sedentary, you are still underestimating how many calories you are burning. This is thanks to …
THE THERMIC EFFECT OF EXERCISE
Physical activity can make up between 15 and 30% of the total calories burned in a day , this ratio can change depending on a lot of factors (how much you eat, how high your RMR is etc) but it is basically dependant on how active you are. People think that active exclusively means “time spent in the gym or running in a park” but physical activity is basically performing any movement at all.
Of course exercising will burn a lot more calories than sitting at a desk typing an email, but the act of typing will still burn calories! And if you spend 6 hours sitting at that desk typing then you will have burned 336 calories (typing burns 56 calories/hour in a 150lb man) . In other words you could probably manage 1.5 Snickers bars and still lose weight!
This form of activity is known as Non Exercise Activity Thermogenesis (NEAT) and it covers all forms of movement that are not exercise: walking, climbing stairs, doing the washing up, cooking, cleaning, even fidgeting whilst watching a movie. The calories burned per activity are barely significant when looked at individually, but they add up to a lot of calories burned during the day.
Remember that these ratios we mentioned (60-75% RMR, 10% TEF, and 25-40% TEE) are not set in stone, and to a point you can out-train a bad diet (though this is obviously not optimal).
There are two ways in which the temperature outside can affect you, it’s either too hot or too cold. When it’s too hot your body will try to cool you down using 4 processes, these are: Radiation, Conduction, Convection, and Evaporation.
Heat will evaporate from your body via sweat and respiration, your body will also transfer warm blood to superficial blood vessels (i.e. ones close to the skin). This can lead to a flushed or reddened face.
When it is too cold outside and you are trying to preserve heat, your body will also make changes. It will divert blood away from your extremities (face, hands, feet etc) and sends it to your core, which will then keep you better insulated. Your body can also increase your thermogenesis by shivering, this can greatly increase your metabolism and keep you warm as a result.
It is for this reason that if you travel to a very cold climate you are required to increase your daily calorie intake due to the heightened metabolism you would automatically get. However this does not mean that you would lose a load of weight, as your NEAT levels would also lower to compensate.
A lot of people believe that training in very hot or very cold climates would lead to increased calories burned, but as awesome an idea as that is, it’s sadly untrue. The problem is that whilst your calories would increase in a cold environment, your performance would suffer. This would mean that you were unable to exercise at the same intensity, which means that you wouldn’t be able to burn any additional calories.
The same issue would affect anyone trying to train in an overly hot environment, as Hettinga et aldiscovered in their study: training at high temperatures led to poorer performance in a 20 minute cycle . The fact is that if you want to burn calories through exercise, then you should put your efforts into creating the optimal conditions in which to exercise – that will lead to you being able to work out harder, and therefore burn more calories.
Trying to burn calories by wearing a sauna suit is like trying to run better by wearing concrete shoes, yes it is more difficult, but all it would do is prevent you from running properly!