What happens in your body while you are losing weight?

Before you figure out your way through the jungle of diets, weight loss and fitness tips, it is important to know what exactly happens in your body while you are losing weight. What your body absorbs and what it breaks down easiest?

When you eat, your pancreas secretes a hormone, called insulin. It regulates the metabolism of carbohydrates and fats by promoting the absorption of glucose from the blood to skeletal muscles and fat tissue and by causing fat to be stored rather than used for energy.

The insulin moves along the blood system, collects sugars, fats, amino acids. They are being absorbed from the blood into fat cells, muscle cells and liver cells, where under stimulation by insulin, they are transformed into fat molecules and stored as fat droplets.

The body absorbs the fats, coming from food easiest

For our body it is much easier to absorb the fats, coming from food, than the glucose or amino acids. The conversion of carbohydrates or protein into fat is 10 times less efficient. If in your bloodstream are floating 100 extra calories from fat (about 11 grams), fat cells can store it using only 2.5 calories of energy. On the other hand, if in your bloodstream are floating 100 extra calories from glucose (about 25 grams), it takes 23 calories of energy to convert the glucose into fat and then store it. So the fat cell will grab the fat and store it rather than the carbohydrates because fat is so much easier to store.

If you are not eating – the insulin in the blood is little. But to function, your body is always using energy, so if it can’t get this energy from food it uses its internal stores of complex carbohydrates, fats and proteins. Various organs in your body secrete hormones: pancreas – glucagon, pituitary gland – growth hormone, pituitary gland – ACTH(adrenocorticotropic hormone), adrenal gland – epinephrine (adrenaline), thyroid gland – thyroid hormone. These hormones have the opposite effect on insulin on your liver, muscle and fat tissue.

The body breaks down the carbohydrates, coming from food easiest

For our body is easiest to break down the carbohydrates first, when it needs extra energy. Your body’s primary source of energy is glucose. It supplies almost all the energy for the brain, so its availability influences also psychological processes. When glucose is low, psychological processes requiring mental effort (e.g. self-control, effortful decision-making, attention, memory) are impaired.

The first thing, that your body does to get this energy is breaking down the carbohydrates, or glycogen, into simple glucose molecules. Next, your body breaks down fats into glycerol and fatty acids. The fatty acids can then be broken down directly to get energy, or can be used to make glucose through a multi-step process – gluconeogenesis. In gluconeogenesis, amino acids can also be used to make glucose.

In the fat cell, other types of lipases activated by various hormones, such as glucagon, epinephrine and growth hormone work to break down fats into fatty acids and glycerol. Once broken down, the fatty acids and glycerol travel trough the bloodstream to the liver, where they can be either further broken down or used to make glucose.

Where goes the fat that has been “burned” by your body?

In total 150 doctors, dietitians, and personal trainers were asked the question “When somebody loses weight, where does it go?” On Figure 1, below you can see their answers. It is surprising how many health professionals could not give a solid answer on what EXACTLY happens to fat when it’s lost.

Figure 1 – Responses of a sample of doctors, dietitians, and personal trainers to the question “When somebody loses weight, where does it go?” (Correct answer CO₂)

The correct answer is that most of the mass is breathed out as CO₂.

In a study, published in the British Medical Journal, Professor Andrew Brown and Ruben Meerman – a physicist and Australian TV science presenter – show that losing 10 kilograms of fat requires 29 kilograms of oxygen to be inhaled and that this metabolic process produces 28 kilograms of CO₂ and 11 kilograms of water. (Figure 2)

Figure 2 When somebody loses 10 kg of fat (triglyceride), 8.4 kg is exhaled as CO₂. The remainder of the 28 kg total of CO₂ produced is contributed by inhaled oxygen.

In the process of “burning” fat, the glucose in your body is oxidized and forms CO₂ and water, producing energy mostly in the form of Adenosine triphosphate (ATP).

What is the role of dopamine in the process of weight loss?

Scientists have recently found some similarities between the addictiveness to cocaine or alcohol and to food. When subjects at Monell Chemical Senses Center in Philadelphia were shown the names of foods they liked, the parts of the brain that got excited were the same that activate in drug addicts. It may be connected with dopamine, the hormone linked to motivation and pleasure, say researchers at Brookhaven National Laboratory in Upton, New York. If obese people have fewer dopamine receptors, they may need more food to get that pleasure.

When there is a greater gap between your meals throughout the day, your body will have lower dopamine levels, leading you to overindulge your hunger cravings. You eat and you get pleasure from food, which is much higher as if you eat more often throughout the day. Your mind is programmed to seek what gives you pleasure and send impulses to do it again. When your dopamine levels immediately fall, your body sends signals to your brain, which make you look for food and eat it immediately and in bigger quantities than usual. As your dopamine levels deplete, your food cravings will return because the body needs to have stabilized levels of the chemical.

When you lose weight, the number of fat cells in your body remains the same. What changes is their size – they get smaller. Which means, that a healthy weight has to be maintained via a balanced diet and active way of life (regular exercises, sport, walking etc.). Depending on your weight, age, height and sex your body needs different amount of calories to maintain your current weight. You can use our BMR Calculator to calculate how many calories you need to take per day, to maintain your current weight. If you take more than this, you’ll gain weight and if you take less – you will lose weight – simple like this! What matters is from where these calories are coming in and how easy it is for your body to process them or store them. Have also in mind, that as you lose weight, the body’s energy requirements decrease.

Useful links:
Does it matter what you eat if you want to lose weight? – http://fatorwhat.com/what-to-eat-to-lose-weight/
Insulin – https://en.wikipedia.org/wiki/Insulin
Glucose as an energy source – https://en.wikipedia.org/wiki/Glucose#Energy_source
Chylomicron – https://en.wikipedia.org/wiki/Chylomicron
BMR Calculator – http://fatorwhat.com/bmr-calculator/
Adenosine triphosphate (ATP) – https://en.wikipedia.org/wiki/Adenosine_triphosphate
Glycolysis – https://en.wikipedia.org/wiki/Glycolysis
When somebody loses weight, where does the fat go? – http://www.bmj.com/content/349/bmj.g7257 http://www.science.unsw.edu.au/news/study-when-you-lose-weight-where-does-fat-go
Dopamine – https://en.wikipedia.org/wiki/Dopamine