Effect of weight loss on hormones

Sympathetic Nervous System Stimulation [1st day]

The first thing that will happen when you cut your food intake, your body will activate the sympathetic response. You might feel more energetic and more focused than typical. Your body is in a fight or flight response, so you can go find and kill that mammoth. I noticed these changes in my own experience. Despite the fact that I was eating less, I felt more focused, and energized. This made me think that dieting could be a great tool not only to lose weight but to endure hard times in our lives. Final exams, deadlines, stressful life situations – diet or fasting can help to maintain the energy and stay sharp.

Metabolic Adaptations [4th-5th day]

When experiencing reduced energy intake, you body takes over and does two things:

  1. Reduce Energy Expenditure
  2. Once Food Available – Regain Fat ASAP

Hormones regulate our body’s energy expenditure. For example, hormone Leptin drops 50% on the 3rd-4th day of dieting and continues to decline gradually over the course of weight loss. This hormone is being produced by your fat cells, therefore the more body fat you’ve got, the greater concentration of it is in your body. This is a satiety hormone, which regulates your hunger. The fatter you are  – the less hungry you should be (in theory). The lesser body fast you have – the lesser Leptin concentration, hence you feel hungrier. Got it?

Weight loss is a great stress for your body. In response to stress, you will have elevated stress hormones like Cortisol. As a result of this – your blood sugar level will also rise. Add to this cardio exercises, stress at work, lack of sleep and your brain will become resistant to Leptin – satiety hormone. You will easily overeat, because you don’t feel full anymore. 

This all leads to reduced metabolic rate. This is how your body adapts. It doesn’t care that you need six pack abs or want to look great for a wedding. The one thing that your body cares about is to survive at all costs.

Also, it’s worth mentioning that your body can do extraordinary things to conserve energy. It can turn on and off your emotions because they use up to 20% of the energy. Someone will tell you a joke, but you will react with a poker face. You will feel indifferent to dramatic movies during which you used to cry before. Forget about sex – no libido. Your body canal also turns that function off. Spontaneous activity decreases. Your movements will become much slower and predictable. The lower your body fat levels – the worse these symptoms can get. Your brain can even control how far you see, to decrease the amount of incoming information. This will save energy to process this information.

You can’t fool your body. Once you start dreaming about food – you’ve reached the bottom.