How losing weight works
First you need to understand how your metabolism ties into weight loss. To lose weight, you need to take in fewer calories (eat less) than you burn off (your resting metabolic rate plus activity). Seems straight forward, adjust your calorie intake based on your calorie expenditure and you’re done. Unfortunately, this is very hard to measure precisely and on top of that, it’s not a static equation!
Your body is smart it wants to avoid starvation
The human body went through millions of years of evolution and has survival, not aesthetics, as top priority. If you start eating less, the calorie intake goes down. In response, your body expends less energy too to match the new intake and protect the current weight. Your body doesn’t care that you want to look shredded it wants to avoid losing energy reserves at all costs. How does it save energy when you eat less and start losing weight?
1. Calories not absorbed go down as your body tries to get more out of less food.
2. Calories burned through exercise (and other activities) go down since you weigh less.
3. Thermic effect of eating goes down because there’s less food coming in.
4. Resting metabolic rate goes down because you weigh less.
5. On top of that, eating less also causes hunger signals to intensify. All of this results in less weight loss than would be predicted be the static calories-in and calories-out equation.
Gaining and losing fat changes how your brain regulates body weight
Losing weight is accompanied by adaptive metabolic, neuroendocrine, autonomic, and many other internal changes. The above described metabolic adaptations alone show that those who have lost weight will expend fewer calories than people who were always slim. Studies confirm this, they show that these changes can add up to 5 – 15 % less energy expended than what would be predicted based on just weighing less.
This means that someone who was always lean might need 3000 calories to maintain their weight, while someone who had to diet down to that weight may need only 2550 – 2850 calories to do the same. Some studies have also shown that this lowered energy expenditure lasts for 7 years after losing weight and possibly longer.
No damage done
Even though that might sound discouraging the good news is that after losing weight, even repeatedly, there’s no damage to your metabolism. You could say that the body just gets more effective and sensitive to hormones and neurotransmitters accompanying fat storage changes. So, if that’s your case, just make sure to keep adjusting food quantity as you go down in weight and don’t expect weight loss to go as well as some calorie calculators suggest.