There is a common misconception that the fewer calories you eat, the faster you will lose weight. Although this is mostly true, there is a cutoff where you shouldn’t eat any fewer calories. Why is this? It turns out most of the calories you burn are from your normal bodily processes such as digestion, breathing, pumping blood, etc. Your body needs a certain amount of calories per day for these processes, and this rate of calorie burn is called your Basal Metabolic Rate (BMR).
If you eat fewer calories than your BMR, your body doesn’t have enough energy to perform its basic functions, and you begin to go into starvation. Your body will go into a process called ketosis, which means your body is breaking down fats to feed your body. Sounds great right? Well not really, although your body will break down fats faster, it plays havoc with the rest of your health. Your brain can’t use these broken down fats, and begins using ketones for energy instead. However, your brain can only get about 75% of its energy from ketones, and your mental capacity is reduced. Your brain will also begin to want the remaining 25% capacity to be filled, and will want more glucose. This may cause sugar cravings, and if you manage to beat the cravings, your body will start breaking down proteins (your muscles) to get that glucose. Your body begins cannibalizing itself. In extreme cases, your immune system will break down, and organ failure may begin.
The moral of the story is to not eat fewer calories than your BMR. To calculate you BMR you can visit www.bmi-calculator.net/bmr-calculator. The calculator will ask you for your height, weight, age, and gender. Using these it can give you an estimate of what your BMR is. Then when you are planning for your next diet, plan to never go below this caloric value, or your body will become less efficient, and you will at the very least become very ‘hangry’.