When your calorie intake is too low, you may not get all the nutrients your body needs. Additionally, your body's natural response to a decrease in food can lead to your body's metabolism slowing so that your body can conserve energy. In the long run, this slowing metabolism can lead to weight gain.
One of the biggest reasons people gain weight is simply NOT eating enough food! If you aren't providing your body with the energy it needs to fuel your daily activities, then it will have to begin sourcing it from somewhere else.
Can eating too few calories decrease your metabolism?
The body is a very intelligent machine in the sense that it knows how to effectively regulate its many processes to support homeostasis (keeping a constant weight).
In the context of dieting and weight loss, this means that if you restrict your food intake too drastically, your body will simply decrease its metabolic rate so it is burning fewer calories.
Of course, if your body begins to burn fewer calories each day, then it is going to be far more difficult for you to lose weight, but the problem is even greater than that.
If you aren’t providing your body with the energy it needs to fuel your daily activities, then it will have to begin sourcing it from somewhere else. You might be thinking the first place it will look is your stored body fat, but it will also begin breaking down your lean muscle mass so it can be converted to glucose and burned for energy.
This result is a snowball effect, where you are holding less muscle, meaning your metabolism begins to dwindle even further.
Why undereating could be hurting your health!
If you do decide to continue eating very few calories, you should know that there’s a chance that you’re putting your health at risk.
When your body goes into starvation mode, you are at increased risk of both physical and mental complications, including
Abnormally low blood pressure and slow heart rate
Heart rhythm abnormalities
Loss of menstrual periods in women
Swelling in your joints
Undereating can also often lead to an unhealthy relationship with food, obsessively thinking about food, and potentially eating disorders.