According to WHO(World Health Organisation) "overweight" and "obesity" are defined as abnormal or excessive fat accumulation that may impair health.
So, how to define overweight or obesity?
Body mass index (BMI) is a simple index of weight-for-height that is commonly used to classify overweight and obesity in adults. It is defined as a person's weight in kilograms divided by the square of his height in meters (kg/m2). For instance, a person who weight are 75 kilograms and height 2 meters. This person BMI equal to 75/(2*2)= 18,75
For Adults,
WHO defines overweight as follows:
overweight is a BMI greater than or equal to 25,
obesity is a BMI greater than or equal to 30,
BMI, powerful measure to define health status. However, it may not correspond to same degree of fatness in different individuals. Likewise, it has high reliability.
So, you may be overweight, obese or you want to be fit(according to BMI, lower than 25). What should do you in this situation? Exactly, you are starting to loss weight. Basically, I will explain to you weight loss/gain mechanism. That is simple and effective.
Everyone eat vegetables, fruits, etc, aren't they? So, we intake this nutrient to our body consume this energy. We consume energy for living. After energy, we need macros(carbohydrate, protein, fat). Each gram of carbohydrate or protein provides 4 kcal energy. Each gram of fat provides 9 kcal energy. Every nutrient (we eat it) contain macros. Therefore, nutrient contain energy. Every person need this macros particular rates.
So, how to work weight loss/gain mechanism?
In healthy population(it is not just about your BMI. It is about with your health status, hormones, disease and etc), consume particular energy every day. Therefore, nutrition crucial part of human life. Every people have particular energy expenditure rate which is called "Basal Metabolic Rate(BMR)". (On the internet, a lot of tool calculate your BMR approximately what you need in a day) This is floor level of your daily intake. For healthy weight loss you have to intake much more approximately 100-200 kcal of your BMR. For keep your weight you need to intake approximately 350-600 kcal of your BMR. This is simple mechanism to manage of your weight.
I am not medical provider. So best result and for your health consult your dietitian/medical doctor. This article write for understand mechanism of weight loss.
Thanks for reading.