Obesity can be defined as an excessive accumulation of fats in the body(tissue, organs or systems). It occurs when energy consumed (food) is far greater than energy expended(work, exercise).
Medically, Obesity is defined as a Body Mass Index(BMI) greater or equal to 30kg/m 2. The body mass index ( BMI ) is a value derived from the mass ( weight ) and height of an individual. The BMI is defined as the body mass divided by the square of the body height(in metres), and is universally expressed in units of kg/m 2 , resulting from mass in kilograms and height in metres.BMI is calculated as the weight of an individual in kg divided by the square of the height in meters. The BMI is an attempt to quantify the amount of tissue mass ( muscle, fat, and bone) in an individual, and then categorize that person as underweight, normal weight , overweight , or obese based
on that value. However, there is some debate about where on the
BMI scale the dividing lines between categories should be placed.
Commonly accepted BMI ranges are underweight: under 18.5 kg/
m 2 , normal weight: 18.5 to 25, overweight: 25 to, 29.9, obese: over
30.That is the more your weight the more the chance of being obese and the more your height the less the chances of being obese.
Overweight and Obesity should not be confused.

Overweight (a BMI of 25-29.9) leads to obesity. Apart from the adverse effect of obesity, it can be an expressway for other non-communicable diseases such as diabetes, cardiovascular diseases, coronary artheriosclerosis and sometimes eye diseases.
Fat accumulates in different body parts and vital organs causing serious health problems. For example, when fats surrounds the human heart, it limits its expansion thereby receiving less blood during diastole. This means less blood will be available to some tissues and cells causing serious problem if not properly attended to.
According to the WHO fact sheet that was in reviewed in February 2018;

In 2016, 1.9 billion adults were overweight and of these, 650 million were obese.

Worldwide obesity has nearly tripled since 1975.

41 million children under the age of 5 were overweight or obese in 2016.

Over 340 million children and adolescents aged 5-19 were overweight or obese in 2016.

Obesity is preventable.
Obesity doesn’t just happen overnight. It doesn’t only occur in adults too but it also occur in children. Overweight and Obesity also occur in children but has a different way of measurement different from that of adults.

Some major causes of Obesity.

Genetics: The chances are higher to be obese if one or both parents are obese. This has a direct relationship.

Eating many saturated fats: Most processed foods and junks contains saturated fats. Studies have shown that saturated fat prolong food health before getting rancid(spoilt, offensive smell). Most animal fat are saturated fats. Eating too much saturated fat increases blood cholesterol, diabetes etc. Saturated fats are solid at room temperature.

Overeating: Overeating leads to obesity; eating high calorie food without burning them up leads to fat accumulation. Like the definition goes, “obesity occurs when energy consumed is far greater than energy expended.”

Leptin Resistance: Leptin (an hormone; also called satiety hormone or starvation hormone) regulates body weight. It is produced by fat cells and the target organ is the brain. The function of Leptin is to tell the brain that we don’t need to eat when we have enough fats in our body.

Sugars: Consuming excess sugar may provide excess calories which will be stored in the body as fats. Fruits has an advantages as they overcome this problems. Eat more fruits.

Eating late at night: Basal Metabolic Rate is reduced at night and most digested food are stored as excess fats.

Does Obesity have a cure?

Well, the answer to this question all depends on our personal opinion. According to the WHO, Obesity is Preventable.

Nevertheless, a slightly obese person can have a Normal BMI. It all depends on how you can discipline yourself and how long you can wait.

You can try out the following;

Fat consumption should be shifted from saturated fats to unsaturated fats. This means that more fats of plant and fish origin should be consumed, other than animal fats.

Energy expended should be greater that food consumed. This makes you store less fats and burn more fats. This should not make us skip meals

Eating Healthy diets

: For example, eating food such as vegetables which does not increase body fats.

Exercise: Working with a fitness instructor daily/weekly is a major and fastest way to promote fat loss or burn excess fat.

Leptin gene therapy: Leptin is injected into the body and helps to reduce starvation urge, thereby eating less food and storing less fat. Note that this is only done by a specialist.

Eating early before sleep: Only eating when you are hungry and not just because it’s time to eat.

References

Textbook of clinical Medicine by Parveen Kumar and Michael ClarK 8th edition Clinical Biochemistry and Metabolic Medicine B Martin A Crook 8th edition, WHO fact sheets.