There are various causes of rapid weight gain like change in life style, people are more into junk food rather than home cooked food, these processed foods contain high amount of salts and sugars, and they are made from processed flour which is less in fiber content. These processed foods add extra calories to body and are the major cause of rapid weight gain.
There are other causes of rapid weight gain like consumption of alcohol, when people consume alcohol they tend to eat snacks along with it, these snacks are fried and have lots of calories in them, and also alcohol is high in calorie count. Things get worse if people who consume alcohol do not exercise regularly, it adds to sudden weight gain.
There are other reasons of rapid weight gain like hypothyroidism, organ disease, medicines, essential fatty acid deficiency, hypertension and insomnia.
People who are suffering from hypothyroidism tend to gain weight very fast. In this condition weight gain is due to protein deposits in the body. Weight gain in such conditions can be seen in form fat accumulation and fluid retention. Deficiency of essential fatty acids also causes weight gain as this deficiency reduces metabolic rate of the body.
Reaction to certain foods can also result in weight gain, the results may not be immediate, but later it can result in bloating and swelling of hands, legs, abdomen.Much of the weight gain in such cases is due to fluid retention and release of certain hormones.
Some medically prescribed drugs are also major cause of rapid weight gain; these drugs can be anti cancer drugs, oral contraceptive pills that contain estrogen that causes fluid retention and increase in appetite. Other drugs that can cause weight gain are various types of steroids, anti-inflammatory drugs, diabetic medicines; antidepressants. Weight can also be caused by organ enlargement like ovary cyst and obstruction of lymph fluid.