I believe that the lack of exercise facilities and opportunities, besides stress that triggers cortisol, is at least partly the reason for high prevalence of NCDs among the migrants.  Perhaps the migrants have added stress of being separated from some close family members in a rather distant part of the world.  Non-migrants would be more familiar to the environment and are well adjusted to living conditions, and probably do not have excess stress.

"Weight Gain, Heart Disease, and Diabetes

Chronic long-term exposure to stress hormones disrupts the body’s metabolism causing elevated blood sugar, high cholesterol, high blood pressure, and increased body fat levels due to increased appetite. Stress stimulates cravings for sweet, calorie dense foods and salty, high carbohydrate snacks. The combination of high cortisol, low DHEA and low growth hormone production causes the body to store fat, lose muscle and slow the metabolic rate."

http://teeccino.com/building_optimal_health/148/Six-Tips-To-Reduce-The-Stress-Hormone,-Cortisol.html

I think it is important to also look at changes in their diets.  My guess is that most of the gulf immigrants are coming from poorer nations and thus are transitioning to high fat, high sugar, and calorie denser diets than they were accustomed to.  Also consider other phycosocial factors associated with eating -e.g. food is likely to be comfort and/or entertainment for some.  Are these immigrants getting food aid? If so, what is the food basket like? 

In my opinion where  the migrants are coming from is an important determinant. I believe mostly they are from Africa and other low and middle income countries. These countries are hit by NCD and its effects. The problems may not be picked by the health system . Prevention and treatments  efforts may not be in place.  Race may play a role in some of the NCDs. 

Stress at workplace , lack of family support to releive stress as most of the times migrants come alone changes in lifestyle including dietary habbits,addiction

Very well discussed, just to add their previous genetic predisposition, obesity, stresses, hypertension, lifestyle sedentary including all other risk factors for non-communicable diseases.

Malnutrition, stress, weather exposure cold or hot, 

Over all gulf people are highly obese compared with people around the world which is the independent risk factor of many NCDs including diabetes. For hypertension and obesity, lack of exercises due to work pressure, unhealthy food consumption resulted from low income and living alone without family are the very common risk factors.   As Miranda Yeoh explained correctly that stress is another least but partly responsible for high prevalence of NCDs among the migrants.

Thank you for the all the responses 

All the suggested factors are contributing to the epidemic of NCDs and risk factors in this vulnerable population 

Dear Shamim, Overall NCD risk factors and disease high alomg these population iireespective of migration. Lot of factors including socio-demographic , cultural, life style contributing in it. However the additional 2.5 times risk in migrants, may be due to higher income, sedentary lifestyle, diet pattern etc. at place of destination is important to study. You might have studied this as ell. I just wanted to know, health seeking behaviour, health system response, also being addressed in this context ?

Dear Shamim, In addition to what have been indicated as risk factors among the migrants for NCDs, the migrants have no control over the types of foods(High calorie, high fat etc.) because of the poverty they faced. Secondly, there is high stress level which could be associated with increased food intake at times. Migrants are also more likely to experience behavioral risk factors including tobacco use, alcohol misuse, physical inactivity and inadequate intake of fruits and vegetables. Substances use and abuse is also rampant among this segment of population.