Answer: This is actually a myth. There was a recent large metanalysis done compiling several studies that looked at over 288,000 people.
What this study look at is a measure called the BMI. What they are doing is taking the weight and dividing it by the height. So, what they are trying to do is normalize essentially that taller people should weigh a little bit more than shorter people.
Normal is defined as less than 25. 25 to 30 is considered to be overweight and greater than 30 to 35 is grade one obesity. Grade 2 is between 35 and 40 and greater than 40 is grade 3.
They divided people into these quartiles and essentially looked at them as did you live, did you die, what did you die of .
They compared people between these different levels. One would think the more obese you are, the more likely you are to die of anything, whether it is heart disease or cancer or any other respiratory illness.
They found that grade two and grade three were both associated with a higher all cause mortality than those grade one, overweight or non-obese.
Really, there was no significant difference between grade one and non-obese people.
So, I think the lesson here is you may not be able to lose as much weight as you would like to get to your ideal body weight but any amount of weight loss can potentially be helpful to you.