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How many people does it take to change a light bulb?
One, as long as the light bulb wants to be changed.
No matter what the reasoning or rationalisation, weight loss is ultimately a result of the body's energy expenditure being in excess of energy intake. There is a real limit to what one can do to exercise at a time, but there is a far bigger range in how much calories a person can ingest in a day.
As for the people who either deny being obese, or think it can be healthy while being obese:
Some challenged the "science" of BMI measurement (which was first used almost 150 years ago) and wanted to change the goalposts from BMI = 25 in spite of the fact that it is only during the last 30 years that the average cohort BMI has increased drastically within 2 generations.
There are some who think anyone suggesting that an obese person should lose weight is akin to fat shaming and bullying.