How do certain people like the obamas stay so slim? Good genes? Chef? Let's move program?

Genetics + diet. Many have genes that will allow them to infact waste calories they ingest which keeps them thinner (you know them - people who seem to be able to eat and eat and never gain weight). Others have efficient genes which hold onto calories and these easily gain weight. Intelligent diet and exercise will work for all to get to ideal weight, but is always hard to accomplish.
How people stay/slim. One word descipline discipline in eating properly, enough exercise and good genes as well.