Sorry for the posting bait, but I think some equal time is called for...
Some could say that there's no reason for anyone to be skinny (no matter what your genetics do with your metabolism). It's just a lifestyle choice. Especially if you suffer from negative self-image, anorexia, bulimia, or are hyperthyroid, or are too poor to afford enough food and/or only have access to high starch, high sugar, high fat foods, and go to sleep hungry most every night. You should just exercise less and eat more, because it's just a balance between calories in and calories out.
Okay, how does this sound, compared to "Being Fat is NOT OKAY?"
Especially since the research shows that genetics and environmental factors are very important for both overweight AND underweight people.
Genetics play a large role in how bodies respond to environmental impact (especially food, but also toxins and exercise and such), but genetics very rarely make someone unhealthily fat or skinny without an environmental catalyst.
This dramatic change in one generation was
not from changing genetics:
(Nor was it from a mass-bodybuilding craze, for those that would point out that bmi is misleading.)
It was from changes in diet, for the most part.
Being thin is usually healthy unless a person has an eating disorder, or is skinny from some extreme thing like cancer, or if they live in the arctic, or if they have a reasonable chance of facing a famine in the near future. I've been self-conscious about being skinny for much of my life (my bmi is about 18, even with a lot of muscle tone and strength), but I accept that it's just where my body chooses to be when I eat as much whole, real food as I want. When I was younger and I drank a lot of sugar and ate an unhealthy diet, I didn't gain weight, but instead got excessive cavities and felt bad. Rather than having genes leading to weight gain, I likely have genes related to mineral issues in enamel. A change in diet has largely addressed that. Other people have genes that are more likely to manifest as obesity and related disorders.
Obesity, and in particular excess body fat around the abdomen, is strongly associated with disease, and usually only manifests due to a problem of some variety, rather than being one of the healthy, naturally-occurring body types. (In contrast, being big-boned or voluptuous due to a variety between ethnicities can still be quite healthy, in some cases even healthier than being thin, since the fat is not from metabolic disorder and is not placed around the abdomen). The global epidemic of diabetes and obesity is a complicated mix of economics (poor people have trouble affording healthy food), corporate interests (they influence government nutritional guidelines and even things like doctors' diabetes associations, they market to children, they put soda and Pizza Hut in schools), governments promoting incorrect and outdated nutritional science, people eating out and eating processed foods rather than cooking and eating whole foods, dramatic rises in sugar intake, etc.