Tobacco use (and actually, all forms of smoke inhalation) has a specific, acute mechanism whereby use increases the chances of lung cancer and other respiratory problems. We do not have that kind of causal link for obesity-related diseases. There is a correlation between weight and several so-called lifestyle diseases, but the causal link is fuzzy.
That lack of causation is why reducing the obesity problem to a simple matter of weight control is a bad idea. There are other mechanisms at play, particularly related to body composition, that appear to be sensitive to diet composition and activity levels. Telling people they can be sedentary as long as they don't eat too much (which is basically what the original post I was replying to was saying) is dangerous.
You are absolutely correct in the same way that saying "there do exist conditions that cause twins to be born such that their bodies are fused together at one or more points." It's true but the vast majority of the time it is an irrelevant fact.
I don't think many people assume all problems are purely a result of weight. That being said if your knees bother you and you're clinically obese, perhaps tracking your calories and getting on a stationary bike occasionally is probably a better long-term decision than double knee replacement surgery.
> Being obese is neither necessary nor sufficient to develop ... health problems.
I'm curious how you think most diagnosed cases of hypertension and Type 2 Diabetes are caused, then.
Vast majority is not 100%. As I replied elsewhere, I was reacting to the laziness of the statement more than trying to assert it is not generally the case.
> I'm curious how you think most diagnosed cases of hypertension and Type 2 Diabetes are caused, then.
That is a good, unanswered question. Along with why people who have never been overweight in their life also develop hypertension and Type 2 diabetes and why so many obese people never do. There is certainly a correlation, but there is no causal link as yet to anything in particular.
The hormone resistin links obesity to diabetes[1]
Excerpt:
Type 2 diabetes...is strongly associated with obesity; however, the mechanism by which increased adiposity causes insulin resistance is unclear. Here we show that adipocytes secrete a unique signalling molecule...increased in diet-induced and genetic forms of obesity.
Pigment Epithelium-Derived Factor Contributes to Insulin Resistance in Obesity[2]
Excerpt:
Herein, we show that the noninhibitory serine protease inhibitor, pigment epithelium-derived factor (PEDF), plays a causal role in insulin resistance. Adipocyte PEDF expression and serum levels are elevated in several rodent models of obesity and reduced upon weight loss and insulin sensitization.
[0] http://diabetes.diabetesjournals.org/content/43/11/1271.shor...
[1] http://www.nature.com/nature/journal/v409/n6818/full/409307a...
[2] http://www.sciencedirect.com/science/article/pii/S1550413109...
Then they should eat less than a normal diet. You can get all the right nutrients without as many calories.
(1) The big fat truth "More and more studies show that being overweight does not always shorten life — but some public-health researchers would rather not talk about them."
(2) Scientists now think that being overweight can protect your health
(1) http://www.nature.com/news/the-big-fat-truth-1.13039
(2) http://qz.com/550527/obesity-paradox-scientists-now-think-th...
Being obese is neither necessary nor sufficient to develop metabolic and other health problems. Those problems arise from lack of activity, diet composition, and other factors beyond simply weight. Those problems are also the core plague of the "obesity epidemic", so it would behoove society not to focus so narrowly on weight and to focus on overall health (of which weight is a component).