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...
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.