Misleading title, it is not "western diet" what is bad for health, it is fast food, and sugar sweety food what is. What Americans were eating 70-50-30 years ago was healthy and "western". It has been people eating industrial foods instead of someone making the food what has changed. I use to look at obese people shopping cart and I see a lot of Coca Cola, pizza, industrial bread, industrial buns,cookies, chocolate,no…
So, then, what is the "Western diet" if it isn't what the Western people eat? (I see your point, though; it's been changing over time, and you're right: it is getting more and more processed and less balanced {and dare I say "healthy"}). Regarding obesity, exercise is far more important than diet. You can eat all kinds of, well, crap, and if you exercise, you'll still be physically fit and probably even look healthy.…
This might be true, and I suspect that it is, but it's not true of the trivial amounts of exercise prescribed by doctors to improve health. There was a Cochrane Review meta-analysis finding only a very small weight loss induced by exercise (something like 2kg) across a lot of studies, and this well-controlled experiment just published in the International Journal of Obesity found only a 1.8kg average weight loss in the exercise group:
http://www.nature.com/ijo/journal/v35/n3/full/ijo2010147a.ht... Adiposity changes after a 1-year aerobic exercise intervention among postmenopausal women: a randomized controlled trial
But the mean duration of exercise per week in the exercise group was 178.5 minutes, just under three hours. The Afghans and Inuit being discussed here as a point of comparison probably get a great deal more than three hours of exercise per week. I'm thinking it's more like 30-60 hours.
Unfortunately, I haven't been able to find any obesity studies comparing groups that are matched, except that one of them gets about 40 hours a week of exercise. Maybe a study looking at people who changed between physically-strenuous and non-physically-strenuous jobs?
(Me, I got three hours of exercise on Sunday. I bicycled 20km to go to two events, and at one of the events, I danced pretty intensely for more than an hour. I'm doing something similar tonight.)
Exercise has a lot of other good effects, though. Even the trivial amount of exercise often prescribed can substantially increase muscle mass, lower blood pressure, increase strength, reduce stress, and improve insulin sensitivity.
But it's not adequate to cure obesity.