The food being served in developed countries are highly processed, and make us very prone to gaining weight. Highly processed carbs turn into blood sugar very easily, and if you live a sedentary lifestyle, like most of us, then that blood sugar gets turned into body fat. It's very basic biochemistry. The reason why we are eating highly-processed carbs is because food manufacturers get a high profit margin from feeding us from pre-processed food rather than original ingredients.
If you want to lose weight, the key is to either burn the blood sugar by exercising, or by denying your body the blood sugar in the first place, through a low-highly-processed carb diet.
But what that entails is rejecting the current 21st century lifestyle of eating quick, convenient meals, and working so much that you spend your entire life in front of a computer. You really need to change your lifestyle in order to lose weight and have a healthier body.
I spent several years working and doing nothing after college and gaining massive weight (over 50 lbs). About 8 years ago, I decided to lose weight, and just by exercising and eating marginally less, I went down down about 20 lbs. But the vast amount of my weight loss came when I did the South Beach diet, and lost another 30 lbs. That's when I realized how terrible highly processed carbs are.
I kept that weight off for about 3 years, until I started focusing on side projects and working about 16 hrs a day in total. I stopped exercising completely for the last 3 years and since then, I've gained back about 20 lbs.
My goal this year is to lose those 20 lbs (actually in the next 4 months, fingers crossed), and to work less. I've already started cooking the majority of our meals, and having complete control of the ingredients helps a lot.