Answer:
Companies can only take part of the blame. The thin about big companies is that they adjust serving sizes and tweak them to look healthier. For example, if a bottle of juice says just 65 calories per serving, but the serving sizes are 1 tablespoon? It's not that healthy. That's an extreme example, but that happens all the time in the food industry. When humans diet, they look for lower calories. These poor people gain weight accidentally because companies trick them into thinking it's healthy. However, people also say they'll diet...and then don't. People make their own choices, and one could argue it's their own fault for not reading labels. Really, it's the companies and consumer's fault.
(I hope this is 300 words, you can edit to size if needed)