Peter Singer.

This is the definitive book on the ethics of where our food comes from, what it takes to get there and how we treat the nonhuman animals that we rely entirely on (food products, leather, labour etc) and yet utterly disregard and mistreat as not worthy of any human consideration. The book is not at all preachy, it does not attempt to tell you not to eat meat or animal products, it simply informs one on the practices used, the attitudes that certain societies have and how one inevitably increases the demand for the horrific treatment of domesticated animals (factory farms in particular). Luckily it does not go into too much detail of the inner workings of slaughterhouses (one massive reason I feel people are  ignorant to these issues, because they don't want to see it). The book follows three American families and their daily diets. One family lives on junk food,  cheap meat and anything easy and accessible. One family is trying to be atleast mildly ethical by buying local and organic food. And one  family is entirely vegan (including their two children). 

One learns, for example, that most salmon has been reared in salmon farms, so close together that their skin rubs off and they are in constant distress (in the wild they would see only two or three salmon in their lifetime). They are feed food colouring to make their flesh pink (it is naturally grey and only becomes pink due to their consumption of kelp in the wild). They are feed antibiotics to increase growth rabidly Antibiotics which are thrown into the ocean for other sea creatures to consume. They also frequently escape from their cage, breed with wild salmon and create a hybrid fish which is neither. Hence, even if salmon is labeled wild, it is probably a genetically modified salmon that has escaped from a salmon farm.

Peter Singer (Australia) is one of my all time favourite Philosophers and animal welfare advocates. 

Everyone should read this book. Even if you do not think that your consuming practices are unethical, you may learn a lot about the world regardless.