There's good solid science that's been around for a long time and vigorously ignored by the food industry. That science says that refined carbohydrates and the industrially-produced "healthy" vegetable fats are killing us.
In a nut shell, insulin and glucagon are two hormones produced by the pancreas to manage blood sugar. When blood sugars are low, glucagon levels rise. Glucagon stimulates the liver to break up glycogen (long strands of glucose molecules stored in the liver) and release the glucose into the blood. If glycogen levels are low, the glucagon stimulates the process of converting body fat into glucose to be used for energy.
When blood sugars are high, insulin is released. Insulin drives glucose into the cells (including fat cells leading to obesity).
When we eat a healthy, well-balanced diet of unrefined foods, glucagon and insulin levels work as they should in their regular feedback loop.
When we eat excessive or highly processed carbohydrates, insulin levels soar and glucagon levels plummet. In addition to obesity, chronically high insulin levels cause myriad other serious health problems from inflammation to atherosclerosis and diabetes.
Barry Sears has done some great work and writing on how to eat like we were designed to eat. Some Barry Sears' Books
The other critical thing to understand is fats. In short, we need to eat fats found in nature (tasty dead animals, natural dairy products, nuts, olive oil etc...) rather than the industrially-created vegetable fats so beloved by food scientists. Anyone wanting to learn more about fats would do well to study Mary Enig's Work and Sally Fallon's books..
I'd also highly recommend studying the works of Weston Price and Francis Pottinger. Here's a little Video that gives an introduction to their research. I'd recommend both of Their books.