Two hundred years ago we didn't have cars, television or other electronics, and we tended to work hard by manual labor all day. Take a look at your great-grandmother's china if it's still in the family. Her dinner plates were the size of what we now call a luncheon plate. Also, food was scarce and the idea of second servings was a very special occasion. Life expectancy of a baby born in 1850 was 38 years. A 20-year old born in 1830 who survived infant mortality could expect to see 60 on average by 1850. Now we think people in their mid-80s still have another 10 years to live.
We aren't the same people living in the same conditions as those who lived 200 years ago. Eating and living like them requires much more than just the types of things we put on our plates.
There's also a genetic component. My grandmother was born in 1891. She was obese (as were her siblings) by the time I was born in 1956. My family tree has a lot of obese people. They weren't lazy, some probably ate more than others, but the propensity to put on weight runs in families.
There are some very easy changes you can make in today's world that add up to real lbs lost (or at least not gained in the future). Minimizing processed foods, sugar, salt, large plates, and second servings can drop upwards of 20lbs in a year.
There is one book written by a food scientist that I can recommend. Some of his studies are for clients who want to entice their customers to eat more. Others are for clients who want to help their patients/clients eat less. His observations are sometimes fascinating.
Dr. Wansink is a food psychologist who specializes in the investigation of the mental and emotional factors that cause us to eat. This book demonstrates that we can lose weight, simply by being more mindful of our eating habits. It contains interesting and humorous case studies that highlight those mindless activities that add 200 or 300 calories to our diet each day and which can add up to 20 or 30 excess pounds in the course of a year.
The author provides practical suggestions at the end of each chapter that will help you to make the simple changes that will allow you to lose 2 or 3 pounds per month without resorting to conventional diet techniques that are doomed to failure. Although this book is based upon scientific research and extensively end-noted, it is enjoyable to read, easy to understand and quite funny at times.
edit: The extensive endnotes may be what you're looking for in terms of scientific discussion.