If you are interested in what people ate in the past have a browse through this website:
It has a huge amount of books and resources from the past organised by year. You can read most of the old articles and books online for free. 19th century diets were vary varied. Judge for yourself how healthy it seems.
An example is this one: TREATISE ON BREAD, AND BREAD MAKING (1837).
There are probably few people in
civilized life, who were the question
put to them directly - would not say,
that they consider bread one of the
most, if not the most important
article of diet which enters into the
food of man.
And this one: The Frugal Housewife, or, Complete woman cook (1803).
This book and the 1807 Rundell, A New
System of Domestic Cookery, offer an
excellent overview of the English
contributions to what has become
American cooking. Many of the
traditional English recipes found in
Mrs. Rundell's work also appear in
this volume. But this book does have a
most intriguing group of recipes in a
brief appendix "Containing Several New
Receipts Adapted to the American Mode
of Cooking." The recipes listed make
fascinating reading: Baked Indian
Pudding, An Indian Pudding Boiled,
Mush, Buck-Wheat Cakes, Pumpkin Pie,
Dough Nuts, To Make Sausage,
Blood-Pudding, Cranberry Tarts, To
Pickle Peppers, To Pickle Beets, Peach
Sweetmeats, Quince Sweetmeats, Green
Gage Sweetmeats, A Receipt to Make
Maple Sugar, Maple Molasses, Maple
Beer, Receipt to Make the Famous
Thieves Vinegar, Method of Destroying
the Putrid Smell which Meat Acquires
during Hot Weather, Spruce Beer out of
the Essence, Spruce Beer out of Shed
Spruce, Eel Pie, Pork Pie, Raised Pork
Pie, Bath Pudding, Pot Pie, Short
Gingerbread, Waffles, Crullers and
Method of Rearing Turkeys, to
Advantage...translated from a Swedish
Book, entitled Rural Oeconomy.
I particularly liked this bit "Method of Destroying the Putrid Smell which Meat Acquires during Hot Weather".
As far as what they died of the following charts give a good idea and show the leading causes of death as a percentage of all deaths in the United States, 1900 and 1997. Infectious diseases were a much more important cause of death than now. These probably had little to do with diet apart from contaiminated food and water sources. Charts from here.
Leading Causes of Death, 1997
Leading Causes of Death, 1900*
*Not all States are represented.
Source: Centers for Disease Control and Prevention, National Center for Health Statistics. National Vital Statistics System and unpublished data. 1997.