To have an insight into people's health in the 19th century, all you have to do is to take a look at the old daguerreotype photographs of cowboys, gunslingers, and farmers that lived in those days. In all these photos, you will not see a single obese American citizen as all of them look slim and fit, with flat stomachs and angular and lean faces. If you also take a look at 1900s daguerreotypes of the Argentinean gauchos, who were also slim and wiry, you will come to the conclusion that health and diet go hand in hand; what you eat determines what your physiological/metabolic condition is going to be.
Until the beginning of the 20th century, people did not eat much carbs as agriculture did not produce carbohydrates-containing products in large quantity as the mill industry had not developed the wheat flour refining technology. Meanwhile the sugar industry was still in a very primitive stage as beetroot and cane sugar was extremely expensive in the 19th century. As a result, in those days, the American diet was mainly based on meat (beef, pork, chicken), and plenty of eggs and they used tallow and lard to cook instead of vegetable oil.
Back then, they did not know margarine, which is made from unhealthy trans fat. They did not eat much carbs (pancake, maple syrup, cereal, potatoes, cookies, soda, beer, etc) as they used to have only bacon, eggs, and sausage for breakfast. Meat, eggs, and butter had not yet been vilified by big pharma, which control mass media; thus, diabetes, cancer, and neurological conditions (multiple sclerosis, Alzheimer disease, etc.) were virtually non-existent.
Back in the 19th century, people, especially children, died from other medical conditions, such as bacterial and fungal infections (meningitis, pneumonia, gangrene, septicemia (blood-poisoning), etc), because antibiotics (penicillin and sulfonamides) had not been discovered yet. If they were struck by measles or smallpox, which were viral diseases, sometimes they developed bacterial complications. Another cause of death was dehydration in old persons and especially during the feverish stages of a bacterial disease; you either lost a lot of fluids through perspiration or through a bacterial diarrhea when drinking stagnant waters. Intravenous route to hydrate a patient with fluids did not exist back then!
Below, a late 19th century cowboy and his breakfast (eggs and bacon). With his brain fasciculi fully developed, he had determination and will as he lived in a rough environment full of danger.
19th Century American breakfast, bacon and eggs.
Below, a 21st century's obese American, in the pre-diabetes phase and the beginning of coronary artery issues.
By Carlos B. Camacho, biological anthropologist