From https://www.westonaprice.org/health-topics/food-features/broth-is-beautiful/#gsc.tab=0

Grandmother Knew Best

Science validates what our grandmothers knew. Rich homemade chicken broths help cure colds. Stock contains the broken-down material from cartilage and tendons–stuff like chondroitin sulphates and glucosamine, now sold as expensive supplements for arthritis and joint pain.

Fish stock, according to traditional lore, helps boys grow up into strong men, makes childbirth easy and cures fatigue. “Fish broth will cure anything,” is another South American proverb. Broth and soup made with fish heads and carcasses provide iodine and thyroid-strengthening substances. 

When broth is cooled, it congeals due to the presence of gelatin. The use of gelatin as a therapeutic agent goes back to the ancient Chinese. Gelatin was probably the first functional food, dating from the invention of the “digestor” by the Frenchman Papin in 1682. Papin’s digestor consisted of an apparatus for cooking bones or meat with steam to extract the gelatin. Just as vitamins occupy the center of the stage in nutritional investigations today, so two hundred years ago gelatin held a position in the forefront of food research. Gelatin was universally acclaimed as a most nutritious foodstuff particularly by the French, who were seeking ways to feed their armies and vast numbers of homeless in Paris and other cities. Although gelatin is not a complete protein, containing only the amino acids arginine and glycine in large amounts, it acts as a protein sparer, helping the poor stretch a few morsels of meat into a complete meal. During the siege of Paris, when vegetables and meat were scarce, a doctor named Guerard put his patients on gelatin bouillon with some added fat and they survived in good health. 

The French were the leaders in gelatin research, which continued up to the 1950s. Gelatin was found to be useful in the treatment of a long list of diseases including peptic ulcers, tuberculosis, diabetes, muscle diseases, infectious diseases, jaundice, and cancer. Babies had fewer digestive problems when gelatin was added to their milk. The American researcher Francis Pottenger pointed out that as gelatin is a hydrophilic colloid, which means that it attracts and holds liquids, it facilitates digestion by attracting digestive juices to food in the gut. Even the epicures recognized that broth-based soup did more than please the taste buds. “Soup is a healthy, light, nourishing food” said Brillant-Savarin, “good for all of humanity; it pleases the stomach, stimulates the appetite and prepares the digestion.”