The concept of “bone broth” has become quite popular. There are even commercial bone broth products available. I see people taking the term literally, however, using only bones to make broths, including stripping away any soft tissue residues such as meat or tendons. I believe that this is a mistake.
While many people make or purchase bone broths to obtain minerals, the quantity obtained is minor. A better reason to make broths is to increase your intake of collagen and hyaluronic acid, factors largely absent from modern diets. But, if you make broths from bones only without soft tissue components such as tendons, ligaments, skin, and meat and organ remnants, you obtain very little of either. Only low quantities of important amino acid precursors of collagen such as hydroxyproline, proline, and glycine are present when broth is made from bone alone.
A substantially better idea would be to make “carcass broth.” It may not sound very appealing, but making broths or soups from the entire carcass yields a greater quantity of important nutrients than bone broth. With chicken, for example, buy the whole chicken complete with skin, bones, tendons, ligaments, and perhaps some organs. (You can appreciate how silly it is to purchase boneless, skinless chicken breast that is so popular.) Yes, include the bones, especially if they contain bone marrow and have ligaments and tendons attached. But it’s the nutrients mobilized from the soft tissue remnants that you really want.
Some additional insights into broths coming out from the handful of research studies:
- Release of magnesium and calcium from bone is linear: the longer you cook, the greater the release into the broth, especially beyond 8 hours. Despite this, broths remain a minor source of minerals such as magnesium, typically providing no more than a few milligrams per serving. (Recall that we aim for an intake of around 450-500 mg magnesium per day.)
- Acidification of the broth, e.g., by adding vinegar, does indeed dramatically increase extraction of magnesium and calcium from bones. Magnesium extraction, for instance, is increased 20-fold with acidification (but still remains very low).
- Bones can be a significant source of collagen but only if the marrow is contained and exposed.
- Lead release is indeed an issue. Lead is released almost immediately upon cooking and does not increase with more prolonged cooking times, unlike mineral release that is time-dependent. Lead release is also doubled by acidification. Typical lead content is around 8.0 micrograms per quart (approx. one liter) of broth. The Environmental Protection Agency (EPA) and Centers for Disease Control have recently stated that the safest amount of lead intake in water is zero, but up to maximum allowable content of 15 micrograms per liter, with some authorities arguing that this is too high and should be no more than 10 micrograms per liter. Bone broths approach these limits.
Bottom line: Ignore the hype. Bone broth is not what you want, as it lacks crucial nutrients and risks exposure to lead that is not readily cleared from the body. Instead, make carcass broth, do not use extended cooking times, certainly not beyond 12 hours, do not add vinegar that increases lead content, and be sure to include as much soft tissue such as meat, organs, tendons, ligaments, and bone marrow as possible.