The Negative Effects of Protein on Bone Health – and How to Counter Them

Beginning 20 years ago, numerous studies were published on how consuming animal or vegetable protein affects bone composition. Many studies found that animal-based protein made bones less sturdy than plant-based protein. Some studies found that there was more osteoporosis (thin bone tissue) and fractures in people who ate a lot of meat.

Healthy bones maintain a constant balance between how much old bone is broken down to be reabsorbed (resorption) and how much new bone is built (modeling). Most people know that calcium and vitamin D are important for building and maintaining healthy bones. However, based on earlier research, a hypothesis grew that protein affected the body’s natural chemistry in such a way that too much calcium was being excreted in urine.

Recent studies add new insights

Thankfully, scientific exploration is a living, evolving process involving new methods for testing older theories. Today, there is a richer understanding of the body’s chemistry at the level of molecules and ions (atoms with a positive or negative electric charge). This raises more complex questions. How does animal protein differ from vegetable protein? Is calcium loss inevitable in protein-heavy diets?

As more recent insights emerge, it now appears that protein in itself is not the only factor that affect the healthy balance of bone resorption/modeling. Clinical and demographic studies show two things:

1. Diets that are heavily protein-based, whether animal or vegetable, are correlated with loss of bone density.
2. On the other hand, other constituents that make a difference in bone composition (calcium, potassium, phosphorus, isoflavones, antioxidants, salt, oxalate, phytates and caffeine) can offset the excretion of calcium in urine that is associated with protein-heavy diets.

Protein is not the “bad guy”

Instead of assuming that protein is responsible for thinning bones due to loss of calcium, it’s important to understand that mineral consumption counters that chemistry. Protein is not the “bad guy”, but eating protein to the exclusion of other important nutrients can throw the body off balance. Many of the earliest studies did not take into account the biochemical effect of other compounds and minerals contained in the overall diet of the population they were studying. For example, it is now clear that the calcium loss related to protein intake is the most adverse when the diet is lowest in calcium intakeⁱ. Thus, consuming foods rich in calcium, vitamin D and vitamin K can counter the potential negative effect of high protein consumption.

Talk to your doctor about bone health

One person’s diet, and how it relates to their overall condition as well as bone health, will vary from another’s. For example, age-related guidelines for calcium intake show that different life stages require different amounts of calcium. Undoubtedly, we have all heard from childhood onward that it’s important to maintain strong, healthy bones. Diet alone is insufficient; weight-bearing exercise encourages bones to keep up the process of absorption/remodeling needed to keep from losing bone mass to disease or aging.

Individual consultation and guidance is important, especially for people with risk factors osteoporosis. Remember that bones respond to a balanced diet and they like to be “challenged” by walking, jogging, weight-lifting, etc. If you are unsure you’re doing the right things, start with your internist or primary care doctor to find out how you can optimize your bone health.

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ⁱMassey LK. Dietary animal and plant protein and human bone health: a whole foods approach. J Nutr. 2003 Mar;133(3):862S-865S.