Must Weight Loss Lead To Osteoporosis?

Obesity and osteoporosis are two leading health problems in the U.S. Generally, weight loss leads to an increased risk of osteoporosis. There has been controversy about whether increased protein in the diet also leads to an increased risk of osteoporosis. Higher protein weight loss diets have become more popular and seem to lead to better adherence to a weight loss diet, and better fat loss while preserving more lean mass. So it would be a shame if these good effects came with a greater likelihood of osteoporosis.

Traditional View Of Dietary Protein And Bone Density

Many previous studies had shown that increasing protein intake leads to increased calcium in the urine. The increased calcium in the urine had traditionally been felt to represent calcium loss from bone.

A Crack In The Traditional View

However, more and more studies are contradicting that view. A study in 2005 (1) showed that increased protein in the diet leads to increased calcium absorption. So the increased calcium in the urine may not be coming from bone. Instead it may simply be coming from the calcium absorbed from the diet.

The Crack Widens With A Weight Loss Study

A study from a few years ago (2) looked at a weight loss diet with more protein and dairy than a typical weight loss diet. It checked the bone mineral density over the course of a year. The study subjects went on a weight loss diet for 4 months and then were on a weight maintenance diet for 8 more months. Contrary to what had been the traditional view, the results showed that higher protein and dairy intake while losing weight, lead to better maintenance of bone mineral density.

The people in the study were divided into two groups, with the protein group getting approximately 30, 40 and 30% of energy from protein, carbohydrates and fat. The carbohydrate group got approximately 15, 55, and 30% of energy from protein, carbohydrates, and fat. Additionally, the protein group got 3 daily servings of dairy, whereas the carbohydrate group got only 2 servings of dairy daily.

The researchers studied calcium excretion in urine and bone mineral density at four, eight and twelve months. Those who got more protein and dairy in their diet had more calcium in their urine, but this most likely came from the increased absorption of calcium from food. Those who got more protein and dairy maintained their bone mineral density at the spine, hip and throughout the whole body as they lost weight. Those who got less protein and dairy lost bone density at those locations as they lost weight.

Problems

One problem with this study and most other studies of bone density changes during weight loss is the lack of measuring potassium and sodium in the diet. Potassium and sodium have a strong effect on bone density. If they are not measured, it is difficult to know if most of the better bone density came from the protein and dairy, or if it was from a change in the potassium sodium ratio.

A Clue

Another recent study (3) of women on a high protein calorie restricted diet gives a clue that increased protein does help bone density, beyond the help from an increased potassium sodium ratio. The women were studied for 4 years. Those on the high protein diet had less bone loss than women on a normal diet.

This occurred even though the women on the high protein diet had more sodium in their diet. Sodium is known to cause a greater loss of calcium in the urine. So the high protein in their diet helped overcome the effect of sodium. Most likely this is because protein in the diet helps the body to absorb more calcium from the diet. When more calcium is absorbed, less calcium in the urine will come from bone.

Where To Find Tables Of Potassium And Sodium In Food

So to help retain bone strength while losing weight, in addition to maintaining a high potassium sodium ratio in the diet, it is important to get a good amount of protein and an adequate amount of calcium. You can find tables of the potassium and sodium content of different foods by looking under the List of Posts tab. On that page look for a table of the food group that contains the food you are interested in.
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1. The impact of dietary protein on calcium absorption and kinetic measures of bone turnover in women. Kerstetter JE, O'Brien KO, Caseria DM, Wall DE, Insogna KL. J Clin Endocrinol Metab. 2005 Jan;90(1):26-31. Epub 2004 Nov 16.

2. A diet high in protein, dairy, and calcium attenuates bone loss over twelve months of weight loss and maintenance relative to a conventional high-carbohydrate diet in adults. Thorpe MP, Jacobson EH, Layman DK, He X, Kris-Etherton PM, Evans EM. J Nutr. 2008 Jun;138(6):1096-100.

3. Areal and volumetric bone mineral density and geometry at two levels of protein intake during caloric restriction: a randomized, controlled trial. Sukumar D, Ambia-Sobhan H, Zurfluh R, Schlussel Y, Stahl TJ, Gordon CL, Shapses SA. J Bone Miner Res. 2011 Jun;26(6):1339-48. doi: 10.1002/jbmr.318.