Effect of Normal Versus High Protein Diet on Bone Mineral Density During Weight Loss

Background

Weight loss through caloric restriction can lead to a decrease in bone mineral density and greater fracture risk. Risk factors are prevalent in the older population due to decreased calcium absorption. High protein diets have shown to have a positive effect on bone mineral density and can reduce the risk of bone fractures in the elderly.  However, if calcium intake is low, increased fracture risk persists.  Previous studies have found that high dairy diets will prevent bone loss, yet few have studied the direct effect of high protein diets on the protection of bone mineral density.

Purpose

To study the effects of a high versus normal protein diet on bone mineral density during calorie restriction and adequate levels of vitamin D and calcium.

Population

60 postmenopausal women between the ages of 50-70, who have not menstruated for at least two years, and were free of diseases and/or medications that affect normal bone formation and breakdown.

Procedure

Women were randomly divided into two groups: a high protein diet group where 30% of consumed calories were from dietary protein or a normal protein diet group where 18% of calories were from dietary protein.  Each participant were measured for their resting energy expenditure and given a diet with a 500-600 calorie deficit.  Physical activity and food intake was recorded.  All participants consumed 1.2 grams of total calcium via diet and supplementation per day.  All participants also received daily multivitamins with 400 IU of vitamin D. Additionally, the high protein group received whey protein powder.  Body composition and bone density, strength, and composition were measured at the beginning of the study, at 6 and 12 months.  Blood and urine were collected regularly to measure bone turnover markers and hormones.

Results

Both groups lost weight, lean mass and fat mass in roughly the same amount. However, the high protein group lost less bone mass. The high protein diet group also had high insulin-like growth factor-1, which is known to positively influence bone.

Limitations

The participants were unable to reach 30% protein diet goal, attaining only 24% protein. However, the difference between high protein and normal protein group was still significant and may be more useful in practical applications of the diet for better adherence in most individuals.

Conclusion

A higher protein intake during dieting may prevent bone loss that normally occurs with weight loss.

 

The full text, titled Areal and volumetric bone mineral density and geometry at two levels of protein intake during caloric restriction: A randomized controlled trial.It is in the 2011 issue of  J Bone Min Res, 26(6), 1339-1348.The authors are Sukumar, D., Ambia-Sobhan, H., Zurfluh, R., Schlussel, Y, Stahl T, Gordon CL, Shapses SA.

 

Written by Nickolas A. Low-Beer and Lauren Kronisch,
Dept. Nutritional Sciences, Rutgers University-NewBrunswick
Edited by SA Shapses PhD, RD