Research Review By Demetry Assimakopoulos©

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Date Posted:

April 2012

Study Title:

Diets Higher in Dairy Foods and Dietary Protein Support Bone Health during Diet- and Exercise-Induced Weight Loss in Overweight and Obese Premenopausal Women

Authors:

Josse AR, Atkinson SA, Tarnopolsky MA & Phillips SM

Author's Affiliations:

Departments of Kinesiology, Pediatrics and Medicine, McMaster University, Ontario Canada

Publication Information:

Journal of Clinical Endocrinology and Metabolism 2012; 97(1): 251-260.

Background Information:

Nutritional intervention and weight bearing exercise are modifiable ways to accumulate and preserve bone mineral density (BMD). Specifically, dairy, a food group that supplies several essential nutrients including calcium, potassium, magnesium, vitamins D and B complex and protein, assists in reducing circulating parathyroid hormone concentrations, and increases and maintains BMD (1-4).

Caloric restriction is often utilized as a means of weight loss. This reduction of body mass that can be achieved with restriction of energy intake has been associated with a loss of BMD (5): this decrease in BMD has been shown to offset with increased consumption of dietary protein, specifically dairy protein (5).

The researchers conducted a weight loss intervention entitled the Improving Diet Exercise and Lifestyle (IDEAL) for Women Study. This intervention is designed to produce weight loss, emphasizing loss of fat mass and the preservation of muscle mass. Additionally, they endeavored to support and preserve bone health during their weight loss. Their main hypothesis is that during the 16 weeks of caloric restriction, daily exercise, and the consumption of dairy, protein and calcium above their respective recommended daily intakes would provide sufficient levels of nutrients to preserve bone density and positively impact bone health in overweight/obese, premenopausal women. Additionally, they surmised that body weight and fat loss would positively affect levels of adiponectin and leptin (adipokines), and that changes in adipokine levels would relate to changes in bone markers in the blood.

Participants were separated into three groups for study (for more specific information, please see the Study Methods section):
  • High protein and high dairy (HPHD)
  • Adequate protein and medium dairy (APMD)
  • Adequate protein and low dairy (APLD)

Pertinent Results:

Nine women dropped out of the study, leaving only 81 participants for study. None of the baseline measurements were significantly different between groups.
  • Despite similar weight loss across all groups (pooled mean -4.3 ± 0.7 kg), HPHD group had greater total and visceral fat loss, and greater lean muscle gains.
  • No significant changes in BMD were observed in any group over the 16 week study period.
  • Serum vitamin D increased significantly in the HPHD group. The APMD group showed no change in vitamin D status. The APLD group showed a significant reduction in the vitamin D quantity. At the end of the 16 weeks, the APLD and APMD groups both showed significantly less serum vitamin D quantity than the HPHD group.
  • The APMD and HPHD groups had a significant reduction of circulating parathyroid hormone (PTH; indicates less need to remove calcium from bone in order to replace lost blood calcium levels). There was a greater, and more significant, reduction of PTH in the HPHD group.
  • All markers of bone formation increased in both the HPHD and APLD groups, with the exception of bone specific alkaline phosphatase. These changes were not found in the APMD group.
  • All markers of bone resorption increased significantly in the APLD group. These increases were significantly greater than those changes found in the APMD and HPHD groups. The HPHD group did not experience any change in markers of bone resorption.
  • Leptin decreased significantly in the APMD and HPHD groups. No significant change was found in the APLD group. The HPHD group showed significantly lower leptin levels than the APLD group.
  • Adiponectin increased in the APMD and HPHD groups. No significant change was found in the APLD group. At the end of the study, the HPHD group had significantly lower adiponectin levels than the APMD and APLD.
  • Adiponectin levels at week 16 were correlated with changes in body fat, visceral fat volume, and some markers of bone breakdown and bone density increase.

Clinical Application & Conclusions:

Higher consumption of dairy and high quality dietary protein resulted in greater quantities of serum markers of bone health and calcium metabolism in overweight and obese premenopausal women over a 16 week diet and exercise induced weight loss program.

Serum vitamin D only rose significantly to a level sufficient for bone health in the HPHD group. Over the 16 weeks, the APLD group showed a significant, yet small, decrease in serum vitamin D.

The HPHD and APMD groups showed a number of positive changes in bone health and bone-related processes. Positive changes in bone matrix turnover, bone collagen turnover and osteoclast differentiation were found. The APLD group went in the opposite direction of the other two groups. Therefore, these results suggest that higher dairy food and calcium consumption during diet and exercise induced weight loss augments bone formation

Leptin decreased and adiponectin increased significantly in the HPHD and APMD groups, with no change in the APLD group. Leptin has been shown to inhibit bone remodeling, while adiponectin has been shown to promote remodeling. Diets higher in bone-supporting nutrients from dairy foods positively affect markers of bone turnover, favoring bone formation, decreased serum PTH and increased serum vitamin D.

In summary, the researchers demonstrated that the consumption of diets higher in protein, emphasizing dairy foods, while undergoing a diet and resistance training weight-loss strategy, positively affected markers of bone turnover and adipokine levels, as well as calcium, serum vitamin D and signals of bone metabolism. Additionally, diets allowing protein intakes at or above the current recommended dietary allowance, with at least 1000 mg/day of calcium (APMD group), or calcium and protein levels of 1200 mg/day and .84 g/kg respectively (HPHD group), offer favorable bone benefit, compared with diets with no or low consumption of dairy. It is reasonable to recommend consumption of dairy foods to aid in weight loss, specifically fat loss, with a concomitant gain in muscle mass, and the promotion of bone health in young, premenopausal women.

Study Methods:

Ninety women were recruited for this study. Premenopausal, overweight or obese (BMI of 27 – 40 kg/m2) women between the ages of 19-45 were included. These patients were otherwise healthy (no history of illness identified though questionnaire), consumed < 600 mg of dairy calcium per day, were generally sedentary, regularly menstruating, neither pregnant nor nursing and not consuming a daily vitamin/mineral prescription.

The subjects were placed into 1 of 3 groups: the high protein and high dairy (HPHD) group, adequate protein and medium dairy (APMD) group or the adequate protein and low dairy (APLD) group. The HPHD and APMD groups all had quantities of dietary calcium and vitamin D intakes that were above the dietary reference intakes. The APLD group maintained a stable baseline of dairy intake (0-1 serving/day), and consumed no greater than 15% of their daily caloric intake from non-dairy sources of complete protein (meat, eggs, chicken etc). The APMD group had 3-4 servings of dairy/day and accumulated 15% of their daily calories from high quality proteins. The HPHD group had 6-7 servings of dairy/day and consumed 30% of their daily energy from high quality proteins. Bi-weekly meetings were scheduled for all participants with dietitians and research nutritionists throughout the study.

The Miffin-St. Jeor equation was used to calculate maintenance energy requirements with a sedentary factor for each participant (for those subscribers who are unfamiliar with this term, the Miffin-St. Jeor equation is utilized to calculate individual daily caloric needs. It has been found to be the most accurate formula to estimate one’s daily caloric intake. This equation can be refined to further identify with each client/patient, as “sedentary” or “very active” modifiers can be added. The equation, for those interested, is: Men = (10 x (kg)) + (6.25 x (ht in cm)) – (5 x age (years)) + 5; women: (10 x kg) + (6.25 x (ht in cm)) – (5 x age (years)) – 161. For more information, check out the American Journal of Clinical Nutrition 1990; 51(2): 241-7). Once their caloric intake was calculated, 500 kcals were subtracted –sum was used as the subject’s maximum energy intake level.

All subjects performed supervised aerobic exercise, 5 days/week and an additional 2 unsupervised aerobic exercise sessions the remaining 2 days of the week. They also engaged in a supervised and progressive resistance training program 2 days/week (upper and lower body split).

All participants underwent DXA scans to gain an appreciation for their whole-body BMD. Additionally, blood samples were taken before and after the study, between the hours of 6:30 – 10:30 am after an overnight fast of 10-12 hours. PTH, vitamin D, OPG, RANKL, leptin, and adiponectin were measured. Serum and urinary biomarkers of bone mineral density were also quantified.

Study Strengths / Weaknesses:

Strengths:
  • The authors exercised great control over the caloric intake/expenditure for each subject.
  • The use of the Miffin-St. Jeor equation as opposed to the Harris-Benedict equation.
Weaknesses:
  • Having only three groups, APLD, APMD and HPHD, makes it difficult to ascertain whether or not some of the results were due to a higher protein intake or a higher dairy intake. The study necessitates the inclusion of either an adequate protein high dairy group, or a high protein moderate dairy group. However, due to the major control in caloric intake, it is unlikely that any additional difference would have been observed.

Additional References:

  1. Heaney RP. Dairy and bone health. J Am Coll Nutr. 2009; 28(Suppl 1):82S–90S.
  2. Gao X, Wilde PE, Lichtenstein AH & Tucker KL. Meeting adequate intake for dietary calcium without dairy foods in adolescents aged 9 to 18 years (National Health and Nutrition Examination Survey 2001–2002). J Am Diet Assoc. 2006; 106:1759–1765.
  3. Weaver CM. Role of dairy beverages in the diet. Physiol Behav. 2010; 100:63–66.
  4. Heaney RP & Layman DK. Amount and type of protein influences bone health. Am J Clin Nutr. 2008; 87:1567S–1570S.
  5. Villareal DT, Fontana L, Weiss EP, Racette SB, Steger-May K, Schechtman KB et al. Bone mineral density response to caloric restriction-induced weight loss or exercise-induced weight loss: a randomized controlled trial. Arch Intern Med. 2006;166:2502–2510.
  6. Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA & Koh YO. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241-7.