Increased consumption of dairy foods and protein during diet- and exercise-induced weight loss promotes fat mass loss and lean mass gain in overweight and obese premenopausal women


Journal Title (Medline/Pubmed accepted abbreviation): J. Nutr.
Year: 2011
Volume: 141
Page number: 1626-1634
doi (if applicable): 10.3945/jn.111.141028

Summary of background and research design:

Background:When people who are overweight or obese are losing weight, it is most healthful if they maintain lean body mass and lose mostly fat mass.  There is some evidence that low fat milk products, in combination with restricted energy intake and increased exercise, can help maintain muscle while losing fat mass.

Hypothesis: When participants consume a high protein, high milk product diet they will lose a larger ratio of fat mass:lean body mass than participants consuming an adequate protein diet with moderate or low dairy products during an intervention with energy restriction and an exercise routine

Subjects: A total of 90 premenopausal women were recruited, age 19-40 y, BMI between 27-40 kg/m 2.

Experimental design: randomized, stratified by BMI so that there was no difference in BMI between groups

Treatments :random assignment to 1 of 3 groups: 
1) adequate protein, low dairy (APLD, <2% energy from dairy protein )
2) adequate protein, moderate dairy (APMD, 7.5% of protein from dairy products, 3-4 servings/day)
3) high protein, high dairy (HPHD, 15% of protein from dairy, 6-7 servings/day)
The adequate protein groups consumed 15% of energy from protein, the high protein group consumed 30% of energy from protein (both 30% fat).
Study drinks were provided to the participants in the form of a chocolate flavored, milk-like beverage.  Two drinks were consumed per day, one 5 hrs before exercise and one immediately after exercise.

Protocol : The height, weight, and body composition (using DEXA) of the participants were determined first.  They were then assigned to one of the 3 study groups, all of which consumed a diet 500 kcal deficient of energy.  A combination of aerobic and resistance training was led 5 days/wk, during the week, and the participants exercised on their own on the weekends.  Workouts were designed so that the participants burned about 250 kcal.  The diet and exercise routine continued for 16 wks.  Body composition was assessed again at 8 wks and 16 wks.  A subset of women also underwent MRI imaging for confirmation of body composition assessment.  Strength and aerobic capacity were assessed before and after intervention.­ Blood samples were acquired before and after intervention and analyzed for calcium, glucose, insulin, and lipids, and markers of inflammation.


Summary of research findings:
  • Regardless of the group, all of the participants lost a similar amount of total body weight (-4.3 ± 0.7 kg, p < 0.01).
  • During the first 8 wks, body weight loss was similar between groups, but the HPHD group lost more weight during the second half of the study.
  • Lean body mass increased in the HPHD group during the intervention.  However, those in the APMD group experienced no change in lean body mass and those in the those in the APLD group lost lean  body mass (-0.7 ± 0.3 kg).
  • By MRI analysis, visceral adipose tissue volume was reduced the most in the HPHD group (p < 0.05).
  • All groups exhibited increased strength post-intervention.  The HPHD group had greater strength gains than the APLD group in the seated row and hamstring curl (p < 0.05).
  • Interleukin-6 (IL-6) decreased over time most in the APMD group, some in the HPHD group, and not in the APLD group, which is correlated with inflammation.
  • Blood lipid levels improved in the HPHD and APLD groups.

Key findings:

While engaging in a diet and exercise program, consuming a high protein, high dairy (low fat dairy, specifically) was more effective at retaining lean muscle mass while overweight and obese women lost weight.  From this experiment, also, it is hypothesized that the higher intakes of calcium led to a greater reduction of inflammatory biomarkers (IL-6 and C-reactive protein) as well as aiding in fat loss.

Limitations:

There was not a group that consumed high protein but not high dairy, so it is unclear whether the higher loss of fat and lower loss of muscle arose from the increase in total protein or the increase in dairy protein specifically. In addition, it would have been interesting to see if the increased dairy (and therefore calcium) intake led to an increase in bone density.

 
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