Effects of a dairy supplement and resistance training on lean mass and insulin-like growth factor in women

Journal Title (Medline/Pubmed accepted abbreviation): Int J Sport Nutr Exerc Metab
Year: 2011
Volume: 21
Number: 3
Page numbers: 181-188
doi (if applicable):

Summary of Background and Research Design

Hypothesis:The authors hypothesized that overweight women participating in a weight loss/resistance training program would have greater muscle mass and strength gains and lose more body fat when fed yogurt 20 min before and immediately after exercise sessions as compared with an isoenergetic carbohydrate placebo.

Subjects:: A total of 29 healthy but overweight women (body mass index from 25-30 kg/m2; age 29-45 years) completed the study (15 in the yogurt group, 14 in the control group). There were 35 participants originally recruited but 6 withdrew before completing the intervention (1 because of pregnancy in the yogurt group and 2 and 3 subjects in the yogurt and control groups, respectively, for personal reasons). Subjects were not allowed to use dietary supplements and several medications affecting body weight were part of the exclusion criteria.

Experimental design:Randomized, controlled trial

Treatments:6 oz yogurt (100 kcal, 5 g protein, 20 g carbohydrate, 0 g fat) or 6 oz carbohydrate solution (100 kcal, 25 g carbohydrate) fed 20 min before and immediately after each exercise session

Protocol:The subjects underwent a 16-week weight loss/resistance training program. The subjects performed whole body resistance training 3 times per week. The subjects were instructed, with the help of a registered dietitian, to consume a nutritious diet targeting a daily energy deficit of ~250 kcal from weight maintenance needs. Strength (1-repetition maximum), anthropometry/body composition (dual energy X-ray absorptiometry), and hormone response indicators (IGF-1 and IGFBP-3) were measured at the baseline, midpoint, and end of study. Two random 24-hour dietary recalls were obtained before randomization, at midpoint, and at study endpoint for nutrient analysis.

Summary of research findings:
  • The diet and resistance training program significantly (P<0.01) decreased body mass and body fat mass and increased lean body mass over time. Trunk fat, waist circumference, and saggital diameter were reduced as well by the program as well.
  • Strength in 4 exercises (bench press, squat, deadlift, and rows) increased from 48 to 161% by the end of the diet and exercise program.
  • There were no significant effects of the yogurt versus control interventions on any of the variables measured. There were also no time effects on IGF-1 or IGFBP-3.
    • The changes in body composition were somewhat more positive in the yogurt versus control group, but the differences were not significant.
  • There were significant changes in energy intake (decrease), protein as percent of energy (increase), fat intake (decrease), and calcium intake (increase) over time, but no effects between groups.

Interpretation of findings/Key practice applications:

It appears that the 16-week diet and exercise program employed in this study positively impacted both body composition and strength in this cohort of women. Further the strength increases were of a pretty large magnitude. It would be interesting to see if the women reported any significant improvements in quality of life associated with these increases in strength. The yogurt intervention did not provide additional benefits. It is possible that the total amount of additional protein (10 g/day) was too small to provide further increases in lean body mass.
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