Dietary protein needs of octogenarian women and effects on body composition and health in adults with weight loss

Minghua Tang, Purdue University

Abstract

Weight loss via energy restriction can effectively reduce obesity-related complications. Study 1 (Chapter 2) and 2 (Chapter 3) assessed the effects of a high- vs. normal-protein, energy restricted diet on total and regional body composition, including bone, and indices of metabolic health in overweight and obese men and women. Overweight and obese men (n=43) and women (n=45) consumed a 750 kcal/day energy deficit diet with either 0.8 (normal-protein) or 1.4 (high-protein) g·kg-1·day-1 and 25% of fat for 12 weeks. Body composition and metabolic health were measured at baseline and post-intervention. Over time, subjects lost significant amounts of body weight, fat mass and lean body mass. Subjects on the high-protein diet lost less lean body mass and the same amount of fat mass. Independent of diet, the levels of cholesterol, LDL, HDL, triacylglycerol, insulin, HOMA, blood pressure all decreased and the men lost more fat from the trunk and less from the legs than the women. The majority of lean mass loss occurred in legs and men on the normal-protein diet lost the most lean mass. Bone mineral density loss occurred in women only and was not affected by the diet. In conclusion, energy restriction over a short-period of time effectively improves multiple clinical indicators of cardiovascular health and glucose control. Consuming a high- protein, energy-restricted diet can help attenuate lean mass loss from appendicular regions without affecting fat mass loss. In addition, men may benefit more from a weight-loss diet than women by showing greater improvements of fat distribution and maintenance of bone mineral density during weight loss. Study 3 was designed to determine the protein requirement of elderly women aged 80 y and older using the indicator amino acid oxidation technique. Six Caucasian women aged 80-87 y (82 ± 1 y and BMI 26 ± 2 kg/m 2, mean ± SEM) completed a 3-day protocol 7 times. Each woman consumed an adaptation diet for 2 days and on day 3 consumed a crystalline amino acid mixture with one of 7 protein intakes (0.1, 0.3, 0.6, 0.9, 1.2, 1.5 or 1.8 g·kg-1·day-1) tested randomly. Group-based protein requirement was assessed using a nonlinear mixed model of protein intake and L-[1-13C] phenylalanine oxidation. The break point, at which there was no further decline in the 13C rate of appearance in breath, represented the mean protein requirement. The mean protein requirement (and 95% confidence interval) was 0.85 g·kg-1·day -1 (0.60, 1.09). The corresponding Recommended Dietary Allowance was 1.15 (0.77, 1.54). This requirement is 29 % higher than the current Estimated Average Requirement (EAR) for adults of 0.66 g·kg-1·day -1 based on nitrogen balance. This study is the first to assess the dietary protein requirement of women in their 80s and the first to use the indicator amino acid oxidation technique with elderly participants. These findings bring into question the accuracy and adequacy of the current EAR and RDA for elderly women.

Degree

Ph.D.

Advisors

Campbell, Purdue University.

Subject Area

Womens studies|Nutrition

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