Exercise and Protein Effects on Strength and Function With Weight Loss in Older Women

Ellen M. Evans; Chad R. Straight; Rachelle A. Reed; Alison C. Berg; David A. Rowe; Mary Ann Johnson

Disclosures

Med Sci Sports Exerc. 2021;53(1):183-191. 

In This Article

Discussion

Aim, Hypotheses, and Novelty of Data. Our data are novel as they are the first to compare the effects of a higher protein diet and exercise treatment with a conventional protein treatment, with or without exercise, using a longer-term protocol and participant-selected and prepared foods (i.e., not supplements) in older overweight/obese inactive women. Contrary to our hypothesis, a higher protein diet combined with exercise did not augment the beneficial effects of weight loss on body composition change, muscle strength, or LEPF in comparison with a conventional protein control diet combined with the same exercise treatment. However, the importance of exercise training, inclusive of resistance training, was apparent as the nonexercise group, despite being higher protein, experienced reductions in strength and attenuated improvements in LEPF compared with the exercise groups.

Higher Protein Weight Loss Diets, Exercise Training, and Physical Function in Older Women. There is a substantial literature, regarding the importance of habitual exercise, especially resistance training, for optimal body composition and strength and physical function with advancing age.[14] Recently emergent paradigms suggest that a diet higher in protein may be of benefit not only to augment fat mass loss but also for lean mass preservation, especially under weight loss conditions.[5,6,11] However, a more limited literature exists regarding higher protein weight loss diets, especially when combined with exercise, in the older adult cohort. Our previous work, which informed the current study, demonstrated in middle-age adults that (a) a higher protein weight loss diet leads to greater weight and fat mass loss and a relative preservation of lean mass compared with an isocaloric conventional higher carbohydrate control diet[17] and (b) the effect of exercise and dietary protein appears to be additive in that the most beneficial body composition changes occurred with a higher protein diet and resistance exercise training.[18]

Literature targeting weight loss and physical function specifically in older adults suggests variable effects of a higher protein diet. Our own data determined that a higher protein calorically restricted diet combined with a low-intensity walking protocol elicited greater weight loss but did not influence changes in lean mass, strength, or physical function compared with a conventional protein weight loss diet plus walking in older women over 6 months.[9] Porter Starr and colleagues[10] assessed the potential benefit of a meal-based higher protein weight loss diet (i.e., protein intake spread throughout the day) compared with an isocaloric control diet for physical function in frail (based on the SPPB, 4–10), sedentary, and obese (BMI > 30 kg·m−2) older adults using a 6-month protocol. The older adults lost a similar amount of weight with comparable reductions in lean mass (as measured by air displacement plethysmography); however, the higher protein group had greater physical functional improvements relative to the control group. Using a shorter-term intervention, Backx et al.[7] reported, in the absence of exercise training, a higher protein diet compared with a normal protein weight loss diet over 12 wk induced similar weight and lean mass loss, reductions in leg strength, and improvements in walking speed. A design closer to the present study, Verreijen et al.[8] reported that when a higher protein weight loss diet was combined with resistance training, it produced similar reductions in weight and fat mass loss and improvements in handgrip muscle strength and physical function compared with an isocaloric control diet with the same resistance training protocol in overweight older adults. However, the higher protein diet did provide benefits to appendicular lean mass preservation compared with the control diet. The inconsistency of the results of these studies renders the viability of increased dietary protein intake in the weight loss diet as a strategy for improving physical function unclear.

Differences in key research design factors affect the integration of our results with the literature cited above. First, our study targeted only women, whereas Porter Starr et al.,[10] Backx et al.,[7] and Verreijen et al.[8] used a mixed-sex sample. Our previous work suggests that the protein content of the weight loss or calorically restricted diet affects regional body composition differently in middle-age men and women.[19] Second, our intervention length matched Porter Starr et al.,[10] whereas the Backx et al.[7] and the Verreijen et al.[8] studies were only 12 and 13 wk in duration, respectively. Third, as described above, participants in these studies also varied based on degree of frailty and baseline weight status, potentially influencing the magnitude of change in physical function that occurred. Fourth, although the cited studies included older adults, age range varied and our cohort spanned 65 to 77 yr with an average age of ~70 yr, which was older than several studies. This may be of importance given the known effect of age-related anabolic resistance in response to dietary protein and/or exercise.[11]

Important characteristics of the dietary intervention also varied as many of the previous studies provided meals or used supplements, which likely strengthened internal validity but may limit translation, especially for longer-term interventions. Alternatively, whole foods may not be as effective for increasing protein intake to desired levels for adherence reasons. Porter Starr et al.[10] targeted >30 g of protein at each meal reached in part by supplying ≥420 g of protein per week in the form of cooked then frozen/chilled very lean beef. Backx et al.[7] provided 1.7 g·kg−1·d−1 with 90% of the diets being provided to the participants, likely enhancing dietary compliance. Alternatively, Verreijen et al.[8] provided both groups with a supplement with the higher protein group receiving a high whey protein-, leucine-, and vitamin D–enriched supplement (~20 g of protein) and the control receiving an isocaloric placebo (150 kcal) with one serving consumed before breakfast and three servings consumed immediately after exercise training. This is similar to the Mojtahedi et al. study,[9] which provided a 90% whey protein isolate or isocaloric placebo in powder form with directives to consume half of the supplement in the morning and the other half in the afternoon or evening. Regarding protein intake, it is possible that (a) the protein distribution across the day, (b) the actual magnitude of protein grams per day, and (c) the variability in adherence influenced the results of our study with respect to those cited.

Regarding protein grams per day and variability in adherence specifically, it is recognized that although our participants obtained, on average, the targeted ~30% of daily energy intake of protein, adherence was variable and grams per kilogram per day (relative to body weight) fell short of the recommended 1.6 g·kg−1 BW·d−1 traditionally designated as "higher protein." The dietary aspects of our intervention were very well conducted with intensive educational and social support. However, notably we did not provide any supplements, food, or meals/snacks to our participants. Thus, our intervention was using participant-selected and prepared whole foods and protein supplements commonly found in the marketplace. Although more realistic and sustainable, it is recognized that this aspect of our design may have attenuated protein intake in the PRO groups. Importantly, there were significant differences between the PRO groups and the CON in protein intake regardless of expression (i.e., grams per day or expressed per body weight or lean body mass). Moreover, highly salient is that the PRO groups were above the recommended protein intake of 1.0 g·kg−1·d−1 advocated for older adults undergoing weight loss,[1] whereas the CON group fell short. It is important to recognize that for the average older overweight/obese women in our study with an average weight (~82 kg) and body composition (i.e., ~48% fat mass; ~52% lean mass), energy intake needs to be reduced to ~1200 kcal·d−1, even with a reasonable exercise program, to disrupt energy balance enough to meet the recommended weight loss trajectory. To meet the 1.6 g·kg−1 BW·d−1 protein intake, at the start of the weight loss protocol, this would require consuming ~131 g·d−1 with 44% of energy intake being protein. This is certainly theoretically possible; however, from a practical sustainable perspective, this goal is extremely behaviorally challenging for many individuals, particularly when selecting whole foods to meet this goal. Also, given the body composition of this cohort, it may be more appropriate to evaluate daily protein intake based on whole-body lean mass given muscle metabolic needs.

The exercise aspects of our intervention also varied greatly compared with literature cited. Regimens ranged from no prescribed exercise or physical activity[7,10] to supervised but low-intensity walking[9] to supervised muscle endurance focused resistance exercise only[8] to the present study, which used a supervised multicomponent exercise intervention. The selection of the multicomponent exercise regimen is aligned with the 2018 Physical Activity Guidelines for Americans and other current recommendations for older adults in general[14] and for weight loss in older adults specifically.[1] The cardiorespiratory endurance exercise aided energy expenditure, whereas the strength training enhanced preservation of muscle mass and strength. In addition, the balance and functional exercises confer benefits for physical functional ability and fall prevention. Certainly, these intervention design factors influenced the changes in primary outcomes of interest, likely in a complicated and interactive manner.

Theoretically, based on previous work in our laboratory,[9,17,18] a higher protein weight loss diet was anticipated to cause the greatest weight and fat loss while attenuating lean mass loss and subsequently enhancing the improvements in LEPF. However, for all the beneficial effects of the multicomponent exercise intervention, which included a moderate-intensity strength training regimen, it is speculated that the exercise effects, being very large, may have masked the potential dietary protein effects on body composition and LEPF. Notably, although the PRO group had greater protein, absolute and relative to body weight and lean mass, they did not achieve the functional benefits of CON + EX (Figure 2) who exercised but actually had, on average, protein intakes lower than the recommended 1.0 g·kg−1 BW·d−1 for older adults undergoing weight loss.[1] It may be that multicomponent exercise training is more important than protein intake for improving body composition and LEPF during a weight loss program in older women, at least at the achieved protein intakes in this study. Notably, in support of the multicomponent exercise aspects of our research, recent work[20] demonstrated in obese older adults that under weight loss conditions, the greatest improvement in physical function occurred in the combined aerobic and resistance training group compared with either mode alone.

Strengths and Limitations. Although our novel data are of interest in a contemporary research and clinical area of public health, it is not without limitations. First, the design has an apparent absence of a fourth group assessing a conventional protein diet with no exercise, which limits our ability for full cross-group comparisons. However, given current recommendations, it would not be considered best clinical practice to prescribe a weight loss program with a diet that is marginally adequate in protein and no exercise component to older women. Second, although the dietary intervention was prescribed to distribute protein across meals throughout the day, and there is confidence this occurred, no food products (e.g., prepared beef) or supplements (e.g., whey protein) were provided to assist adherence to this dietary prescription. Finally, although the multicomponent exercise program could be considered a strength, it might also be limited in translational value because of the comprehensive nature and high degree of supervision required. These limitations are tempered by numerous strengths of this study, including the high degree of dietary instruction and oversight, a supervised exercise program aligned with current recommendations, the length of intervention, the community-dwelling older women as participants, and the use of readily available whole foods which enhances external validity.

Conclusions and Future Directions. The results of this weight loss study suggest that a higher protein diet compared with a conventional protein diet when combined with exercise inclusive of resistance training does not confer additional benefits to body composition, muscle strength, and LEPF in overweight older women. Our data also reinforce the importance of exercise to prevent loss of muscle strength and to enhance improvements in LEPF under conditions of weight loss. Moreover, our results highlight that increasing dietary protein intake, especially up to the levels commonly recommended for older adults losing weight (1.0 g·kg−1 BW·d−1) or to be designated higher protein (1.6 g·kg−1 BW·d−1) with intake spread across all meals and throughout the day,[1,11,12] is behaviorally challenging using whole foods available in the marketplace and will likely require dietary prescriptions mixing animal, plant, and supplement/powder forms of protein. More research is needed to explore the potential interactions of dietary protein, from variable sources, and realistic dietary regimens and exercise or physical activity programs for optimal weight loss success and to enhance LEPF in obese older adults, especially older women at higher risk for physical disability compared with their male counterparts. Management of obesity in older adults, especially older women, remains a public health challenge.

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