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Does Soy Protein Really Inhibit Resistance Training-Induced Strength Gains In Older Adults? Part 2

January 14, 2020 seanwilso Leave a comment

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Where Good Research Leads To Poor Interpretation

In my last research article review titled “Muscle strength gains during resistance exercise training are attenuated with soy compared with dairy or usual protein intake in older adults – part 1” (see here), no additional benefit for improvements in strength, body composition, physical function, or quality of life when additional protein from either dairy or soy versus usual protein intake were seen after 12 weeks of progressive resistance training exercise in healthy older adults.

The focus of this article – part 2 of this review – is to discuss the findings that suggest that increased soy protein intake attenuated improvements in muscular strength compared to dairy protein and usual protein. I want to explore some of the results of this study that are discordant with the conclusions reached by the authors. Their take-home message I believe is therefore misleading and misrepresents what the study actually showed.

The biggest problem with this is that the vast majority of media (print, TV, social media etc), websites, blogs and other avenues used to report on this study, haven’t taken the time to analyse or assess whether or not the conclusions reached are valid. In fact, when I Googled the net for websites, pages or blogs that wrote about, and reported the results of the study in question, I could not find ONE that had even questioned or scrutinised the conclusion against the actual results produced.

This highlights a bigger issue regarding the veracity of health, exercise, fitness and nutrition news that is reported and shared – following publication – in the blink of an eye. Whilst I do not want to explore this further today, it is certainly something that bothers me and something I would like to write about soon.

Let’s look at some of the issues with the conclusions reached by the authors of this paper.

Problem #1 – One of the main findings claimed to have been shown by this research was that:

Increased soy protein intake attenuated gains in muscle strength during resistance training in older adults compared with increased intake of dairy protein or usual protein intake” (pg. 27).

Now unless you read the whole study and scrutinised the results there would be no way of knowing if this conclusion is well-founded or not; so let’s have a look at the results table to see if this is a fair assessment of their data (click on table to expand).

Strength gain with Soy protein versus Dairy protein in older adults — Strength improvement results for each diet intervention

The first thing you’ll notice is that the only exercise that soy protein attenuated gains in muscle strength was leg press 8RM (RM; maximum weight lifted for eight repetitions); for all other exercises no differences were found for protein source and subsequent strength improvement. More specifically, there were no significant differences between the soy, diary and usual protein group for strength improvement in isometric knee extensor strength, handgrip strength, chest press, knee extension, lat pulldown and leg curl. Thus, strength training adaptation from resistance training in older adults for all exercises, bar one (leg press), was the same irrespective of the protein source provided. The significant difference found therefore for the sum total 8RM lifted for all 8RM exercises was most likely due to the difference in leg press 8RM. (Note: percentage improvement in lat pulldown 8RM was greater in usual protein vs dairy but with no difference vs soy; this doesn’t, however, detract from the core proposal above).

Strength increases through Leg press — Leg Press for increasing lower body muscle strength

If that is the case, the question that needs to be asked is, why was this ignored and not explored in the discussion? There are certainly some intriguing possibilities regarding this result. Does soy protein, for example, possibly attenutate gains in lower body but not upper body strength? Is there any other explanation for the attenuated strength for Leg press and, if so, would that mean that there are essentially no differences between the source of the protein and the strength improvement? I’m not sure what mechanism of action you would propose to explain a differential for strength gain between lower and upper body when consuming soy versus dairy protein? The authors do hypothesise that the inhibition of strength gain due to soy protein could have been hormonally based by stating:

Instead, it is more likely that the attenuation of the strength increase in the HP-S group was due to some effect of the soy inhibiting the increase in strength. Soy foods not only contain soy protein, but also contain isoflavones, which exhibit estrogenic properties [Barnes 2012]. A recent study demonstrated that 14 days of soy protein supplementation in resistance trained young men during training reduced serum testosterone concentrations in the first 30 min post-exercise compared with whey protein or a carbohydrate control [Kraemer et al. 2013]. It was proposed that this blunted serum testosterone response might reduce the anabolic response in skeletal muscle, thus attenuating the accretion of contractile protein and muscle strength gains. This may explain the attenuated increase in strength gains observed in the HP-S group in the present study (pg. 32).

However, I don’t think that the abovementioned soy-induced reduction in serum testosterone has been shown to affect muscle contractile properties in an appendicular specific manner (i.e. lower body responds differently to upper body). Moreover, in contrast to the authors proposition above, post-exercise testosterone response does not appear to correlate with, nor is it in any way indicative of subsequent strength gains following resistance training as shown, for example, by the work of Morton and colleagues (2016).

Problem #2: Assessing the results listed in table 2 for Leg Press highlights another interesting difference between the soy and dairy protein groups. The baseline strength values for the dairy and usual protein groups are significantly lower than the soy protein group (55.0 vs 77.3 vs 56.6). In fact, the 8RM baseline strength value for the soy protein group is approximately 40% higher than the other protein groups. Such a large difference would have been unexpected following randomisation with most other baseline values relatively comparable. How this difference affected the statistical analysis is difficult to say but I would have liked the authors to discuss this to put such a baseline disparity into perspective.

Given what was discussed in problem number 1, a separate statistical analysis should have been conducted on all 8RM exercises with leg press 8RM excluded. This assessment would have been able to tease out if the attenuated strength gain seen in the leg press also applied to the 4 other exercises. Based on the data for each individual exercise (excluding leg press), no differences were observed; however, there may have been insufficient power to detect any real differences. By grouping these 8RM exercises together this question could have been answered. As it stands, soy-induced strength gain attenuation can only be claimed for the 8RM leg press.

gym training for strength gain — Are functional strength gains limited by machine-based training?

In relation to the training sessions, what is not particularly clear is whether the participants trained one-on-one with their instructor in solitude or whether the sessions involved small groups. It is feasible that if participants trained individually and at the same time but with different instructors, or in small mixed groups, those allocated to the dairy and usual protein experimental diets may have inadvertently or surreptitiously observed what the ‘stronger’ leg press soy participants were lifting and been incentivised to ‘push’ that bit harder in an attempt to bridge the gap.

Final comments: Based on the results of this study, I would have worded the conclusion very differently to that which was put to print by the Thomson et al. Something like the following would have probably been more apt:

Increased soy protein intake appeared to attenuate gains in leg press muscle strength only, compared with increased dairy protein or usual protein intake. With all other exercises there were no notable differences. Further research is required to explore the possibility that soy protein may specifically inhibit lower body strength gains from resistance training in older adults.

Post-script: Following further analysis and publication of part 2 of this blog, I wrote a letter to the Editor of Clinical Nutrition Journal outlining, what I believed, were some of the flaws regarding the interpretation of the results of this trial. Upon peer review this was accepted for publication and can be found here. If you are unable to access this correspondence and the authors reply to my letter, please contact me and I should be able to assist.

References

Barnes S. (2004) Soy isoflavones-phytoestrogens and what else? J Nutr 134:1225S-8S.

Cermak et al. (2012) Protein supplementaiton augments the adaptrive response of skeletal muscle to resistance-type exercise training: a meta-analysis Am J Clin Nutr 96: 1454- 64.

KraemerWJ et al. (2013) The effects of soy and whey protein supplementation on acute hormonal reponses to resistance exercise in men. J Am Coll Nutr 32:66-74.

Morton RW, Oikawa SY, Wavell CG, Mazara N, McGlory C, Quadrilatero J, et al. Neither load nor systemic hormones determine resistance training-mediated hypertrophy or strength gains in resistance-trained young men. J Appl Physiol July 1, 2016;121:129-138.

Thomson et al. (2016) Muscle strength gains during resistance exercise training are attenuated with soy compared with dairy or usual protein intake in older adults: A randomized controlled trial. Clinical Nutrition. 35: 27-33

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Strength, Weight/Fat loss, Nutrition, Mobility

Muscle strength gains during resistance exercise training are attenuated with soy compared with dairy or usual protein intake in older adults – part 1

January 5, 2020 seanwilso 2 Comments

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On a global scale, the number of people over 60 yr is expected to more than double from 841 million in 2012 to more than 2 billion by 2050. This change in demographics will have profound implications for many aspects of life (Thomson et al. 2016). Furthermore, Government bodies worldwide will be faced with considerable challenges related to ageing policy and how best to deal with this new reality.

ageing, loss of muscle mass, strength, sarcopenia — Courtesy @LeighBreen PhD (Twitter): Sarcopenia presentation

Of the many things that occur during the ageing process one of the most obvious signs is the loss of skeletal muscle mass and strength, with decrements in physical function and potential predisposition to disability. In academic speak, this is known as sarcopenia. The research and interest in this area has been gradually increasing as evidenced by the below graph that shows – since the term sacropenia was first coined in 1989 – a massive increase has occurred. To enhance functional physical capacity and reduce disability into older age, it is therefore critical to develop strategies that facilitate the attenuation of skeletal muscle mass and strength. With more than 30 years of scientific evidence to show that exercise – and, more specifically, resistance training – as both very effective and safe methods to maintain skeletal lean muscle tissue mass and strength (see here and here), current recommendations strongly advocate this form of exercise for older adults.

Interestingly, gains in skeletal lean muscle tissue and muscular strength may be potentiated through the application of appropriate nutritional strategies and in particular increased protein intake. A recent meta-analysis by Cermak and colleagues (2012) reported ~35% greater enhancement in muscle mass and strength can be achieved in older adults undertaking resistance training who consumed at least 1.2 g/kg of body weight/d of protein through supplementation or diet compared with other control groups that were either non-protein, lower protein diet or exercise training with no nutrition co-intervention. Thus, protein quality or source may further augment the effect of the resistance training stimulus by eliciting a greater stimulatory effect on muscle protein synthesis. Dairy protein compared to soy protein has been shown to be more effacacious post-exercise in stimulating increases in lean mass in young healthy males. In older adults though this response to resistance training and increased protein intake may be blunted which necessitates that higher doses of protein are required to bring about an increase.

The aim of the study under review for this article was to determine whether increased dairy or soy protein intake combined with resistance training improved strength gains in older adults.

Soy protein, strength, muscle mass, testosterone — Does Soy Protein Suppress Strength Gains?

Researchers recruited one hundred and ninety two older adults (age, 50-79 yr; BMI, 20-35 kg/m²) by public advertisement. Participation was allowed if they were physically active but not engaged in formal exercise. Those that meet the inclusion criteria undertook a resistance training program for 12 weeks. Randomisation to one of three experimental diets was performed:

High dairy protein diet (HP-D)
High non-dairy (soy) protein diet (HPeS)
Usual protein diet (UP).

DIET: Each diet was isocaloric and low-fat (30% fat, <8% saturated fat) and aimed to maintain energy balance. The diets provided ~1 g/kg of body weight/d of dietary protein, mainly from lean meat sources. HP-D including additional dairy protein of ~27 g per day in the form of a shake (475 g Devondale Smart reduced fat milk, 200 g Nestle Soleil diet no fat yoghurt & 20 ml Bickfords vanilla milk mix syrup). The HP-S providing in the form of a shake – 300 g So Good reduced fat soy milk, 100 g Kingland soy yoghurt, 20 g Nature’s Way instant natural protein powder & 15 g poly-joule – which added an extra ~27 g of soy protein. Protein intake was distribtuted evenly across the day with the three main meals providing >20 g per feed; this is consistent with best practice for optimising muscle protein synthesis in older adults. Following resistance training sessions participants consumed the appropriate additional foods immediately after training and that represented the main meal of that day. Participants were supplied with key foods specific to their allocated diet for the duration of the study to facilitate adherence. Energy and macronutrient intakes from daily food checklists were analysed to monitor food intake and dietary compliance.

Strength training and ageing — Resistance training: a key component of healthy ageing?

RESISTANCE TRAINING: All subjects participated in a whole body resistance training program three days per week on non-consecutive days for 12 weeks and the principles of progressive overload were applied. Five exercises on weight stack pin loaded machines were performed: leg press, chest press, knee extension, lat pull down and leg curl, and seated bent knee hip flexions. Trainees started with one set x 8 repetition maximum (RM; maximum weight lifted for eight repetitions), this was maintained until individuals could perform three sets of 12 repetitions and then the load was increased. This cycle was repeated again for the duration of the trial. Assessment of muscle strength, body composition, physical function and quality of life was conducted at baseline and 12 weeks. All exercise training was completed in the research gymnasium at the University of South Australia under the supervision of gymnasium staff.

Assessment of muscle strength using handgrip, isokinetic dynamometry and 8RM was completed. The leg press, chest press, knee extension, lat pull down and leg curl were tested with 8RM and a summed total 8RM for all exercises was recorded Dominant handgrip strength was measured using hydraulic handgrip dynamometer and isometric strength of the knee extensor muscles of the right leg was assessed using an isokinetic dynamometer.

resistance training slows down aging — You don’t have to lift weights to do resistance training

RESULTS: 83 participants completed the intervention being adherent to both diet and resistance training protocols. HP-D and HP-S had higher protein intakes compared with UP (HP-D 1.41 ± 0.14 g/kg/d, HP-S 1.42 ± 0.61 g/kg/d, UP 1.10 ± 0.10 g/kg/d; P < 0.001 treatment effect). Baseline characteristics, compliance with the intakes of the additional protein foods and adherence to the resistance training program in those that meet all relevant study protocols was not different between groups.

Increase in muscular strength as ascertained by total 8RM was significantly less in HP-S compared with HP-D and UP (HP-D 92.1 ± 40.8%, HP-S 63.0 ± 23.8%,UP 92.3 ± 35.4%; P=0.002 treatment effect). 8RM percent improvement in leg press was much greater in HP-D and UP compared with HP-S (HP-D, 136.8 ± 88.2%; HP-S, 64.8 ± 35.2%; UP, 135.0 ± 62.0%; P < 0.001). For most other exercises, 8RM was not signficantly different for each diet group. Total training volume over the 12 weeks was not different between groups.

Weight, waist circumference and total body fat decreased and lean mass and the distance covered during the 6 min walk test increased significantly increased with no difference between diets. As expected absolute protein intake (g) and relative protein intake (per kg body weight) were different with HP-D and HP-S greater than UP. Dairy protein in HP-D was significantly greater compared with both HP-S and UP with the amount of non-dairy protein in HP-S significantly greater compared with both HP-D and UP.

DISCUSSION: This study has demonstrated that 12 weeks of progressive resistance training exercise in healthy older adults did not provide any additional benefit for improvements in strength, body composition, physical function, or quality of life when additional protein from either dairy or soy is compared to usual (lower) protein intake. Perhaps of more significant interest is that results suggested that increased soy protein intake attenuated improvements in muscular strength. I am going to publish this article before it is entirely finished as I believe this is important research for those interested in this area and facilitating discussion on this topic should start now.

Over the next week or so I will be posting a part 2 in relation to this study as there is a lot more to explore. For example, why did the authors fail to acknowledge or discuss the fact that the attentuated strength improvement in the HP-S was confined exclusively to the leg press exercise? For all other exercises, no difference for dietary influence on strength improvement was found. Whilst not a criticism, it seems rather odd that whey protein was not included as one of the intervention dietary arms of the study. The evidence for whey protein augmenting the development of strength and facilitating the accretion of lean muscle mass from resistance training is well documented. Comparing this with the other diets would have provided some interesting insights into whether there are any further benefits of whey protein to older adults. Finally, one thing that does disappoint me about many of the studies that investigate the efficacy and safety of resistance training in older adults is the reliance on exercises that are machine-based.

CONCLUSION: Increased soy protein intake attenuated gains in muscle strength during resistance training in older adults compared with increased intake of dairy protein or usual protein intake.

Look out for part 2 (see here) titled “Does Soy Protein Really Inhibit Resistance Training Induced Strength Gains In Older Adults?” where I will discuss some of the things I mentioned above in more depth and some possible mechanisms of action as to why soy protein may or may not suppress strength gains from resistance training.

Post-script: Following further analysis and publication of part 2 of this blog, I wrote a letter to the Editor of Clinical Nutrition Journal outlining some of the, what I believed, flaws regarding the interpretation of the results of this trial. Upon peer review this was accepted for publication and can be found here. If you are unable to access this correspondence and the authors reply to my letter, please contact me and I should be able to assist.

References

Cermak et al. (2012) Protein supplementaiton augments the adaptrive response of skeletal muscle to resistance-type exercise training: a meta-analysis Am J Clin Nutr 96: 1454- 64.

Wilson, SA (2016) Comment on: Muscle strength gains during resistance exercise training are attenuated with soy compared with dairy or usual protein intake in older adults: A randomized controlled trial. Clinical Nutrition. 35(6):1575-1576

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