Ah yes, dairy vs. soy. The purpose of this blog is not to necessarily vilify soy further than needed, as I don't really buy into the bad press that soy has received over time. Soy has taken a bad rap recently due to its apparent ability to reduce testosterone on top of a few other strikes against it. Although I don't necessarily think that soy is terrible for you, I generally recommend that individuals target more bio-available proteins from animal sources (when possible).
We know that animal-based protein sources such as eggs, chicken, red meat, fish, dairy, etc. have a higher bioavailability score than plant-based sources. What does this mean? Well, when a protein source has a higher bioavailable score, your body is able to extract and utilize more of the amino acid chains found in said protein. Not only that, but animal sources are (arguably) the only way to get all of the essential amino acids (EAA) needed from a single source. Plant sources can contain all EAAs, but at times are quite deficient in some way, so must be supplemented correctly to cover all of the bases.
An essential amino acid or indispensable amino acid is an amino acid that cannot be synthesized de novo (from scratch) by the organism, and thus must be supplied in its diet. The nine amino acids humans cannot synthesize are phenylalanine, valine, threonine, tryptophan, methionine, leucine, isoleucine, lysine, and histidine (i.e., F V T W M L I K H).
Anyways, a recent study took a look at high dairy protein ingestion vs. high soy protein ingestion, and even included a "usual protein" control group.
Maintenance of muscle mass and strength into older age is critical to maintain health. The aim was to determine whether increased dairy or soy protein intake combined with resistance training enhanced strength gains in older adults.
179 healthy older adults (age 61.5 ± 7.4 yrs, BMI 27.6 ± 3.6 kg/m(2)) performed resistance training three times per week for 12 weeks and were randomized to one of three eucaloric dietary treatments which delivered >20 g of protein at each main meal or immediately after resistance training: high dairy protein (HP-D, >1.2 g of protein/kg body weight/d; ∼27 g/d dairy protein); high soy protein (HP-S, >1.2 g of protein/kg body weight/d; ∼27 g/d soy protein); usual protein intake (UP, <1.2 g of protein/kg body weight/d). Muscle strength, body composition, physical function and quality of life were assessed at baseline and 12 weeks. Treatments effects were analyzed using two-way ANOVA.
83 participants completed the intervention per protocol (HP-D = 34, HP-S = 26, UP = 23). Protein intake was higher in HP-D and HP-S 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). Strength increased 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). Lean mass, physical function and mental health scores increased and fat mass decreased (P ≤ 0.006), with no treatment effect (P > 0.06).
Let's first discuss the giant elephant in the room:
"The study was supported by a competitive peer-reviewed grant from the Dairy Health and Nutrition Consortium, Australia (Bega Cheese/Tatura Milk Industries, Fonterra Australia, Lion Dairy and Drinks, Murray Goulburn Co-operative, Parmalat Australia, Warrnambool Cheese and Butter, Geoffrey Gardiner Foundation, Dairy Australia, and Dairy Innovation Australia)."
Despite the potential biases or agenda from the monetary support of this study, the results do align with previous research, the sample size is a decent size, and the methods appear to be sound. But, if you wish to discredit this study due to the funding partner, be my guest.
Ok, so as for the results, there are a few noteworthy tidbits:
The "usual protein" (<1.2 g of protein/kg body weight/d) participants' results were not far behind the high protein (>1.2 g of protein/kg body weight/d) test subjects' results when it came to strength improvements.
HP-D 92.1 ± 40.8%, HP-S 63.0 ± 23.8%,UP 92.3 ± 35.4%
I think it worth noting that the study participants were older (age 61.5 ± 7.4 yrs) and untrained placing them squarely in a "noob gains" category. In other words, simply adding in some resistance training and hitting a bare minimum, protein consumption-wise, would be extremely beneficial in improving strength gains regardless of diet. Which makes the next point even more startling....
Strength increased less in HP-S compared with HP-D and UP
So, not only did the high protein participants increase strength by supplementing with dairy, but the usual protein participants also improved strength despite the fact that their overall protein consumption was less than the high-protein soy group. This solidifies the fact that quality of protein is certainly of greater importance than quantity of protein.
So what is the final takeaway from all of this? Well, in my opinion, animal-based protein sources continue to display greater benefits than plant-based sources. If you choose to only ingest plant-based sources due to health or personal reasons, so be it, I will never criticize or fault anyone for that, but considering I've written in the past about the importance of increasing protein consumption with age (which is the true reason this study was conducted), aging individuals should try and consume as much quality protein as possible. Animal sources continue to test well, so even if you wish to not consume dairy, or simply cannot digest dairy (intolerance), then try and get as many other dairy-free sources as you can - eggs, fish, meat, etc.