Table 2 In vivo studies about the influence of soybean isoflavone on muscle

Kataoka et al. [39]

Wistar rat

Casein (C), Soy protein concentrate (SPC), Soy germ protein concentrate (SGPC)

Rats were divided into three dietary groups (the C, SPC, and SGPC groups) and skeletal muscles of them were measured

The weights of the gastrocnemius, plantaris, tibialis anterior, hindlimb muscle, and total hindlimb muscles were significantly higher in the SGPC group than in the C group

SGPC diet can enhance muscle hypertrophy at higher levels than the C diet

Park et al. [27]

Sprague Dawley female rat (old ~ 12-month-old, young ~ 7-weeks-old)

(1) 0.5 g casein, (2) 0.15 g silk peptides (SPs) plus 0.35 g casein/kg BW/day(Low-SP), (3) 0.5 g SPs/kg BW/day (High-SP)

The skeletal muscle and grip strength of each group were measured

Relative loss of skeletal muscle mass was prevented in both SP groups compared to the Aged-group

The Low-SP and High-SP groups exhibited forelimb grip strength similar to the Young-group

SP intake protected against the reduction of LBM and grip strength in middle-aged female rats

Kurrat et al. [40]

Wistar rat

(1) isoflavone(ISO)-free or ISO-rich control diet (CON ISO: 467 mg/kg diet)

(2) Western diet (WD) in the absence or presence of ISO (WD ISO: 431 mg/kg diet)

Rats received a control diet in the absence or presence of ISO. female pubs were randomly grouped into either ovariectomized (OVX) group, which were ovariectomized, or intact group without surgery. Animals switched to WD (containing 20% sugar and 23% fat) in the absence or presence of ISO for 12 weeks

In WD OVX groups ISO increased soleus muscle weights by 20% (p << 0.0001) when compared to WD OVX

Lifelong ISO exposure increases muscle mass in OVX rats

Qiang et al. [41]

Spinal and bulbar muscular atrophy (SBMA) transgenic mouse

Soy-free diet, an identical diet supplemented with genistein (2.5 g/kg of food)

Treatments with genistein were initiated when mice reached 6 weeks of age and continued until the age of 25 weeks

Mice received a soy-free diet or an identical diet supplemented with genistein

AR expression in muscle, rotarod behavior, grip strength, and survival rate were calculated

Treatment with genistein diminished mutant AR monomer in the muscle

Mice who received genistein exhibited less deterioration than control. And also, genistein increased the survival rate, grip strength, and step distance of SBMA transgenic mice

Genistein treatment promotes the dissociation

of AR and thus induces AR protein degradation. Through promoting mutant AR degradation, genistein inhibits neuronal nuclear accumulation of mutant AR in neurons and considerably ameliorates the motor phenotypes in mouse models of SBMA