First, the argument assumes that depression and fatigue are just as readily diagnosed in
Asia as in North America. However, it is entirely possible that Asians suffering from these
problems do not complain about them or otherwise admit them. For that matter, perhaps Asian
medical doctors view certain symptoms which North Americans would consider signs of
fatigue and depression as signs of some other problem.
Secondly, the argument assumes that the difference in soy consumption is the only possible
explanation for this disparity in the occurrence of fatigue and depression. Yet the argument
fails to substantiate this assumption. Common sense informs me that any one of a myriad of
other differences---environmental, dietary, and genetic--might explain why North Americans
suffer from these problems to a greater extent than Asians do. Without considering and ruling
out alternative reasons for this disparity, the argument's conclusion that soy is the key to the
disparity is indefensible.
Thirdly, the argument unfairly infers from the fact that soy is known to possess disease
preventing properties that these properties help prevent fatigue and depression specifically.
The argument supplies no evidence to substantiate this assumption. Moreover, whether
fatigue and depression are appropriately classified as diseases in the first place is
Finally, even if the properties in soy can be shown to prevent fatigue and depression, the
argument unfairly assumes that eating soy is the only means of ingesting the key substances.
It is entirely possible that these same properties are found in other forms, and therefore that
North Americans need not increase soy consumption to help prevent fatigue and depression.