The problem I have with this is not that they give bad advice, it's just that there are a myriad of nutritionists that give better advice, many of them completely for free. I've read more than a dozen of these books and have also seen most of them speak Vegetarian Soiciety of Hawaii
is one place where you can start if you're interested.
Why would you choose to listen to, as you yourself say, mediocre advice (have some junk food, eat oil, etc.) when you can actually take advice that would be optimum (eat whole plants)? You can of course stray from this path and indulge and the people I'm talking about have nothing against that (as long as you don't have immediate heart disease) but still why would you choose to read this book over books that give you the whole story?
The reason, I believe, is because they are both outspoken about the animal rights perspective. Many, if not most of the people I would recommend are also animal rightists (Brenda Davies, Jeff Novick, John Robbins, Neal Barnard, etc) or sympathizes with the cause but do not publicly talk about it because it's not their main objective.
This to me is like buying a book about training that devotes time to describing how to most properly sit your ass on a couch while watching TV. I don't have anything in particular against such advice, I just don't want it in the book about training that I just bought and would rather buy a book that is just about training.
Let me also explain what I meant about the different approaches.
We have for a long time seen evidence that seems to say that eating more whole plants is beneficial for your health. We have had indications that it reduces the risk of heart disease, some common cancers (breast, prostate, colon), some auto immune disease (MS, asthma, alzheimer's) and obesity. This observation mostly comes from what is called epidemiological studies which is when you follow a large group of people over a long period of time to get connections between, for example what they eat and how it affects their general health. Nurses health study, Framingham heart study, The China Study and Okinawa Centenarian study are a few examples of studies like this. The problem with these studies is that they they don't provide causality but only correlation and sometimes only loosely so. If you have a population of people in a remote part of the world that live on banana leaves and sweet potatoes that never gets heart disease it's hard to make the diet the cause of this. It might be that they take afternoon strolls or pisses more often than the average German. It might also be that if Germans just started to eat banana leaves once a day it would cure their heart disease. These complicated questions is why you have people dissing these results, for good reason. However, this doesn't mean that the results are pointless as some would argue, you just have to do more studies. When it comes to the connection between whole plant foods and the chronic diseases the other options (like taking strolls in the afternoon or a lower incident of telephone poles) have been pretty much exhausted, according to many. There have even been a few studies that have taken people with heart disease and only changed the way they eat and it stopped and even reversed the disease. Same thing with diabetes-2 and MS. There have also been (at least) test on prostate cancer with similar result (I would like to add though that cancer is a more complicated issue than heart disease, before people get all jumpy). Still, this doesn't prove that there is a causation between these two, just that it seems likely that there are a correlation.
The correlation, according to some of the people I would recommend listening to, is so strong that the diet is actually the cause of many of the chronic diseases that befalls us and the cure is a whole foods plant based (vegan) diet.
This approach is what I called non-reductionist because it doesn't really care why this happens, just that it does. It might be fibre, antioxidants, phytochemicals or whatever else in the plants or it might be the reduction in cholesterol, saturated fat, total fat or sulfur containing amino acids that is the cause. The fuck I do not give about this is immense. It works.
The other road to travel is by causation. Instead of not giving a fuck about the biochemical reactions in the body, this becomes central. If you have inflammation you see that omega-3 reduces it. If we can in turn figure out why then we can make a pill so that you can fix the problem of too much inflammation. One reason this approach is popular is because it sometimes produces pills. The problem with it are what we don't know. Say, for example, that beta-carotene enhances the production of a particular enzyme (a type of protein) in a particular cell and people that have asthma produces too little of this enzyme and we know that this enzyme is involved in the occurrence of asthma attacks. We can now recommend that people with asthma supplements with beta-carotene to get their values up. One question that now have to be asked is how much we don't know about this issue. Why is there an underproduction of this enzyme? How many other biochemical reactions is beta-carotene involved in and how will they be effected? Out of a whole "objective" picture/truth about this we might know 95% but we might also just know 3%. We don't know. This, however, haven't stopped us from making decisions based on this information. This is why almost all supplements in large scale have been shown to have negative side effects even though they seemed promising at first.
As I see it, both of these approaches are useful if you understand their limitations. Norris and Messina, from my experience, is more with the second category than the first, i.e. to try to micro-manage your bad diet with supplements. Since we know too little we are basically wrong all the time, which time has told us all the time since these recommendations change all the time. One problem with this is of course that having a fancy title doesn't really help. If you go to school and you delve in a problem that we only know 3% about and you go out giving advice from your knowledge it might be good but it might also be outright dangerous. The dietary advice given to diabetics and heart patients from normal MDs and RDs is not curing the disease although it is curable, for example.
Sorry for the long post