As for the healthiness of vegan diet, see the study

Key TJ, Fraser GE, Thorogood M, Appleby PN, Beral V, Reeves G, Burr
ML, Chang-Claude J, Frentzel-Beyme R, Kuzma JW, Mann J, McPherson K.
Mortality in vegetarians and nonvegetarians: detailed findings from a
collaborative analysis of 5 prospective studies.
Am J Clin Nutr. 1999 Sep;70(3 Suppl):516S-524S.
<http://www.ajcn.org/cgi/content/full/70/3/516S>

which investigated the mortality in people following five different
types of diet: regular meat-eaters, occasional meat-eaters,
fish-eaters, lactoovovegatarians and vegans. The study found no
statistically significant differences between groups in mortality from
various cancers, but in all-causes mortality the fish-eaters and
lactoovovegetarians fared statistically significantly better than
vegans and regular meat-eaters. Below the abstract of this study:

   "We combined data from 5 prospective studies to compare
   the death rates from common diseases of vegetarians with
   those of nonvegetarians with similar lifestyles. A summary
   of these results was reported previously; we report here
   more details of the findings. Data for 76172 men and women
   were available. Vegetarians were those who did not eat any
   meat or fish (n = 27808). Death rate ratios at ages 16-89
   y were calculated by Poisson regression and all results
   were adjusted for age, sex, and smoking status. A random-
   effects model was used to calculate pooled estimates of
   effect for all studies combined. There were 8330 deaths
   after a mean of 10.6 y of follow-up. Mortality from
   ischemic heart disease was 24% lower in vegetarians than
   in nonvegetarians (death rate ratio: 0.76; 95% CI: 0.62,
   0.94; P < 0.01). The lower mortality from ischemic heart
   disease among vegetarians was greater at younger ages and
   was restricted to those who had followed their current
   diet for >5 y. Further categorization of diets showed
   that, in comparison with regular meat eaters, mortality
   from ischemic heart disease was 20% lower in occasional
   meat eaters, 34% lower in people who ate fish but not
   meat, 34% lower in lactoovovegetarians, and 26% lower in
   vegans. There were no significant differences between
   vegetarians and nonvegetarians in mortality from
   cerebrovascular disease, stomach cancer, colorectal
   cancer, lung cancer, breast cancer, prostate cancer, or
   all other causes combined."

See also

TABLE 7. All-studies death rate ratios and 95% CIs and the number of
deaths by diet category
<http://www.ajcn.org/cgi/content-nw/full/70/3/516S/T7>

from which we see that the all-causes death rate ratios for regular
meat-eaters, occasional meat-eaters, fish-eaters, lactoovovegatarians
and vegans were 1.00, 0.84, 0.82, 0.84, and 1.00, respectively, when
compared with regular meat-eaters. The table also gives 95% confidence
limits for these ratios.

Michael Greger, M.D. and a vegan, is concerned about the healthiness
of vegan diet, and writes about it in the article

Maximizing Vegetarian Nutrition by Michael Greger, M.D.
<http://vegnews.org/modules.php?name=News&file=print&sid=121>

as follows:

    "August of this year, the BBC reported that the British
    Advertising Standards Authority attacked a vegetarian
    organization for making "alarmist" and "unsubstantiated"
    claims about the risks of eating meat. Headlines like
    "Vegetarian group slammed over advertising" splashed across
    the evening news. What "exaggerated" claims were targeted by
    the Agency? The vegetarian group claimed that meat-eaters were
    at increased risk of dying from heart disease and stroke, and
    that vegetarians lived longer than meateaters. How could the
    agency possibly find fault with such incontrovertible facts?
    because, simply put, our "facts" aren't true.

    The latest science and the best science that we have that we
    have suggests that we vegetarians do not live longer than our
    meat-eating counterparts. The latest published results came
    out January, 2002 in a journal called Public Health Nutrition.
    Eight thousand vegetarians were followed for 18 years, and no
    survival advantage was found. Then April, 2002 the results of
    a study twice that size were released at the International
    Congress on Vegetarian Nutrition held at Loma Linda
    University. A study involving seventeen thousand vegetarians
    followed for about 9 years confirms the bad news-no survival
    advantage for vegetarians. Even more worrisome, both this huge
    studies found that vegetarians had an increased risk of dying
    from degenerative brain diseases."

As for the association between fish eating and cancer see for example
the following studies:

Wolk A, Larsson SC, Johansson JE, Ekman P.
Long-term fatty fish consumption and renal cell carcinoma incidence in
women.
JAMA. 2006 Sep 20;296(11):1371-6.
PMID: 16985229 [PubMed - in process]
<http://jama.ama-assn.org/cgi/content/full/296/11/1371>

Terry P, Wolk A, Vainio H, Weiderpass E.
Fatty fish consumption lowers the risk of endometrial cancer: a
nationwide case-control study in Sweden.
Cancer Epidemiol Biomarkers Prev. 2002 Jan;11(1):143-5.
PMID: 11815413 [PubMed - indexed for MEDLINE]
<http://cebp.aacrjournals.org/cgi/content/full/11/1/143>

Terry P, Lichtenstein P, Feychting M, Ahlbom A, Wolk A.
Fatty fish consumption and risk of prostate cancer.
Lancet. 2001 Jun 2;357(9270):1764-6.
PMID: 11403817 [PubMed - indexed for MEDLINE]
<http://www.thelancet.com/journals/lancet/article/PIIS0140673600048893/fulltext>
(requires a free registration)

Larsson SC, Kumlin M, Ingelman-Sundberg M, Wolk A.
Dietary long-chain n-3 fatty acids for the prevention of cancer: a
review of potential mechanisms.
Am J Clin Nutr. 2004 Jun;79(6):935-45. Review.
PMID: 15159222 [PubMed - indexed for MEDLINE]
<http://www.ajcn.org/cgi/content/full/79/6/935>

Holy McHamburgers! I've now read more pages of debate over the book than
of the book itself, and still have no idea how valid are Campbell's
study and book. I'm putting the book on a shelf and resuming my regimen
of primarily Mediterranean diet principles applied to global cooking
(e.g., Mediterranean Mexican, Mediterranean Chinese, Mediterranean
desserts, Med southern U.S.). If I'm still alive when the protein debate
dust begins to settle, and if someone finds something better than 1%
milk to pour over a huge bowl of whole grain cereal and fruits and nuts,
maybe I'll look into it again.

Thanks for the leads, Matti. You've compiled a very impressive body of
research with no obvious bias. But given the endless disagreement among
peer-reviewed studies in almost every field of medicine, I suspect our
health efforts beyond smoking cessation, weight moderation, and
fast-foods avoidance are best spent in the single arena in which
virtually all research agrees: exercise. It is clinically and visually
obvious that my playtime and gym time have knocked decades off my
chronological age and physical work/play capacity, so even if my cancers
nail me, I'm having a great time on my way to the grave. *That* we can
all control to some degree, and although the later we start the faster
the improvement, the sooner we start the greater the overall benefits.

I.P.