minded, as it ignores the other important scientific information currently available, e.g., the evidence of evolution and anthropology. (Of course, some formal dietary studies are ecological [epidemiological] and are based on the aggregation of large amounts of data. However, such studies require followup clinical studies to confirm hypotheses suggested by the ecological data. So, one ends up right back [again] with clinical studies.)
One example of the information to be gained from evolutionary and/or "paleo"-type studies is the data available from research on hunter-gatherers regarding the health effects of their omnivorous diets (which are much different than various versions of the SAD/SWD omnivorous diet utilized in most clinical research), which was discussed earlier here in Part 8. Another area of research, one closely related to evolutionary studies, is the newly emerging biomolecular study of genes and their effects. These offer the promise of not simply new information but also a new way of thinking about dietary problems.
Genetic studies offer a new paradigm for giving insights into optimal diets for INDIVIDUALS, rather than blanket recommendations based on clinical studies of GROUPS. With the mapping of the entirety of the human genome currently in progress, insights will be (and are already beginning to be) gained into the actual purpose and design of the human organism's functioning at the level of genes/molecular biology (the most fundamental "physiological" level possible). In conjunction with paleoanthropological insights regarding evolutionary adaptation, this understanding of the body's actual genetic design--when applied to nutritional questions--stands to give us a newly detailed understanding of the consequences of various eating patterns at the lowest nuts-and-bolts level. Eventually this will result in the ability to ascertain the actual step-by-step mechanisms governing the consequences of how foods are handled in the most unmistakable, fundamental way, and how their operation may vary from one individual to another.
Because they are based on studies of groups, clinical trials are vulnerable to yet-to-be-discovered confounding factors based on individual (genetic) differences. By definition, of course, these confounding factors can unfortunately be discovered only after the fact. Nevertheless, clinical studies are based on the assumption that with tightly-enough-controlled protocols, eventually all confounding variables can be eliminated. The desired objective in this is to be able to make dietary recommendations based on the outcomes of such trials that can be applied more or less equally to all individuals fitting the parameters controlled for. In itself, this is certainly logical.
However, controlling for all--or progressively more and more--confounding variables may eventually show that beyond a certain level of commonality, individual uniqueness becomes more important. Indeed, in Part 7 of this paper, we saw how there may be significant, telling differences between different individuals at the genetic level in regard to the problems both of insulin resistance and hereditary hemochromatosis, depending on one's evolutionary heritage. It's important to note here, also, that these types of genetic differences are not "genetic disorders"--they are normal (polymorphic) variations in genes that can occur between human populations or individuals depending on their evolutionary background. (Also see The Late Role of Grains and Legumes in the Human Diet, and Biochemical Evidence of their Evolutionary Discordance for a few other examples of genetic differences that may play a role in diet and disease.)
Genetics should greatly individualize the study of diet. One outcome of the unique insights to be had from the new paradigm of evolutionary and genetic studies should be the potential to greatly individualize the study of diet. This is something that clinical studies by their nature--as studies of groups based on statistical averages, rather than of individuals based on the interaction of actual (and unique) genetic mechanisms--are not as readily geared to explore.
Of course, clinical studies may still be required to test hypotheses about the interaction of genes with diet (by including controls for genetic differences between individuals) if such effects cannot be ascertained from genetic research at the physiological level alone. However, ultimately, the consequence of increasing genetic insights into diet will be the ability to evaluate which diets, or dietary patterns, work best for different individuals. To some extent, this places limits on the currently prevailing paradigm of clinical studies based on the statistically averaged results of groups. In so doing, it highlights the tendency of dietary idealists to use clinical studies as fodder for blanket recommendations meant to apply equally to everyone, or that assume one type of "ideal" diet can, should, or will work optimally for everyone.
Common sense and anecdotal evidence deserve consideration in certain circumstances
Relying exclusively on clinical studies also ignores anecdotal evidence. Although anecdotal evidence is indeed unreliable, at times it is the only evidence available. Despite its unreliability, it may be useful, under some circumstances, when no published studies are available on the topic of interest or when clinical data is skimpy or equivocal. Again, similar to what was noted above in regard to genetic issues, such circumstances may well depend on individual differences that escape the notice of clinical trials.
- Potential self-selection effects in long-term adherents of special diets. An often unaddressed issue involved when ruling out anecdotal evidence in the case of vegetarian and/or vegan diets (whether raw or conventionally vegan) that may be relevant is the problem of self-selection bias that can exist in some of the more formal studies. Even by the acknowledgment of those in the veg*n community interested in scientific assessments, the ranks of long-term veg*ns are comprised of the few left among a continuing stream of people trying such diets but later dropping out. (See archives of the Sci-Veg internet listgroup for past discussions of problems in arriving at reliable demographic or other more mundane statistics about veg*ns in the general population, for instance, due to sampling problems of this sort. One relevant thread runs from 6/17/98 to 6/29/98, on the topic "Survey Results"--search for the phrase "stock-vs-flow" to locate the most relevant passages on self-selection bias.) This can be a potentially large source of bias in long-term longitudinal studies that follow a chosen group over time.
- Dropouts from veg*n diets that may be due to "failure to thrive" (FTT) go largely unaccounted for. (Note: See the later section in Part 9 on failure to thrive for a brief discussion of this syndrome.) The problems of social pressures that keep people from adhering to diets that differ significantly from cultural norms, over the long term, are much discussed and often cited as the dominant factor responsible for dropouts; and such pressures can certainly be acknowledged as looming large among the potential reasons. (This is actually a problem with any diet significantly different from the norm, and not unique to veg*nism.)
However, at the same time, a continuing blind spot in the veg*n community seems to be a refusal to seriously consider the possibility some people simply may not do their best health-wise on a veg*n diet no matter what manipulations of it are tried. We include here among such people normal individuals without congenital enzymatic deficiences or other such syndromes. (This is mentioned because citing such syndromes, or carping over nitpicking-type details, is often the standard reply given in the veg*n community--in response to counterexamples--why the failures are held not to be indicative of possible problems with the diet itself.) Here, basic common sense should suggest the possibility that those who do the best on veg*n diets may be the ones who would tend to predominate among the ranks of long-term adherents. (Again, this could also be expected to apply not just to veg*nism but to any special diet significantly different from a culture's norm.)
- Anecdotal reports are of potential value in assessing "failure to thrive" given longitudinal studies are of those voluntarily veg*n. Thus, long-term studies of self-selected veg*n populations (rather than studies that randomly select individuals from the general population) may not be reliable in impartially assessing the full range of possible physical effects of veg*n diets that may occur in a more random sample of individuals. Consequently, when long-term studies of people who remain on vegan or vegetarian diets (or any diet, for that matter) for fairly significant periods of time are composed of those who consciously have chosen to be on the diet themselves, self-selection effects cannot logically be ruled out. (This of course is one reason why random or other sampling techniques designed to eliminate bias are so important in setting up target and control groups.)
- Moral ostracism as a masking effect obscuring awareness of "failure to thrive." Additionally, one of the thorniest problems that, in the opinion of this writer, continues to face the study of veg*n diets--given that they are often ideologically/morally based (in addition to whatever scientific merit they may also have)--is that those who "fail" or otherwise "abandon" the diet normally face significant ostracism from their former peers. Given this situation, there is justifiable merit in considering the value of anecdotal reports as potential indicators of what the full spectrum of physical outcomes on veg*n diets over the long-term may actually be, which would include equal attention to those who abandon diets. (Note: This caveat obviously does not apply to studies [usually much shorter-term, of course] composed of randomly selected individuals to make up a pool of test subjects.)
- Most who abandon veg*n diets do not come forward publicly without encouragement. This problem of morally based social disapproval from other adherents of veg*n diets is an additional factor beyond just the self-selection effect that compounds matters, making it very difficult procedurally for those wanting to study the situation to get an accurate sampling of the vegan dropout population to check the incidence of possible negative long-term problems. Often such former adherents understandably do not want to come forward very publicly or make known any "failure" they may have experienced, for obvious reasons (personal attacks, shame, being stigmatized by former associates, etc.).
Rather than seeking to understand to what degree FTT might exist, most often one can sense an almost palpable eagerness on the part of staunch adherents to explain away such problems or assign them into one or the other kind of irrelevance where the actual adequacy of the diet itself may be concerned. Given this prevailing atmosphere, it generally takes a proactively supportive environment before people will willingly and openly discuss any problems they may be having without withholding information.
- Examples of FTT. Within the rawist vegan community (a population that has yet to be scientifically studied) it is only very recently that anecdotal reports of the physically based problems that are one aspect of what, apparently, leads to the low long-term adherence rate have become more commonplace. This is primarily due to the emergence of communication groups and other "safe," "support" forums that have been created in recent years for people on such diets (some on the Internet). As mentioned above, without such proactive encouragement, it is unlikely those in the mainstream of vegetarianism will ever hear about more than a dribble of such cases.
(See The Psychology of Idealistic Diets on this site for an in-depth discussion of one pool of such anecdotal reports from the Natural Hygiene movement--a well-known subculture of vegans, some of whom eat raw vegan diets, others a more conventional-style vegan diet. Also see our Dietary Problems in the Real World page for first-person accounts of problems some individuals have experienced on various forms of such diets, some of which relate to possible FTT.)
- "Cheating" and dietary "exceptions" as a potential confounding variable to vegan research. It would be remiss at this juncture not to mention another important and potential "confounding variable" that faces those who would study the effects of diets such as veg*nism (particularly strict veganism) that restrict or eliminate an entire food class (animal foods) the body has been genetically programmed to expect by evolution.
Anyone who has ongoing access to personal conversations with a wide range of individuals practicing vegan diets, and who has had the chance to gain their confidence and cross-examine them in a friendly, sympathetic way, and is honest, will tell you that "cheating" on vegan diets (making occasional "exceptions" or eating foods not strictly "allowed") is not that unheard of, depending on the individual. Not that any given individual(s) may not be a perfect adherent. However, in some instances these dietary "exceptions" can be fairly regular and significant (anywhere from weekly to monthly "exceptions," perhaps) such that they add up over time. Despite the best of intentions, then, some individuals find themselves craving non-veg*n foods and cannot stick as faithfully to the diet as they might wish.
Role of dietary "exceptions" a particular concern with vegan research when deficiency questions are at issue. This is (or ought to be) a significant issue given that vegan research is often concerned with potential deficiency concerns (as opposed to problems of excess). Being able to track or account for behaviorial "exceptions" thus represents a serious obstacle to robust experimental design when attempting to evaluate the adequacy of strict vegan diets (for a range of individuals) over the long-term. If the diet is supposed to be strict, but the behavior may not be, and you do not have a way of rigorously checking for it, then your research methodology has problems if such noncompliance is implicated in preventing deficiencies.
Certainly the issue of the reliability of self-reports given by test subjects about food consumption in interviews or on questionnaires is a potential concern with any dietary research. However, with veganism it assumes special significance given the restrictive nature of the diet--in the sense that animal foods are eliminated, yet these are the very foods (usually dairy or eggs) partaken of in "exceptions" to the diet. Where deficiencies may be at issue, driblet amounts can sometimes be significant, in that it may not take a huge amount of a food to have an effect vis-a-vis deficiency. For vegan research, therefore, this possibility represents an important potential source of confounding error to address.
Unfortunately, this is not a problem that appears to be openly acknowledged or discussed much among those relying entirely on clinical research about vegan diets. Here again, therefore, anecdotal reports are not without their value in getting some idea of the importance that unmeasured "exceptions" may have, or the role they may play, in individuals following diets that are nominally vegan but perhaps may not always be completely so, in reality.
Hateful approach of certain fruitarian extremists. In contrast to the reliance on clinical studies by conventional vegans, the approach of many raw veg*n advocates differs. Some quote clinical studies very selectively, ignoring any that challenge their dogma (the usual rationalization is that it is from a "mixed" diet, and hence non-representative of results one might achieve on a raw vegan diet), while aggressively promoting any studies that appear to support their dogma (even if the results are for "mixed" diets).
A few fruitarian extremists reject (effectively) all clinical studies and science, and certain fruitarian crank science promoters selectively reject scientific research that challenges their dogma, on the hateful grounds that (the particular) science in question is the product of the minds of people who eat cooked foods (i.e., is "cooked science"), hence is wrong, worthless and/or cannot be trusted. The analogy to racism is obvious here; recall Hitler denouncing "Jewish science" if the analogy is not clear to you.
Other factors in evaluating clinical studies
Some of the limitations and problems inherent in clinical studies that may be relevant depending on the situation are:
- Statistical deficiencies. Some studies are based on small samples, short-term experiments (when long-term experiments are needed), and/or the statistical analysis is deficient (e.g., no control group, failure to measure covariates, uncontrolled confounding by external factors, errors in the choice of methods used for data analysis, etc).
- Creative intrepretation possible. One can usually find a (single) study, or interpret the results from a study in a way that supports a particular viewpoint--even if the view is known to be false.
- Potential for bias. Some studies are paid for by special-interest groups, and the objectivity of such studies may be dubious. One wonders if there may be some bias in the research.
Thus one should be cautious in interpreting the results of clinical studies. It is good to use multiple studies, review papers (those that look at or analyze the overall data from a wide range of studies), or standard reference books whenever possible, to avoid the problems of relying on only one study.
In summary
Clinical studies are a tool, to be used in an appropriate manner. Like any other tool, they can be used incorrectly. Finally, no number of clinical studies based on SAD/SWD data can overcome the logical fallacy (common in raw/veg*n circles) of claiming that results from such studies (SAD/SWD data) apply to all possible omnivore/faunivore diets.
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(The Cornell China Project: Examining the Vegan Claims)
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SEE REFERENCE LIST
SEE TABLE OF CONTENTS FOR:
PART 1 PART 2 PART 3 PART 4 PART 5 PART 6 PART 7 PART 8 PART 9
GO TO PART 1 - Brief Overview: What is the Relevance of Comparative Anatomical and Physiological "Proofs"?
GO TO PART 2 - Looking at Ape Diets: Myths, Realities, and Rationalizations
GO TO PART 3 - The Fossil-Record Evidence about Human Diet
GO TO PART 4 - Intelligence, Evolution of the Human Brain, and Diet
GO TO PART 5 - Limitations on Comparative Dietary Proofs
GO TO PART 6 - What Comparative Anatomy Does and Doesn't Tell Us about Human Diet
GO TO PART 7 - Insights about Human Nutrition & Digestion from Comparative Physiology
GO TO PART 8 - Further Issues in the Debate over Omnivorous vs. Vegetarian Diets
GO TO PART 9 - Conclusions: The End, or The Beginning of a New Approach to Your Diet?
Back to Research-Based Appraisals of Alternative Diet Lore
