|05-25-2007, 09:05 AM||#1|
| EricT |
Experience: 7-10 Years
Join Date: Jul 2005
It's about time someone did this kind of research review. Hope to see more in the future. I've mentioned this before and everyone should be aware of how important sources really are and just how biased those sources can be when you are reading some article touting the benefits of this or that food or sup. The next time you read about the amazing superiority of, for instance whey hydrosolates, consider the research funding. Chances are it was paid for by a sup company and the actual study was done using their whey product. Or just look at pretty much anything related to milk and the most likely finding source listed....Dairy Council.
Relationship Between Funding Source and Conclusion Among Nutrition-Related Scientific Articles
Lenard I. Lesser; Cara B. Ebbeling; Merrill Goozner; David Wypij; David S. Ludwig
Background: Industrial support of biomedical research may bias scientific conclusions, as demonstrated by recent analyses of pharmaceutical studies. However, this issue has not been systematically examined in the area of nutrition research. The purpose of this study is to characterize financial sponsorship of scientific articles addressing the health effects of three commonly consumed beverages, and to determine how sponsorship affects published conclusions.
Methods and Findings: Medline searches of worldwide literature were used to identify three article types (interventional studies, observational studies, and scientific reviews) about soft drinks, juice, and milk published between 1 January, 1999 and 31 December, 2003. Financial sponsorship and article conclusions were classified by independent groups of coinvestigators. The relationship between sponsorship and conclusions was explored by exact tests and regression analyses, controlling for covariates. 206 articles were included in the study, of which 111 declared financial sponsorship. Of these, 22% had all industry funding, 47% had no industry funding, and 32% had mixed funding. Funding source was significantly related to conclusions when considering all article types (p = 0.037). For interventional studies, the proportion with unfavorable conclusions was 0% for all industry funding versus 37% for no industry funding (p = 0.009). The odds ratio of a favorable versus unfavorable conclusion was 7.61 (95% confidence interval 1.27 to 45.73), comparing articles with all industry funding to no industry funding.
Conclusions: Industry funding of nutrition-related scientific articles may bias conclusions in favor of sponsors' products, with potentially significant implications for public health.
The extent of industrial funding for pharmaceutical research, and its implications for public health, have been extensively considered in recent years. Moses et al. reported that pharmaceutical firms provided 30% of the almost $100 billion spent on biomedical research in the United States in 2004. These expenditures raise concerns about the integrity of pharmaceutical research. A meta-analysis by Bekelman et al. of 37 original quantitative studies of bias in pharmaceutical research found significant association between industry sponsorship and pro-industry conclusions (odds ratio [OR] 3.6; 95% confidence interval [CI], 2.63 to 4.91).
In contrast, little information is available regarding the prevalence or impact of funding by the food industry on nutrition research. Whereas bias in pharmaceutical research could have an adverse effect on the health of millions of individuals who take medications, bias in nutrition research could have an adverse effect on the health of everyone. Findings of nutrition research influence the formulation of governmental and professional dietary guidelines, the design of public health interventions, and regulation of food product health claims. In addition, these findings may receive widespread publicity in the popular media, directly affecting consumer behavior.
Nestle examined a convenience sample of 11 studies from food, beverage, or supplement companies, reporting that "it [was] difficult to find studies that did not come to conclusions favoring the sponsor's commercial interest". Levine et al. found that authors taking a supportive compared to a critical or neutral position on the fat substitute olestra were much more likely to have a financial relationship with the manufacturer (80% versus 11% or 21%, respectively; p < 0.001). However, a systematic investigation of bias in nutrition research has not been conducted.
The aim of this study was to examine financial sponsorship of nutrition-related scientific articles, and whether sponsorship affects published conclusions. We hypothesized that scientific articles funded exclusively by the food industry or affiliated organizations would be more likely to have favorable conclusions than articles without industry-associated sponsorship. In 2003, approximately 10,000 nutrition-related scientific articles were published on many foods and nutrients, examining a variety of endpoints relating to numerous health states, and employing widely varying study designs (Medline literature search using the terms "nutrition" or "food" or "beverage," limited to 2003, conducted on 15 March 2006). To avoid the methodological challenges arising from such great heterogeneity, we chose to focus our investigation on soft drinks, juices, and milk. The health risks and benefits of these three beverages have been the subject of much recent controversy, and the beverage industry is large and highly profitable, arguably creating an environment in which scientific bias might occur.
To avoid potential bias in our study design, coinvestigators independently selected articles for inclusion, analyzed article conclusions, and examined financial sponsors. Article conclusions were classified as "favorable," "neutral," or "unfavorable" by two coinvestigators who had no knowledge of financial sponsors. Funding source was classified as "all industry," "no industry," "mixed," or "not stated" by another coinvestigator who had no knowledge of article conclusions. In addition, relationship of sponsors to the beverage being studied was characterized according to whether a favorable finding would have "benefit," "no relationship," or "antagonism" to apparent financial interests. Then, associations between funding source and article conclusion were calculated, with adjustment for relevant covariates in some models.
Selection of Articles
We aimed to take the broadest view of the literature within the area of beverages and health, and therefore included a range of article types in the categories of interventional studies, observational studies, and scientific reviews. Scientific reviews -- but not commentaries, editorials, or letters -- were included because these articles are abundant, often cited, and potentially influential, and generally presumed to be objective. (However, we found very few scientific reviews that declared a source of funding; therefore, the numerical contribution of these articles to analyses of potential bias was small. We also conducted an analysis with scientific reviews excluded, focusing on only interventional studies.)
Articles included in this study were initially identified by the study coordinator (LIL) using OVID-Medline literature searches. The literature searches were designed in consultation with a medical librarian to have high sensitivity and intermediate specificity for inclusion criteria using the following terms to identify articles focusing on the beverages of interest: soft drinks, carbonated beverages; fruit juice, apple juice, orange juice, prune juice, cranberry juice, grapefruit juice, grape juice, guava juice, pear juice, pineapple juice, vegetable juice, carrot juice, tomato juice; milk. Additional terms for health and disease states of interest were included in the searches.
We used six inclusion criteria for study articles: (1) The topic relates directly to soft drinks, juices, or milk, or an inherent component of one of these beverages (e.g., calcium in milk). (2) At least one main endpoint relates directly to health, disease, or a disease marker. For example, an article demonstrating a health benefit of antioxidants in juice would be included, whereas an article describing manufacturing techniques to maximize antioxidant concentrations in juice would be excluded. (3)
The article involves or considers research with humans or clinical materials derived from humans. (4) Conclusions relate directly to the beverage under study. For example, an article examining the effect of dietary calcium on bone mineral density would be included only if implications to the health effects of milk consumption are stated explicitly. (5) The article is classified as an interventional study, an observational study, or a scientific review according to standardized criteria listed below (see Assessment of Covariates). Articles in the categories of commentaries, editorials, letters, and miscellaneous were excluded. (6) The article was published in the 5-y period between 1 January 1999 and 31 December 2003.
Articles identified by literature search were then examined individually by the study coordinator and removed if any inclusion criteria were not met. Several additional articles were removed from the study for the following reasons: article was coauthored by one of the coinvestigators involved in this study (to avoid potential bias); one of the coinvestigators involved in classifying article conclusions had previous knowledge of the article's sponsorship (also to avoid potential bias): or both coinvestigators involved in classifying article conclusions determined that all inclusion criteria were not met. (A list of included articles is available from the authors upon request.)
Classification of Article Conclusions
The study coordinator provided two coinvestigators (CBE and DSL) with each article's abstract and discussion/conclusion section (as available). The coinvestigators were given no information relating to the identity of the article (e.g., journal, title, authors) or to financial sponsorship. When electronic documents were available, a simple text file was utilized. For articles without electronic versions, photocopies were made that excluded or obscured any identifying information. The coinvestigators classified article conclusions independently and then met to resolve discrepancies, using the categories outlined below.
Favorable -- if both coinvestigators agreed that: (1) the conclusions suggested beneficial health effects or absence of expected adverse health effects, and (2) no statements were made that cast the product in a negative light.
Unfavorable -- if both coinvestigators agreed that: (1) the conclusions suggested adverse health effects or absence of expected beneficial health effects, and (2) no statements were made that cast the product in a positive light.
Neutral -- if the coinvestigators agreed that the conclusions were neither favorable nor unfavorable, or if the coinvestigators could not agree on classification.
Characterization of Financial Sponsorship
The study coordinator examined each article (and supplemental material, if relevant) in its entirety for information about financial sponsorship. A coinvestigator (MG) was given a list of all sponsors of each article linked to the type of beverage under study (soft drinks, juice, or milk). The coinvestigator was given no further information relating to the identity of the article (e.g., journal, title, authors) or to its methods or results.
The coinvestigator used generally available information, obtained in part by Internet searches, to characterize each sponsor as: (1) industry -- including for profit and nonprofit affiliations (e.g., US National Dairy Council), (2) industry-associated -- including governmental agencies that work with industry to promote consumption of specific foods or commodities (e.g., US Department of Agriculture), (3) nonindustry -- including governmental agencies with no industry association (e.g., US National Institutes of Health), university, and independent foundations, philanthropies, and other nonprofit organizations, and (4) unknown. Funding source was then classified for each article as outlined below.
All industry -- if all sponsors were classified as category (1) above.
No industry -- if all sponsors were classified as category (3) above.
Mixed -- if any sponsor was classified as category (2) or (4) above, or if the article had sponsors that were classified into more than one category.
We considered the possibility that an industry sponsor might fund a study or scientific review examining a competitor's product. For example, milk and soft drink consumption are reciprocally related among children; thus, a negative conclusion relating to soft drinks would arguably be advantageous to a dairy-affiliated organization. For this reason, the relationship of a financial sponsor to the beverage under study was characterized as outlined below.
Benefit -- if a positive finding appeared to be in its commercial interest.
Antagonism -- if a negative finding appeared to be in its commercial interest.
No relationship -- if the sponsor appeared to have no commercial interest at stake.
Unknown -- if commercial interest could not be determined.
Sponsors with no association or affiliation with the food industry (e.g., government, university, independent nonprofit) were characterized as "no relationship." No articles in the "all industry" category had sponsorship that was characterized as "no relationship" or as "unknown," nor did any have multiple sponsors in different categories. Thus, each "all industry" article could be subcategorized as "benefit" or "antagonism."
Assessment of Covariates
Three covariates were examined: publication year (available from Medline), article type, and potential author conflict.
Article type was classified according to the following definitions: interventional study -- if humans consumed, or if human tissue was exposed to, a food or food component with the intention of measuring a biological response; observational study -- if data were collected on participants without the intervention of the investigators; and scientific review -- if no original data were reported and if published research was analyzed in a systematic fashion.
Potential author conflicts for each article were identified if an explicit statement to this effect was made in the article about any author; or if a coinvestigator (MG) determined that the declared affiliation for any author might benefit from a positive conclusion relating to the beverage under consideration.
To evaluate changes over time in the percentage of articles with declared funding, we used the Mantel-Haenszel chi-square test for trend and exact binomial 95% CIs.
For analyses of the relationship between conclusion and funding source, we focused on the most discrete categories of funding: all industry -- benefit, no industry, and all industry -- antagonism. Studies with mixed funding were excluded because they represent a heterogeneous group, with different proportions of industry funding, potentially obscuring underlying relationships. Studies with no listed funding were also excluded from these analyses.
We evaluated the association between article conclusion (favorable, neutral, and unfavorable) and funding source using an exact linear-by-linear association test, pooling all article types. When evaluating this association for only interventional studies, we used Fisher's exact test, collapsing articles with favorable and neutral conclusions.
Using logistic regression analysis, we calculated ORs of conclusions for all industry compared to no industry funding. We computed two sets of ORs, one collapsing articles with a favorable or neutral conclusion and the other eliminating those with a neutral conclusion. Adjusted analyses controlled for relevant covariates, including publication year, beverage type, and potential author conflict of interests. One all industry -- antagonism article was categorized as unfavorable, a situation in which the sponsor was perceived to benefit from a negative conclusion about a competitor's product (see above). Therefore, we considered this article as favorable to the sponsor's interests, and reclassified it as such for the purpose of calculating ORs, per a priori hypothesis.
Figure 1 depicts the flow diagram for inclusion of articles in the study. A total of 538 articles were retrieved in the searches, of which 332 were excluded. Descriptive data for the remaining 206 articles are presented in Table 1 . Financial sponsorship was declared in 111 articles (54%). As shown in Figure 2, the proportion of articles disclosing sponsorship increased significantly from 1999 to 2003 (p for trend = 0.004). Considering all years together, 62% of interventional articles, 67% of observational articles, and 19% of scientific reviews indicated a funding source. Of those that reported sponsorship, 22% had all industry support, 47% had no industry support, and 32% had mixed funding.
Bars extend to the confidence limits of the exact binomial 95% CI. (Overall, funding declared for 62% of interventional studies, 67% of observational studies, and 19% of scientific reviews.)
Overall, article conclusion was significantly related to funding source, as shown in Table 2 (p = 0.037). Among interventional studies, those with all industry compared to no industry support were much less likely to have an unfavorable conclusion (0% versus 37%; p = 0.009) ( Table 3 ).
The OR for a favorable or neutral versus unfavorable conclusion, comparing all industry to no industry support, was 6.18 (95% CI, 1.20 to 31.92) after adjustment for relevant covariates ( Table 4 ). For the same comparison eliminating neutral articles, the OR was 7.61 (95% CI, 1.27 to 45.73).
The main finding of this study is that scientific articles about commonly consumed beverages funded entirely by industry were approximately four to eight times more likely to be favorable to the financial interests of the sponsors than articles without industry-related funding. Of particular interest, none of the interventional studies with all industry support had an unfavorable conclusion. Our study also documented industry sponsorship was very common during the study period, indicating considerable potential for introduction of bias into the biomedical literature. In view of the high consumption rates of these beverages, especially among children, the public health implications of this bias could be substantial.
The strengths of this study include a systematic method for identifying articles using objective criteria, a multi-level review process in which separate groups of coinvestigators collected data about conclusions and sponsorships without access to information that might bias judgment, and examination of a dynamic period in financial disclosure, during which the proportion of articles indicating funding had increased.
The primary limitation of the study is that we included only articles pertaining to three beverage categories; thus, the generalizability of our findings to other areas of nutrition is unknown. Because the articles varied greatly in approach, we were unable to collect meaningful information about factors that might reveal specific causes of bias, such as study quality. In addition, we made no attempt to obtain independent information about study sponsorship beyond that declared in the articles, nor did we assess other types of financial support, such as provision of supplies. Inaccurate or incomplete information about financial sponsorship may have caused us to underestimate the true magnitude of the relationship between conclusion and funding source. During the study period, declaration of financial support remained incomplete, especially for scientific reviews.
Studies of research supported by the pharmaceutical industry have suggested several ways that bias might be introduced into clinical trials,[7-9] and some of these might apply to nutrition research. We speculate that our findings may relate to one or more of the following possibilities: (1) Industrial sponsors may fund only those studies that they believe will present their products in a favorable light, or their competitors' products in an unfavorable light. In support of this possibility, all studies funded entirely by industry were characterized as "benefit" or "antagonism" with regard to the product under study (none were characterized as "no relationship"). That is, industrial organizations do not seem to sponsor articles about products in which they have no financial interest. (2) Investigators might formulate hypotheses, design studies, or analyze data in ways that are consistent with the financial interests of their industrial sponsors. (3) Industrial sponsors or investigators may choose to delay or not publish findings that have negative implications to the sponsor's product. (4) Authors of scientific reviews may search and interpret the literature selectively, in ways consistent with the sponsor's interests. (5) Scientific reviews arising from industry-supported scientific symposia, often published as journal supplements, may over- or under-represent certain viewpoints, if presenters whose opinions conflict with the sponsor's financial interests are not invited to participate.
Some might question the significance of our findings, arguing that no investigator could ever be completely free of bias. We agree that financial conflict is not the only cause of bias. Indeed, the hallmark of modern scientific method, the a priori hypothesis, indicates a preconceived notion of how an experiment will unfold. Moreover, long-standing scientific viewpoints, career considerations, and even political opinions might color study design or interpretation. However, these types of individual bias tend to cancel themselves out among large groups of scientists over the long term. While one investigator's career may rise on a cherished theory, another's may rise by debunking that theory. We contend that financial conflict of interest is qualitatively different, producing selective bias that acts consistently in one direction over time. This contention receives support from a study by Kjaergard and Als-Nielsen, who found that authors' financial competing interests, but not their other competing interests, biased the conclusions of clinical trials.
If the findings of our study are supported by additional research, several ways to reduce bias among nutrition articles could be considered, including voluntary refusal by scientists to accept industrial support, regulations by academic institutions ensuring that publication decisions and editorial control remain with the researcher, and more stringent policies by journals for publication of industry-sponsored studies and scientific reviews. Ultimately, increased government and other independent support for nutrition research will diminish the attractiveness of industry funding to investigators and dilute any bias resulting from publication of industry-funded science.
Much of the money available for doing medical research comes from companies, as opposed to government agencies or charities. There is some evidence that when a research study is sponsored by an organization that has a financial interest in the outcome, the study is more likely to produce results that favor the funder (this is called "sponsorship bias"). This phenomenon is worrying, because if our knowledge about effectiveness and safety of medicines is based on biased findings, patients could suffer. However, it is not clear whether sponsorship bias extends beyond research into drugs, but also affects other types of research that is in the public interest. For example, research into the health benefits, or otherwise, of different types of food and drink may affect government guidelines, regulations, and the behavior patterns of members of the public. Were sponsorship bias also to exist in this area of research, the health of the wider public could be affected.
Why Was This Study Done?
There is not a great deal of evidence about whether sponsorship bias affects nutritional research (scientific studies that look at the relationship between food and/or drink, and health or disease states). Therefore, the group of researchers here set out to collect information from published nutritional research papers, to see if the type of sponsorship for the research studies was in any way linked with whether the main conclusions were favorable or unfavorable to the sponsor.
What Did the Researchers Do and Find?
The research study reported here used the scientific literature as a source of data. The researchers chose to examine one particular area of nutrition (nonalcoholic drinks including soft drinks, juices, and milk), so that their investigation would not be affected too much by variability between the different types of nutritional research. Using literature searches, the researchers identified all original research and scientific review articles published between January 1999 and December 2003 that examined soft drinks, juices, and milk; described research carried out in humans; and at the same time drew conclusions relevant to health or disease.
Then, information from each published article was categorized: the conclusions were coded as either favorable, unfavorable, or neutral in relation to the health effects of the products being studied, and the article's funding was coded as either all industry (ie, food/drinks companies), no industry, or mixed. 206 published articles were analyzed and only 54% declared funding. The researchers found that, overall, there was a strong association between the type of funding available for these articles and the conclusions that were drawn. Articles sponsored exclusively by food/drinks companies were four to eight times more likely to have conclusions favorable to the financial interests of the sponsoring company than articles which were not sponsored by food or drinks companies.
What Do These Findings Mean?
These findings suggest that a high potential for bias exists in research into the health benefits or harms of nonalcoholic drinks. It is not clear from this research study why or how this bias comes about, but there are many different mechanisms that might cause it. The researchers suggest that certain initiatives might help to reduce bias, for example, increasing independent funding of nutrition research.
We thank Dr. David Blumenthal for stimulating discussions and Dr. Martin Lesser for statistical advice. We thank Alison Clapp, medical librarian, for help in designing the literature searches, and Michael Leidig for logistical support.
This study was supported by a grant from the Charles H. Hood Foundation (Boston, Massachusetts, United States) and discretionary funds from the Department of Medicine, Children's Hospital Boston (Massachusetts, United States) to DSL. LIL was supported by a medical student research fellowship from the University of Rochester School of Medicine and Dentistry (Rochester, New York, United States). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
|05-29-2007, 12:56 PM||#5|
| hrdgain81 |
Rank: Light Heavyweight
Experience: 5-7 Years
Join Date: Mar 2005
I didnt read it, but i think its important none the less to understand where the money comes from for these published medical studies.
Its easy to point the finger at sup companys who do this shit, but many people dont realize that every related industry (be it food,drug,med tech) does the exact same shit. Its just people dont want to open thier eyes an see it.
good post eric
|05-29-2007, 01:10 PM||#6|
| EricT |
Experience: 7-10 Years
Join Date: Jul 2005
Oh absolutely. And just so everyone knows I wasn't trying to single out sup companies cuz it is widespread just like Hrdgain said. But for our particular purposes more people fall for "supplement studies" hook line and sinker. It's like a blind spot for many trainers (which is an obvious statement I know). More trainers seem to take food studies with a grain of salt than they do sup studies.
|05-31-2007, 03:58 PM||#7|
| EricT |
Experience: 7-10 Years
Join Date: Jul 2005
Research and the Mass Media--An Introduction
Department of Nutrition -Harvard School of Public Health
Over the past 100 years, great strides have been made in improving the health of people the world over. In the United States, for example, life expectancy has increased by about 25 years for men and 30 years for women, largely due to scientific advances that have helped prevent and treat many serious diseases.
The end results of science undeniably benefit us, but to people who don't work in the field, the scientific process can also be frustrating. This is particularly true for anyone trying to make important decisions about his or her health. What should I eat? How much exercise should I get? How often should I see the doctor for health checks? We all expect that science--specifically, health research--will provide answers to these very important and personal questions.
Unfortunately, it's often hard to get a straight answer. One day the "experts" say one thing. The next, they seem to say another. Then it all appears to switch back again. Such flip-flops can be maddening, especially when you're making your best effort to live a healthy lifestyle. Why go to the trouble of making big changes when today's highly recommended choice may be tomorrow's bad example?
The classic case of such flip-flopping in nutrition is the butter-versus-margarine question. More than 30 years ago, as research began to suggest that saturated fat might be bad for the heart, recommendations were made that encouraged people to switch from butter, which is high in saturated fat, to low-saturated-fat margarine. However, further research showed that, in many cases, margarine contained a type of fat (known as trans fat) that's even worse for the heart than saturated fat. This seeming about-face led many people to throw up their hands in frustration.
But the butter-versus-margarine question is also a well-known, if somewhat vexing, example of how research often works. Scientific research is a dynamic process that moves forward slowly. Recommendations are made based on the best science available at the time. However, with new research and new results, these recommendations may be revised.
On the other hand, such radical shifts in advice are rare today. There's far more research on diet and health available now than there was 30 years ago, when the original recommendation to switch to margarine occurred. This means that contemporary diet recommendations tend to be better-grounded--based on the results of many studies--and involve much less guesswork than in the past.
But contradictions in research results still occur. They are an inevitable part of the scientific process. Researchers are constantly performing studies and reporting their results. And when so many different people study each topic in so many different ways, it's natural that the results won't always be the same. What is the key, though, and what drives health recommendations is the weight of evidence on a particular topic--what all the results as a whole point to.
The research process is like placing stones on an old-fashioned balance scale. When enough weight accumulates on one side, the scale tips in favor of a particular recommendation. And the more weight there is on one side, the stronger the recommendation is and the more evidence it would take to change it.
If, on one side of the scale, you have over 40 studies showing that moderate alcohol intake can lower the risk of heart disease and, on the other, one or two studies that contradict those results, the scale would hardly budge. The weight of evidence would still be greatly in favor of moderate alcohol intake protecting against heart disease. Indeed, the link between alcohol and heart disease is so strong that it's known as an established relationship.
But not all topics are as clear-cut as this. Often, the weight of evidence is not as great. In some cases, only a handful of studies have addressed a particular question. In other cases, a large number of studies may lie on one side, but there may also be some particularly significant studies on the other side as well--just enough to cast some doubt. In these instances, we'd say that there is a probable link between a behavior and a disease. The value of eating moderate amounts of nuts to protect against heart disease is an example of a probable link.
There are also possible links, where the weight of evidence is still less and, in effect, the scale only tips slightly to one side. Possible links often develop in new, emerging areas of study, where a few studies have found a relationship, but more studies need to be done to confirm the results. A high intake of trans fat and an increased risk of diabetes is an example of a possible relationship that needs to be confirmed.
To carry this analogy further, the scale's likelihood of tipping reflects not only the number of stones placed on one scale, but also the size of those stones. Bigger stones will make the scale tip faster than smaller ones. Likewise, big, well-designed studies tend to play a more important role in establishing a relationship--and in shaping health recommendations--than smaller, less-well-designed studies.
Although the details can get complicated, large studies that follow human participants over time (randomized trials and cohort studies) tend to provide more reliable results than smaller studies that ask people about their past activities (case-control studies).
Different Types of Research Studies
There are many different types of research studies, and each has distinct strengths and weaknesses. In general, randomized trials and cohort studies provide the best information when looking at the link between a certain factor (like diet) and a health outcome (like heart disease).
Laboratory and Animal Studies
These are studies done in laboratories on cells, tissue, or animals. Laboratories provide strictly controlled conditions and are often the genesis of scientific ideas that go on to have a broad impact on human health. However, laboratory studies are only a starting point. Animals or cells are no substitute for humans.
These studies look at the characteristics of one group of people who already have a certain health outcome (the cases) and compare them to a similar group of people who do not have the outcome (the controls). While case-control studies can be done quickly and relatively cheaply, they aren't ideal for studying diet because they gather information from the past. People with illnesses often recall past behaviors differently from those without illness. This opens such studies to potential inaccuracy and bias in the information they gather.
These studies follow large groups of people over a long period of time. Researchers regularly gather information from the people in the study on a wide variety of variables (like meat intake, physical activity level, and weight). Once a specified amount of time has elapsed, the characteristics of people in the group are compared to test specific hypotheses (like the link between carotenoids and glaucoma, or meat intake and prostate cancer).
Though time-consuming and expensive, cohort studies generally provide more reliable information than case-control studies because they don't rely on information from the past. Cohort studies gather the information all along and before anyone develops the disease being studied. As a group, these types of studies have provided valuable information about the link between lifestyle factors and disease. Two of the largest and longest-running cohort studies of diet are the Harvard-based Nurses' Health Study and Health Professionals Follow-up Study.
Like cohort studies, these studies follow a group of people over time. However, with randomized trials, the researchers actually intervene to see how a specific behavior change or treatment, for example, affects a health outcome. They are called "randomized trials" because people in the study are randomly assigned either to receive or not receive the intervention. This randomization helps researchers hone in on the true effect the intervention has on the health outcome.
However, randomized trials also have drawbacks, especially when it comes to diet. While they are good at looking at topics like vitamin supplements and cancer, when the change in diet is more involved than say taking a vitamin pill, participants begin to have trouble keeping to their prescribed diets. Such involved interventions can also become very expensive.
For example: Fiber and Colon Cancer--Following the Scientific Trail
Because science is such a dynamic process, you can never exactly tell where it is going to lead you. Conclusions that once seemed logical and fairly solid may be revised--or completely overturned--as more and better research is done on a particular topic. One example of this is the relationship between fiber and colon cancer.
Starting about 30 years ago, a high fiber intake was regularly recommended as one way to lower the risk for colon cancer. This recommendation was largely based on observations that countries with a high fiber intake tended to have rates of colon cancer lower than the rates found in countries with a low fiber intake.
But such descriptive studies don't provide the most definitive information. While they are often good points to start a scientific journey, they only take a broad look at large groups of people. Descriptive studies generally can't address all of the factors that might account for differences in rates of disease. Fiber intake could indeed have something to do with the differences in colon cancer rates, but those differences could also involve many other things that differ between countries, including other diet or lifestyle factors.
When studies that can take such things into account on an individual level began to look at the issue of fiber and colon cancer, the picture became much less clear. A number of case-control studies found that a high fiber intake was linked to a lower risk of colon cancer, but many did not. Given these wavering results--and because case-control studies are not an optimal way to assess food intake, relying as they do on participants' recollections of what they ate in the past--more research using better methods was needed. In the meantime, many health professionals still regularly recommended a high fiber intake for people trying to lower their risk of colon cancer.
Not until the results of cohort studies came out did this recommendation begin to lose its backing. Because cohort studies observe a group of people over time, their findings are generally stronger than those of case-control studies, especially when it comes to something like diet and colon cancer. What most of these cohort studies found was that fiber intake had very little, if any, link with colon cancer.
Such findings were further bolstered by the results of randomized trials--types of studies that many consider the gold-standard of research. These studies took a group of people and randomly assigned individuals to one of two groups. One group was put on a high fiber diet, while the other group followed a lower fiber diet. After 3-4 years, the two groups were compared and no difference was found in rates of colon polyps--noncancerous growths that can turn into cancer. Of course, colon polyps are not cancer, but since it's thought that all colon cancers start as polyps, it is strong evidence that fiber intake has no direct link with colon cancer.
In this case, the path of discovery led from widespread belief in a clear link between fiber and colon cancer to acceptance of the likelihood that there was no strong link between the two. As such, it's an excellent example of how research can often develop. What may start as a clear connection based on findings from broad, descriptive studies can slowly unravel as more and better-quality research unveils the true nature of a relationship. However, keep in mind that a weak relationship is difficult to exclude altogether. Further studies might yet demonstrate a weak effect of fiber on colon cancer, although such a finding wouldn't alter the conclusion that other means must be sought to prevent colon cancer.
Deciphering Media Stories on Diet
Even at its best, science is a painstaking, deliberate process, which doesn't fit very well into the cut-and-dry, newer-is-always better world of the mass media. And it's the media reports on health that are responsible for much of the frustration the public feels toward the public health community. With their emphasis on short, "newsworthy" pieces, the media often only report the results of single studies, and many stories are chosen simply because the results run contrary to current health recommendations. Because such reports provide little information about how the new results fit in with other evidence on the topic, the public is left to assume that, once again, the scientists screwed up and are now backtracking.
Fortunately, in many cases it only takes a few incisive questions to get at the heart of a research-related news story and see how important the results are for you personally. One of the most crucial things to keep in mind is the issue we've already discussed above: how a given study fits into the entire body of evidence on a topic. Whenever reading or watching a news story on health, keep these questions in mind:
*Are they simply reporting the results of a single study? If so, where does it fit in with other studies on the topic?
*Only very rarely would a single study be influential enough for people to change their behaviors based on the results.
*How large is the study?
*Large studies often provide more reliable results than small studies.
*Was the study done in animals or humans?
*Mice, rats, and monkeys are not people. To best understand how food (or some other factor) affects human health, it must almost always be studied in humans.
*Did the study look at real disease endpoints, like heart disease or osteoporosis?
*Chronic diseases, like heart disease and osteoporosis, often take many decades to develop. To get around waiting that long, researchers will sometimes look at markers for these diseases, like narrowing of the arteries or bone density. These markers, though, don't always develop into the disease.
*How was diet assessed?
*Some methods of dietary assessment are better than others. Good studies will have evidence that the methods have validity.
*With these tips and a better understanding of the world of health research, you can look at health information with a more discerning eye. While this won't be a guarantee against frustration, it should help you embrace health recommendations--and the healthy lifestyle they promote--with more confidence.
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