Trans Fatty Acid: Unhealthy or Undebated (4) Final Analysis

Finally, the epidemiologic evidence to either support or refute the claimed association between trans fat intake and heart disease will be presented below. There are just six studies with overt examination of trans fat intake and it’s association with heart disease. Below is a list of the important studies, followed by a discussion of the strengths and weaknesses of each.

Study Findings: No association between trans fat intake and heart disease
1. Euramic Study: (1995)
2. Health Professionals Study (1996)
3. Scottish Heart Study (1996)


Study Findings: Association found between trans fat intake and heart disease
4. Finnish Study (1997)
5. Nurses Health Study (1997)
6. Zutphen Elderly Study (2001)


The No Association Studies
Of the studies listed above not finding an association between trans fat intake and heart disease is one that has been basically swept under the rug. The Health Professionals Followup Study followed a group of 43,757 men from 1986 to 1992 looking at a number of risk factors for heart disease including trans fat intake. The key is fiber intake. In those with high trans fat intake, fiber intake was low. In those with low trans fat intake, fiber intake was high. When the authors of the study adjusted for fiber intake, the statistical significance between trans fat intake and heart disease disappeared. The message seems to be that a dietary regimen low in fiber is a marker for a diet high in trans fat. High fiber intake has without question shown to be associated with a lower risk of heart disease. Thus one might conclude that fiber intake and not trans fat was the factor in their diets most associated with (or offering protection from) heart disease.

The Scottish Heart Study simply found no association between trans fat intake and heart disease in a widely followed cohort of men in Scottland.

The Euramic Study is widely criticized by those promoting the ill effects of trans fat (primarily those investigators at the Harvard School of Public Health). The Study sampled from 10 separate centers in 9 countries. The bottom line is this: No association between trans fat intake and heart disease was found. Detractors like to post hoc the findings and state that if Spain’s results were pulled out, there would be a significant finding. Sorry, too late. Taking two large centers (making up one-sixth of all those studied) out of the study is too convenient.


Studies Finding An Association
Of the studies finding an association between trans fat intake and heart disease, the Zutphen Elderly Study is the most compelling, but with marginal statistical significance. The one criticism I might level from the start is the study looked at an older population, age 64 to 84. We all know the risk of heart disease rises with rising age, and the key to significance in this study was making sure the participants were really disease free at the start of the 10 year analysis. The study began in 1960 and followed 878 men from Zutphen, Netherlands born between the years 1900 and 1919. Of the 878 men, 667 were given a questionnaire in 1985 regarding dietary intake. Of those 667 men, 435 and 225 were again surveyed in 1990 and 1995. Those with overt disease, angina or post myocardial infarction were excluded from the start. Doing the math, at the final analysis in 1995, the youngest member of the study would be 76 years old. At that age, we might find an association between nearly any variable and heart disease. The authors found that in the highest intake of trans fat (4.8% of calories) after fully adjusting for other possible confounding variables, there was an association between trans fat and heart disease. However the data were so marginal, that asking the question what is the risk of heart disease from various sources of trans fat for each 0.5% increase in energy, found no statistically significant data.

The Nurses Health Study is widely cited as the nail in the coffin for trans fat. The study followed 80,082 women over many years. The study found a very significant relationship between trans fat intake and heart disease. However, the authors noted that those consuming the highest amount of trans fat consumed the lowest amount of fiber. And those in the lowest intake of trans fat had the highest intake of fiber. The authors did not adjust their findings for fiber intake. A fatal flaw.


Conclusion:
The evidence attributing trans fat intake to heart disease is equivocal at best. The authors of the cited studies finding an association have heralded the elimination of trans fat from foods without hard evidence (other than the Nurses Health Study) that it might be harmful. Studies necessarily need to control for fiber intake to be taken seriously. However, no study has attributed trans fat intake in American men (Health Professionals Follow-up Study) to heart disease. Indeed, if the authors, primarily a small group of investigators from the Harvard School of Public Health, advocated as rigorously to include more dietary fiber in the average diet, trans fat intake would not be an issue. To attribute so fervently that trans fat is without question associated with heart disease makes me suspicious. Possible sources of secondary gain (again, primarily from those at the Harvard School of Public Health) include all the following trappings of large university syndrome:
1. Grant monies from the NIH,
2. Being identified as a world leader in public health
3. Lending credibility to a science that is so fraught with variable findings

In the end, trans fat doesn't have a study which anyone could identify as a smoking gun. Although the Nurses Health Study is widely cited as the final answer to the association between trans fat intake and heart disease, again, the authors did not adjust the findings for dietary fiber intake. And even if this study was the definitive answer, it was conducted in women and thus generalizable only to women. Any serious analysis of the studies leaves one skeptical about the strength of the public health message compared to the results found. As an aside, the industry is changing and any further study of trans fat will be difficult at best.