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Heavy reliance on surrogate markers doesn’t tell full story of diet advantages

Vegetarian and Mediterranean diet may be equally effective in preventing heart disease

Our Review Summary

vegetarian diet, Mediterranean diet, vegetablesThe subject of the news release is a newly published, randomized, controlled study comparing the effects of a Mediterranean diet and a lacto-ovo vegetarian diet (which excludes meat and fish but allows eggs and dairy) on total body weight, BMI, fat mass, and cholesterol levels.

The release clearly outlines the differences in the two diets and makes it clear this is the first head-to-head comparison of these two diets within groups of meat consumers.

But the news release falls short in not including many of the study’s limitations, as well as making it clear to readers that the study outcomes are based on surrogate markers that cannot draw direct conclusions about “preventing heart disease” or stroke as implied.


Why This Matters

According to the CDC, heart disease is the leading cause of death in the U.S., with more than  600,000 deaths per year. Dietary patterns are known to affect our risk for heart disease, and represent an opportunity for each of us to modify that risk.

What concerns most of us is having the duration or quality of our life affected by a heart attack, stroke, or other cardiovascular disease. So studies which actually look at hard outcomes like that — rather than surrogate markers such as cholesterol levels measured over just a few months — are more relevant to more people.

Furthermore, studies which look at the effect of diet on major diseases like cancer, heart disease, diabetes, and stroke aren’t just widespread, but often lead to wide-ranging and wide-reaching news coverage. Such studies usually have significant limitations, debatable outcomes, and are prone to unjustified or hyperbolic language. This places a premium on journalists covering such studies to look for independent viewpoints, and a premium on readers for staying skeptical.


Does the news release adequately discuss the costs of the intervention?

Not Satisfactory

At first glance it might seem appropriate that costs are not mentioned. However, the comparative costs of these two diets could vary considerably depending on what part of the world you live in (ie. in some locations, a Mediterranean diet is either not feasible or prohibitively expensive).

Also, the subjects in this study received both nutritional counseling and diet plans which, may not only have influenced the outcomes of this study, but also would carry a price tag in the real world.

Does the news release adequately quantify the benefits of the treatment/test/product/procedure?


Both the lacto-ovo vegetarian diet (Vd) and the Mediterranean diet (Md) were effective in reducing body weight, body fat, and body mass index with no significant differences between them. The release presents these benefits in absolute numbers. However, the Md led to greater reductions in triglyceride levels, while the Vd led to greater reductions in low-density lipoproteins (so called “bad” cholesterol). These were well covered in the news release.

But the latter benefits are changes in surrogate markers measured over just 3 months in people at a low risk for cardiovascular disease. Whether these results translate into meaningful, sustained, and clinically relevant outcomes that actually affect people’s risk for developing heart or vascular disease can not be answered by this small randomized, controlled study.

Does the news release adequately explain/quantify the harms of the intervention?

Not Applicable

Both diets used in the study are generally safe for most people. Food intolerances aside, the only potential harm we could see in the diets used in the study is that the calorie quota (about 2100 calories per day) may not be appropriate for all people.

Does the news release seem to grasp the quality of the evidence?

Not Satisfactory

Although the news release does mention one study limitation (“the fact that participants were at ‘relatively low’ risk of cardiovascular disease”) it did not mention two other important limitations; mainly, a relatively small study size (in a ‘low-risk country for cardiovascular disease’ as the authors mention) and a short study duration of just 3 months.

It’s also not mentioned that the subjects received nutritional counseling and menu plans which — as with the limitations mentioned above — limits how relevant these findings may be to people trying to incorporate either of these diets into their lives.

Finally, this study shows very short-term outcomes with surrogate markers (such as weight, BMI, body fat). It did not look at hard outcomes of cardiovascular disease — like heart attacks, strokes, or death — as the headlines suggest.

Does the news release commit disease-mongering?


No disease mongering but the news release walks a very fine line of equating surrogate markers with actual cardiovascular disease.

Does the news release identify funding sources & disclose conflicts of interest?


The release noted “this research received no specific grant from any funding agency, commercial, or not-for-profit sectors.” No conflicts of interest are identified in the published study.

Does the news release compare the new approach with existing alternatives?


This study was designed to strictly compare just two types of diets. So not bringing up other dietary options seems appropriate.

Does the news release establish the availability of the treatment/test/product/procedure?

Not Applicable

The release didn’t specifically address availability.  We do acknowledge that while different fruits and vegetables are limited in different parts of the world, it is feasible to adopt a Mediterranean style or vegetarian style diet almost anywhere by substituting some vegetables and protein sources for others.

Does the news release establish the true novelty of the approach?


The news release clearly establishes the novelty of this study (which is also mentioned in the published study):

Previous separate studies have shown that the Mediterranean diet reduces certain risk factors for cardiovascular disease, as does a vegetarian diet; however, this was the first study to compare effects of the two distinct eating patterns.

Does the news release include unjustifiable, sensational language, including in the quotes of researchers?

Not Satisfactory

The headline of this news release is not justified because the study did not investigate the impact of these diets on preventing heart disease.

Also, stating that these two diets are “likely equally effective in reducing the risk of heart disease and stroke” is not supported by the study, which looked at surrogate markers, not disease incidence or prevalence.

Total Score: 5 of 8 Satisfactory


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