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Vegetarian diet study recap avoids cause-and-effect language but veers off into speculation

New meta-analysis finds a plant-based vegetarian diet is associated with lower cholesterol

Our Review Summary

This news release reports on a meta-analysis that examined the effects of a plant-based vegetarian diet on cholesterol and triglyceride levels measured in the blood. The release does a good job of describing the benefits of a plant-based vegetarian diet compared to other diet types as it relates to cholesterol. It also makes mention of other mechanisms that could account for the observed changes seen in cholesterol levels and appropriately uses terms like “association” and “correlation” when describing the findings rather than cause-and-effect language.

However, the release goes too far in crediting a vegetarian diet for reductions in heart attacks, strokes, and premature death. Those outcomes weren’t part of the analysis.

Other things that would have made the release better: less reliance on a very subjective anecdote and an explanation of the limitations of observational studies. It would have also been good to note that cholesterol is a surrogate marker for heart disease, not a specific health outcome. Finally, readers would be better served with a more balanced comparison with other types of diets, including the Mediterranean diet.

 

Why This Matters

A healthy diet can be used as a form of prevention and treatment for many chronic diseases including heart disease, diabetes, and cancer. However, what makes a diet “healthy” can vary from person to person. Research from both observational studies and randomized clinical trials can help healthcare providers and patients identify a diet type that best suits a patient’s medical and lifestyle needs.

It’s important that when reporting on this research journalists don’t minimize the efforts required to implement and sustain these changes.

Criteria

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

Not Satisfactory

The release gives a brief nod to costs, acknowledging that the diet would fit into “nearly every” budget. But we’d like to see a bit more. The costs of adhering to a plant-based vegetarian diet could be prohibitive for some, particularly those without easy access to fresh produce markets. While it would take some effort to estimate the annual cost of eating this way for a person or family, the cost consideration could at least be acknowledged.

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

Satisfactory

This release clearly states the benefits of a plant-based vegetarian diet for cholesterol. In clinical trials, a plant-based diet was reported to lower total, high-density lipoprotein (HDL) and low density lipoprotein (LDL) cholesterol levels by 12.5 mg/dL, 3.4 mg/dL, and 12.2 mg/dL respectively. In observational studies, a plant-based diet was associated with reductions in total, HDL, and LDL cholesterol levels of 29.2 mg/dL, 3.6 mg/dL, and 22.9 mg/dL respectively. The release also included information on the lack of association between dietary patterns and blood triglyceride (a type of fat) levels — an important mention of results that were not statistically significant.

However, the case description based on the physician’s subjective personal experience was over the top and detracted from the more balanced aspects of the release.

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

Not Applicable

The release doesn’t address harms but does suggest registered dietitians and the menus found in federal recommended dietary guidelines could help people transition to a plant-based diet. There is mounting evidence that plant-based diets may be associated with reduced risk for many health conditions, as long as one eats a balanced diet and in moderation. We’ll rate this one Not Applicable.

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

Not Satisfactory

The release does some things well here. It provides details on the types of studies analyzed and the findings from each type (randomized or observational). It addressed why there were greater risk reductions seen for total, HDL, and LDL cholesterol levels in the observational studies compared to the clinical trials — “…likely due to long-term adherence to plant-based eating patterns and changes in body composition.” It also mentions some of the underlying mechanisms that may be responsible for a plant-based diet’s effects on cholesterol, such as lower body weight, a reduced intake of saturated fat, and an increased intake of plant foods.

But the release goes too far in crediting a vegetarian diet for reductions in heart attacks, strokes, and premature death. That wasn’t the study outcome and it’s very unlikely a randomized clinical trial was performed measuring these outcomes.

The release would have been stronger if it had pointed out that cholesterol is a surrogate marker for heart disease, not a health outcome, and if it had mentioned the limitations of meta-analysis and of observational studies — the main one being that observational studies do not show cause and effect.

Does the news release commit disease-mongering?

Satisfactory

There is no evidence of disease mongering.

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

Satisfactory

The release notes that the research is funded by the Physicians Committee for Responsible Medicine. Reporters will have to dig a little deeper to learn that group supports an activist agenda on behalf of animal rights, which may have a bearing on its health and diet recommendations. But the release meets our minimum standard for a satisfactory grade.

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

Satisfactory

This release compares the effects of several other diet types on cholesterol levels to a plant-based vegetarian diet. Readers learned that a plant-based vegetarian diet is associated with greater reductions in total, HDL, and LDL cholesterol levels than omnivorous (diets based on both animals and plants), low-fat, calorie-restricted, or conventional diabetes diets. However, the release lumps most of these alternative diets into one group to arrive at a comparison between vegetarian diets and the others. Since there are large differences in cholesterol levels between the plant-based vegetarian diet and each alternative diet type it would have been helpful to readers to break these comparisons down by individual diet.

More importantly, it could be argued that these benefits may also apply to a “plant-based” diet that’s not vegetarian. Strong clinical trial evidence supports a Mediterranean style of eating that doesn’t require completely cutting out meat.

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

Satisfactory

The release notes that registered dietitians can help people transition to a plant-based vegetarian diet. It also recommends the vegetarian diet plans contained in the 2015 Dietary Guidelines for Americans.

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

Not Satisfactory

Is it novel to show that vegetarian diets are associated with lower cholesterol? Other studies have examined the relationship between vegetarian diets and plasma lipid levels, and comparing them with omnivorous diets, found there was no difference in high density lipoprotein cholesterol (HDL-c).

We wondered if there was some other aspect of the study that made it novel. The release notes that the study goal was to examine the association between a vegetarian diet and plasma lipid levels “throughout the lifespan.” According to the published study, this was the first meta-analysis to do so on a “long-term” basis. However, to be included in the analysis, clinical trials and observational studies only had to be 4 weeks of duration — hardly “long-term.”

 

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

Satisfactory

Overall, the release did not raise any of our red flags for sensational language. However, caution should be exercised before making statements such as that found in the physician testimonial:

“Within the first month of making the dietary change, he effortlessly lost 10 pounds.”

Losing weight by making and sustaining dietary changes is rarely an effortless process. It takes time, commitment, and often, social support from family and friends. This characterization can be misleading for readers.

Total Score: 6 of 9 Satisfactory

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