This news release from the Hass Avocado Board, an agriculture promotion group, summarizes findings from a retrospective analysis that involved combing through hundreds of studies on avocados to find 10 very small ones that addressed the fruit’s impact on cholesterol. When data from the studies were analyzed together the researchers found support for the assertion that eating 1 or 1.5 fresh avocados a day reduces total cholesterol, low density lipoprotein cholesterol and triglycerides. In its description of the benefits and evidence the release omits needed quantification and limitations of the research.
Cholesterol is one of many risk factors for cardiovascular disease, which is the leading cause of death in the US. Dietary changes that improve the cholesterol profile may in turn lower the risk of heart disease. However, it is the overall dietary pattern in addition to other known risk factors (smoking, hypertension, obesity, family history, among others), that influence ultimate risk of cardiovascular disease. The addition of a single food to the diet is not expected to result in meaningful changes in overall risk.
Avocados are expensive and that should be acknowledged when advising consumers to add 1 or 1.5 daily to their diets. According to the Hass Avocado Board’s own website, the average retail price of a conventionally grown avocado is $.89, while an organic one is $1.52. A family of four could potentially spend $25 to $42 a week on avocados alone were they to adopt the release’s recommendation.
There are several benefit claims but no quantification is provided. For example:
“Researchers found avocado consumption (1 to 1.5 per day) significantly reduced total cholesterol (TC), “bad” low density lipoprotein cholesterol (LDL-C) and triglycerides (TG) when they were substituted for sources of saturated fat.”
How much is a significant reduction? From what level to what level?
“Interestingly, our results indicate that even healthy subjects with a relatively normal baseline TC (100 to 240 mg/dL), LDL-C (75 to 150 mg/dL), and TG (50 to 175 mg/dL) had significant reductions,” says Sachin Shah, PharmD, corresponding author and expert in cardiovascular health.”
Again: what were the actual reductions?
Statistically significant findings are not the same as clinically important findings, and the public needs to know how much cholesterol reduction was found in the study. It would also be useful to point out that cholesterol changes do not necessarily equate to reduced risk of actual heart attacks and strokes.
It could have been noted that adding an avocado or two a day to one’s diet would also add to daily caloric intake. An average avocado has around 250 calories and 21 grams (about one-third of the recommended daily allowance) of fat. Additional caloric intake can result in weight gain and stored fat, which in turn impacts metabolic markers (such as increased insulin production and inflammatory markers) and cardiovascular risk.
The release tells us that the meta-analysis looked at 10 studies that together comprised 229 volunteers, suggesting an average participation of 23 people per study. Those are very small studies.
According to the study, in its Discussion section, “Although the overall analysis effectively evaluated the use of avocados in improving lipid profiles, the subgroup analyses by health status or baseline diet are difficult to assess due to the small sample size in each subgroup.”
It bears noting that even a meta-analysis can reach the wrong conclusion if studies it includes themselves had design flaws.
The news release contradicts itself when first stating that benefits were seen after daily consumption of 1 to 1.5 avocados but then states elsewhere, “However, the optimal amount of avocado and frequency of use needs further evaluation along with the nutritional similarities and differences between other different MUFA sources.”
This suggests that the researchers really weren’t sure how much and how often avocados should be consumed to see benefit.
The news release does not engage in disease mongering. Heart disease is clearly important and that is not overstated.
The release states that the research was “conducted at the University of the Pacific and independently funded.” The published study doesn’t tell us who funded the study either. Under “Financial disclosures” it states “The views expressed in this material are those of the authors and do not reflect the official policy or position of the U.S. Government, the Department of Defense, the Department of the Air Force or University of the Pacific.” That statement has nothing to do with financing the study.
The beneficial cholesterol-lowering ingredient in avocados is monounsaturated fatty acid (MUFA) which can be found in other foods. The news release doesn’t mention these alternate food sources for MUFA but the study did. It states:
“Specific types of nuts are also a good source of MUFA. In a pooled analysis of 25 studies that looked at a variety of nuts (almonds, walnuts, pistachios, peanuts, and macadamias), a mean LDL-C reduction of 7.4% was evident.”
It’s common knowledge that avocados are widely available so it doesn’t need to be addressed in the news release.
The release makes it clear that the study is an analysis of previous research and that it lends further support to the idea that avocados may be beneficial to one’s diet. It’s evident that the “news” here is the study, and that the idea that avocados lower cholesterol isn’t novel in and of itself.
The release misinforms when it claims that meta-analysis studies such as the one described here are “considered the best evidence and an unbiased overview of the body of knowledge on a specific topic. ” In reality, a randomized, controlled, blinded clinical trial involving an adequate sample of participants would likely provide better evidence and less chance of bias than a retrospective review of hand-selected previously published research.