New Research Reveals Avocados Can Slash Heart Disease Risk

The last time we ‘chewed the fat’ on avocados in a blog post we were celebrating a bumper crop. Well, this year has been quite a rollercoaster of weather woes, causing the price of avocados to skyrocket to over $7 each. Now prices have unexpectedly plummeted to less than $1 each.

One possible reason for this dramatic price shift could be the avocados' quality not meeting export standards, resulting in an abundant domestic supply that benefits us all.

While we grapple with soaring grocery prices, avocados seem to buck the trend, offering much needed relief. And with yet another study published by a group in the US on the health benefits of consuming avocados — the news just keeps getting better.

Avocados are chock full of unsaturated fat and phytonutrients and contain decent amounts of fibre and micronutrients such as potassium, magnesium, and folate. Although there’s heterogeneity in the literature, there are good quality clinical trials that show consuming an avocado a day reduces LDL cholesterol ­– a critical marker of cardiovascular disease (CVD). These types of trials are designed to measure intermediate endpoints of chronic diseases rather than the diseases themselves.

Attempting to measure disease incidence or mortality through RCTs would require large numbers of participants, a long intervention period, and a ton of money ­– just not feasible.

Instead, cohort studies are our go to design here. Until recently there was no data on avocado consumption and disease outcomes. But we now have evidence from an analysis of two large cohort studies.

New research findings

The analysis included 68,786 women from the Nurses’ Health Study (NHS) and 41,701 men from the Health Professionals Follow-up Study (HPFS). The authors set out to assess the association between avocado consumption and hard clinical endpoints of CVD, including coronary heart disease (CHD), and stroke. They also took their investigation a step further by exploring the impact of substituting avocados for other high fat foods like butter, margarine, nuts, and vegetable oils.

Diet was assessed using a validated semi-quantitative FFQ comprising over 130 items ­– completed at baseline and at 4 yearly intervals over 30 years. One item asked how frequently on average participants consumed a portion (½ a fruit or ½ a cup) of avocado. The question had 9 responses (ranging from never or less than once a month to 6+ per day), which were collapsed into 4 categories: never or less than once per month, 1 to 3 times per month, once per week, and ≥2 times per week.

The primary outcome was incident cases of total CVD — a composite of fatal CHD, nonfatal myocardial infarction, and fatal and nonfatal stroke. Secondary outcomes included incident cases of total CHD (a composite of fatal CHD and nonfatal myocardial infarction) and total stroke.

After adjusting for dietary and lifestyle factors, compared to non- and low- consumers, those who consumed at least 2 serves of avocado a week had:

• 16% lower risk of total CVD (HR: 0.84; 95% CI 0.75, 0.95)
• 21% reduction in total CHD (HR: 0.79; 95% CI 0.68, 0.91) 
• But no reduction in total stroke

The news gets even better

Each half serve increase was associated with a significant 20% reduction in total CVD. There was evidence of a dose-response where more avocado meant less disease.

In the substitution analysis, including half a serve per day of avocado (1/4 of an avocado) in place of an equivalent amount of margarine, butter, eggs, cheese, processed meat, and yoghurt significantly reduced the risk of CVD by 16%, 22%, 18%, and 13%, 18%, and 11%, respectively.

There was no evidence of a benefit when substituting avocado for nuts, dairy foods, mayonnaise, olive oil, and other plant oils. This suggests you get more bang for your buck when swapping out avocado for less healthy foods.

Mechanisms of action

The authors propose several mechanisms for the observed reduction in CVD. Avocados, with their high monounsaturated fat (MUFA) content, particularly oleic acid, play a vital role in enhancing various aspects of cardiovascular health. These include:

• improving blood lipids and lipoproteins
• enhancing endothelial function
• mitigating hypertension
• reducing inflammation
• boosting insulin sensitivity

Avocados also contain reasonable amounts of plant sterols and fibre, which further contribute to the improvement of lipid and lipoprotein profiles, adding to their positive impact on heart health.

Strengths and Limitations

As always there are several discussion points that are worth considering when interpreting the study’s findings.

1. Avocado consumers had better diet quality and although the authors adjusted for diet and lifestyle factors, we can’t rule out residual confounding (uncontrolled or unmeasured variables that can still distort the observed association between an exposure (in this case avocado) and an outcome (CVD risk) in a study). Because of possible confounding, observational studies can’t directly infer causality. But we can evaluate the likelihood of causality from epidemiological studies by seeing how the evidence stacks up against the Bradford-Hill criteria. For this study, five of the nine principles were met including: (1) there is biological plausibility, (2) results are consistent with RCTs, (3) exposure precedes the outcome, (4) there is evidence of a dose-response relationship, and (5) there are analogies with lower CVD risk seen with the consumption of other foods rich in MUFA such as nuts and olive oil.
2. The population was largely white Americans and so generalisability of the results may be questionable. However, the mechanisms of action suggest the effects seen here are also likely to be observed in other populations.
3. Dietary intake was collected through self-reporting, a common approach – but one that warrants caution as it is subject to potential biases. Also, while FFQs seem straightforward to complete at first glance, they actually require a certain level of literacy and numeracy. The NHS FFQ asks: ‘Please try to average your seasonal use of foods over the entire year’. Given avocados are seasonal, some calculations are needed. In the US (the home of these 2 cohorts) the avocado season is from Spring to Autumn with the most popular varieties available from March to mid-September. So, if you eat a serve of avocado once a day during the 7-month season, your average over 12 months would be 4 times per week. Not rocket science but some mental arithmetic is needed (and in my case a calculator!) — and remember there are 130 items in the FFQ. Moreover, defining a serving size as half an avocado or half a cup adds to the complexity. This means additional calculations are needed if you eat a whole avocado per sitting or only a quarter — or perish the thought — you mix it up. On a positive note, diet was assessed multiple times during the follow-up period, helping to reduce random measurement errors.
4. Like nuts, avocados are high in fat, which means people may have concerns about weight gain. Although not formally analysed in this study, the highest consumers of avocados had on average a lower BMI than non- and low- consumers. This was nearly one BMI unit lower in the NHS cohort and nearly over half a unit lower in the HPFS.
5. There were some interesting differences between the two cohorts. For example, in the fully adjusted model total CVD was significantly reduced in the HPFS (HR: 0.82 (95% CI; 0.71, 0.95)) with ≥ 2 serves of avocados per week, but this was not statistically significant in the NHS (HR: 0.88 (95% CI; 0.73, 1.06)). The lower incidence of CVD in the NHS could be a possible explanation.

Takeways

• Encourage regular avocado consumption — at least 2 per week 🥑🥑
• Substituting avocados for less healthy, high fat foods alternative like butter and processed meat for added benefits

So go take advantage of the current high domestic supply and enjoy your avocados while the price is right!