[toc]It’s not that Americans ever disliked guacamole, but throughout much of history it was a rarely consumed fruit outside of Latin cuisine. Avocados on salads and sandwiches in the Midwest were definitely not something you would encounter in the 1980’s.
Even the authentic Mexican restaurants in many parts of the country wouldn’t incorporate avocado in their dishes, due to limited supply and high cost.
That all begun to change in the late 90’s. Thanks to marketing and more widespread adoption of other cultural cuisines, the per capita consumption of avocado is nearly 400% higher than it was 20 years ago (1).
But as with any food, just because we don’t notice side effects, that doesn’t always guarantee it’s safe to eat. It’s important to research if there are any unintended side effects lurking behind the scenes.
The health benefits
Everyone, from mainstream media to niche nutritional sites, all love to praise the many benefits of eating avocado. Indeed, there’s lots to talk about. Research has suggested a number of reasons why they may be good for you to eat on a regular basis, even when you’re on a diet. There seems to be no end in sight of booming growth for this crop.
1. Vitamins, minerals, and phytonutrients
No ones claiming they’re a low calorie food. 1 cup of diced avocado (150 g/5.3 oz) clocks in at about 240 calories, but it also packs a lot of vital nutrients. That same serving size provides the following percentages for your daily value of:
- pantothenic acid – 42%
- vitamin K – 35%
- folate – 30%
- vitamin B6 – 23%
- vitamin E – 21%
- potassium – 21%
- vitamin C – 20%
This food is also a natural source of the antioxidants lutein and zeaxanthin, which research has associated with eye health. Yes they’re high calorie, but also high fiber; providing you with 40% of the daily value for that same aforementioned serving size.
2. May lower LDL “bad” cholesterol
There have been at least eight human studies conducted and while most were quite small, their findings seem to suggest a similar conclusion; this food has a beneficial effect on blood lipids.
One of the most recent – and largest – was carried out by Pennsylvania State University and published in 2014 (2). They wanted to compare 3 different diets which were believed to have cholesterol lowering effects:
- Low fat diet, where carbs were used to help replace saturated fats (43 participants).
- Moderate fat diet, high in the healthier monounsaturated fats and low in saturated fats. Avocado was excluded (42 participants).
- Moderate fat diet with avocado, which was identical to the above in terms of fat ratios consumed, however it included eating one Hass avocado per day (43 participants).
- Control group. No special diet (45 participants).
Avocados are an excellent source of monounsaturated fats. In theory, this “good” fat content should not have changed things though, since the other moderate fat diet had also used the same ratio of monounsaturated fats, albeit from different sources.
While all 3 of the diets “significantly decreased” LDL and total cholesterol versus baseline, look which one did best:
- Low fat diet: -7 mg/dL
- Moderate fat diet: -8 mg/dL
- Moderate fat diet with avocado: -14 mg/dL
3. Weight loss
Being chock full of fat, one would assume that frequent consumption would lead to obesity. It definitely could, but there is some limited research to suggest the opposite might happen too; people may eat less afterward due to the high satiability of the fruit.
Published in a 2013 edition of Nutrition Journal, this randomized crossover study involved 26 overweight people (3). They were broken up into 3 groups, each receiving a different lunch; avocado-free, avocado inclusive, or avocado added.
The avocado added group, who intentionally consumed 1/2 of a Hass at lunch daily, experienced:
- 23% increased satisfaction after eating their lunch versus the control group
- 28% decreased desire to eat following lunch
These were based off of measurements taken at specific intervals in the 5 hours following lunch.
The fine print is that this group was also consuming an extra 112 calories, which likely has something to do with it. Though even considering that, it’s a sizeable and sustained decrease in appetite, which might help with weight loss in conjunction with a healthy diet and exercise.
Why exactly it increased satiability is unknown. The additional 5 grams of fiber may have played a part. But even ignoring that, the creamy consistency is something that just about anyone finds satisfying.
To avoid confusion though, this study did not claim it is something for you to eat to lose weight.
The dark side no one talks about
Those 3 things are just a few of the numerous avocado health benefits which have been suggested to date. While many appreciate those things, without a doubt it’s that rich buttery taste which is largely responsible for our skyrocketing consumption. Even people who hate veggies think they’re good.
But is there a dark side to this delicious fruit?
We already know that it contains a poison which is toxic to many animals, but safe in humans (more on that below).
Different from that topic, there is also research which used in vitro testing and the results suggest it might be genotoxic to human blood cells (we stress the word might, don’t jump to conclusions yet).
What is a genotoxin? Chemical or physical agents which have the ability to damage DNA. This causes lesions which may result in cell death or mutations. Cancer is caused by mutations to the DNA.
Now to be clear, not all mutations lead to cancer. Far from it, in fact. As humans it has been theorized that every day, our body experiences anywhere from 10k to 1M molecular lesions (4). These are bad for you, but fortunately it is believed our body is able to repair most of them. Though not all are repairable and some slip through the cracks.
It is those unrepaired genetic alternations which might lead to problems. One of those problems could be cancer.
While similar in definition, the term genotoxin should not be confused with mutagen.
All mutagens are genotoxic, but not all genotoxins are mutagens.
In a nutshell, genotoxins are not always mutagens, since they might not cause permanent DNA alternations. When they do cause permanent alterations, then they are both a genotoxin and a mutagen.
The potentially bad news
Before you abstain from that great avocado on your salad, it’s important to keep in mind that:
- This finding is from in vitro research. Checking for this same toxic effect on DNA in real live humans has not been done, to the best of our knowledge. The only research done (and it’s limited) is in vitro, which means it takes place outside of the human body. Think cultured human cells in Petri dishes and test tubes. It’s important to point this out because what happens in vitro does not necessarily mean it will happen in vivo (in the body).
- Eating avocado vs. direct cell application. In the research, the cultured human blood cells were exposed to an extract containing the fruit. That is different from when you eat an avocado (or any other food) because it first goes through your stomach acid, then digestive enzymes, and followed by your liver which acts as a detoxifier. All those processes take place before the compounds in food have contact with your blood cells as they circulate throughout your body.
In short, what happens in a Petri dish may or may not happen in the human body.
With those caveats said, there is at least some in vitro evidence which suggests that avocados might be bad for you, if the same reactions seen in the laboratory also occur inside the human body after digestion.
The shocking study results
This isn’t exactly breaking news. The first study we will address was published in 2010 (5). Despite being around for several years now, it seems almost no one discusses it.
You will see very detailed articles reviewing the benefits of avocado and the authors sometimes even discuss possible (yet unproven) side effects, but they seem to be totally oblivious to this genotoxicity research. The title of the study is:
In vitro evaluation of genotoxicity of avocado (Persea americana) fruit and leaf extracts in human peripheral lymphocytes.
It was conducted at a cancer hospital and research center in India.
Basically, the researchers took avocado and diluted it in a solution, which was then dripped on healthy human white blood cells which were alive in a Petri dish. Afterward, they checked to see if any DNA damage occurred.
Not only did DNA damage occur, but it seemed to be quite prevalent.
This is actually one of the more mild photos, as some others showed higher numbers of mutations which included:
- acrocentric association (AA)
- dicentric chromosome (DC)
- Robertsonian translocation (RT)
- premature centromeric division (PCD)
Even more worrying was that they tested 3 different dosages; 100 mg/kg, 200 mg/kg, and 300 mg/kg. The higher the amount of avocado used, the higher the number chromosomal mutations.
This bar graph here shows “Fruit 1” which is the lowest concentration of avocado at 100 mg/kg, while “Fruit 3” is the highest at 300 mg/kg. As you see, the number seen in all 3 concentrations is much higher than the control group (when no avocado is added).
The same pattern is seen in the leaf extract, which were also tested using the 3 different dosages. It appears the leaves are potentially more poisonous to DNA. Thankfully, no one eats those.
The first three sentences in the study’s conclusion can sound quite scary…
“To conclude our study suggests that the extracts of both avocado fruit and leaves can potentially induce significant genomic instability and some genetic damage in human lymphocytes in vitro. If the same effect occurs on somatic cells in vivo, it could result in loss of function, apoptosis, or neoplastic trans- formation of those cells. The genotoxic effect on germ cells of adults could lead to infertility, recurrent abortions, early fetal loss, or inherited defects in their offspring.“
For you or your wife during pregnancy, that quote can sound particularly frightening.
After that however, it does go on to discuss that it is unknown if there are any toxic effects when consumed as a food, for reasons along the lines as we previously discussed. That’s why the very last sentence of the conclusion is; “Thus, it is essential to carry out in vivo studies for genotoxicity before making a final remark on the genotoxicity of the plant extract.”
Is the poison persin causing this?
While the current opinion is now somewhat divided as to their toxicity in dogs and cats, the consensus among scientists seems to be in agreement that avocados are poisonous to birds, rabbits, horses, pigs, cows, and some other large animals. This is because of a poison they contain called persin.
There are at least 59 research papers listed in the FDA poisonous plant database about this poison affecting ostriches, goats, mice, rats and other species (6). Aside from the danger of death, pregnancy complications and risks while breastfeeding their babies are concerns with some livestock.
However in humans, persin is considered to be completely safe, including for pregnant women and those who are breastfeeding. We don’t suffer the side effects that the aforementioned animals do when they eat avocado. Instead, the vast majority of the research suggests we actually experience benefits of health instead, such as those mentioned at the start.
Even if persin is not poisonous to humans, some wonder if it might play a role in the genotoxicity seen in vitro. While nothing more than a theory, it is interesting to note that the leaves, bark, skin, and pit of the fruit have the higher concentrations of persin… not the fruit.
As seen in the study, it was also the leaf extract which demonstrated in vitro toxic effects which were significantly worse.
Other research
Published in 2013 by researchers in Guadalajara, Mexico is another study titled (7):
Acute Toxicity and Genotoxic Activity of Avocado Seed Extract (Persea americana Mill., c.v. Hass)
This one isn’t very relevant, since they were only looking at the potential toxicity of the seed extract. The researchers claimed this was the first study to evaluate the seed in that regard.
Obviously, people don’t eat the seeds… or at least, sane and rational people won’t attempt to eat a golfball-sized pit that’s as hard as a rock.
The reason why they were testing it was because some cultures use seed derivatives as an herbal remedy for various diseases.
Aside from the part tested, there were some other major differences:
- They added it to the diet of living rodents (mice). No human cell cultures were used.
- The acute toxicity test used the following dosages; 125, 250, 500, 1,000, and 2,000 mg/kg. These were administered to the mice using an orgastric tube (a dropper). Whether they “passed” the test was simply whether they were alive or dead after 24 hours.
- The genotoxicity test used only one dosage; 250 mg/kg. Blood samples weren’t collected until 36 hours later.
The results?
As far as acute toxicity (lethal poisoning) there were not deaths using the lower dosages, but it did produce death at 500 mg/kg and above:
- 500 mg/kg dose = 20% mortality after 24 hours
- 1,000 mg/kg dose = 60% mortality
- 2,000 mg/kg dose = 80% mortality
For the genotoxicity test, the blood samples (which remember, weren’t harvested until 36 hours had passed), were viewed under a fluorescence microscope.
1,000 peripheral reticulocytes (immature red blood cells) were analyzed per mouse. The results were as follows…
| Samples | Dose (mg/kg) | MNRET/1000 RET | |
|---|---|---|---|
| Number | Percentage | ||
| Alcohol-water solution | 10.6±1.1 | 1.06±0.11 | |
| P. americana seed extract | 250 | 16.4±4.5 | 1.64±0.45 |
| Colchicine | 4 | 189.2±19.3 | 18.92±1.93 |
The researchers stated:
“There is no statistically significant difference between the group administered with the extract of P. americana seed and control group; however, there is a significant difference between both these groups in regard to the positive control.”
The positive control – colchicine – is medication used to treat gout. It was used as a control because it is known to be genotoxic and hence, they wanted a known toxin to compare the results to.
While it is true that effects of colchicine are off the charts relative to the alcohol-water and the avocado pit extract solutions, notice how the number for the pit is still higher versus the alcohol-water solution (16.4 vs. 10.6). Though as mentioned, they said this was not statistically significant.
The study is interesting since it involves ingestion of an avocado, unfortunately it’s using animals and did not involve the flesh of the fruit which is what people consume. Therefore, it’s hard to conclude much from this study, either.
Should you stop eating them?
More research – a lot more – needs to be done.
The fact that it’s not being done is no surprise. Many clinical studies and pieces of research touting the advantages of avocados are funded, at least in part, by marketers of this produce. Those who have a vested interest in selling them and highlighting their many great traits.
For the possible benefit of decreased hunger while you’re on a diet, that study had received a grant from the Hass Avocado Board. Likewise for the one about LDL cholesterol in overweight adults, which looked at the effect that fruit had while dieting.
It might be risky for them to fund research for this genotoxicity topic, because rather than calm fears, what if the results of further studies only amplified them?
Using the “innocent until proven guilty” mindset, it would be wrong for someone to claim that they’re toxic to your DNA. Because as of right now, the effects in vivo (in the human body) have not been studied. As mentioned, Petri dish toxicity is different than what might happen after the substance has been digested. Only then does it come in contact with your bloodstream.
So right now, one can ask the question if it is toxic, but no one can claim it is toxic to humans after consumption. There’s no proof of that.
However on the flip side, there are many people who believe that while avocados are good for you probably, to be extra safe, they are minimizing or eliminating consumption. We heard from one woman who was avoiding them while pregnant. They are waiting until this topic is further researched.
Until the jury is in, I think it’s reasonable given this new data, for people to consider reducing their intake.
That quote was expressed in a video a few years back by Dr. Michael Greger, in reference to the 2010 study. He is a leader in nutritional research and author of the New York Times bestseller How Not to Die: Discover the Foods Scientifically Proven to Prevent and Reverse Disease.
Would you like guac with that, still?