It would be an euphemism to say that avocado has gained some popularity in the last couple of years. In The Netherlands, the avocado craze reached the ultimate point (so far) in 2017 when the first avocado-based restaurant opened. The Avocado Show features “stunning avocado dishes”, such as poke bowls with elegant names (salvocado, salamango), açai bowls, colorful pizzas, stuffed sweet potatoes and special guacamole. It doesn’t go extremely crazy but at least if you like avocado you are sure to find a significant amount of it on your plate. But why an avocado-based restaurant? Because “our favorite superfruit in the world is nutritious, versatile, yummy, good looking and basically life” according to the founders and owners of the restaurant [1].
Avocado, a fruit?
Yes, and this despite the fact that many supermarkets classify avocado as a vegetable, which makes me lose 5 minutes every time I am looking for the avocado picture on the fruit&veggie scale. Yes, 5 minutes – and yes, every time because I don’t learn from my mistakes. Avocado is a single-seeded berry fruit, a.k.a., the matured ovary of the avocado-tree flower.
*2 points for having already scored the word “ovary” while this post has just started.*
Avocado, a fruit. But avocado, a nutritious superfruit and basically life?
The hashtag #avocado has 8.7 million posts on Instagram. Slightly different than #carrot (2.3 million posts) and #pear (1.1 million). Instagram confirms that avocado is basically life, but (please pay attention, what follows is essential information) Instagram does not always hold the truth.
Let’s go deeper into this smooth pale green flesh and try to decipher the truth about avocado.
Avocados are obtained from the avocado tree, Persea americana. Like banana, the avocado matures on the tree but ripens off the tree, in one or two weeks. The most common variety of avocado is called “Hass” and accounts for around 80% of cultivated avocados in the world. Mexico leads the worldwide production of avocado, covering roughly one third of the overall production.
The recommended serving size of an avocado is 30 g (1 ounce), which corresponds to one fifth of the fruit [2]. If you are an avocado lover, your next reaction should be “whuuuuaaaat – one fifth of the fruit, only? ONLY?” – and you are correct, since the average consumption is rather closer to one-half of an avocado (around 68 g) [3]
So what kind of nutrients do we find in these 68 g of Hass avocado fruit?
As for other fruits and vegetables, avocado mostly contains water, which accounts for 72% of its total weight. It might sound a lot, but compared to other fruits (which score more than 90-95% of water content) it is relatively low. This also partly explains why avocadoes are relatively more caloric than an average fruit, with 114 kcal per half-fruit [2].
In terms of micronutrients, Hass avocadoes contain a fair amount and numbers of vitamins – including the liposoluble vitamins A, E, and K which are present at higher concentrations than in watery fruits, minerals (mostly potassium) and compounds called phytochemicals such as lutein, cryptoxanthin and zeaxanthin, which are the biologically active compounds of the plant and might show potential health benefits [4].
Cryptoxanthin – what a fancy name! But what about the more conventional stuff like sugar, protein and fat?
Protein content is relatively high for a fruit, which makes it very interesting for vegetarians and vegans (one half contains 1/10 of the protein content of a conventional steak). With 0.2 g of sugar per half-fruit, avocado is one of the least sweet fruits, and at the same time high in fibers (4.6 g). This already sounds exciting but the most interesting feature of avocado – and why it makes such a buzz – is its fat content.
More than the absolute concentration, it is the proportion between the different types of fat that is important. Avocado contains 71% of monounsaturated fatty acids, 13% of polyunsaturated fatty acids and 16% of saturated fatty acids [2].
Oh no – again these polyunsaturated fatty acids! These omega 3, omega 6, omega 1635637 – and still no one has really understood what it is and how to interpret that. Please. Help. Us.
Ladies and gentlemen (*drums rolls on*), we reach one of my favorite moments – the chemical intermezzo. Sit down, grab a coffee and open your eyes.
A fatty acid is a compound that has the following structure:
So basically a chain of carbon atoms and a group called “carboxylic acid” (the “COOH” on the figure).
Depending on the number of carbons, i.e., the length of the chain, a fatty acids can be either:
- A short-chain fatty acid (less than 6 carbon atoms)
- A medium- or long- or very long chain fatty acid (between 6 and 28 carbon atoms)
Beside the number of carbon atoms, another important aspect is if the fatty acids is “saturated” or “unsaturated”. Disclaimer: this has nothing to do with water content or blood alcohol concentration.
- A saturated fatty acid does not have any double bond between two carbons.
- An unsaturated fatty acid has at least one double bond between two carbons
A double bond is a type of chemical bond where the two bond atoms share four electrons rather than the usual two. Double bonds are shorter and stronger than single bonds. The more the number of double bonds, the more rigid the compound will be.
An unsaturated fatty acids with one double bond only is called “monounsaturated” while an unsaturated fatty acid with at least 2 double bonds is called “polyunsaturated”. Both the number of carbon atoms and the number of double bonds are important in the effect a fatty acid can have on our organism.
Before going deeper, a small example of a saturated short-chain fatty acid (4 carbon atoms, no double bond) and an unsaturated long-chain fatty acid (20 carbons, 4 double bonds):
Ok, monounsaturated and polyunsaturated fatty acids – so far so good. But this doesn’t explain what this “omega” thing means!
The omega part is linked to the position of double bond(s) in unsaturated fatty acids. Let’s take docosahexaenoic acid as an example:
In the omega (ω) nomenclature, the first carbon atom located at the opposite site of the carboxylic acid is consider the carbon #1, as shown in red in the figure. Each carbon atom can then be further numbered with 2, 3, 4, etc. Omega is the last letter in the Greek alphabet, and therefore represents the “last carbon” in the carbon chain.
In docosahexaenoic acid, the first double bond that we encounter if we start with the “last carbon” is at the position ω3. It is always the first double bond from the “last carbon” side which is taken into account for this classification – irrespective of the total number of double bonds in the molecule. Docosahexaenoic acid is therefore an omega-3 fatty acid.
Docosahexaenoic acid – isn’t it the one that we all know as DHA? An omega-3 polyunsaturated fatty acid that is supposed to be good for us?
That is correct. There is plenty of literature supporting the fact that a higher intake of the omega-3 fatty acids docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) via the diet may have positive effects on our health – mostly related to cardiovascular diseases, diabetes, cancer, metabolic syndrome, Alzheimer’s disease, dementia, depression, etc. [5]. Despite this abundant literature, there is however a lot of disparity between studies and the possible mechanistic explanations – disparity that Dr. Iza keeps for another post.
While everyone was busy investigating the role of these omega-3 polyunsaturated fatty acids on our health, we tend to have forgotten the possible health benefits of monounsaturated fatty acids. If you have not fallen asleep so far, you probably recall that monounsaturated fatty acids represent the biggest proportion of fat in avocado.
Besides avocado, monounsaturated fatty acids are also abundant in a lot of fishes (saury, herring, and mackerel – an information which will make my Dutch friends very happy), as well as in olive oil [6]. Many of the benefits of the Mediterranean diet are therefore thought to be also associated to the high levels of monounsaturated fatty acids of fish and olive oil, with positive effects on cardiovascular risk factors, metabolic syndrome, diabetes, inflammation, and overall lipid metabolism. However, the overall positive effects are not only linked to fatty acids content but also to other bioactive active compounds. We are also only at the beginning of investigating the effects of monounsaturated fatty acids on health.
Fish and olive oil sound also very interesting but we were initially talking about avocado, weren’t we?
An increased number of interesting trial studies focusing on the potential positive effects of avocado on cardio-metabolic risk, obesity or cardiovascular diseases have been published in the last couple of years. A study on overweight and obese participants investigated the effects of a low-fat diet, a moderate-fat diet, as well as a moderate-fat diet supplemented with one avocado per day [7]. All diets decreased the blood levels of LDL (the “bad” cholesterol) and total cholesterol, but this effect was greater in the diet with avocado supplementation. Other positive cardiovascular effects were observed, suggesting that the benefits attributed to avocado are probably also explained by other bioactive compounds present in avocado, in addition to their healthy fat composition. Another study, also conducted in overweight/obese adults, investigated the effect of replacing carbohydrates during breakfast by half- or whole-avocado, which led to better lipidic and glycemic blood profile – therefore also showing potential positive effects on cardiovascular risks [8].
However, we still miss more randomized controlled trial studies which would include a larger diversity of participants, a larger number of participants, a larger number of clinical outcomes measured, as well as more long-term studies before we can really draw strong conclusions on the potential effects of avocado on health.
Hey, it is not the first time that you mention something like “there is still not enough clinical studies” or “we still lack proper scientific evidence” – what are you guys doing with our taxes? It doesn’t sound like an efficient use of our money.
That is probably what everyone is asking, and I will share with you a nice Editorial that I liked a lot, published in the British Medical Journal in 2013 entitled “lmplausible results in human nutrition research – definitive solutions won’t come from another million observational papers or small randomized trials” [9]. Would you be interested in human nutrition research and interpretation of data – then I strongly advise you to read this Editorial here.
In other words: yes, there are some preliminary results showing that avocado may be good for you in the context of cardiovascular risks and metabolic disorders. But…
- No, it is not totally clear yet what exact consequences on overall health and mortality this might have, as well as which mechanisms are underlying this positive effect.
- No, we do not exactly know yet what effect avocado might have on other clinical conditions (like Alzheimer’s disease and dementia, for instance)
- No, we cannot tell you if avocado can help you losing weight if you already have a body max index (BMI) lower than 20*.
*mini-take-home-message: if you read/see/hear somewhere the information “avocado is good for you”, do not forget to ask “in terms of what? Decrease mortality? Make me happier? Make me skinnier? Give me more muscles? Make my skin smoother? Make my stepmother softer?”. This is also valid for any other “[please add any superfruit or fancy food here] is good for you”.
You like avocado? Go for it. You are afraid of putting on weight? Limit the daily consumption to the recommended intake and/or replace other sources of fat by avocado. You are suffering from irritable bowel syndrome (IBS) or other gastrointestinal issues? Stay tuned because avocado also contains a substantial amount of sorbitol which tends to be malabsorbed in IBS patients, leading to severe pain. The role of sorbitol in IBS will be discussed in one of the next posts.
Dr. Iza
tl;dr
- In the large diversity of self-proclaimed “superfoods”, avocado seems to be a strong candidate.
- Some randomized control studies have shown that avocado may have a positive effect on cardiovascular risks and metabolic disorders. Randomized control trials are considered the “gold standard” in intervention studies, meaning that they should deserve more attention (more than observational studies).
- We do need more studies with a larger number of subjects, as well as studies investigating the long-term effects of avocado on health.
- The positive effects of avocado are probably linked to its fats composition, with a large proportion of monounsaturated fatty acids, and to bioactive molecules – but this remains to be proven.
- Avocado might also have a positive effect on other diseases but this also remains to be investigated.
- The recommended serving size is 1/5 of avocado which corresponds to 30g. Studies having investigated the effect of avocado used different serving size, from 1/5 of an avocado to one full avocado. This makes it also difficult to evaluate if this recommended serving size is adequate or not.
- Avocado? Closer to a superfood than a supermyth but the final decision will rely on future studies and stronger scientific evidence.
References
[1] The Avocado Show, Amsterdam, The Netherlands. https://www.theavocadoshow.com/ (accessed 11th November 2018).
[2] L. Dreher, A.J. Davenport, Hass avocado composition and potential health effects. Crit Rev Food Sci Nutr 53 (2013) 738
[3] L. Fulgoni, M.L. Dreher, A.J. Davenport, Consumption of avocados in diets of US adults: NHANES 2011-2006 (2010). Boston, MA: American Dietetic Association.
[4] S. Department of Agriculture, Avocado, almond, pistachio and walnut composition: nutrient data laboratory. USDA National Nutrient Database for Standard Reference, Release 24 (2011).
[5] Shahidi, P. Ambigaipalan, Omega-3 polyunsaturated fatty acids and their health benefits. Annu Rev Food Sci Technol 9 (2018) 345.
[6] H. Yang, B. Emma-Okon, A.T. Remaley, Dietary marine-derived long-chain monounsaturated fatty acids and cardiovascular disease risk: a mini review. Lipids Health Dis 15 (2016) 201.
[7] Wang, P.L. Bordi, J.A. Fleming, A.M. Hill, P.M. Kris-Etherton, Effect of a moderate fat diet with and without avocados on lipoprotein particle number, size and subclasses in overweight and obese adults: a randomized, controlled trial. J Am Heart Assoc 4 (2015) e001355.
[8] Park, I. Edirisinghe, B. Burton-Freeman, Avocado fruit on postprandial markers of cardio-metabolic risk: a randomized controlled dose response trial in overweight and obese men and women. Nutrients 10 (2018) E1287
[9] P.A. Ioannidis, Implausible results in human nutrition research. BMJ 347 (2013) f6698.
Post illustration: Nick Youngson / Alpha Stock Images.
