Smooth creamy guacamole, crescent shaped segments of avocado in a delicious green salad, St Patrick's day coloured smoothies - what's not to love about avocado?
Some foodies claim that avocados are loaded with phytonutrients, vitamins, fibre and protein which help with diabetes, the metabolic syndrome, dyslipidemia and arthritis (and lots more).
Does avocado actually have any health benefits or does it just taste good?
What So Good About Avocado?
Avocado (Persea americana) is classified as a member of the Lauraceae family and from a botanical perspective belongs to the berry family. This means that avocado is a fruit and not a vegetable as many people think. Unlike most other fruits, avocados are low in sugar.
Archaeological digs suggest that avocados date back at least 15,000 years. Avocados originally came from South Central Mexico. Avocados were introduced into Spain in 1601 and the USA in 1825. Avocados are now cultivated in tropical and sub-tropical areas. It is an evergreen flowering tree that can grow up to 20 meters tall.
There are three main varieties of avacodos:
- Guatemalan and
- West Indian.
There are at least 500 named cultivars of avocados and the most famous are probably the Haas and Fuerte cultivars. The avocado fruit can vary in color from green to red to purple and can vary in shape from spherical to pyriform. The fruit itself is used as a human food source and functional food while the leaves, seed and peel are also used for medicinal purposes.
Avocados are best stored at room temperature and can take (on average) five days to ripen. To speed up the ripening process, avocados can be placed in a brown bag with an apple or banana which works a charm.
World production of avocado is approximately 5 million tons per year. Mexico is the largest producer of avocado worldwide and produces about one third of the worlds avocado supply.
Avocado bioactives may be divided into:
- alkanols (also sometimes termed “aliphatic acetogenins”)
- terpenoid glycosides,
- furan ring-containing derivatives,
- glycosylated abscisic acid,
- polygalacto urease,
- cytochrome P-450 and
- volatile oils (1).
- One half of an avocado (68 grams), provides:
- dietary fiber (4.6 g),
- total sugar (0.2 g),
- potassium (345 mg),
- sodium (5.5 mg),
- magnesium (19.5 mg),
- vitamin A (43 μg),
- vitamin C (6.0 mg),
- vitamin E (1.3 mg),
- vitamin K1 (14 μg),
- folate (60 mg),
- vitamin B-6 (0.2 mg),
- niacin (1.3 mg),
- pantothenic acid (1.0 mg),
- riboflavin (0.1 mg),
- choline (10 mg),
- lutein/zeaxanthin (185 μg),
- phytosterols (57 mg)
- high-monounsaturated fatty acids (6.7 g) and
- 114 kcals or 1.7 kcal/g (2).
Avocado Soybean Unsaponifiables
These are worth a special mention as some of the studies relate directly to avocado soybean unsaponifiables (ASU). ASU is made of one-third avocado oil and two-thirds soybean oil. Unsaponifiable means that the oil blends don't make soaps when added to potassium hydroxide.
Is There Any Research?
There are 1246 publications relating to avocado, which includes 33 clinical trials. Let's compare this to another fruit that is sometimes mistaken as a vegetable, tomatoes. There are over 22,000 publications on tomatoes which includes over 2000 clinical trials.
Is It Really So Good For Healthy Fats?
Over the last few years, we have revised our attitude to fats and what constitutes a healthy fat. We are moving away from a focus on low fat and are moving towards healthy fats. Fats accounts for approximately one third of the standard American diet and play a key role in our physiology and biochemistry.
There are four main types of fats:
- triglycerides which are composed of three fatty acid chains that are chemically bound to a glycerol molecule and account for 95% of dietary fats
- saturated fatty acids which lack double bonds in the fatty acid chain which makes them solid at room temperature and less susceptible to oxidation
- mono-unsaturated fatty acids contain one double bond in their long carbon chain and are liquid at room temperature
- polyunsaturated fatty acids contain two or more double bonds in their long carbon chain, are liquid at room temperature and at susceptible to oxidation.
Avocados are rich in monounsaturated fats. Diets rich in monounsaturated fat such as the Mediterranean diet are associated with decreased mortality. That is the theory, what about the evidence?
Mexican investigators examined the effects of avocado on plasma lipid concentrations in 16 healthy volunteers. This was a three phase study .
Phase one: volunteers consumed a diet rich in monounsaturated fatty acids (75% of the total fat content came from avocado) and with a restriction of saturated fatty acids.
Phase two: subjects ate as they wished, with the addition of avocado.
Phase three: subjects consumed a low fat diet, without avocado.
Each phase lasted for two week. The study found that avocado was a rich source of monounsaturated fatty acids, without any undesirable effects on HDL and triacylglycerols.
Australian investigators evaluated the effects of either a diet:
- high in monounsaturated fatty acids,
- enriched with avocado or
- a high-complex-carbohydrate diet on blood lipid concentrations.
The avocado arm was significantly more effective in decreasing total cholesterol, and, unlike the high carbohydrate arm did not decrease HDL concentrations .
A total of 13 patients with dyslipidemia were included in a trial in Mexico comparing:
- a vegetable diet,
- a diet with 60% carbohydrate, 10% protein and 30% lipids (75% of the lipids were supplied by avocado) or
- an avocado-free diet.
The study showed that all three diets reduced HDL level. A low-fat, carbohydrate rich diet decreased LDL and this was not corrected by the addition of avocado. The authors concluded that to obtain the beneficial effects of avocado, a lower amount of carbohydrate and polyunsaturated fatty acids are needed .
A second study from the same Mexican group of investigators enrolled 16 patients with dyslipidemia in a cross-over study . One option involved 30% fat, with 75% of the total fat coming from avocado, and a restriction of saturated fatty acids. The other option involved low saturated fatty acids without avocado. As an added quality measure, patients were observed consuming their meals at a clinical trial unit, though of course we do not know what patients ate outside of this observed meal time.
Each diet period lasted for four weeks. Significant decreases in total cholesterol and LDL cholesterol were noted in both arms of the study. The avocado arm reduced triglycerides while the avocado-free arm increased triglycerides. The authors concluded that avocado is a good source of monounsaturated fatty acids and offers some advantage over a low-fat, carbohydrate-rich diet.
In another study, 61 volunteers participated in a randomized control study . Group one consumed 200 grams a day of avocado (30.6 grams of fat) which substituted for 30 grams of other fats. The control group excluded avocado from their diet. A total of 55 subjects completed the study. Anthropometric measurements were taken (body mass, body mass index, percentage fat) and decreased significantly in both groups and the difference was similar in both groups, which dispels the myth that avocados are fattening.
However the caveat here is that avocado needs to be substituted for an equivalent amount of dietary fat. There were no significant differences between the groups in terms of total cholesterol, HDL, hypertension or blood pressure in an energy restricted diet for six weeks.
Avocados are a good source of healthy fats. However, it is imperative that avocados replace other fat sources (or is a food swap) and not an addition to the diet.
Is It Really So Good For Protein?
Not really. Avocados contain 2.23gm of protein per 100gm which compares poorly to a 100gm portion of chicken which contains 14.73 gm of protein.
Avocados are not the best source of protein on a weight for weight basis.
Do It’s “Phytonutrients” and "Carotenoids" Matter?
Phytonutrients are plant derived compounds which include carotenoids, lycopene, resveratrol and phytosterols that are thought to have health-protecting qualities.
Carotenoids are a subclass of phytonutrients and are a group of colored fat soluble pigments.
Avocados are a rich source of phytosterols and stack up well against strawberries weight for weight. Avocados offer 57mg of phytosterols per 68mg as compared to 8mg per 68mg of strawberries.
Avocados are a good source of phytonutrients which are known to offer health benefits.
Is Eating Avocados Good For Heart Health?
UCLA researchers enrolled eleven healthy subjects who on two separate occasions consumed either a 250 gm hamburger patty alone (436 cal and 25 g fat) or together with 68 grams of avocado flesh (an additional 114 cal and 11 g of fat for a total of 550 cal and 36 g fat), a common culinary combination, to assess effects on vascular health .
The addition of the avocado to the hamburger meat protected against vasoconstriction and reduced pro inflammatory NF-kappa B and interleukin 6. The authors concluded that adding Hass avocado to a hamburger patty offered beneficial anti-inflammatory and vascular health effects.
Avocados seem to confer heart health benefits. That is not to say that avocados can replace you heart medications . Based on this study, if I were a beef burger eating carnivore, I would absolutely add some avocado as it would taste great and might just offer health benefits. Ideally you would replace the burger with the avocado (just saying).
Does It Reduce Risk of Metabolic Syndrome?
A group of Mexican investigators looked at 12 women with noninsulin-dependent diabetes. They were assigned to either a diet high in monounsaturated fatty acids, or complex carbohydrates for four weeks. Following four weeks of the assigned diet, patients followed the American Diabetes Association isocaloric diet for a further four weeks and then embarked on the alternate diet regimen to that taken in phase one.
Both diets resulted in similar glycemic control and minor changes in cholesterol. The monounsaturated fatty acid diet was associate with a greater decrease in triglycerides (20% versus 7% in the high-carbohydrate group).
A comprehensive study on avocado consumption and the metabolic syndrome was published in 2103 .
The study evaluated avocado consumption and diet quality, energy and nutrient intakes, body weight and metabolic syndrome risk factors in a nationally representative sample of US adults.
NHANES is a comprehensive project being carried out by the National Center for Health Statistics of the Centers for Disease Control and Prevention with the aim of collecting information on the health and nutritional status of a nationally represented cross-sectional sample of the total civilian, non-institutionalized US population.
Body weight, BMI, and waist circumference were significantly lower (p < 0.01), and HDL-C was higher (p < 0.01) in avocado consumers. The odds ratio for metabolic syndrome was 50% lower in avocado consumers vs. non-consumers.
A significant potential confounder in the study was the fact that avocado consumers had significantly higher intakes of vegetables (p < 0.05)
This means that avocado may just be a marker of an overall healthy diet and lifestyle and that the health benefits may be due to other lifestyle factors.
The positive effects of avocados on the metabolic syndrome may be confounded by the fact that avocado eaters tended to have a healthier diet in general.
Does It Prevent Cancer?
Avocados contain a number of bioactive phytochemicals including carotenoids, terpenoids, D-mannoheptulose, persenone A and B, phenols, and glutathione that have been reported to have anti-carcinogenic properties (2).
However, there is little translational research on this topic.
Phytochemicals extracted from the avocado fruit selectively induce cell cycle arrest, inhibit growth, and induce apoptosis in precancerous and cancer cell lines.
Avocados contain a wide range of compounds that should help protect against cancer but this is just all theory at this stage and as we know theory does not always translate into reality.
Does It Improve Digestion?
There are no human clinical studies looking at avocado for constipation, diarrhoea or digestive issues.
A study in Wistar rats showed that the chloroform-methanol extract of the leaves of avocado possesses significant anti-diarrhoeal effect and may be a potent source of anti-diarrhoeal drug(s) in future .
An in vitro study suggested that extract of avocado can help eradicate Helicobacter which are the causative agent of peptic ulcer disease.
There are no human studies looking at avocados for digestive health.
Is It Good For Skin, Eyes or Hair?
German investigators compared a vitamin B12 cream containing avocado with a vitamin D3 cream in 13 adults with psoriasis, over a period of 12 weeks. The study had an interesting design. Each individual used one of the creams on one side of their body, and applied the other cream to the opposite side of their body. As such each individual effectively acted as their own control which allowed for intra-individual comparison. At the 12 week evaluation point, no significant difference between the creams was noted, in terms of efficacy, but the vitamin B12 avocado cream was better tolerated than the vitamin D3 cream
There are no other human clinical studies looking at avocado for skin, hair or nails.
There are no studies looking at avocados for skin health in the general population
Does It Help Arthritis?
A pilot study evaluated the effect of avocado/soy bean on saponifiables in the treatment of 163 adults with osteoarthritis of the hip. This was a French multicenter randomized placebo controlled trial over two years. The results of the study were a little confusing. The trial failed to show any structural effects of avocado/soy bean on hip osteoarthritis.
A post-hoc analysis (it's always questionable when you do a post-hoc analysis) showed reduced progression of joint space lost in the treatment arm as compared to the placebo arm. The researchers reconciled these two findings by suggesting that avocado/soy beans may act at a structural level.
Another study compared avocado/soy bean unsaponifiable (ASU) at doses of 300 milligrams, 600 milligrams versus placebo in adults. ASU was statistically superior to placebo. A significant difference was noted between the two study groups.
A third study found that avocadosoy beans reduced the need for non-steroidal anti-inflammatories in patients with lower limb osteoarthritis
Studies on ASU (and not regular avocado) suggests that ASU may offer some benefits in osteoarthritis.
Other Interesting Facts
A study in 26 healthy, overweight volunteers showed that there were significant differences in self-reported feelings of satisfaction and desire to eat when incorporating half a Hass avocado into lunch meals .
Is Eating Avocado Safe?
Avocado is considered safe if eaten in food amounts. It should be remembered that avocado contains lots of calories.
There is a rare and unusual syndrome called the 'fruit latex syndrome' . People who are allergic to latex may have a cross allergy to avocado and may experience severe allergic symptoms if exposed to avocado. This occurs most commonly in middle aged woman can can be seen with avocado, chestnut and banana.
Avocado can decrease the effectiveness of blood thinning tablets (warfarin or coumadin). People taken blood thinning should avoid taking medicinal doses of avocado.
Post marketing surveillance of data from the French National Pharmacovigilance registry evaluate all side effects on avocado-soybean unsaponifiables between 1978 and 2008 .
A total of 117 possible side effects were reported. The main side effects were skin eruptions (eczema and urticaria), liver test abnormalities and gastrointestinal (diarrhoea) and coagulation abnormalities.
Almost 40% of the adverse drug reactions were classified as serious but no deaths were reported.
Other rare but real risks of avocados are seen in some countries where avocados grow. In developing countries, children die each year climbing trees to pick avocados and coconuts. Injuries have also been reported from avocados and coconuts falling onto people who happen to be sitting or walking underneath a tree at the wrong time.
There is very little research on avocados which makes it difficult to comment on the possible health benefits. Certainly avocados have plenty of health promoting constituents. The best data on avocados relates to avocados as a source of monounsaturated fatty acids. The most memorable research is probably the fact that avocados prevent hamburger induced vasoconstriction (though maybe avoiding the hamburger might be a better idea all round).
The main take-home message is that avocados should not be just added to the diet but need to replace some other nutrient (and particularly fat dense) foods to confer it's best health benefits.