All About Avocados

Avocados contain a wide array of healthy nutrients that everyone should be looking for in their daily diet. They are a good source of panthothenic acid (Vitamin B5) and most of the other B vitamins, folate, Vitamin E, Vitamin K and Vitamin C, dietary fiber, copper and potassium. They also contain phytonutrients including phytosterols (beta-sitosterol, stigmasterol and campesterol), carotenoids (beta-carotene, alpha-carotene, lutein, neochrome, neoxanthin, chrysanthemaxanthin, beta-cryptoxanthin, zeaxanthin and violaxanthin), flavonoids (epicatechin and epigallocatechin 3-0-gallate) and polyhydroxylated fatty alcohols. Let’s discover how avocados can enhance our health.

 

A LOOK AT THE FAT CONTENT OF AVOCADOS

Besides their rainbow of healthy nutrients, avocados are unusual due to their high fat content. Most fruits contain little to no fat but 71% to 88% of the total calories found in an avocado are derived from their fat content. In fact, avocados are one of the fattiest plant foods in existence. About 14% of the fat in avocados is saturated fat (palmitic acid); 65% is oleic acid; 6% is palmitoleic acid, 14% is omega-6 fatty acids and 1% is omega-3 fatty acids (11).

Added fats are not part of a healthy diet. Extracted oils and other isolated fats are highly processed foods that have been separated from their whole food package with the fiber, vitamins, phytochemicals and other wholesome nutrients removed, leaving only pure fat behind. On the other hand, higher fat whole foods such as nuts and seeds, coconuts and avocados, eaten in their natural state, can be a nutritious source of “good” fat. Because the fat in these foods is imbedded in the structure of the nut, seed or fruit, the human body treats it very differently when it comes to the metabolism and absorption of the fat. (For more information on this have a look at my blog called “The Difference Between Whole Plant Foods and Processed Foods”). Even so it must be remembered that fat is the most calorie-dense macronutrient that we can consume. One gram of protein or carbohydrate delivers 4 calories of energy while 1 gram of fat supplies 9 calories. Put another way, the same quantity of fat provides more than twice as many calories as does carbohydrate or protein. This high calorie density is a drawback of avocados; they need to be eaten in moderation to reap the benefits of their healthy fat without causing weight gain.

Avocados are often touted in the media as a means of losing weight in spite of their fat content. Scientific scrutiny has looked at the effect of avocado consumption on changes in weight. One study added a whole avocado to the diet of the participants for 6 weeks and reported no significant weight gain. In this research, not only was the avocado added to the daily diet, an equivalent amount of fat from oil, margarine and mayonnaise was removed. In so doing, unhealthy fat was taken away and healthy fat including fiber was added in. In their discussion the researchers state that this study proves that the consumption of avocado within an energy-restricted diet does not compromise weight loss when substituted for a similar amount of mixed dietary fat. The percentage fat content of the diet was not changed, just the source of the fat. Fat from the avocado had the same effect on weight as did fat derived from oil, margarine and mayonnaise (9).

A 2013 randomized trial with 26 healthy overweight participants concluded that the addition of one-half of an avocado at lunch can increase feelings of satisfaction by about 25% and decrease the desire to eat for five hours afterward by up to 40% (6). Half an avocado contains about 115 calories. Adding that much energy to a meal might be the reason the participants were less hungry for the next meal. The question is, did the participants actually eat less calories at supper to compensate? Results showed very little or no decrease in the amount of food eaten at the next meal (6). It is clear that future studies are needed to evaluate the true effects of avocado intake on weight management.

BENEFITS OF AVOCADOS

Avocados and phytochemical absorption
The fat in avocados can provide an extra benefit in the absorption of carotenoid phytonutrients from foods. Many fruits and vegetables are rife with these fat-soluble phytochemicals but the extent of their absorption depends on many variables. It has been discovered that ingesting some healthy fat along with a carotenoid source markedly improves the absorption of these phytonutrients. For instance, beta carotene, a provitamin-A that can be converted in the body to Vitamin A, is much more readily absorbed when the source of beta-carotene is eaten along with a source of fat. In a small randomized study of 24 healthy men and women, eating some avocado was shown to increase the absorption of beta-carotene by up to 6.6 times. Additionally, the consumption of high-fat avocado flesh enhanced the conversion of beta-carotene to Vitamin A by up to 12.6 times (10). So avocados, by the very presence of fat in their fruit, can boost the absorption of carotenoids from low- or non-fat foods.

Avocados and inflammation
The ingestion of meat instigates formation of lipid peroxides, free radicals produced during the oxidative degradation of fats that ultimately result in cell damage. A whole plant source of fat such as avocado, eaten with an inflammatory food such as a meat burger, can inhibit this process and indeed studies show that eating avocado flesh along with meat lowers inflammatory biomarkers in the blood. Inflammation levels still increase due to the ingestion of meat but not as much as they would have if the avocado was not present. The mechanism of this effect is thought to stem from the antioxidants contained in avocado, a whole plant food, which act to decrease inflammation and also from the fiber inherent in whole foods with its cholesterol lowering effect. In this study hamburger meat consumption also increased blood triglyceride levels and the addition of avocado caused no further increase. The study concluded that avocado consumption can have beneficial anti-inflammatory and vascular health effects (8).

Avocados and decreasing LDL-cholesterol
Examination of the effects of avocados on the cardiovascular system suggests positive influences on cardiovascular health. For instance, the substitution of avocados for animal fat results in a significant decrease in cholesterol. However, animal fat itself has a potent augmenting effect on cholesterol production. It is unknown how much of the cholesterol reduction observed was the result of removal of the animal fat and what portion was caused by eating avocados (3,4). Unfortunately much of the research on avocados has employed avocado supplements that contain a phytonutrient content equivalent to that of up to twenty avocados instead of whole avocados themselves. These sorts of studies tell us little about the impact of whole avocado consumption on cholesterol levels. Research also shows that the intake of phytosterols, a phytonutrient component of avocados as well as other fruits and vegetables, can lower cholesterol by about 8%. Interestingly, eating only one ounce of nuts will provide a similar 8% drop in cholesterol level as the avocado supplements (13).

In 2015 a randomized and controlled trial looked at avocados and LDL size (4). When it comes to the size of LDL particles it appears that the smaller and denser they are, the more dangerous they are (although all LDL particles, no matter what their size, are associated with heart disease). In this trial animal fat was removed from the diet and replaced with either carbohydrates, vegetable oil or one avocado a day. It is no surprise that LDL-cholesterol levels decreased; simply removing saturated fat by eliminating animal sourced foods results in lower LDL whether you are replacing it with plant oil or with carbohydrates. But replacing the saturated fat with the whole plant food avocado created the most beneficial effect and it was discovered that the addition of avocado decreased both large LDL particles and the extra dangerous small LDL particles. The conclusion was that “avocados have beneficial effects on cardio-metabolic risk factors that extend beyond their heart-healthy fatty acid profile.” (4). These extra benefits may indeed be due to the fiber and phytonutrients of avocado but more study is needed to illustrate whether or not it is avocado in particular causing these beneficial effects or simply the addition of an antioxidant- and fiber-containing whole food.

Avocados and cancer
Currently, the study of direct avocado anti-cancer activity is very preliminary with much of the data based on test-tube studies of human cancer cells, not on the actual ingestion of avocados by human beings. For example, some studies have found that phytochemicals extracted from avocados can induce cell death in cancer cell lines while preserving normal human cells (16,17). One study actually looked at avocado intake in people. Participants included 209 men with prostate cancer and 226 cancer-free men. It was concluded that higher intake of avocado reduced the risk of prostate cancer (7). This study was observational and diet results were collected through a food frequency questionnaire and so these results show an association only. Much more research is needed to illustrate a definite link between eating avocados themselves and reduction of prostate cancer risk.

Avocados and arthritis
A recent review on arthritis management found four double-blind placebo-controlled randomized human clinical trials that looked at the effect of avocado/soybean unsaponifiables (ASU) and their impact on knee and hip osteoarthritis. ASU is a natural vegetable extract consisting of the material remaining after avocado and soybean oils are mixed with a hydroxide in a reaction known as saponification. ASU contains only about 1% of the original raw materials and is composed of one-third avocado and two-thirds soybean-derived material, obviously a substance far removed from the whole avocado fruit. Three of these studies showed some beneficial effects such as decreased use of anti-inflammatory pain medication and increase in joint function after two months of supplementation. The fourth study showed no significant difference in disease markers such as reduced joint space. Though the effect of ASUs on arthritis may show some promise, its effects clearly cannot be transferred to possible outcomes of the consumption of whole avocados on arthritis. (14)

Avocados for AMD (Age-related Macular Degeneration), cataracts and cognitive ability
A 2016 study looked at avocados as a source of lutein and zeaxanthin, phytochemicals from the carotenoid family. These two nutrients accumulate in the retina of the eye and are believed to play a role in good vision by acting as a filter for harmful blue light and also through their antioxidant effects. The density of lutein and zeaxanthin in the retina is also significantly related to cognitive function.

Foods high in lutein and zeaxanthin include green leafy vegetables, squash, broccoli , orange and yellow pepper, corn, peas, tomatoes, tangerines, persimmon and egg yolks (19). Avocados are a particularly bioavailable source because of their fat content; the presence of fat increases the absorption of carotenoids.

This study was designed to compare the effect of avocado consumption to that of potato or chickpeas on cognitive function in older adults. Researchers recruited 48 healthy subjects who were eating low amounts of lutein-rich foods (defined as less than three servings per week of green leafy vegetables, broccoli and eggs). Its randomized controlled design divided participants randomly into two groups; the treatment group was instructed to consume one avocado per day and the control group were told to eat one potato or one cup of chickpeas per day. Results showed that levels of lutein and zeaxanthin in the retina increased in the treatment group by more than 25% at three and six months and, in the control group, by about 17% at three months. The change in the controlled group was not sustained at six months. Several tests of cognitive function were performed on both groups. Both the treatment and control groups showed improvements in the Paired Associate Learning test. The avocado group also showed significant improvement in two other tests, Spatial Working Memory measure and the Stockings of Cambridge test. Researchers concluded that avocados have a positive impact on both lutein status and cognitive function (15).

Whether or not the increased level of lutein or zeaxanthin in a retina results in protection from AMD is inconclusive. A comprehensive summary of studies of macular degeneration found conflicting results and suggests that ongoing intervention trials might shed further light on this subject (5). As far as cognitive effects of lutein and zeaxanthin, results of this small study can only suggest that avocados, through their phytonutrient components, might show benefits of avocado on cognitive ability. Once again, further trials are warranted.

Cataracts are thought to arise from reactive oxygen species (ROS) that damage the lens of the eye. This suggests that nutrients with antioxidant capabilities could protect against this damage. Several prospective studies have examined the relationship between dietary intake of lutein and zeaxanthin and the risk of cataract formation (18). The Nurses’ Health Study found that women with the highest dietary intake of lutein and zeaxanthin had a 22% lower risk of cataracts than those with the lowest intake. The Health Professionals Study also showed benefit with the men having the greatest intake of lutein and zeaxanthin displaying a 19% lower risk of cataracts. The Beaver Dam Eye Study agreed showing that those with the largest intake of lutein and zeaxanthin had a 50% lower risk of early signs of cataract formation compared to those with the lowest intake. However, these are all observational studies that cannot establish definite cause and effect. The US National Eye Institute cautions that the possible benefit of lutein on cataracts remains uncertain and warrants closer examination. None of these studies looked specifically at avocado as the source of lutein and zeaxanthin.

In conclusion, lutein and zeaxanthin are common carotenoids found in most fruits and vegetables, many of which contain a higher concentration of these nutrients than avocados. Further research is needed on all sources of lutein and zeaxanthin as well as randomized and controlled trials regarding the effect of these carotenoids on eye conditions such as AMD and cataracts.

 

COMPARING AVOCADOS TO OTHER HEALTHY FOODS

Avocados contain about 2 gm of protein per 100 grams of fruit giving them the highest protein content among fruits. As a comparison beans contain about 21 grams of protein per 100 grams.

A 100 gram serving of avocado contains 7 grams of fiber, a high amount for a fruit. About 25% of that fiber is soluble fiber (prebiotic fiber that can be broken down and fermented in the colon into beneficial nutrients by the gut microbiota) and 75% is insoluble. A half cup serving of beans contains about 8 grams of fiber with about 38% of that being soluble and 62% insoluble.

Avocados are much lower in sugars than other fruits with a sugar content closer to that of vegetables.

Everyone knows that bananas are a good source of potassium but it may be surprising to note that avocados contain about 40% more potassium by weight than bananas. Leafy greens such as kale and spinach have approximately the same amount of potassium by weight as avocados.

Avocados are rich in phytosterols compared to other fruit due to their high fat content. Phytosterols are fat-soluble and most fruits contain hardly any fat at all (2). Nuts and seeds contain two to four times as many phytosterols by weight as avocados (1). Leafy greens beat avocados in phytosterol levels by seven to twenty times and are also ahead on folate, Vitamin C and Vitamin K (12). Chocolate contains twice as many phytosterols by weight as avocados.

 

THE VERDICT ON AVOCADOS

Avocados consumed in their whole state can be an excellent source of vitamins and phytonutrients. As well, avocados are a good source of healthy fat. Ingestion of avocado along with a source of carotenoid phytonutrients boosts both the absorption of beta-carotenes as well as the conversion of beta-carotene to Vitamin A. Additionally their consumption has been shown to decrease the inflammation caused by eating inflammatory foods such as meat. Other research on avocados indicates other possible health benefits including decreased cholesterol levels, decreased LDL particles including the more harmful small, dense LDL particles, increased cancer cell death, arthritis pain relief, prevention of AMD and cataracts and improvement of cognitive function.

The healthful nutrients found in avocados are not exclusive to avocados. All plant foods are excellent sources of a wide range of phytonutrients, vitamins, minerals and fiber. Much more investigation is required to determine if avocados provide special benefits above and beyond the fact that they are a whole plant food. Furthermore, diminishing the strength of the results of many studies on avocados is their use of isolated extracted fractions of the fruit, not the whole fruit itself. Effects induced by individual components of the fruit cannot be extended to the whole fruit.

Bottom line – avocados can be a delicious source of healthy fat. Because of their fat and fiber content they are filling and satisfying. Be aware however that they are high in calories with a medium-sized avocado containing around 230 calories. If you add avocados into your present diet without changing anything else you are likely to see a slow but inevitable weight gain. A good plan is to enjoy avocados in moderation as a replacement for unhealthy fats such as trans-fats or saturated fats.

 

SOURCES:

1 Phillips, K.M., Ruggio, D.M., Ashraf-Khorassani, M. . Phytosterol composition of nuts and seeds commonly consumed in the United States. J Agric Food Chem. 2005 Nov 30; 53(24):9436-9445

2 Dreher, M.L., Davenport, A.J. Hass avocado composition and potential health effects. Crit Rev Food Sci Nutr. 2013; 53(7):738-750.

3 Peou, S., Milliard-Hasting, B., Shah, S.A. Impact of avocado-enriched diets on plasma lipoproteins: A meta-analysis. J Clin Lipidol. 2016 Jan-Feb; 10(1):161-171.

4 Wang, L., Bordi, P.L., Fleming, J.A., Hill, A.M., M. Kris‐Etherton, P.M. 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. 2015 Jan; 4(1): e001355.

5 Weikel, K.A., Taylor, A. Nutritional Modulation of Age-Related Macular Degeneration. Mol Aspects Med. 2012 Aug; 33(4): 318–375.

6 Wien, M.,Haddad, E., Oda, K., Sabaté, J. A randomized 3×3 crossover study to evaluate the effect of Hass avocado intake on post-ingestive satiety, glucose and insulin levels, and subsequent energy intake in overweight adults. Nutrition Journal 2013; 12:155

7 Jackson, M.D., Walker, S.P., Simpson-Smith, C.M., Lindsay, C.M., Smith, G., McFarlane-Anderson, N., Bennett, F., Coard, K.C., Aiken, W.D., Tulloch, T., Paul, T.J., Wan, R.L. Associations of whole-blood fatty acids and dietary intakes with prostate cancer in Jamaica. Cancer Causes Control. 2012 Jan; 23(1):23-33.

8 Li, Z., Wong, A., Henning, S.M., Zhang, Y., Jones, A., Zerlin, A., Thames, G., Bowerman, S., Tseng, C.H., Heber, D. Hass avocado modulates postprandial vascular reactivity and postprandial inflammatory responses to a hamburger meal in healthy volunteers. Food Funct. 2013 Feb 26; 4(3):384-391.

9 Pieterse, Z., Jerling, J.C., Oosthuizen, W., Kruger, H.S., Hanekom, S.M., Smuts, C.M., Schutte, A.E. Substitution of high monounsaturated fatty acid avocado for mixed dietary fats during an energy-restricted diet: effects on weight loss, serum lipids, fibrinogen, and vascular function. Nutrition. 2005 Jan; 21(1):67-75.

10 Kopec, R.E., Cooperstone, J.L., Schweiggert, R.M., Young, G.S., Harrison, E.H., Francis, D.M., Clinton, S.K., Schwartz, S.J. Avocado Consumption Enhances Human Postprandial Provitamin A Absorption and Conversion from a Novel High–β-Carotene Tomato Sauce and from Carrots . The Journal of Nutrition August 2014; 144(8): 1158–1166.

11 Nutrition Data.com 2013. Avocados, raw, all commercial varieties, per 100 grams.

12 www.myfooddata.com

13 Ras, R.T., Geleijnse, J.M., Trautwein, E.A. LDL-cholesterol-lowering effect of plant sterols and stanols across different dose ranges: a meta-analysis of randomised controlled studies. Br J Nutr. 2014 Jul 28; 112(2):214-219.

14 Christiansen, B.A., Bhatti, S., Goudarzi, R., Emami, S. Management of Osteoarthritis with Avocado/Soybean Unsaponifiables. Cartilage. 2015 Jan; 6(1): 30–44.

15 Scott, T.M., Rasmussen, H.M., Chen, O., Johnson, E.J. Avocado Consumption Increases Macular Pigment Density in Older Adults: A Randomized, Controlled Trial. Nutrients 2016, 9(9), 919.

16 Ding, H., Chin, Y.W., Kinghorn, A.D., D’Ambrosio, S.M. Chemopreventive characteristics of avocado fruit. Semin Cancer Biol. 2007 Oct; 17(5):386-94.

17 Ding, H., Han, C., Guo, D., Chin, Y.W., Ding, Y., Kinghorn, A.D., D’Ambrosio, S.M. Selective induction of apoptosis of human oral cancer cell lines by avocado extracts via a ROS-mediated mechanism. Nutr Cancer. 2009; 61(3):348-56.

18 Christen, W.G., Liu, S., Glynn, R.J., Gaziano, J.M., Buring, J.E. Dietary Carotenoids, Vitamins C and E, and Risk of Cataract in Women – A Prospective Study. Arch Ophthalmol. 2008; 126(1):102-109.

19 USDA Food Nutrient Database for Standard Release 28, 2015

20 http://nutritiondata.self.com/foods-000138000000000000000-5w.html?