Health benefits of Avocado

Avocado

The avocado (Persea americana) originated in Mexico, Central or South America, and was first cultivated in Mexico as early as 500 BC ¹⁾. The first English language mention of avocado was in 1696. In 1871, avocados were first introduced to the United States in Santa Barbara, California, with trees from Mexico. By the 1950s, there were over 25 avocado varieties commercially packed and shipped in California, with Fuerte accounting for about two-thirds of the production. As the large-scale expansion of the avocado industry occurred in the 1970s, the Hass avocado cultivar replaced Fuerte as the leading California variety and subsequently became the primary global variety ²⁾. The Hass avocado contains about 136 g of pleasant, creamy, smooth texture edible fruit covered by a thick dark green, purplish black, and bumpy skin. The avocado seed and skin comprise about 33% of the total whole fruit weight ³⁾. Avocados are a farm-to-market food; they require no processing, preservatives or taste enhancers. The avocado’s natural skin eliminates the need for packaging and offers some disease and insect resistance, which allows them to be grown in environmentally sustainable ways.

Although the U.S. Nutrition Labeling and Education Act defines the serving size of an avocado as one-fifth of a fruit, or 30 g (1 ounce), the National Health and Nutrition Examination Survey 2001–2006 finds that the average consumption is one-half an avocado (approximately 68 g) ⁴⁾.

The nutrition and phytochemical composition of avocados is summarized in Table 1.

One-half an avocado is a nutrient and phytochemical dense food consisting of the following: dietary fiber (4.6 g), total sugar (0.2 g), potassium (345 mg), sodium (5.5 mg), magnesium (19.5 mg), vitamin A (5.0 μg RAE), 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), cryptoxanthin (18.5 μg), phytosterols (57 mg), and high-monounsaturated fatty acids (6.7 g) and 114 kcals or 1.7 kcal/g (after adjusting for insoluble dietary fiber), which may support a wide range of potential health effects (USDA, 2011; ADA, 2009). Avocados contain an oil rich in monounsaturated fatty acids (MUFA) in a water based matrix, which appears to enhance nutrient and phytochemical bioavailability and masks the taste and texture of the dietary fiber (USDA, 2011; Unlu et al., 2005). Avocados’ are a medium energy dense fruit because about 80% of the avocado edible fruit consists of water (72%) and dietary fiber (6.8%) and has been shown to have similar effects on weight control as low-fat fruits and vegetables (USDA, 2011; Bes-Rastrollo et al., 2008). An analysis of adult data from the NHANES 2001–2006 suggests that avocado consumers have higher HDL-cholesterol, lower risk of metabolic syndrome, and lower weight, BMI, and waist circumference than nonconsumers (Fulgoni et al., 2010b). One avocado fruit (136 g) has nutrient and phytochemical profiles similar to 1.5 ounces (42.5 g) of tree nuts (almonds, pistachios, or walnuts), which have qualified heart health claims ⁵⁾ (Table 2).

Table 1. Avocado Calories – Carbs –  Protein – Fiber – Nutrition Content

[Source: United States Department of Agriculture, Agriculture Research Service. USDA Food Composition Databases. ⁶⁾]

Table 2. Avocado compared to tree nut qualified health claims reference amount

[Source: United States Department of Agriculture, Agriculture Research Service. USDA Food Composition Databases. ⁷⁾]

How To Choose and Use Avocado

There are hundreds of types of avocados, but seven avocado varieties (Bacon, Fuerte, Gwen, Hass, Lamb Hass, Pinkerton, Reed and Zutano) are grown commercially in California. The Hass variety accounts for approximately 95 percent of the total crop each year – which runs from Spring to Fall.

Many varieties are available as certified organic fruit.

How to know when your avocado is ripe

• The best way to tell if an avocado is ripe and ready for immediate use is to gently squeeze the fruit in the palm of your hand. Ripe, ready-to-eat fruit will be firm yet will yield to gentle pressure.
• Color alone may not tell the whole story, because some avocado like the Hass avocado will turn dark green or black as it ripens, but some other avocado varieties retain their light-green skin even when ripe.
• Avoid fruit with dark blemishes on the skin or over-soft fruit.
• If you plan to serve the fruit in a few days, stock up on hard, unripened fruit.

How to Ripen your Avocados

• The easiest way to ripen an avocado is to place it on your counter or in your fruit bowl for a few days until it gives slightly to gentle squeezing in the palm of your hand.
• To speed up the process of ripening avocados, place the fruit in a plain brown paper bag and store at room temperature 65-75° F until ready to eat (usually two to five days).
• Including an apple or kiwifruit in the bag accelerates the process because these fruits give off natural ethylene gas, which will help ripen your avocados organically. Ethylene is a plant hormone that triggers the ripening process and is used commercially to help ripen bananas, avocados and other fruit. When placed in a paper bag, you are containing the ethylene and encouraging the fruit to ripen faster. For best results, use red or golden delicious apples. These old varieties produce more ethylene than newer varieties (e.g. Gala or Fuji) that have been bred to ripen slowly to maintain their crisp texture, and will be the most effective when it comes to ripening avocados ⁸⁾.
• Tip: The more apples or kiwifruit you add, the quicker your avocados will ripen !
• Soft ripe fruit can be refrigerated until it is eaten, and should last for at least two more days.
• Refrigerate only ripe or soft avocados.
• Putting your avocado into the oven or microwave is not recommended. The avocado will soften, but it just won’t have the flavor or taste. It will actually taste like unripe avocado (because it is).

If you are cutting into an avocado and there are black spots, vascular bundles (stringiness) or bruises, discard those areas. Vascular bundles (stringiness or stringy avocado fibers running through the avocado pulp) are generally the result of fruit from younger trees, improper storage conditions or transitional times between origins (from one country to the next). Often times the fibers or strings will disappear or become less noticeable as the avocado season goes on and/or trees mature ⁹⁾.

That being said, it’s very difficult to predict whether your avocados will have strings or not without cutting into them first.

Avocado and Weight Management

The availability and consumption of healthy foods, including vegetables and fruits, is associated with lower weight ¹⁰⁾ and body mass index (BMI) ¹¹⁾. Over the last several decades, there has been the general perception that consuming foods rich in fat can lead to weight gain, and low-fat diets would more effectively promote weight control and reduce chronic disease risk ¹²⁾. However, a key large, randomized, long-term clinical trial found that a moderate fat diet can be an effective part of a weight loss plan and the reduction of chronic disease risk ¹³⁾. Strong and consistent evidence indicates that dietary patterns that are relatively low in energy density improve weight loss and weight maintenance among adults. Three randomized controlled weight loss trials found that lowering food-based energy density by increasing fruit and/or vegetable intake is associated with significant weight loss ¹⁴⁾, ¹⁵⁾, ¹⁶⁾. The energy density of an entire dietary pattern is estimated by dividing the total amount of calories by the total weight of food consumed; low, medium, and high energy density diets contain 1.3 kcal, 1.7 kcal, and 2.1 kcal per g, respectively ¹⁷⁾. Avocados have both a medium energy density of 1.7 kcal/g and a viscose water, dietary fiber and fruit oil matrix that appears to enhance satiety ¹⁸⁾. This is consistent with research by Bes-Rastrollo et al. ¹⁹⁾, which suggests that avocados support weight control similar to other fruits.

Several preliminary clinical studies suggest that avocados can support weight control. The first trial studied the effect of including one and a half avocados (200 g) in a weight loss diet plan. In this study, sixty-one healthy free-living, overweight, and obese subjects were randomly assigned into either a group consuming 200 g/d of avocados (30.6 g fat) substituted for 30 g of mixed fats, such as margarine and oil, or a control group excluding avocados for 6 weeks ²⁰⁾. Both groups lost similar levels of weight, body mass index (BMI), and percentage of body fat to confirm that avocados can fit into a weight loss diet plan. A randomized single blinded, crossover postprandial study of 26 healthy overweight adults suggested that one-half an avocado consumed at lunch significantly reduced self-reported hunger and desire to eat, and increased satiation as compared to the control meal ²¹⁾. Additionally, several exploratory trials suggest that monounsaturated fatty acid (MUFA) rich diets help protect against abdominal fat accumulation and diabetic health complications ²²⁾, ²³⁾, ²⁴⁾.

Avocado and Cardiovascular Health Benefits

Avocados provide nearly 20 essential nutrients, including a good source of fiber and folate, potassium, Vitamin E, B-vitamins, and folic acid.

Avocados are a potent source of nutrients as well as monounsaturated fatty acids (MUFAs). According to a recent study, adding an avocado a day to a heart-healthy diet can help improve LDL levels in people who are overweight or obese.

There are eight preliminary avocado cardiovascular clinical trials summarized in Table 3 ²⁵⁾, ²⁶⁾, ²⁷⁾, ²⁸⁾, ²⁹⁾, ³⁰⁾, ³¹⁾, ³²⁾.

Table 3. Avocado cardiovascular health clinical overview

[Source ⁴¹⁾]

The first exploratory avocado clinical study demonstrated that the consumption of 0.5–1.5 avocados per day may help to maintain normal serum total cholesterol in men ⁴²⁾. Half the subjects experienced a 9–43% reduction in serum total cholesterol and the other subjects (either diabetic or very hypercholesterolemic) experienced a neutral effect, but none of the subjects showed increased total cholesterol. Also, the subjects did not gain weight when the avocados were added to their habitual diet.

In the 1990s, a number of avocado clinical trials consistently showed positive effects on blood lipids in a wide variety of diets in studies on healthy, hypercholesterolemic, and type 2 diabetes subjects ⁴³⁾, ⁴⁴⁾, ⁴⁵⁾, ⁴⁶⁾, ⁴⁷⁾, ⁴⁸⁾, ⁴⁹⁾. In hypercholesterolemic subjects, avocado enriched diets improved blood lipid profiles by lowering LDL-cholesterol and triglycerides and increasing HDL-cholesterol compared to high carbohydrate diets or other diets without avocado. In normolipidemic subjects, avocado enriched diets improved lipid profiles by lowering LDL-cholesterol without raising triglycerides or lowering HDL-cholesterol. These studies suggest that avocado enriched diets have a positive effect on blood lipids compared to low-fat, high carbohydrate diets or the typical American diet. However, since all these trials were of a small number of subjects (13–37 subjects) and limited duration (1–4 weeks), larger and longer term trials are needed to confirm avocado blood lipid lowering and beyond cholesterol health effects.

In a randomized crossover study of 12 women with type 2 diabetes, a monounsaturated fat diet rich in avocado was compared with a low-fat complex-carbohydrate-rich diet for effects on blood lipids ⁵⁰⁾. After 4 weeks, the avocado rich diet resulted in significantly lowered plasma triglycerides and both diets maintained similar blood lipids and glycemic controls. Additionally, a preclinical study found that avocados can modify the HDL-C structure by increasing paraoxonase 1 activity, which can enhance lipophilic antioxidant capacity and help convert oxidized LDL-C back to its nonoxidized form ⁵¹⁾.

Avocado and Fatty Acids

Avocados can fit into a heart healthy dietary pattern such as the DASH (Dietary Approaches to Stop Hypertension) diet plan. Avocados contain a monounsaturated fatty acids (MUFA)-rich fruit oil with 71% MUFA, 13% polyunsaturated fatty acids (PUFA), and 16% saturated fatty acids (SFA). As the avocado fruit ripens, the saturated fat decreases and the monounsaturated oleic acid increases ⁵²⁾. The use of avocado dips and spreads as an alternative to more traditional hard, saturated fatty acids rich spreads or dips can assist in lowering dietary saturated fatty acids intake ⁵³⁾.

Table 4. Hass Avocado Spread and Dip Comparison

Spread and Dip Nutritional Comparison
	Fresh Avocado	Butter	Sour Cream	Margarine	Cheddar Cheese	Mayonnaise, Regular
Serving Size	50g (1/3 of a medium avocado)	1 Tbsp.	2 Tbsp.	1 Tbsp	1 oz. (1 slice)	1 Tbsp.
Calories	80	100	45	100	110	90
Total Fat (g)	8	12	4.5	11	9	10
Sat Fat (g)	1	7	3	2	5	1.5
Cholesterol (mg)	0	30	10	0	30	5
Sodium (mg)	0	90	10	95	180	90

[Source Avocado Central. Hass Avocado Spread Comparison ⁵⁴⁾]

Note: A 50g serving of fresh avocados contain 0mg of cholesterol, 0mg of sodium, 1g saturated fat. Nutritional values are for the item listed only; not as consumed with other foods or ingredients.

Avocado and Dietary Fiber

Avocado fruit carbohydrates are composed of about 80% dietary fiber, consisting of 70% insoluble and 30% soluble fiber ⁵⁵⁾. Avocados contain 2.0 g and 4.6 g of dietary fiber per 30 g and one-half fruit, respectively. Thus, moderate avocado consumption can help to achieve the adequate intake of 14 g dietary fiber per 1000 kcal as about one-third this fiber level can be met by consuming one-half an avocado.

Avocado and Sugars

Compared to other fruits, avocados contain very little sugar. One-half an avocado contains only about 0.2 g sugar (e.g., sucrose, glucose, and fructose). The primary sugar found in avocados is a unique seven-carbon sugar called D-mannoheptulose and its reduced form, perseitol, contributes about 2.0 g per one-half fruit but this is not accounted for as sugar in compositional database as it does not behave nutritionally as conventional sugar and is more of a unique phytochemical to avocados ⁵⁶⁾, ⁵⁷⁾. Preliminary D-mannoheptulose research suggests that it may support blood glucose control and weight management ⁵⁸⁾. The glycemic index and load of an avocado is expected to be about zero due to its very low carbohydrate content.

Avocado and Potassium

Clinical evidence suggests that adequate potassium intake may promote blood pressure control in adults ⁵⁹⁾. The mean intake of potassium by adults in the United States was approximately 3200 mg per day in men and 2400 mg per day in women, which is lower than the 4700 mg per day recommended intake ⁶⁰⁾. Avocados contain about 152 mg and 345 mg of potassium per 30 g and one-half fruit, respectively. Also, avocados are naturally very low in sodium with just 2 mg and 5.5 mg sodium per 30 g and one-half fruit, respectively ⁶¹⁾. The health claim for blood pressure identifies foods containing 350 mg potassium and less than 140 mg of sodium per serving as potentially appropriate for this claim.

Avocado and Magnesium

Magnesium acts as a cofactor for many cellular enzymes required in energy metabolism, and it may help support normal vascular tone and insulin sensitivity ⁶²⁾. Preliminary preclinical and clinical researches suggest that low magnesium may play a role in cardiac ischemia ⁶³⁾. In the Health Professionals Follow-up Study, the results suggested that the intake of magnesium had a modest inverse association with risk of coronary heart disease in men ⁶⁴⁾. Magnesium was shown to inhibit fat absorption to improve postprandial hyperlipidemia in healthy subjects ⁶⁵⁾. Avocados contain about 9 and 20 mg magnesium per 30 g and one-half fruit, respectively ⁶⁶⁾.

Avocado and Vitamins

• Antioxidant Vitamins

Avocados are one of the few foods that contain significant levels of both vitamins C and E. Vitamin C plays an important role in recycling vitamin E to maintain circulatory antioxidant protection such as potentially slowing the rate of LDL-cholesterol oxidation. Evidence suggests that vitamin C may contribute to vascular health and arterial plaque stabilization ⁶⁷⁾. According to a recent review article, vitamin C might have greater cardiovascular disease protective effects on specific populations such as smokers, obese, and overweight people; people with elevated cholesterol, hypertension, and type 2 diabetics; and people over 55 years of age ⁶⁸⁾. Avocado fruit contains 2.6 mg and 6.0 mg vitamin C per 30 g and one-half fruit, respectively ⁶⁹⁾. Avocados contain 0.59 mg and 1.34 mg vitamin E (α-tocopherol) per 30 g and one-half avocado, respectively ⁷⁰⁾. One randomized clinical study suggested that a combination of vitamin C and E may slow atherosclerotic progression in hypercholesterolemic persons ⁷¹⁾.

• Vitamin K1 (phylloquinone)

Vitamin K1 functions as a coenzyme during synthesis of the biologically active form of a number of proteins involved in blood coagulation and bone metabolism ⁷²⁾. Phylloquinone (K1) from plant-based foods is considered to be the primary source of vitamin K in the human diet. Vitamin K1 in its reduced form is a cofactor for the enzymes that facilitate activity for coagulation ⁷³⁾. The amount of vitamin K1 found in avocados is 6.3 μg and 14.3 μg per 30 g and one-half fruit, respectively ⁷⁴⁾. Some people on anticoagulant medications are concerned about vitamin K intake; however, the avocado level of vitamin K1 per ounce is 150 times lower than the 1000 μg of K1 expected to potentially interfere with the anticoagulant effect of drugs such as warfarin (Coumadin) ⁷⁵⁾, ⁷⁶⁾.

• B-vitamins

Deficiencies in B-vitamins such as folate and B-6 may increase homocysteine levels, which could reduce vascular endothelial health and increase cardiovascular disease risk ⁷⁷⁾. Avocados contain 27 μg folate and 0.09 mg vitamin B-6 per 30 g and 61 μg folate, respectively, and 0.20 mg vitamin B-6 per one-half fruit ⁷⁸⁾.

Avocado and Phytochemicals

• Carotenoids

The primary avocado carotenoids are a subclass known as xanthophylls, oxygen-containing fat-soluble antioxidants ⁷⁹⁾ (Table 1). Xanthophylls, such as lutein, are more polar than carotenes (the other carotenoid subclasses including β-carotene), so they have a much lower propensity for pro-oxidant activity ⁸⁰⁾. Avocados have the highest lipophilic total antioxidant capacity among fruits and vegetables ⁸¹⁾. In a relatively healthy population, the DASH diet pattern clinical study reported reduced oxidative stress (blood ORAC and urinary isoprostanes) compared to a typical American diet ⁸²⁾, which appears primarily due to the DASH diet providing significantly more serum carotenoids, especially the xanthophyll carotenoids lutein, β-cryptoxanthin, and zeaxanthin, as a result of increased fruit and vegetable consumption. Xanthophylls appear to reduce circulating oxidized LDL-C, a preliminary biomarker for the initiation and progression of vascular damage ⁸³⁾. The Los Angeles Atherosclerosis Study, a prospective study, findings suggest that higher levels of plasma xanthophylls were inversely related to the progression of carotid intima-media thickness, which may be protective against early atherosclerosis ⁸⁴⁾. Although this research is encouraging, more clinical studies are needed to understand the cardiovascular health benefits associated with avocado carotenoids.

The consumption of avocados can be an important dietary source of xanthophyll carotenoids ⁸⁵⁾. Hass avocado carotenoid levels tend to significantly increase as the harvest season progresses from January to September ⁸⁶⁾. In Hass avocados, xanthophylls lutein and cryptoxanthin predominate over the carotenes, contributing about 90% of the total carotenoids ⁸⁷⁾. USDA reports lutein and zeaxanthin at 81 μg and 185 μg per 30 g and one half fruit, respectively, and cryptoxanthin at 44 μg and 100 μg per 30 g and one-half fruit, respectively ⁸⁸⁾. However, a more comprehensive analysis of avocados including xanthophylls has found much higher levels ranging from 350–500 μg per 30 g to 800–1100 μg per one-half fruit at time of harvest ⁸⁹⁾. The color of avocado flesh varies from dark green just under the skin to pale green in the middle section of the flesh to yellow near the seed ⁹⁰⁾. The total carotenoid concentrations were found to be greatest in the dark green flesh close to peel ⁹¹⁾.

The intestinal absorption of carotenoids depends on the presence of dietary fat to solubilize and release carotenoids for transfer into the gastrointestinal fat micelle and then the circulatory system ⁹²⁾, ⁹³⁾. Avocado fruit has a unique unsaturated oil and water matrix naturally designed to enhance carotenoid absorption. For salads, a significant source of carotenoids, reduced fat or fat free salad dressings are common in the marketplace and these dressings have been shown to significantly reduce carotenoid absorption compared to full fat dressings ⁹⁴⁾. Similar clinical research has demonstrated that adding avocado to salad without dressing, or with reduced fat/fat free dressing and serving avocados with salsa increases carotenoid bioavailability by 2–5 times ⁹⁵⁾.

• Phenolics

Preliminary evidence suggests beneficial effects of fruit phenolics on reducing cardiovascular disease risk by reducing oxidative and inflammatory stress, enhancing blood flow and arterial endothelial health, and inhibiting platelet aggregation to help maintain vascular health ⁹⁶⁾, ⁹⁷⁾, ⁹⁸⁾, ⁹⁹⁾. Avocados contain a moderate level of phenolic compounds contributing 60 mg and 140 mg gallic acid equivalents (GAE) per 30 g and one-half fruit, respectively. The avocado also has a total antioxidant capacity of 600 μmol Trolox Equilvalent (TE) per 30 g or 1350 μmol TE per one-half fruit ¹⁰⁰⁾. This places avocados in the mid-range of fruit phenolic levels. Avocados have the highest fruit lipophilic antioxidant capacity, which may be one factor in helping to reduce serum lipid peroxidation and promoting vascular health ¹⁰¹⁾.

• Phytosterols

Avocados are the richest known fruit source of phytosterols ¹⁰²⁾ with about 26 mg and 57 mg per 30 g and one half fruit, respectively ¹⁰³⁾. Other fruits contain substantially less phytosterols at about 3 mg per serving ¹⁰⁴⁾. Although the avocado’s phytosterol content is lower than that of fortified foods and dietary supplements, its unique emulsified fat matrix and natural phytosterol glycosides may help promote stronger intestinal cholesterol blocking activity than fortified foods and supplements ¹⁰⁵⁾. A recent economic valuation in Canada of the potential health benefits from foods with phytosterols suggests that they may play a role in enhancing cardiovascular health and reducing associated health costs ¹⁰⁶⁾.

Avovcado and Healthy Aging

• DNA Damage Protection

Several clinical studies suggest that xanthophylls, similar to those found in avocados, may have antioxidant and DNA protective effects with possible healthy aging protective effects. One study was conducted involving 82 male airline pilots and frequent air travelers who are exposed to high levels of cosmic ionizing radiation known to damage DNA, potentially accelerating the aging process ¹⁰⁷⁾. There was a significant and inverse association between intake of vitamin C, beta-carotene, β-cryptoxanthin, and lutein-zeaxanthin from fruits and vegetables and the frequency of chromosome translocation, a biomarker of cumulative DNA damage. In another trial, lipid peroxidation (8-epiprostaglandin F2a) was correlated inversely with plasma xanthophyll levels ¹⁰⁸⁾. In other studies, inverse correlations were found between lutein and oxidative DNA damage as measured by the comet assay, and in contrast to beta-carotene ¹⁰⁹⁾, ¹¹⁰⁾. National Health and Nutrition Examination Survey analysis suggests that xanthophylls intake decreases with aging ¹¹¹⁾.

• Osteoarthritis

Osteoarthritis (OA) is characterized by progressive deterioration of joint cartilage and function with associated impairment, and this affects most people as they age or become overweight or obese ¹¹²⁾, ¹¹³⁾. This joint deterioration may be triggered by oxidative and inflammation stress, which can cause an imbalance in biosynthesis and degradation of the joint extracellular matrix leading to loss of function ¹¹⁴⁾. A cross-sectional study reported that fruits and vegetables rich in lutein and zeaxanthin (the primary carotenoids in avocados) are associated with decreased risk of cartilage defects (early indicator of OA) ¹¹⁵⁾.

Avocado and soy unsaponifiables (ASU) is a mixture of fat soluble extracts in a ratio of about 1(avocado):2(soy). The major components of ASU are considered anti-inflammatory compounds with both antioxidant and analgesic activities ¹¹⁶⁾, ¹¹⁷⁾, ¹¹⁸⁾, ¹¹⁹⁾, ¹²⁰⁾, ¹²¹⁾, ¹²²⁾. In vitro studies found that pretreatment of chondrocytes with ASU blocked the activation of COX-2 transcripts and secretion of prostaglandin E2 (PGE2) to baseline levels after activation with lipopolysaccharide (LPS). Further study revealed that ASU can also block tumor necrosis factor-α (TNF-α), IL-1β, and iNOS expression to levels similar to those in nonactivated control cultures. Additional laboratory studies suggest that ASU may facilitate repair of OA cartilage through its effect on osteoblasts ¹²³⁾.

Clinical support for ASU in the management of hip and knee OA comes from four randomized controlled trials ¹²⁴⁾, ¹²⁵⁾, ¹²⁶⁾, ¹²⁷⁾ and one meta-analysis ¹²⁸⁾. All studies used 300 mg per day. The clinical trials were generally positive with three providing OA support and one study showing no joint cartilage improvement compared to placebo.

• Eye Health

Lutein and zeaxanthin are selectively taken up into the macula of the eye (the portion of the eye where light is focused on the lens) ¹²⁹⁾. Relative intakes of lutein and zeaxanthin decrease with age and the levels are lower in females than males ¹³⁰⁾. Mexican Americans have the highest intake of lutein and zeaxanthin than any other ethnicity and they are among the highest consumers of avocados in the United States. Observational studies show that low dietary intake and plasma concentration of lutein may increase age-related eye dysfunction ¹³¹⁾. Research from the Women’s Health Initiative Observation Study found that MUFA rich diets were protective of age-related eye dysfunction ¹³²⁾, ¹³³⁾. Avocados may contribute to eye health since they contain a combination of MUFA and lutein/zeaxanthin and help improve carotenoid absorption from other fruits and vegetables ¹³⁴⁾. Avocados contain 185 μg of lutein/zeaxanthin per one-half fruit, which is expected to be more highly bioavailable than most other fruit and vegetable sources.

• Skin Health

Skin often shows the first visible indication of aging. Topical application or consumption of some fruits and vegetables or their extracts such as avocado has been recommended for skin health ¹³⁵⁾. The facial skin is frequently subjected to ongoing oxidative and inflammatory damage by exposure to ultraviolet (UV) and visible radiation and carotenoids may be able to combat this damage. A clinical study found that the concentration of carotenoids in the skin is directly related to the level of fruit and vegetable intake ¹³⁶⁾. Avocado’s highly bioavailable lutein and zeaxanthin may help to protect the skin from damage from both UV and visible radiation ¹³⁷⁾. Several small studies suggest that topical or oral lutein can provide photo-protective activity ¹³⁸⁾, ¹³⁹⁾, ¹⁴⁰⁾.

A cross-sectional study examined the relationship between skin anti-aging and diet choices in 716 Japanese women ¹⁴¹⁾. After controlling for covariates including age, smoking status, BMI, and lifetime sun exposure, the results showed that higher intakes of total dietary fat were significantly associated with more skin elasticity. A higher intake of green and yellow vegetables was significantly associated with fewer wrinkles ¹⁴²⁾. Several preclinical studies suggest that avocado components may protect skin health by enhancing wound healing activity and reducing UV damage ¹⁴³⁾, ¹⁴⁴⁾.

• 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 ¹⁴⁵⁾. The concentrations of some of these phytochemicals in the avocado may be potentially efficacious (Jones et al., 1992). Currently, direct avocado anti-cancer activity is very preliminary with all data based on in vitro studies on human cancer cell lines.

Cancer of the larynx, pharynx, and oral cavity are the primary area of avocado cancer investigation. Glutathione, a tripeptide composed of three amino acids (glutamic acid, cysteine, and glycine) functions as an antioxidant ¹⁴⁶⁾. The National Cancer Institute found that avocado’s glutathione levels of 8.4 mg per 30 g or 19 mg per one-half fruit is several fold higher than that of other fruits ¹⁴⁷⁾. Even though the body digests glutathione down to individual amino acids when foods are consumed, a large population-based case controlled study showed a significant correlation between increased glutathione intakes and decreased risk of oral and pharyngeal cancer ¹⁴⁸⁾. One clinical study found that plasma lutein and total xanthophylls but not individual carotenes or total carotenes reduced biomarkers of oxidative stress (urinary concentrations of both total F2-isoprostanes and 8-epi-prostaglandin) in patients with early-stage (in situ, stage I, or stage II) cancer of larynx, pharynx, or oral cavity ¹⁴⁹⁾. Xanthophyll rich avocado extracts have been shown in preclinical studies to have anti-Helicobacter pylori activity for a potential effect on gastritis ulcers, which may be associated with gastric cancer risk.

Dietary carotenoids show potential breast cancer protective biological activities, including antioxidant activity, induction of apoptosis, and inhibition of mammary cell proliferation ¹⁵⁰⁾. Studies examining the role of fruits and vegetables and carotenoid consumption in relation to breast cancer recurrence are limited and report mixed results ¹⁵¹⁾. In preclinical studies, total carotenoids and lutein appear to reduce oxidative stress, a potential trigger for breast cancer ¹⁵²⁾. In women previously treated for breast cancer, a significant inverse association was found between total plasma carotenoid concentrations and oxidative stress ¹⁵³⁾, but more clinical research is needed to confirm this finding.

Mammographic density is one of the strongest predictors of breast cancer risk ¹⁵⁴⁾. The association between carotenoids and breast cancer risk as a function of mammographic density was conducted in a nested, case-control study consisting of 604 breast cancer cases and 626 controls with prospectively measured circulating carotenoid levels and mammographic density in the Nurses’ Health Study ¹⁵⁵⁾. Overall, circulating total carotenoids were inversely associated with breast cancer risk. Among women in the highest tertile of mammographic density, elevated levels α-carotene, β-cryptoxanthin, lycopene, and lutein/zeaxanthin in the blood were associated with a 40–50% reduction in breast cancer risk . In contrast, there was no inverse association between carotenoids and breast cancer risk among women with low-mammographic density. These results suggest that plasma levels of carotenoids may play a role in reducing breast cancer risk, particularly among women with high mammographic density. There are no direct avocado breast cancer clinical studies.

Exploratory studies in prostate cancer cell lines suggest antiproliferative and antitumor effects of avocado lipid extracts ¹⁵⁶⁾. Lutein is one of the active components identified. There are currently no human studies to confirm this potential lutein and prostate cancer relationship.