Purseglove (1968), In his authoritative textbook,
labeled the avocado "...the most nutritious of all fruits." Noted food
writer Gaylord Hauser once said of it: "In this single delectable fruit
are combined the protein of meat, the fat of butter [but much more
wholesome!],
the vitamins and minerals of green vegetables, the flavor
of nuts, a six course dinner ".
America's greatest plant explorer, David Fairchild is attributed
"...the avocado is a food without rival among the fruits, the veritable
fruit of paradise."
And in 1959, cereal pioneer John H. Kellogg
maintained that "of all edible fruits, it stands pre-eminent as a source
of concentrated nutriment adapted to human use. For purity,
wholesomeness, ease of digestibility, and adaptation to human needs, it
has few rivals and none that can fill its place." (Quotation courtesy of
J. S. Shepherd).
Avocado usage is reduced because of
negative misconceptions. The avocado has various uses as a natural
cosmetic, with advantages in rapid skin penetration, and as a superior
natural sunscreen.
Avocado oil has several culinary and health benefits.
The greater use of whole fruit has important advantages: usefulness in
human weight control, high nutritional density, source of major
antioxidants, stroke prevention, fruit protein source, fiber source; as
baby food, and other dietary benefits. Erroneous public perceptions of
avocado calorie content and of cancer influences are noted.
Many people appreciate the delicious flavor of
avocado, but are afraid of them for (mistaken) dietary reasons. They
therefore avoid avocados or eat less than they could, because of
incomplete or erroneous nutritional information. Most of us connected
with the avocado industry have encountered such errors in understanding
among friends or chance acquaintances. Indeed, on occasion, one even
encounters them among "avocado" people.
These errors are diverse and recurrent. One
sometimes feels a bit like Hercules of classical mythology battling the
ugly Hydra: as soon as one evil head is cut off, two more grow in its
place! Its seems worthwhile, therefore, to make a summary of the
scientific findings concerning the avocado. We will begin with a brief
look at cosmetics, then examine the more important food attributes, and
close with an analysis of misconceptions in the press and among the
public.
Avocado Cosmetics
Increasing recognition of unhealthful consequences
from additives, preservatives, processing, and artificial products
generally gives the avocado a major advantage as a food and also as a
cosmetic. With increasing concern for the environment, an added plus for
avocado cosmetics is that they are biodegradable. Consumers are
beginning to favor basic, natural ingredients. Swisher (1988) discusses
use of the avocado as a skin moisturizer, cleansing cream, makeup base,
sunscreen, lipstick, bath oil, and hair conditioner. Toxicological tests
of avocado oil products have provided an official health/safety
assessment.
In skin care, the two major advantages of the
avocado are its marked softening and soothing nature and its notable
absorption. Compared with almond, corn, olive, and soybean oils, avocado
oil had the highest skin penetration rate (Swisher, 1988).
In sunscreens, chemicals like PABA have superior
effectiveness but cause skin irritation in some people. Because they are
synthetic, there are lingering questions about long-term safety. Among
eight plant oils, avocado oil proved the most effective sunscreen
(Swisher, 1988).
Avocado Oil
Like olive oil, avocado oil is predominantly
monounsaturated, a property which is thought to confer distinct health
benefits. The avocado as a refined cooking oil has additional advantages
(Swisher, 1988).
-
It is unusually light, so it mixes well with other foods.
-
It has a mild, delicate flavor, which enhances and brings out the flavor of other foods, instead of dominating them such as olive oil and other oils.
-
Avocado oil withstands a high cooking temperature before breaking down, i.e. its "smoke point" is about 255C (490F), which is much higher than that of olive oil.
Fried foods presently have an undesirable health reputation, but use of olive and avocado oil could change that.
Whole fruit pulp
This is by far the most important human use of the
avocado and will constitute the remainder of this article. We will look
at several nutritional qualities which sometimes overlap.
Weight control
Contrary to popular assumptions, the avocado can be
a helpful part of a successful weight-management program. It brings
several advantages.
-
Its monounsaturated fat speeds up the basal metabolic rate, as compared with saturated fat. #
-
Its high fat content gives a quicker feeling of satiation ("fullness"), thus helping to reduce overeating.
-
Its high fat content makes an overall sound diet more palatable, reducing the temptation to binge on foods high in sugars or saturated fats.
-
Its rich supply of vitamins and minerals also makes the diet more wholesome and satisfying and thus more conducive to overall health and to moderation in consumption.
The high fat content of most avocados (up to 90% of
its calories) will make some people dubious about its positive effects
on weight control. Not only does fat have over twice as many calories
per unit weight as does carbohydrate or protein, but also if excess
calories are consumed, the body apparently burns about three times as
many calories when storing calories from carbohydrate or protein as it
burns when calories from fat are stored.
Recent evidence, however,
suggests that calories are not the whole story for body weight, with
timing of both consumption and exercise as factors and with calories
from fat also a possible added handicap.
So, what is known from experiments with the
avocado? The next part of this article will discuss in detail results
from the three studies of known changes in cholesterol resulting from
the addition of avocado to the diet. In each of the three studies, there
was an average small weight loss associated with avocado consumption.
In the most pertinent experiment (Grant, 1960), a mean of just over one
California avocado a day for a mean of 33 days increased average daily
calories by a calculated 24% and fat by 54% but resulted in a weight
loss averaging approximately 1 kg (2.2 lbs).
This remarkable result
(under exceptional and tightly controlled hospital conditions) should
not be taken as a universal guarantee; individual results will vary
depending upon complex individual metabolic histories and interactions.
What can be said is that eating avocado has been shown to be fully
compatible with good weight control.
Very few people will have rapid weight loss as a
result of increasing their consumption of avocado; however, the more
slowly one loses weight, the less likely one is to regain it. It has
become clear that an effective solution to the widespread overweight
problem will not come from simply eating less. Indeed, such 'dieting'
can actually make things worse by causing muscle loss so that the usual
'yo-yo' weight rebound leaves one fatter than ever and subsequent weight
loss more difficult to achieve than ever.
Goodrick and Foreyt reported
in the October, 1991, issue of the American Dietetic Journal that even a
combination of behavioral self-management training plus sharply reduced
calories gave a discouraging 90% eventual relapse level. Part of the
reason is genetic: we tend to inherit our body fat amount and
distribution. Part of the solution is more exercise which, of course, is
good for us for other reasons.
The emerging picture is quite complex. In the
February, 1990, issue of the American Journal of Clinical Nutrition,
Bouchard reported from Canada that women who were small eaters (mean of
1488 calories/day) as compared with similarly exercising 2393
calories/day eaters, actually weighed 10 lbs (22 kg) more on the
average, plus having 22% more body fat.
The explanation is probably a
combination of average differences in both genes and food consumption:
i.e., reducing calorie intake can lower an individual's metabolic rate
and thus defeat its purpose. We need to eat enough healthful food to
keep our metabolism high, and to provide the sated feeling that
eliminates binge eating.
Calorie-counting, dieting, advertised gimmicks and
quick weight loss are recipes for failure; whereas exercise plus healthy
food habits as a permanent way of life can bring success. The situation
is analogous to that of personal philosophy: Focus on happiness and it
will probably elude you; focus on wholesome living and happiness is a
likely by-product. Similarly, focus on weight loss and it will probably
elude you; focus on wholesome eating and weight control is a likely
by-product.
This insight was expressed years ago by Wood (1983)
in a book hailed by one health magazine as the finest method for weight
reduction known to them. Wood emphasized 'playful' exercise, but his
introduction begins: "The solution to our national overweight problem is
to encourage people to eat more." He counseled eating fresh plant food
"heartily." And his recommended list of "ingredients for a healthy diet"
included the avocado.
Americans spent an estimated $32 billion in 1989 on
diet foods and products with the annual amount increasing at a rate
that could reach $50 billion by 1995. It is difficult for me to avoid
the conclusion that we would be healthier as a nation if we spent a tiny
fraction of that amount to buy more avocados and pocketed most of the
remaining money.
High nutritional density
The fourth reason given above for the avocado's
role in weight control is its "rich supply of minerals and vitamins."
More important than a food's calorie content is its total nutritional
contribution to human needs. A good measure is nutrients per calorie.
Different avocado analyses have given somewhat variable results.
The
most detailed publication is that of Slater et al. (1973). Their data
indicate that one half of a 'Hass' avocado, about 80 g edible fruit,
provides a substantial percentage of the daily nutritional needs of a
child aged 7 to 10 (adult percentages are generally a little lower,
especially iron for females) (Table 1).
The avocado contains little vitamin B 12 and
calcium, limited zinc and modest phosphorus. Its half-a-fruit quota of
riboflavin and thiamine for children is about 9.5 and 8%, respectively,
hence about equal to its relative calorie contribution.
But the striking
thing is that no less than eight essential nutrients are apparently
present in about a 2: 1 calorie ratio. Nor is that all; three additional
nutrients, potassium, copper and pantothenic acid, (for which I could
not find precise Recommended Dietary Allowances) are also estimated to
be present in avocado at about twice the calorie content. Per calorie,
the avocado is indeed remarkably nutritious.
There is not space here to discuss either the human
body's uses or the status in typical diets of these various nutrients.
Judgments vary; several surveys have concluded that one or another of
them is deficient in a considerable portion of American diets. Next we
will look briefly at one of the least discussed vitamins in the group of
nutrients provided by the avocado.
Vitamin B6 (pyridoxine) is important for the
nervous system, red blood cells, teeth and gums. The Harvard Health
Letter for March, 1991, reported 1990 data indicating that most
Americans consume too little of vitamin B6. Among good sources they list
watermelon and banana (overlooking avocado).
Polansky and Murphy (1966)
compared the 86 content per unit weight of 26 vegetables and fruits.
For total chromatographed 86' banana and avocado had the highest
amounts, the remaining 24 vegetables had from 1/5 to 1/25 of the amount
of the avocado, with watermelon 1/6. A more recent report by William
Sears, M.D., privately printed Nature's Guide to First Foods"(1988)
reports that avocado has three times as much B6 per gram as banana.
Antioxidants and free radicals: cancer, cataracts and ageing
The
University of
California at
Berkeley Wellness Letter for October, 1991, discusses the basic role
of oxygen for human cellular energy and for life, but notes that an
inevitable by-product of this activity is the formation of highly
reactive "free radicals." These unstable troublemakers can affect
various cell constituents: perhaps artery walls or LDL cholesterol
advancing coronary heart disease; eye lens tissue causing cataracts; a
critical gene leading to cancer; perhaps arthritis; or DNA (the genetic
material) causing gradual deterioration and aging.
The human body has two main defenses against these
free radicals: enzymes and other blood compounds that depend on trace
minerals and good general nutrition and three potent antioxidants
vitamins C, E, and beta carotene (vitamin A precursor).
An article in
the June, 1991, issue of the American Journal of Clinical Nutrition
indicates that only about 57% of nonsmokers may be getting enough
vitamin C daily (for smokers the deficit is much greater). Men's Health
(June, 1991) concluded that most of us are not getting enough vitamin E.
A number of nutritionists have called for greater consumption of beta
carotene.
As we have discussed, the avocado provides about
twice as high a proportion of our daily needs for the above three
antioxidant vitamins as its calorie proportion. Recall also that the
avocado is rich in copper and iron, two mineral constituents of
antioxidant enzymes.
Nutritionists usually recommend that we get our
needs met from basic food rather than from supplements. And while the
risk of colon cancer, for example, has been associated with fat
consumption, the Harvard Health Letter for March, 1991, reported that
while meat indeed increased that risk sharply, there was no association
with plant fat. Thus, eating avocados could be an enjoyable way to help
protect ourselves against cancer, heart disease, arthritis, and eye
cataracts; it may even delay the processes of aging.
Stroke prevention
Heart disease, cancer and stroke are the three
leading causes of death in the
United States. Additionally, stroke can cause many years of partial
or total incapacitation and tragic crippling. The Associated Press,
15 October, 1987, reported an interview with Dr. Louis Tobian of the
University of
Minnesota on protection from strokes by fruit and vegetable
consumption, in particular, by high potassium intake.
Dr. Tobian is
quoted as suggesting that bachelors may die earlier than married men
because they have less balanced diets, specifically insufficient in
potassium. As the best sources of potassium, he included strawberry,
banana, citrus juice, potatoes, and milk (avocado is not mentioned).
Smith et a/. (1983) measured potassium in 100 g
portions of 10 tropical fruits (including avocado), seven common fruits,
nine common vegetables, and eight tropical vegetables. The seven common
fruits, including strawberry, banana and orange, ranged from 1/5 to
less than half the potassium content of avocado. Similarly, the nine
common vegetables ranged from less than 1/4 (summer squash) to less than
2/3 (carrots) the avocado level.
The other, lesser used, tropical
fruits ranged from 1/2 to just over half the potassium supplied by
avocado. Tropical vegetables, which are rare in the
United States, ranged upward from 1/5 to about the same potassium
richness of avocado.
Prevention magazine for August, 1987, reported the
results of a 1 2-year study of stroke entitled "Potassium was the key.",
conducted jointly by the Schools of Medicine of the University of
California San Diego and Cambridge University in England.
A 40%
reduction in stroke risk was associated with an average daily increase
in potassium consumption of about 400 mg, the amount supplied by less
than half an avocado! Moreover, blood pressure, a stroke factor, was
linked in the same article to potassium-sodium imbalance, namely to a
sodium excess.
The avocado has about 52 times as much potassium as
sodium. For the touted potassium-rich carrot, the potassium to sodium
ratio is less than 7 to 1 according to the brochure by Dr. William Sears
cited earlier. Moreover, vegetables high in potassium which include the
common potato and winter squash, are commonly eaten cooked. Boiling can
remove up to 30% of potassium originally present, according to a
researcher cited in the above Prevention article, giving the avocado an
additional advantage.
Finally, avocado and olive oils are the two chief
foods that are very high in monounsaturated fats, while being
comparatively low in both polyunsaturated and saturated fats.
An Italian
epidemiological survey of 4,903 people (reported in a press release in
February, 1990, based on an article in the Journal of the American
Medical Association), found that while both monounsaturated and
polyunsaturated fat were associated with lower blood cholesterol as
compared with saturated, only monunsaturated fat was also associated
with lower blood pressure.
The next part of this paper will look at
factors contributing to a healthy heart and related to avocado
consumption. There is evidence to indicate that eating avocado may
reduce the incidence of all three of the major causes of death in the
United States.
Protein
Cultivars vary somewhat but the dominant 'Hass' is
about 2.4% protein on a fresh weight basis (Slater et al., 1975). This
is unusually high for a fruit. Hall et al. (1980) compared the essential
amino acid content of 15 fruits: the avocado was second only to the
rare Tucuma from Brazil which had about three times as much as mango,
orange, peach and persimmon, and about six times as much as the two
other common fruits listed, apricot and apple. Polansky and Murphy
(1966) compared the protein content of 26 more common fruits and
vegetables (41 entries counting separate cultivars and years).
The
avocado was in first place with about two to ten times the protein
content of the others. The avocado is a "complete food" in terms of
protein, containing all 9 essential amino acids, although not in the
ideal proportions.
The fact that the avocado is an excellent source of
essential protein is of little interest to most residents of the United
States and other industrialized countries who are already consuming
more protein than they need. It could be of increasing importance as
health concerns move people away from meats and toward more vegetarian
dishes, especially for those who do not care to consume many legumes. It
could already be of significant benefit in tropical areas where protein
consumption is insufficient (Hall et al., 1980).
Fiber
A review paper by
Anderson (1990) noted that "fiber has emerged as a leading dietary
component in chronic disease prevention. High fiber intake lowers the
risk for cardiovascular disease, some cancers, hypertension (high blood
pressure), diabetes, and obesity" He gives references for each of these;
as well as for therapeutic benefits from fiber treatment of each of
these conditions, except cancer, and with the addition of
gastrointestinal diseases. For some disorders, a mixture of both soluble
and insoluble fiber appears to be most beneficial. He also noted that
"most individuals in the West ingest suboptimal amounts of dietary
fiber."
Smith et a/. (1983) compared the fiber content of
16 fruits and 18 vegetables. Of the 34 food sources, only the avocado
had large amounts of both soluble and insoluble fiber (it had,
respectively, 2.1 % and 2.7% by fresh weight). Guava had the highest
fraction of soluble fiber by a wide margin, pears had 2/3 as much as
avocado.
The others all had less than half as much, with the common
fruits ranging from 16% to 30% of the avocado level. Among vegetables,
available data indicate that only broccoli surpassed avocado in soluble
fiber, the others ranged downward to 21 %.
For the complementary
benefits of insoluble fiber, no fruit and only peas and among vegetables
pigeon peas are listed with levels equal to or greater than avocado,
the others ranged downward to 15%.
A frequent recommendation is that the typical
American should double his or her fiber intake. The avocado would be a
very pleasant means toward that end.
Various dietary benefits
The avocado is a mild-bland, oil-rich,
nutrient-rich deliciously-flavored food. This combination gives it an
exceptionally diverse range of dietary advantages. Just in terms of
usage alone, the avocado can be served as an hors d'oeuvre, soup, salad,
dip, sandwich spread, garnish, half-shell spoon-out, entree, dessert,
or beverage with various kinds of use in each category. Such eating
versatility makes it easy to increase consumption in order to gain
greater benefit from its numerous advantages to the human diet.
The blandness, especially of some varieties, has
sometimes been denigrated. But this very quality makes it soothing to
the alimentary tract. Perhaps that is partly why American Indians for
hundred of years have regarded the avocado as especially desirable at
times of illness. Linoleic fatty acid is an essential polyunsaturate,
i.e., the human body cannot manufacture it. Our analyses (unpublished)
indicate that the linolenic oil content of the 'Hass' avocado averages
just over 21 %, only the content of the monounsaturate fat oleic acid
was higher.
Diabetes
The
27 September, 1988, issue of the New England Journal of Medicine
reported a 4-week comparison of individuals on the traditional type II
diabetic's diet of low fat-high carbohydrate with those on a diet lower
in carbohydrates and higher in monounsaturated fat (the dominant kind in
avocados). The monounsaturated diet offered better control of blood
sugar levels, accompanied by lower triglycerides and higher HDL ("good"
cholesterol). However, this needs confirmation, including more careful
monitoring. Moreover, there is a report that avocado has an odd sugar
type that depresses insulin production. Diabetics probably should
consume avocados cautiously.
Baby food
Dr. William Sears (1988) notes that avocado is "one
of the first fresh fruits a baby can enjoy." It is a time-saver, served
raw. "Low in sodium and cholesterol-free, avocados contain [many]
valuable nutrients ". For example, "Ounce for ounce, avocados contain
more potassium than 45 other fruits, juices or vegetables... and they
are one of the only fruits or vegetables which contain monounsaturated
fats, essential for baby's development.”
In an interview with the California Grower
(October, 1989), Dr. Sears stated, "When you think about it, ...avocados
are an ideal first food for infants. Avocados have a delicate flavor
and a smooth, creamy consistency which makes them a perfect food for
babies. ...Avocados provide infants with more vitamin B1 B2 niacin,
folacin, potassium and magnesium per 1 5 gram serving than any of the
other frequently recommended fruits and vegetables [and are second to
the highest in several other vitamins and minerals.]"
Seventy years earlier, long before these dietary
details were understood, Pasadena nurseryman D. W. Coolidge addressed
the annual meeting of what was then the California Avocado Association:
"The fruit of the avocado is about the most tasteful and nourishing that
grows out of the ground The strongest people physically and mentally,
the happiest and most beautiful children, will be those who make the
avocado, instead of meat, their daily diet. I have often marveled how
babies and very young children take to the avocado at once. If I have a
greater love for anything than the avocado, it is for ruddy, happy
children."
Misconceptions
"Avocados are high in fat and therefore bad for the heart"
Right premise, wrong deduction. A number of
articles discusses this misconception in detail. A brief answer is given
here: avocados have been shown to maintain good cholesterol while
reducing bad cholesterol. They are good for your cardiovascular system.
For a more complete explanation, please see the Avocado and Human
Nutrition part II, Avocados and Your Heart.
"But their high fat content makes them very high in calories"
We have already noted that increased avocado
consumption has been shown experimentally to be compatible with good
weight control, and we have suggested why the very fact of its high fat
content may help in human weight control. Nevertheless, one keeps
encountering warnings, even from dieticians, about the avocado being
"very high" in calories, so let's look at the facts.
The number of kilocalories per avocado fruit varies
with race, variety, size, and season; an average for a California-grown
avocado might be 300 (Slater et al., 1975). Number of kilocalories per
person per day for normal maintenance varies with weight, age, sex,
activity level, and personal metabolic rate. For moderately active
individuals aged 19 to 50, a 125 lb (57 kg) woman needs about 2100
kilocalories, and a 157 lb (71 kg) man about 2800 kilocalories
(University of California, Berkeley, Wellness Letter for May, 1991).
Thus, our "average" people, if they were to get all their daily calories
from avocado, would have to eat 7 or 9, respectively. That is a lot of
avocado! With its high fat content, one would expect pronounced
satiation well before the total "allowed" was consumed.
Rinzler (1987) gives a modern comparative food
evaluation. The avocado is rated only moderate in calories per serving,
with such foods as beans, bread, oatmeal, pasta, peas, and rice; less
caloric than peanuts, most nuts and seeds, most cheeses, sugar, and
butter, etc. Yet, the avocado is high enough in calories to be helpful
to the estimated 18% of Americans who are underweight. It is apparently
not so high in calories to be of concern to normal individuals as shown
by the actual weight results cited earlier. In Fit health magazine for
August, 1982, an article on the avocado concluded that in the public
eye, it has somehow become packed "with fictitious calories, avocados
have received the undeserved reputation of being fattening."
Why has this happened? One possibility is that even
diet specialists tend toward the oversimplification that "fat is fat",
overlooking not only the fact that avocado fat is predominantly
monounsaturated, but also that it has a very high nutrient density per
fat calorie. Another possibility is the lament that "everything I love
is illegal, immoral, or fattening." Preferred, high-fat foods from
steaks to deserts now have deservedly bad reputations, and many people
automatically conclude that anything as "sinfully" rich and delicious as
avocado must be fattening and cannot be good for us ("Good" for us are
rather the foods with little appeal to most people, like carrots,
celery, leaf lettuce and spinach). It is an unfortunate irony that two
major advantages of the avocado, high monounsaturated fat content and
exquisite nutty flavor, are in many people's minds twisted into
disadvantages.
Purseglove (1968), In his authoritative textbook,
labeled the avocado "...the most nutritious of all fruits." Noted food
writer Gaylord Hauser once said of it: "In this single delectable fruit
are combined the protein of meat, the fat of butter [but much more
wholesome!], the vitamins and minerals of green vegetables, the flavor
of nuts, a six course dinner ".
America's greatest plant explorer, David Fairchild is attributed
"...the avocado is a food without rival among the fruits, the veritable
fruit of paradise." And in 1959, cereal pioneer John H. Kellogg
maintained that "of all edible fruits, it stands pre-eminent as a source
of concentrated nutriment adapted to human use. For purity,
wholesomeness, ease of digestibility, and adaptation to human needs, it
has few rivals and none that can fill its place." (Quotation courtesy of
J. S. Shepherd).
Anecdotes lack scientific weight, yet sometimes
capture reality more effectively than long scientific discourse. In the
Los Angeles HeraldExaminer for
November 9, 1969, writer Emily Wilkens had a 4-column article, "How
One Woman Keeps a Youthful Look." It tells the story of her friend Lisa,
who was "a super traveling saleswoman in the cosmetics field and could
buy every known external beauty aid at a fraction of its cost.
[Yet] day
by day she looked worse even with the most careful skin care and
makeup. At the same time, her energy for "just living" was flagging, and
she was having a weight problem She consulted eminent diet specialists,
...all to no avail.
One day while out west, she invited a very famous
movie star to have dinner with her to discuss a special promotion for
her company. Lisa watched with wonder as the actress reached into her
handbag and produced a luscious avocado.
On the way home the
actress...revealed her [secret] of beauty through healthful eating
[emphasizing] fresh fruits and vegetables. The very next day, Lisa
embarked on the diet suggested by the actress...Lisa has lost weight and
inches. Her eyes sparkle and her skin glows, and she grows...lovelier
and more vibrant each year."
Avocado health benefits are gradually becoming more
widely recognized. For example, Prevention health magazine for June,
1988, had an article on 'Nutritional nuggets from
California cuisine' ("with
Stanford
University").
It speaks of the "light" and the "lean," "sparkling
with beauty, flavor and good health," an eating style that "may help
prevent heart disease, obesity and cancer, while delighting the senses."
A recommended component: avocado. Similarly, Men's Health Newsletter
for February, 1992, discusses health-conscious sandwiches, to "keep your
energy level high, your wallet fat and your stomach lean."
They
recommend picking one item of bread, condiment and filling from select
lists; then "add as many extras as you like" from a list that includes
various superior vegetables, low-fat cheese and avocado slices.
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