Bob Bergh
Department of Botany and Plant Sciences, University of California,
Riverside, CA 92521-0124, USA
California Avocado Society Yearbook 76
(1992): 123-135.
Nutritious Value of Avocado
Presented by the author at the biennial Conference of the
Australian Avocado Growers' Federation, Gold Coast, Australia, September
28-October, 1992.
Abstract. Wrong ideas about the avocado are reducing its
consumption. Avocados have high nutrient density-per calorie, they are rich in
important human nutrients. This, with their giving a feeling of fullness, plus
their palatability that reduces the urge to over- indulge in excess sugars and
saturated fats, plus other suggested advantages, makes them useful in weight
control. There is recently increasing recognition of our need for antioxidants
for good health; the avocado is rich in three of the most important: vitamins
E, C, and beta-carotene. It may help to prevent strokes; it is high in
potassium and low in sodium. Among fruits, it is exceptional for the quantity
and quality of its protein. It provides exceptional quantities of both types of
dietary fiber. It makes a superior first solid food for babies. The avocado fat
consists predominantly of monounsaturated oleic acid, which has been found to
reduce harmful (LDL) cholesterol while maintaining beneficial cholesterol
(HDL), performing better than the usual low-fat diet. Four current
misconceptions about the avocado and human nutrition are noted.
Nutrient Density
It is now widely recognized that the number of calories per unit weight
is not a very good measure of a food's status in human nutrition. Much more
important is the food's contribution per calorie of essential human
nutrients-particularly those that are likely to be deficient in typical diets.
Unlike foods that are well described as providing mostly "empty
calories," the avocado is nutrition-rich.
The detailed analyses of Stater et al. (1975) indicated that for
no less than eight essential nutrients-vitamin A (beta-carotene), vitamin C,
vitamin E, folacin, niacin, vitamin B6, iron, and magnesium-the avocado
provides about twice as high a proportion of daily human needs as it does daily
calorie needs. Moreover, for three additional essential nutrients for which
there is no established United States Recommended Dietary Allowance- copper,
potassium, and pantothenic acid-the avocado is also estimated to provide about twice as
high a proportion as its calorie contribution. The avocado is remarkably
nutritious per calorie. Survey results vary between countries, regions, and
individuals; but even in prosperous "advanced" societies, significant
deficiencies of these 11 avocado-supplied nutrients have been reported.
It is unfortunate for both avocado growers and the consumer public that
weight-conscious people often shun the avocado because of the mistaken idea
that eating it will tend to increase one's weight. In fact, three experiments
that tested this possibility all found that adding avocado to the diet resulted
in a small average weight loss (see Cholesterol section later in
this paper).
For weight stabilization, the avocado appears to have several benefits:
1) Its high nutrient density
(preceding section) can make the diet more wholesome and better balanced, thus
promoting better general health and well-being, which can minimize fattening
food cravings.
2) Furthermore, its high fat
content makes the diet more palatable, which encourages filling up on the
wholesome food in such a sound diet.
3) Its high fat content gives a
quicker feeling of satiation, which (especially when accompanied by bulky
vegetables and fruits) helps reduce overeating.
4) Avocado weight control
appears to extend beyond the above explanations; a speeding up of the human
basal metabolic rate has been hypothesized (D. Colquhoun, M.D., private
communication).
Fat is now the great evil in popular nutritional advice on weight
control: over twice the calories of carbohydrate or protein, less calories
burned up in storing it, possibly other weight detriments of fat, per se. And
up to 90 % of avocado calories come from fat. Yet, every controlled experiment
that I know of has found that mean weight decreased a bit with increased
avocado consumption. How such is to be reconciled with the dire warnings about
dietary fat is not clear. Perhaps there is a parallel with cholesterol- the
type of fat matters, with saturated fat being bad and monounsaturated (the
major constituent for avocado oil) being good. Perhaps the avocado has some
weight-control feature that is as yet unknown.
However, different health groups and even dietitians keep warning about
the avocado's high calorie content. How valid is that concern? The number of
kilocalories in an avocado fruit vary with its botanical origin, variety, size,
and degree of maturity; in California, the average is about 300 Cal (Slater et
al., 1975). Also varying with several factors are the number of calories
that a person needs per day; for an age of 19-50 and a "moderate"
activity level, a 71 kg man needs about 2800 Cal and a 57 kg woman about 2100
Cal (UC Berkeley Wellness Letter, 5/91). That calculates at 9 and 7
avocados each-so much that satiation is likely well before the daily calorie
"allowance" is reached.
Among the many foods (Rinzler, 1987), avocados have been rated as only
moderate in calories per servings, with such items as beans, bread, pasta,
rice-less caloric than most nuts and seeds, most cheeses, sugar, butter, etc. A
lengthy analysis in Fit health magazine (8/82) concluded that somehow
the avocado has gotten blamed for "fictitious calories ... avocados have
received the undeserved reputation of being fattening'"
Contributing to this misconception has been the tendency of even some
nutritionists to accept the "fat is fat" oversimplification,
overlooking both the avocado's predominance of monounsaturated fat and its very
high nutrient density. Contributing further is the public's tendency to accept
the oversimplification that "if it tastes rich, it's bad for you;"
what's "good" for us is supposedly only the less appealing foods like
carrots, lettuce, spinach.
In any case, it has been repeatedly found that increased avocado
consumption did not cause weight gain.
Antioxidants
Oxygen is essential to life processes, but an inevitable by-product of
its essential activities is the formation of dangerously reactive "free
radicals." These can cause harm to various body cells and organs
(University of California Wellness Letter, 10/91): eye tenses, causing
cataracts; cell mutation, contributing to cancer, or advancing the aging process;
arthritis; cholesterol molecules or the artery wall; contributing to heart
disease.
There are three antioxidant vitamins that are effective in disarming the
free radicals: E, C, and beta-carotene (vitamin A precursor). Various surveys
have turned up deficiencies of all three in America. As we have seen, for each
of the three and for any given daily calorie proportion, the avocado provides
about twice that proportion of the nutrient. Now, the avocado is high in fat,
and fat consumption has been associated with added risk for certain cancers,
particularly of the colon. But, the Harvard Health Letter (3/91)
concluded that although meat fat indeed markedly increases cancer risk, there
appears to be no connection with plant fat.
Hence, eating more avocado could be a delightful way to get more of the
antioxidants that help protect us against such things as arthritis, cancer,
cataracts, heart disease, even aging in general.
Stroke Prevention
The Associated Press (15 Oct. 87) printed an interview with nutritionist
Dr. Louis Tobian of the University of Minnesota on the protection against
strokes provided especially by potassium. As best K sources, he listed
strawberry, banana, citrus juice, potatoes (overlooking the avocado). Smith et
al. (1983) determined the K content of some 34 fruits and vegetables: the
avocado was outstanding, with strawberry, banana, and orange having less than
half as much K per unit weight, and potatoes just over half as much. Prevention
(8/87) reported on a 12-year stroke study conducted jointly by the Schools
of Medicine of Cambridge and UC San Diego: "Potassium was the key."
Strokes were reduced 40% by an increased daily K consumption of about 400
mg-the amount in less than half an avocado.
The same Prevention article linked blood pressure as a stroke
factor with excess sodium in relation to potassium. The avocado is as low in Na
as it is high in K-with about 52 times as much of the latter.
The leading 'Hass' cultivar is about 2.4% protein on a fresh weight
basis- where most of its weight is water (Slater et al., 1975). Polansky
and Murphy (1966) reported that the avocado had from two to ten times as much
protein as 25 other fruits and vegetables that they analyzed. A more recent
study in Florida found that the avocado had three to six times as much as six
other common fruits. (However, the avocado still supplies a lower proportion of
daily protein needs than its calorie contribution; it is not nutrient-dense for
protein). The avocado protein contains all amino acids essential for
humans-unlike most plant sources, it is "complete,” like the egg standard.
Most people in affluent societies are already consuming more protein
than they need. Avocado protein may be valuable for two classes of people: the
impoverished, especially in tropical regions, who often are protein deficient;
and people in industrial societies who, for health reasons, are reducing meat
consumption and becoming more vegetarian. For the latter, the complete nature
of avocado protein makes it a good complement to other plant sources.
Fiber
Anderson (1990) pointed out 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..., diabetes..., and
obesity..." A combination of both soluble and insoluble fibers may be most
effective. "Most individuals in the West ingest suboptimal amounts of
dietary fiber."
Smith et al. (1983) compared 34 fruits and vegetables. Only the
avocado was listed with large amounts of both soluble and insoluble forms (2.1%
and 2.7%, respectively, by fresh weight). Considering the two forms separately, most other fruits
and vegetables had less than half as much as the avocado, down to 1/6 or
so. Nutritionists suggest that we should double our average fiber consumption;
eating more avocados would be an enjoyable way to do so.
Our bodies cannot make linoleic fatty acid, the "essential"
polyunsaturate. Slater et al. (1975) reported that it constituted 7.2 %
of avocado oil; Bergh (unpublished) found a still higher proportion, in the
'Hass' cultivar.
The bland nature of avocado pulp makes it soothing to the alimentary
tract. This helps explain why Native Americans have, for many generations,
recommended avocados especially for the ill.
The exceptional nature of the avocado makes it suitable for a remarkable
wide range of food uses: hors d'oeuvre, soup, salad, garnish, sandwich spread,
dip, in the half-shell, entree, dessert, beverage. And, there are many
variations of each. This versatility facilitates increased consumption so as to
obtain increased benefits from its remarkable advantages for the human diet.
William Sears, M.D., author of several books on infant nutrition, was
interviewed by California Grower (10/88): "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 BI, B2, niacin, folacin,
potassium, and magnesium [per gram] than any of the other frequently
recommended fruits and vegetables, [plus a rich supply of other vitamins and
minerals]." In a brochure privately printed the year before, 'Baby's
Garden: Nature's Guide to First Foods.' Dr. Sears analyzed several infant
foods, with statistics that confirm and extend his avocado comments above. He
noted several additional advantages as infant nutrition, including "[The
avocado is one of the very few] fruits or vegetables that contain
monounsaturated fats, [so beneficial] for baby's development."
Avocado producers can be pleased that their product is so valuable for the "little people." Moreover, there is potential economic gain for the avocado industry far beyond the moderate added market demand from a greatly increased number of babies eating avocado. Little people become big people-and eat many times as much food.
The avocado, unique in many fortunate ways, is unfortunate in the unique
degree of difficulty that many adults have in developing enough fondness for
the fruit to keep buying it. A few adults like it immediately. Most adults
describe their first taste of avocado as something like
"disappointing" or even "distasteful." Some keep trying it, and their attitude
can change to "tolerable '" then to "quite acceptable," and
finally it can become for them also a "prized flavor delight." But
too many adults just give up on it, and decide that avocado is not for them.
How very much easier it is to introduce the fruit to infants.
Frequently, when talking to adults in regions where the avocado has recently
been introduced, one hears: "No, I don't care for avocado-but my children
love it." When infants eat avocados, nearly all will grow up into adults
who like them and eat a lot more of them. By encouraging avocado consumption in
baby food, we are laying the foundation for a larger and more profitable future
industry.
People in most of the modem affluent societies average about twice as
high blood serum cholesterol levels as is considered healthy. The excess
contributes to blockage in our arteries ("atherosclerosis"), a
major-cause of the leading killer in such societies-heart disease. Hence, heart
disease can be reduced by reducing blood levels of harmful cholesterol, the low
density lipoprotein (LDL); but high density lipoprotein (HDL) is considered
heart-protective, so it is "good" cholesterol. Similarly, while the
fats we consume are a major determinant of our blood cholesterol levels, these
fats also are of significantly different kinds: saturated fats increase the
harmful LDL cholesterol, while unsaturated fats reduce it.
Unsaturated fats are classified as monounsaturated or polyunsaturated.
Grundy (1987) reviewed experiments comparing different levels of different
kinds of dietary fat. Compared with the typical diet high in saturated fat,
diets high in monounsaturated, or high in polyunsaturated, or low in all fats
and high in complex carbohydrate, all reduced the level of harmful LDL; but
only the high-monounsaturate diets consistently maintained the level of the
beneficial HDL. Moreover, the other two LDL-reducing diets sometimes increased
the level's of blood triglycerides-recently of increasing concern for cardiovascular
health. Moreover, polyunsaturated fats are problematic because of linkage with
oxidized "free radicals" and other health concerns. Moreover, only
recently have polyunsaturates been used on a large scale in human diets, so
that their long-range effects are little known. Monounsaturates, on the other
hand, have been an important part of the diet of Mediterranean peoples for
thousands of years. The Australian Medical Observer, 17 Aug. 90, quoted
David Colquhoun, M.D.: "For example, in Greece, which spends less money
per capita on health care.... people live longer and are healthier, even though
they smoke a lot and do less physical work ... their diet seems to be
protective ... high in monounsaturates..." These monounsaturated fats come
primarily from olive oil.
Fat analysis varies with different factors; a typical olive oil
breakdown is 77% mono, 9% poly, 14% saturated; nearly all the mono is oleic
acid. One other commonly consumed plant fat has an analysis that averages quite
similar to olive oil-avocado oil. In California, Slater et al. (1975)
obtained an overall 'Hass' average of 82 % mono, 8 % poly, 10 % saturated; and
the mono was 95 % oleic. Bergh and co-workers (unpublished) found that
cultivars combining genes of both the Mexican and Guatemalan horticultural
races had a higher proportion of monounsaturates than "pure7' cvs. of
either race.
What have been the results of actual blood-monitored experiments with'
avocado?
Colquhoun, Australia
David Colquhoun, M.D., is Consulting Cardiologist at Wesley Medical
Centre in Brisbane, Australia. He has shared some of his thinking (private
communication): "The traditional diet propounded by [heart organizations]
has been based on a moderate reduction of total fat with a mild increase in polyunsaturates...
Foods which have been high in monounsaturated fatty acids, such as avocado,
have in fact been advised against. This has been based on the simplistic notion
that avocados are high in fat."
Dr. Colquhoun used 15 subjects to compare a typical diet (fairly high
total fat, much of it saturated), with a low fat (20% of calories)-high
carbohydrate diet, with a diet that included an avocado a day (fairly high
total fat, much of it rnonounsaturated). Result: The "avocado-enriched
diet had ... a significant (7.2 %) decrease in total cholesterol with
preservation of the HDL level. In contrast, the low-fat diet was less effective
in lowering the LDL lipoprotein and also had the disadvantage of lowering the
protective HDL." Thus, the avocado appears to have cardiac benefits via
blood serum cholesterol changes at least as significant as those found for the
more extensively tested olive.
Indeed, Dr. Colquhoun found that avocado enrichment had greater
cholesterol benefits than could be expected from just reducing saturated fat.
He noted further that the avocado-added diet was "nutritionally
balanced," and its good flavor encouraged "excellent
compliance." It was associated with a weight loss of about 1 kg, hence, “...avocados are an important addition to
cholesterol-lowering diets. The inclusion of this versatile food ... should
improve long-term compliance with a healthy diet... A cholesterol-lowering diet
does not have to [be] a very low fat diet, which is often unpalatable."
Moreover, Dr. Colquhoun's subjects were on each diet for only 3 weeks.
A longer period with added avocado may well have given greater benefits (see
Steele).
Dietitian M. G. Steele of the La Mancha Health Centre at Wollongbar, New
South Wales, Australia, conducted this research in 1987 and had it privately
printed with the tide 'Avocados, cholesterol, and heart disease.'
Substituting avocado for butter, margarine, and cheese significantly
reduced blood cholesterol, as was expected. In a second experiment, subjects
who had been on a low-fat diet were "encouraged to eat as many avocados as
possible." This sharp increase in fat consumption, up to triple previous
levels, led to fears of increase in both weight and blood cholesterol. And,
after 4 weeks, average total cholesterol had increased 6 %. Suspecting
that this was a temporary "hiccough" caused by the suddenness of the
fat increase, Mr. Steele persuaded subjects to continue with avocado
enrichment. After another 4 weeks, all participants had total cholesterol below
their initial level, and, even more important, average HDL ("good"
cholesterol) had increased by 16%. Noted Steele, "For those...who were
following the [very low fat] Pritikin diet, the avocado was a welcome addition '"
And, contrary to subject fears, not only did the Pritikin-diet, people actually
improve their cholesterol by adding avocado, they -also lost a little weight on
the average.
Grant (1960) researched before it was understood that there is
"good" and "bad" cholesterol, and that there are important
differences between the kinds of unsaturated fats; hence, he did not collect
certain data that we now know would be of much interest. Nevertheless, his
study remains highly useful.
He worked in a Veterans' Hospital, which gave him excellent dietary
compliance; but at the same time his experimental setup had the limitation of
discharges leading to a treatment period as short as 9 days, and also some of
his subjects had metabolic diseases that could well affect their fat metabolism
and so interfere with the experimental result. In fact, of 12 analyzable
subjects given extra avocado, five had metabolic diseases (including three
diabetics)-all five had their cholesterol decreased, but none to a degree that
was statistically significant; seven had non-metabolic illnesses-and all had a
cholesterol decrease that was highly significant statistically.
There was no breakdown of cholesterol into LDL and HDL, a breakdown
that, as we have seen, would be expected to make the avocado benefits
considerably more striking. Also, the average number of days of treatment- just
over a month-n-tight be too short to overcome the initial increase in
blood cholesterol when there is a sudden increase in oil intake, as Steele
showed. In spite of these effect-diluting factors, the overall averages are as follows (first row
includes all 12, second row in parentheses, includes only the seven without
metabolic disease):
Avocados/day # of days
Calorie Fat Blood Cholesterol Weight
1.04 33.2 +23.9% +53.7%
-19.3% (-55) -1.1
kg
(+30.0 +76.9 -26.5)
Nutritionists tell us that we should reduce our calorie intake if we
wish to reduce our weight, and that we should reduce our fat intake to reduce
both our weight and our cholesterol. Yet, an exceptional but carefully
controlled experiment, that increased calories by an average of almost
one- quarter, and fats by over one-half, actually decreased serum
cholesterol by nearly one-fifth-and even weight by a bit. The avocado is
remarkable nutrition!
Some Current Misconceptions
1. "Fat is fat and fat is bad"
Heart associations in the U.S.A., Australia, and presumably
elsewhere, are campaigning for a desirable reduction in our consumption of the
saturated fat that is clogging our arteries by recommending that we eat less
fat. And it is true that as total fat consumption goes down, so does
consumption of the harmful saturates and the dubious polyunsaturates. But, so
also may consumption of the beneficial monounsaturates, by discouraging the
consumption of olive oil-and avocados. Perhaps these "authorities"
believe that trying to make distinctions among fat sources will confuse the
public; if so, I think they underestimate our capabilities. A similar
oversimplification is, "cholesterol is bad"-but people who are
interested quickly learn that HDL cholesterol is good.
Other authorities counseling that "fat is bad" may be judging
avocados superficially by their high fat content, and therefore assuming
harmful excess calories. Thus, a 10/10/90 letter from the Food Program Manager
of the National Heart Foundation of Australia states that "our dieticians
and home economists often promote avocados as a very good substitute for butter
or margarine as a spread on bread." But, "The reason why we list
avocados in the 'foods to limit' category is ... their high fat content... Excess
fat consumption is one of the leading reasons why more than half of all
Australians are overweight' "
Similarly, a 26/10/90 letter from the president of Pritikin Lifestyle
Association (Brisbane) notes that "unfortunately avocados have a high fat
content. It is our contention that fat is extremely dangerous..."
It is my contention, based on the actual research results surveyed
earlier in this paper, that “unfortunately avocados have a high fat
content." This is largely monounsaturated and so cardiovascular-protective,
and this oil is
part of a remarkably nutrient-dense fruit that has consistently been shown to
assist excellent weight control. The speculative objections to the avocado
founder on the rock of demonstrated fact.
However, the last letter quoted above continued, "the Pritikin
Society has indeed altered its advice ... the suggested amount being one-half
avocado per day." Coming from an organization that has built a solid
reputation for making people healthier by reducing indiscriminate fat consumption
to a very low level, this is a most encouraging and courageous concession. And,
if the average American ate 1/2 an
avocado a day, our industry would fall far short of meeting the demand!
2. Fat per day vs. fat per food
The American Heart Association is conducting a vigorous campaign to
reduce our fat consumption from the present 40 % or so of total calories to no
more than 30%. As we have seen, even a 20% fat level may not give as favorable
blood cholesterol as 40% of calories from fat if the predominating fat
is the oleic monounsaturate that the avocado is so rich in; but if our fat
consumption balance continues heavily to saturated especially, plus polyunsaturated,
then an overall reduction to 30% or less can only be beneficial.
A recent survey in the U.S.A. showed that 2/3 of Americans think that such
a 30% limit would apply to every food we eat-thus discarding the avocado. Notes
the Mayo Clinic Health Letter (12/90): "That's a common mistake.
Limiting fat to about 30 % of daily caloric doesn’t mean eliminating fatty
foods. It means balancing high-fat options with low-fat choices." They
illustrate this by balancing out among all three meals combined.
3. "Avocados may cause cancer"
Perhaps this rather silly speculation has not surfaced in Australia,
and with that hope it will be dealt with only briefly here (I have published a
detailed analysis elsewhere). A 1990 study on breast cancer in Shanghai, China,
found that increased cancer was associated with increased calorie intake which
was due primarily to increased monounsaturated fat. On that tenuous connection,
there actually was newspaper speculation that avocados might increase cancer
risk.
1) Correlation does not prove
causation. Often two consequences are related only through their joining caused
by a third factor. In fact, in this study, the added cancer risk of a
University education (compared with less than high school) was five times
as large as the added caloric-monounsaturated risk!
2)
The authors themselves questioned the calories-monounsaturate
connection. And the added cancer risk was associated with a greater percentage
increase in polyunsaturates and especially saturated fat than monounsaturates.
3) Even in the highly unlikely
event that monounsaturates were somehow to blame, extending this to the avocado
is still more logically questionable. Very little of the Shanghai
monounsaturates would be from avocado, which as whole fruit supplies a rich
spectrum of nutrients including antioxidants.
4) The authors themselves point
out that any hypothesized cancer risk from monounsaturates is contrary to
results obtained elsewhere, notably in Japan and in Mediterranean countries.
5) China has a very low breast
cancer risk compared with Caucasian countries generally. The authors used
Canada as an example, and their data show that the high-risk Canadian women
consume four times as much saturated fat as the Chinese, but average actually
less monounsaturated fat.
The overall evidence in this paper does not support any causative
linkage of monounsaturated fat, let alone that in the avocado, with added
cancer risk. The U.S. Nutrition Action Newsletter (12/91) quoted
physician and epidemiologist Meir Stampher, "...in the Nurses Health
Study, we find virtually no difference in the risk of breast cancer with fat
intake between 29 and 49 percent of calories...." Added Frank Sachs,
physician and diet researchers, in the same issue, "The high fat diets that
are associated with cancer in humans are very low in [plant foods],.... Given a
calorie intake that will [avoid obesity], I don't think it matters whether
calories come from vegetable oils or carbohydrates."
When the needed expensive and long-range experiments are eventually
run, I expect that avocado consumption will prove to be a significant reducer
of the risk of most, if not all, cancers.
4. Misinterpretations
Sometimes newspaper reports misunderstand or overstate research
results. In the present "anti-fat" nutritional climate, we avocadoans
need to be watchful, and quick to point out errors to Food Editors or general
newspaper editors. More serious is when researchers themselves are biased by
the anti-fat propaganda so that they mis-state their own findings.
An example was provided by a four-column headline in my local
newspaper: 'Extra monounsaturated fats not beneficial.’ That was
surprising, and the accompanying article merely reinforced the headline, so I
tracked down the original publication: Ginsberg et at. (1990)-nine
co-authors. They compared three diets: typical American (high fat, much
saturated); Heart Associations Step I (low fat); high fat, much
monounsaturated. The authors concluded (as my newspaper headline stated) that
"enrichment of the Step 1 diet with monounsaturated fat does not [improve
on] the [blood cholesterol] beneficial effects of the Step 1 diet ....” The
first surprise in their actual article was the admission that "Our study,
however, was not between the effects of the Step I diet and those of the Mono
diet....” That shoots down the headlined claim right there. It gets worse.
Their actual results show that, compared with the typical diet, the Mono
reduced total cholesterol about 30 % more than did the Step I (low fat).
Triglycerides decreased about twice as much with Mono as with Step 1.
"Good" cholesterol (HDL) was unchanged with Mono, reduced with Step
1. "Bad" cholesterol (LDL) was reduced to a statistically significant
degree by Mono, not by Step 1. The most meaningful ratio, of total cholesterol
to HDL, was reduced insignificantly by Step 1, more than four times as much and
highly significantly by Mono. And yet the authors concluded as quoted above!
And my newspaper (and presumably many others) simply accepted their wrong
conclusion.
With humans, variable both genetically and in previous food
consumption, research results will sometimes vary and even be contradictory.
And with research procedures also variable, we have added reason to expect
contrary results at times. These we can accept cheerfully, keeping in mind the
overall weight of evidence. What we should not tolerate is careless
researchers, prejudiced by biases such as the present anti-fat fad, who twist
their results into untruth.
Purseglove (1968) in his
authoritative textbook, described the avocado as "the most nutritious of
all fruits." In 1959, cereal nutrition pioneer John H. Kellogg declared
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 ... none that can fill its
place." Summarized America's greatest plant explorer, David Fairchild,
“...the avocado is a food without rival among the fruits, the veritable fruit
of paradise."
Anderson, J. W. 1990. Dietary
fiber and human health. HortScience 25: 1488-1494.
Ginsberg, H. N., S. L. Barr,
A. Gilbert, W. Karmally, R. Deckelbaum, K. Kaplan, R. Ramakrishnan, S.
Holleran, and R. B. Dell. 1990. Reduction of plasma cholesterol levels in normal men on an American Heart
Association Step 1 diet or a Step 1 diet with added monounsaturated fat. New
Eng. J. of Med. 322: 575-579.
Grant, W. C. 1960. Influence
of avocados on serum cholesterol. Proc. Soc. Exper. Biol. Med. 104: 45-47.
Grundy, S. M. 1987.
Monounsaturated fatty acids, plasma cholesterol, and coronary heart disease.
Amer. J. Clin. Nutr. 45: 1168-1175.
.
Polansky, M. M., and E. W.
Murphy. 1966. Vitamin Br, components in fruits and nuts. J. Amer. Dietetic
Assoc. 48: 109-111.
Purseglove, J. W. 1968.
Tropical crops: dicotyledons. Wiley, New York.
Rinzier, C. A. 1987.
Avocados, p. 16-17. In: The complete book of food: a nutritional medical, and
culinary guide. World Almanac, New York.
Slater, G. C., S. Shankman,
J. S. Shepherd, and R. B. Alfin-Slater. 1975. Seasonal variation in the
composition of California avocados. J. Agr. Food Chem, 23: 468-474.
Smith, J., S. Goidweber, M.
Lamberts, R. Tyson, and J. S. Reynolds. 1983. Utilization potential for
semi-tropical and tropical fruits and vegetables in therapeutic and family
diets. Proc. Fla. State Hort. Soc. 96: 241-243.