Mary Enig Interviewed By Richard A. Passwater, Ph.D.
Mary G. Enig, Ph.D., a nutritionist widely known for her research
on the nutritional aspects of fats and oils, is a consultant, clinician,
and the Director of the Nutritional Sciences Division of Enig Associates,
Inc., Silver Spring, Maryland.
She received her PhD in Nutritional Sciences from the University
of Maryland, College Park in 1984, taught a graduate course in nutrient-drug
interactions for the University's Graduate Program in Nutritional
Sciences, and held a Faculty Research Associateship from 1984 through
1991 with the Lipids Research Group in the Department of Chemistry
Dr. Enig is a Fellow of the American College of Nutrition, and
a member of the American Institute of Nutrition. Her many years
of experience as a "bench chemist" in the analysis of
food fats and oils, provides a foundation for her active roles in
food labeling and composition issues at the federal and state levels.
Dr. Enig is a Consulting Editor to the "Journal of the American
College of Nutrition" and formerly served as a Contributing
Editor to "Clinical Nutrition." She has published 14 scientific
papers on the subject of food fats and oils, several chapters on
nutrition for books, and presented over 35 scientific papers on
food and nutrition topics.
She is the President of the Maryland Nutritionists Association,
past President of the Coalition of Nutritionists of Maryland and
was appointed by the Governor in 1986 to the Maryland State Advisory
Council on Nutrition and served as the Chairman of the Health Subcommittee
until the Council was disbanded in 1988.
I first learned of Dr. Mary Enig's research from a 1978 report
in the Federation Proceedings. We met shortly after that, and since
I had written about trans fats several times in Supernutrition,
we had common concerns about the effect that these trans fats from
processed foods were having. We were both concerned particularly
about the misconception that processed margarine was better than
In several visits by Dr. Mary Enig to the Solgar Nutritional Research
Center I quickly learned that she was an exacting scientist who
is not afraid to speak out and who supports good nutrition, not
just going along with the establishment's party line.
While studying for her Ph.D. at the University of Maryland, often
she would first respond with the "correct" answer that
was expected, and then she would explain why new research indicated
"alternatives," such as optimal vitamin and mineral nourishment,
provided a better answer. It is not easy be credentialed by the
"system," while your own research shows other facts.
In her 1978 report, Dr. Enig challenged the speculation concerning
the relationship of dietary fat and cancer causation. She concluded
that correlations between the increase in per capita dietary fat
intake and total cancer mortality over a sixty-year period show
significant positive correlations for total fat and vegetable fat,
and negative correlation for animal fat.
That the cancer rate is higher when the amount of vegetable fat
or total fat is higher in the diet, but the cancer rate is lower
when there there is more animal fat in the diet. These findings
were unpopular then as they are today, but they are still correct.
It is convenient to blame everything on red meat and animal fat,
and believe that vegetable oil is the great dietary salvation-even
if it is partially hydrogenated. At least that is what the vegetable
oil people would like everyone to believe.
Now, we are not saying that lots of dietary fat is good for you
and that vegetables are not good. Eating vegetables, fruits and
other whole foods is very desirable. However, that is not the same
as eating partially-hydrogenated vegetable oils.
Americans eat too much fat (especially partially hydrogenated vegetable
oils) and not enough fruits and vegetables.
The problem is that the typical American is not eating enough whole
foods, but instead, is eating too much partially-hydrogenated vegetable
oil-a fractionated food-that has been made into "funny foods"
such as margarine or added to baked goods. Such "funny foods"
are far differentthan real whole foods.
Hydrogenation ruins the nutritional value of vegetable oils! Why
would anyone want to ruin the nutrition value of vegetable oils?
The purpose of hydrogenation is to solidify an oil so that it can
be made to resemble real foods such as butter.
The hydrogenation process imparts desirable features such as spreadability,
texture, "mouth feel," and increased shelf life to naturally
liquid vegetable oils.
In the hydrogenation process, vegetable oil is reacted under pressure
with hydrogen gas at 250 - 400oF for several hours in the presence
of a catalyst such as nickel or platinum. However, this industrial
process cannot control where the hydrogen atoms are added to the
"unsaturated" double bonds.
Randomly adding hydrogen atoms to polyunsaturated fats converts
natural food components into many compounds, some of which have
never seen before by man until partially hydrogenated fats were
Some of the several dozens of altered compounds created in the
manufacture of partially-hydrogenated fats are "trans"
fatty acids. Fatty acids are the building blocks of fats, much like
amino acids are the building blocks of proteins.
Other new compounds accidentally synthesized include fatty acids
having double bonds translocated to new and un-natural positions,
and various molecular fragments. Many of these altered compounds
are detrimental to health.
Since "trans" fats are so detrimental to our health.
permit me to briefly review the relevance of distinguishing between
"trans" and "cis" fats before chatting with
Dr. Enig. Recently, in the September issue, in the interview with
Dr. Jim Clark and Mr. Lance Schilipalius, we discussed "trans"
isomers of carotenoids. "Trans" means the same thing here.
"Cis" and "trans" isomers refer to how identical
atoms are added to double bonds.
When the atoms are added to the same side of the double bond, the
compound is called "cis" and the molecule is bent because
of the crowding of the atoms on one side.
When the atoms are added on opposite sides of the double bond,
the compound is called "trans" and molecule is "space-balanced"
and straightened. The shape of a molecule is important because enzymes
and their substrates-the molecules enzymes act upon-must fit together
like a key in a lock.
Dr. Enig will discuss this during the interview, but the important
thing to remember is that natural polyunsaturated fatty acids are
"cis" compounds and are bent. Partial hydrogenation produces
many un-natural "trans" fats which are straight and not
intended for use in the human body.
You don't have to understand the difference between "trans"
and "cis," but it is important that you know that there
is a difference because, as Dr. Enig will explain, it can affect
Passwater: Dr. Enig,
a lot of people are interested in "trans" fats now. You
have been researching them since 1977. How are trans fats harmful
Enig: More than a
decade of research at the University of Maryland, as well as research
that was being done at other institutions, showed that consumption
of trans fatty acids from partially hydrogenated (a process that
adds hydrogen to solidify or harden) vegetable fats and oils had
many adverse effects in health areas such as heart disease, cancer,
diabetes, immunity, reproduction and lactation, and obesity.
It is rather easy today to come up with a long list of these adverse
effects from the published research done by many scientists around
the world, as well as the researchers at the University of Maryland.
The reason there is so much recent interest is that during the
past three years there has been a number of major research reports
published in prestigious medical journals that caught the attention
of the press.
These and earlier reports had shown, for example, that consumption
of trans fatty acids lower the "good" HDL cholesterol
in a dose response manner (the higher the trans fat level in the
diet, the lower the HDL level in the blood) and raise the atherogenic
lipoprotein(a) in humans as well as raising the "bad"
LDL cholesterol and total blood cholesterol levels by 20-30 milligram-percent.
These studies have usually been shown in independent non-industry
studies. Perhaps the most significant event though was the report
from researchers at Harvard University, who evaluated more than
85,000 women in a long-term prospective study and found that there
was a significantly higher intake of trans fatty acids in those
individuals who developed heart disease.
As regards to the question of cancer, trans fatty acids induce
adverse alterations in the activities of the important enzyme system
that metabolizes chemical carcinogens and drugs (medications), i.
e., the mixed-function oxidase cytochromes P-448/450.
The initial research in this area was done by the Maryland group
in collaboration with the U. S. Food and Drug Administration, and
was followed by the more extensive evaluation that I did for my
Ph.D. dissertation; several groups around the country and the world
also reported the same or similar results. Several groups around
the world reported a higher intake of partially hydrogenated fats
in those individuals who have developed cancer.
Both primate and human studies have shown inappropriate handling
of blood sugar; trans fatty acids decrease the response of the red
blood cell to insulin, thus having a potentially undesirable effect
in diabetics. The primate research was initiated at Maryland in
collaboration with the U. S. Department of Agriculture and the National
Institutes of Health, and the human research is from the University
of Pittsburgh and quite recent.
One major concern is that trans fatty acids adversely affect immune
response by lowering efficiency of B cell response and increasing
proliferation of T cells. This was shown in research done at Maryland
using a mouse model and although there are reports from clinicians
that there are problems of immune dysfunction in humans it still
needs to be evaluated systematically in humans.
Recent research from outside the U. S. has indicated that trans
fatty acids interfere with reproductive attributes and of concern
is the finding that trans fatty acids lower the amount of cream
(volume) in milk from lactating females in all species studies including
humans, thus lowering the overall quality available to the infant.
The latter research was done at Maryland by my colleague Dr. Beverly
Basically, trans fatty acids cause alterations to numerous physiological
functions of biological membranes that are known to be critical
for cell homeostasis, e.g., appropriate membrane transport and membrane
fluidity, and these fatty acid isomers produce alterations in adipose
cell size, cell number, lipid class and fatty acid composition.
Passwater: Now that
trans fats are becoming of more interest, the term may still just
be a buzz word to many of our readers. Would you explain just what
are trans fats? Where do they come from? How are they formed?
Enig: To understand
what trans fatty acids are you have to understand what fatty acids
are. Fatty acids are basically chains of carbon with a carboxyl
group (COOH) at one end that can react (e.g., combine) with another
When fatty acids are in fats or oils they are combined with glycerol
in the proportions of three fatty acid molecules to one glycerol
molecule and they form triacylglycerols or in common terminology,
Fatty acids come in different chain lengths ranging from three
carbons long (propionic acid) to 24 carbons long (lignoceric acid).
These fatty acids are either "saturated" (with an adequate
number of hydrogen atoms) and chemically stable, or they are "unsaturated"
(missing adequate hydrogens) and chemically unstable.
If a fatty acid is missing two hydrogens, it is called a monounsaturated
fatty acid, and in place of the two hydrogens, the adjacent carbons
"double" bond to each other.
If the fatty acid is missing four or six or more hydrogens, it
is called a polyunsaturated fatty acid, and it is even more unstable
than the monounsaturated fatty acid. Because the double bonds in
naturally occurring plant oil fatty acids are curved with a "cis"
configuration, the fatty acids cannot pack into a crystal form at
normal temperatures so their presence produces a liquid oil. Saturated
fatty acids have a straight configuration and can pack into a solid
crystal at normal temperatures.
If the unsaturated fatty acids are altered by partial hydrogenation
to straighten the chains so that they have some of the physical
packing properties of saturated fatty acids they have had their
"cis" double bond changed to a "trans" double
bond and they turn a technically mostly unsaturated oil into a solid
The trans fatty acids are the same length and weight as the original
"cis" fatty acid they were formed from, and although they
have the same number of carbons, hydrogens, and oxygens they are
shaped differently in space.
The term that is used is that they are "isomers." The
problem arises when a large number of the trans fatty acids are
consumed from foods and they are deposited in those parts of the
cell membranes that are supposed to have either saturated fatty
acids or "cis" unsaturated fatty acids; under these circumstances
the trans fatty acids essentially foul up the "machinery."
Although the trans fatty acids are chemically "monounsaturated"
or "polyunsaturated" they are considered so different
from the "cis" monounsaturated or polyunsaturated fatty
acids that they cannot be legally designated, e.g., monounsaturated
for purposes of labeling. Most of the trans fatty acids produced
by the partial hydrogenation process are chemically monounsaturates.
There have always been small amounts of one kind of trans fatty
acids in the human diet from the ruminant fats (dairy, sheep, goat,
deer, buffalo, antelope, etc.) because the microorganisms in the
rumen try to get rid of the polyunsaturated fatty acids that are
found in the plant foods eaten by these animals.
In the early days of trans fatty acid research, the researchers
assumed that the trans fatty acids found in ruminant fats were no
different than those produced by partial hydrogenation in the factory.
But the studies showed that not only was the amount much smaller
(e.g., the fat in butter might be 2-3% of the ruminant trans), the
effect on the "machinery" in the cell membranes was not
different than without the trans. Yet all studies feeding the trans
produced by partially hydrogenating the vegetable oils showed the
adverse effect on the cell "machinery."
Passwater: Why are
trans fats a problem?
Enig: The various
mechanisms through which the trans fatty acids disrupt function
are related in part to the ability of trans fatty acids to inhibit
the function of membrane related enzymes such as the delta-6 desaturase
resulting in decreased conversion of e.g., linoleic acid to gamma-linolenic
acid or arachidonic acid; interference with the necessary conversion
of omega-3 fatty acids to their elongated tissue omega-3 fatty acids;
and escalation of the adverse effects of essential fatty acid deficiency.
This latter effect was shown especially by the work of Dr. Holman
and his colleagues at the Hormel Institute at the University of
Minnesota, the other effects have been shown by many researchers
including the University of Maryland researchers.
Passwater: What were
your early findings and what got you interested in this area of
Enig: My initial published
research in 1978 when I was at the University of Maryland showed
that trans fatty acids, which were increasing in the food supply
at the time and which had not been catalogued in any of the food
data tables, were the very factors that explained the positive statistical
relationship between the increase in cancer mortality and vegetable
fat consumption in the U. S.
It was clear from the literature that once the trans fatty acids
were identified as products of partial hydrogenation and studies
were engaged in, there were a number of earlier researchers who
questioned the biological safety of the trans fatty acids viz a
viz their relationship to both cancer and heart disease.
In fact, Dr. Ancel Keys had originally claimed that the partially
hydrogenated vegetable oils with their trans fatty acids were the
culprits in heart disease. This was in 1958, and the edible oils
industry was very swift in their squelching of that information;
they shifted the emphasis to "saturated" fat and started
the phoney attack on meat and dairy fats.
Passwater: What have
others added to your findings?
Enig: As you have
noted in some of your writings, we at the University of Maryland
were not the first to raise the issue of trans fatty acids and adverse
health effects; Dr. Fred Kummerow from the University of Illinois,
Dr. George Mann from Vanderbilt University, and Dr. Edward Pinckney
with the American Medical Association had sounded the alarm many
years before my plunge into the foray.
In fact, I had drawn heavily on the research findings of Dr. Kummerow
and the informative writing of Dr. Mann when I first started to
investigate what was known about health effects of trans fatty acids
at the time. Our research findings have been duplicated by others,
but more importantly other independent researchers have extended
and explained many of our findings and concerns.
The Case of the Phantom Fat
OF DIETARY FAT KEY TO HEART RISK