Do
Saturated Fats and Trans Fats Cause Type-2 Diabetes?
By Mary G. Enig, PhD
Question: I am having a very
difficult time defending the benefits of a diet rich in saturated fat. I attend
Bastyr University, a naturopathic medical school, and through all my nutriton
classes, saturated fat has been deemed unhealthy and detrimental to one's
health. For instance, my Diet and Nutrient Therapy class professor cites a 2002
article in the British Journal of Nutrition, "Acute effects of a meal fatty acid
composition on insulin sensitivity in healthy post-menopausal women"1 as showing
that saturated fat reduces insulin sensitivity, thereby contributing to type-2
diabetes. He also cited a 2002 study in Diabetologia, "Substituting dietary
saturated fat with polyunsaturated fat changes abdominal fat distribution and
improves insulin sensitivy." I would be very interested in your comments
on these studies and your views on saturated fat and diabetes.
Answer: Insulin insensitivity
has been postulated to be the underlying factor for type-2 diabetes; that is, a
condition in which the receptors for insulin on the cell membranes do not work
very well. In type-2 diabetes, the pancreas secretes insulin, but since the
receptors don't work, the bloodstream contains chronic high levels of insulin
and glucose, while little gets into the cell where it is needed.
In the first study cited by your
professor, four groups of subjects were fed a breakfast of rice krispies,
banana, skimmed milk, "Nesquik" (presumably a chocolate drink) and something
called "Marvel," along with 40 grams of fat. The first group got mostly
saturated fat from palm oil, the second group got mostly monounsaturated fat
from olive oil, the third group got mostly omega-6 fatty acids from safflower
oil and the fourth group got mostly omega-3 fatty acids from a combination of
safflower oil and fish oil.
Levels of insulin and glucose in the
blood were measured at intervals after breakfast and also after a so-called
low-fat lunch consisting of cheese pizza (said to contain only 5.4 grams of
fat), lettuce, cucumber and tomatoes. Those given the mostly saturated palm oil
had higher insulin levels at about one hour after breakfast and lunch compared
to the other three groups. However, insulin levels were the same as the other
groups two hours after each meal. Blood glucose levels followed a similar curve
for all four groups.
This is a very poor study to justify
a recommendation against saturated fat. All four groups were on a very unnatural
diet high in processed foods, and the fats used do not reflect the type of fatty
acid profiles that we consume in normal diets. Furthermore, the levels of
insulin in the subjects were not chronically high, as one finds in type-2
diabetes, and the glucose curves were normal for all groups. The study tells us
nothing about what happens in real life with people eating real food.
The second study looked at a small
group of subjects—a total of 17—who were told to follow a diet rich in saturated
(by using more dairy products) or polyunsaturated fatty acids (by using more
oils and spreads) for five weeks. When on the saturated fat diet, the subjects
had a slightly lower measure of insulin sensitivity but glucose levels and body
mass indices were virtually identical.
Again, this study has little to do
with real life. The actual amount of saturated or polyunsaturated fat (or trans
fat) in each diet was not measured and the number of subjects was too small to
be meaningful.
Neither of these studies tells us
what happens in real life in subjects who eat a diet high in natural saturated
fats compared to those whose diets contain a lot of vegetable oils. The fact
that the researchers are strong in their condemnation of saturated fats after
such trivial findings is strong evidence of bias.
The real problem is that
recommendations to avoid saturated fats almost invariably result in people
consuming more trans fats. There is no question but that the trans fats have
been shown to have a detrimental effect on the incidence and treatment of type-2
diabetes. The saturated fats, on the other hand, have no effect when appropriate
comparisons are made.
Very good studies indicate that trans
fats interfere with insulin receptors and therefore with insulin resistance. The
saturated fats do not.
The recommendations regarding dietary
saturated fats intake versus trans fats intake for the past number of years have
been very confusing to the public, and judging from the articles, also confusing
to the researchers. Trans fats
are mistaken by many of the health professionals for saturated fats although
they are not similar in their effects on the human body, just similar in the
manner of stability in the baking or cooking realm.
"So Many Nutrition Recommendations
Contradictory or Compatible?" written by a major dietitian from the American
Dietetic Association lists the amounts of fat and different fats that are
acceptable. According to their recommendations, total fats could represent 20-35
percent of the calories in the diets of individuals as listed in the Dietary
Reference Intakes, 25-35 percent as called for by the National Cholesterol
Education Program, but the American Diabetes Association says that fat intake
should be individualized (expert consensus). However, recommendations for the
type of fat mixes the saturated fats and the trans fats, as do almost all of the
writers in these organizations. The report notes that a diet with only 5 percent
of the total energy from saturated fats is adequate; and yet research shows that
the normal level of saturated fats in the tissues is much higher.
Another example of inappropriate
conclusions drawn from a research project comes from Colorado State University,
where researchers decided that a "saturated fat byproduct" was a potential
contributor to type-2 diabetes. This so-called saturated fat metabolite is
ceramide. Ceramide is a lipid molecule made in the body from something called
sphingosine and a fatty acid (which could be oleic acid, a so-called good fatty
acid). This molecule is used to make sphingomyelin, which is one of the
structural elements in the lipid bilayer, as well as being a cellular signal
molecule. Sphingomyelin is one of the lipid building blocks of the myelin sheath
so important for nerves.
Ceramides are interesting molecules
currently being studied for a role in programmed cell death, and substances
known to induce ceramide production are components such as endotoxins and
chemotherapeutic agents more likely to be from the stress of trans fats than
from the normal saturated fats, which are such important building blocks of our
tissues. The saturated fat in the study was based on in vitro measures of free
fatty acids and therefore does not represent a diet intake.
In summary, the studies cited by your
professor and others do not represent what happens in the real world with people
eating real food. Think of it this way: type-2 diabetes is a new disease, one
that has now reached epidemic proportions. Type-2 diabetes did not exist 100
years ago when our diets were very rich in
saturated fats.
Type-2 diabetes appeared when
trans fats came into the diet, and has become epidemic as people are eating
more and more foods containing trans fats. And since we know that trans fats
interfere with insulin receptors in the cells, it is clear that the blame lies
with new industrial fats, not traditional saturated fats.
The above opinionated
views and information serves to educated and informed consumer . The
information provided herein should not be used during any medical emergency or
for the diagnosis or treatment of any medical condition. .It should not replaced
professional advise and consultation. A licensed physician should be
consulted for diagnosis and treatment of any and all medical conditions
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