USA / Jane E. Brody revisits Mediterranean Diet, gives rundown of recent studies
- The New York Times
December 3, 2002
Dietary Advice Takes On Mediterranean Flavor
By JANE E. BRODY
For several decades, experts on heart disease have promoted a
low-fat, low-cholesterol diet as most effective in warding off the
leading killer of Americans.
But in recent years, new evidence has brought this advice into question.
A major problem with the old advice was that it seemed to give people
free rein to overindulge in simple and refined carbohydrates - foods
rich in sugars and white flour, which can produce unhealthy levels of
blood lipids and increase the risk of becoming overweight and
diabetic, raising the coronary risk.
The most significant change in thinking - one, admittedly, that is
still vigorously debated - is that low-fat is not the answer, or at
least, not the best answer.
But before you say "I told you so" and go back to eating all the
steak, butter and eggs you want, a careful analysis of the evidence
clearly shows that it is not a high-fat, low-carbohydrate diet that
Rather, it is a diet like the one consumed by heart-healthy people
along the Mediterranean: rich in vegetables and fruits, whole grains,
nuts, unsaturated vegetable oils and protein derived from fish, beans
and chicken, not red meat.
"Compelling" evidence for this view was thoroughly reviewed last week
in The Journal of the American Medical Association by Dr. Frank B. Hu
and Dr. Walter C. Willett, nutrition and epidemiology experts at the
Harvard School of Public Health, who have followed tens of thousands
of Americans for decades to uncover relationships between diet,
habits and health.
The original heart-saving advice was geared to lowering blood levels
of cholesterol and especially low-density lipoprotein, or L.D.L.,
cholesterol, a waxy alcohol that in large amounts in blood serum can
gum up the arteries and set the stage for life-threatening clots.
But, the scientists wrote, "the original hypothesis was overly
simplistic because the effects of diet on coronary heart disease can
be mediated through multiple biological pathways other than serum
total cholesterol or low-density lipoprotein cholesterol."
In other words, blood levels of cholesterol, or even
L.D.L.-cholesterol, do not constitute the whole story of coronary
risk, a fact widely known but until recently not fully taken into
account when devising dietary advice for the public.
Other important factors include blood levels of triglycerides,
artery-protective high-density lipoprotein (H.D.L.) cholesterol, an
amino acid called homocysteine, cardiac rhythms, clotting tendency of
blood, flexibility of artery walls and levels of blood pressure and
blood sugar. Each, in turn, is influenced by dietary factors beyond
total fat and cholesterol.
The Harvard researchers reviewed a plethora of evidence - studies
conducted under carefully controlled conditions in metabolic wards,
studies of many thousands of free-living people followed for many
years, studies comparing the diets of people who suffered heart
attacks with the diets of comparable people free of heart disease and
studies involving people with heart disease and those free of it,
randomly assigned to different diets to see which was most protective.
Here is what they found:
It is not total fat but rather the kinds of fats consumed that have
the main influence on coronary risk. Saturated fats - those that are
hard at room temperature like the fats in red meats, cheese, butter
and, to a lesser extent, poultry - raise blood levels of harmful
cholesterol and are not to be recommended as a steady diet.
Even more hazardous are the so-called trans fats that form when
vegetable oils are hardened to make most margarines and the
shortenings that are widely used in processed and fast foods. Check
the ingredients on food labels and chances are you will find that
most processed foods contain "partially hydrogenated vegetable oil,"
which nearly always means trans fats are present. And look for
margarines free of trans fats.
In metabolic studies, even small amounts of trans fats in the diet
were found to raise the harmful cholesterol and lower the protective
type. Trans fats also raise blood levels of triglycerides and another
harmful substance, lipoprotein-a. In addition, the trans fats may
impair arterial flexibility and promote resistance to insulin, which
in turn increases the risk of Type 2 diabetes, a risk factor for
Substituting refined carbohydrates for fats is not the answer, Dr. Hu
and Dr. Willett wrote, because such a change raises triglyceride
levels and lowers both harmful and helpful cholesterol, resulting in
no reduction in coronary risk.
Particularly troublesome, especially for people who are already
insulin resistant, are carbohydrate-rich foods with high glycemic
loads: lots of quickly digested sugars or starches, like sweets,
white bread and potatoes.
Pasta, oatmeal and unrefined grains, on the other hand, are digested
slowly and therefore have a low glycemic load and are considered
When oils rich in polyunsaturates and monounsaturates are substituted
for saturated fats and hardened oils, harmful cholesterol levels fall
and beneficial cholesterol either rises or stays the same.
And when polyunsaturates are substituted for saturated fats, insulin
sensitivity may improve and the risk of diabetes may fall, the
Foods rich in monounsaturates include olive, canola, nut and avocado
oils and the foods they come from (especially walnuts); oils rich in
polyunsaturates include safflower, soybean, corn and mustard.
But the most heart healthy of fats are likely to be the omega-3 fatty
acids found in fish and some plants, like flaxseed and purslane,
walnuts and in canola and soybean oils and fish oil capsules.
Just two fish meals a week can significantly reduce the chance of
having a heart attack. Potential benefits of omega-3 fatty acids
include prevention of abnormal heart rhythms, decreased risk of
clots, greater arterial flexibility and lower triglyceride levels.
Also protective are whole grains, especially those rich in soluble
fiber like oats and barley, and folate, a B vitamin found in dark
green leafy vegetables. It is also added to flour now.
Continuing studies of more than 120,000 health professionals showed
significant cardiac benefits of a diet rich in fruits and vegetables,
especially green leafy vegetables and fruits with vitamin C.
A Heart-Healthy Life
As you can see, there is no one food to eat or eliminate that will by
itself protect the heart. Rather, it is an overall dietary pattern,
the researchers noted. This "prudent" pattern is characterized by
"higher intakes of fruits, vegetables, legumes, whole grains, poultry
and fish." A typical Western pattern "characterized by higher intakes
of red and processed meats, sweets and desserts, potatoes, French
fries and refined grains" is associated with a higher cardiac risk.
And, of course, it is not enough just to eat right. In addition to a
healthy diet, protecting one's heart should also include maintaining
a healthy weight, exercising regularly for half an hour or more
daily, consuming a moderate amount of alcohol and not smoking.
Together, such measures could prevent 74 percent of coronary events,
the Harvard researchers concluded.
They also disputed a longstanding argument that it was unwise to
suggest that people could eat more than 30 percent of their calories
from fat, even if it was heart-healthy fat, since so many people are
already overweight. "Long-term clinical trials have provided no good
evidence that reducing dietary fat per se can lead to weight loss,"
they wrote. Rather, it is overconsumption of calories, regardless of
their source, and underexpenditure of energy, that lead to weight
Copyright The New York Times Company