Want Fat With That? A Surprising Way
To Make Vegetables More Nutritious
August 8, 2006; Page D1
Are you getting the most out of your fruits and vegetables?
That's the question researchers are trying to answer as they study
how our bodies absorb the healthful nutrients and compounds in foods.
What they are finding is that in our quest to cut calories and fat
from our diets, we may be cutting out a lot more.
It turns out that some of the best stuff in fruits and vegetables --
certain vitamins and cancer-fighting compounds -- are "fat-soluble."
That means some fat needs to be present for the body to adequately
absorb the nutrients. But studies are now showing that people who opt
for no-fat dressing or who skip adding foods like avocado or cheese
to a dish to avoid fat calories, are getting far less out of their
salads and other veggies.
"What we're finding is that if you don't have some fat in the meal,
all these wonderful" compounds are missed, says Steven Clinton,
program leader for molecular carcinogenesis and chemoprevention and
the Ohio State University Comprehensive Cancer Center in
Columbus. "If the nutrients don't get into your system, then what
good are they?"
Dr. Clinton's latest research looks at how adding avocado -- which is
relatively high in unsaturated fat -- to salsa or a salad affects how
well the body absorbs healthful compounds in the foods. In
particular, the study looked at absorption of carotenoids, the red,
yellow and orange pigments found in many fruits and vegetables that
are believed to have cancer-fighting properties.


For the salsa study, 11 test subjects were first given a meal of fat-
free salsa and some bread. Another day, the same meal was offered,
but this time avocado was added to the salsa, boosting the fat
content of the meal to about 37% of calories. In checking blood
levels of the test subjects, researchers found that the men and women
absorbed an average of 4.4 times as much lycopene and 2.6 times as
much beta carotene when the avocado was added to the food.
Lycopene is the red carotenoid found in tomatoes and watermelon that
is being studied as a potential fighter of prostate and other
cancers. Beta carotene is the orange pigment in fruits and vegetables
that is used in the body's manufacture of vitamin A. Studies suggest
that diets high in fruits and vegetables containing beta carotene are
linked to lower cancer rates.
With the salad test, the impact of adding avocado was even greater.
The first salad included romaine lettuce, baby spinach, shredded
carrots and a no-fat dressing, resulting in a fat content of about
2%. After avocado was added, the fat content jumped to 42%. When the
salad was consumed with the avocado, the 11 test subjects absorbed
seven times the lutein and nearly 18 times the beta carotene. Lutein
is a carotenoid found in many green vegetables and is linked with
improved eye and heart health.
Researchers noted that a small portion of the increased carotenoid
levels in the blood of test subjects could be attributed to the
compounds present in the avocado. However the vast majority of the
increase was attributed to better overall absorption once fat was
present.
Study researchers say they were not only surprised by how much more
absorption occurred with the avocado added to the meal, but they were
taken aback at how little the body absorbed when no fats were
present. "The fact that so little was absorbed when no fat was there
was just amazing to me," says Dr. Clinton.
An earlier study done in 2004 by Ohio State University researchers
showed a similar effect comparing salads consumed with no-fat, low-
fat and full-fat salad dressings. When the seven test subjects
consumed salads with no-fat dressing, the absorption of carotenoids
was negligible. When a reduced-fat dressing was used, the added fat
led to a higher absorption of alpha and beta carotene and lycopene.
But there was substantially more absorption of the healthful
compounds when full-fat dressing was used.
So far there isn't enough research to advise people how much fat they
should consume with vegetables to get the optimal absorption of
carotenoids. The basic advice is to still count calories and don't
overdo the fats, choosing heart-healthy unsaturated fats like avocado
or olive oil rather than foods with a high saturated-fat content.
A recent rat study by German researchers showed that the type of fat
matters. They compared vitamin E absorption in rats that were fed
diets with cottonseed oil or hydrogenated oils -- which contain
unhealthy trans fats. The trans fats actually slowed the absorption
of vitamin E compared with other type of fat.
For people watching their weight and the fat content of their diet,
the balancing act might be tricky. The best nutrient absorption from
the salad, for instance, occurred when diners ate dressing with 28
grams or about two tablespoons of canola oil. That translates to
about 250 extra calories.
Nutritionists say diners should look at the overall fat content of
the meal. A bowl of cereal with berries might be improved by using 2%
milk or full-fat yogurt instead of skim milk. But if you're eating a
meal, dietitians advise clients to choose one food item per meal with
a significant amount of fat, and keep the other foods very low in fat.
"If you are having a hamburger for dinner and strawberries for
dessert, it is not necessary to douse the berries in cream since the
hamburger has plenty of fat to help you absorb the nutrients and
phytochemicals from the berries," says Elizabeth Grainger, Ohio
State research dietitian. "The key is always moderation."