"Take two cups of kale and call me in the morning" may
be among the emerging clinical suggestions to prevent a leading
cause of blindness in adults: age-related macular degeneration (AMD).
Like diabetes, the main topic in this issue of Townsend
Letter, macular degeneration involves the breakdown of nerve
tissue. Nutritional recommendations for diabetes and macular degeneration
are also similar.
No vitamin supplement or medicine has been shown to stall progression
of AMD better than good old green leafy vegetables. That said, many
of our patients have medically related barriers to meeting their
bodies' need for greens. This article centers on how we can
help patients get the nutrients they need from greens.
Greens Should Be Eaten
with Dietary Fat … and Don't Forget about Herbs.
Patients tell me how they eat a salad with fat-free dressing as
their lunch or have a green drink as a snack. Indeed, salad and
juiced green vegetables have healthful properties. But did you ever
wonder why raw salads and veggie juices aren't part of the culinary
tradition of most cultures? The reason may be an important detail
pertaining to your health.
Traditional diets all around the world include dark green leafy
vegetables such as kale, bok choy, turnip greens, mustard greens,
collard greens, chicory, Swiss chard, dark green lettuce, and spinach.
Greens are usually prepared in one of a few ways across cultures.
They are chopped, lightly cooked, and sautéed in a minimally
processed oil; added to soups and stews; or prepared in vinegar.
As it turns out, digesting the nutrients in green vegetables is
best done by a combination of heating, chopping, and oil extraction.
Your tax dollars have been spent on studying this important process:
the US Department of Agriculture has researched how fat-soluble
nutrients can be best absorbed.
Green leafy vegetables are rich in vitamin K, carotenoids, and flavonoids.
These are all fat-soluble nutrients, which means they that need
to be eaten with some form of fat to be absorbed. This is very likely
one reason green leafy vegetables are traditionally eaten with a
Similar reasoning applies to other vegetables. I've watched many
nutritionists roll their eyes when they see ketchup listed as a
vegetable. Indeed, it does leave a lot to be desired. But the decision
rests on often-overlooked science. Ketchup topping a fatty food
may net more lycopene, a fat-soluble nutrient that makes tomatoes
red, than an anemic-looking, underripe hothouse tomato sliced on
lettuce and eaten with fat-free salad dressing.
Herbs are to green leafy vegetables what ketchup is to tomatoes.
We don't usually think of oregano, rosemary, mint, and cilantro
as green leafy vegetables; and it would certainly take a lot of
dashes from the shaker to make one vegetable serving. That said,
herbs are dried and concentrated greens that retain their fat-soluble
vitamins, which are well absorbed.
Herbs may very well be considered eye nutrients in a bottle. However,
I am less confident that science is able to put eye nutrients in
a capsule. Vitamin supplements can and do protect eye health and
demonstrate delay in progression of eye disease. However the only
head to head, toe to toe, test of vitamins verses leafy greens conducted
some decades ago proved Mother Nature's greenery the winner.
So what is in greens that the eyes depend on? One fat-soluble nutrient
in the carotenoid family is lutein. It is one of the many important
nutrients for eye health and has been isolated as a supplement,
but continues to be best obtained from dietary sources.
Patients Who Carry Extra
Body Weight May Need to Eat More Greens.
Adipose tissue (body fat) stores fat-soluble nutrients such as vitamin
D and carotenoids. However, this does not mean that people with
excess adipose tissue have sufficient fat-soluble vitamins. On the
contrary, obesity is a risk factor for inadequate blood levels of
vitamin D and carotenoids. Vitamin D initiated by ultraviolet light
exposure in the skin remains stored in body fat instead of being
activated by the liver and kidneys. Similarly carotenoids are concentrated
in adipose tissue and not released into the circulation or transported
to the eyes.
An observation meriting further study is that in someone undergoing
rapid weight loss, such as during the 6 months following bariatric
surgery, the blood vitamin D levels (and possibly the carotenoid
levels also) increase.
A History of Kidney
Stones Isn't a Reason to Skip Greens.
I've heard another medical myth I'd like to reframe: "I don't
eat spinach because I had a kidney stone." The rationale for
this is as follows: of the many types of stones, calcium oxalate
stones are the most common. Spinach is high in oxalate; therefore
the patient should avoid spinach.
Evidence-based medicine suggests a different approach. First, the
patient's stone would be analyzed to see if it comprises calcium
oxalate. If the stone comprises calcium oxalate and urinalysis demonstrates
hyperoxaluria, there may be some basis to consider limiting oxalate
intake. But even then, dietary studies have not been able to corroborate
significant benefit from avoiding oxalate. On the other hand, there
are several clinical studies that support other dietary modifications:
· Increase fluid intake to 25,000 ml
per 24 hours, mostly as water.
· Maintain a healthful weight and monitor for insulin resistance.
· Screen for hyperparathyroidism, especially related to inadequate
· Optimize vitamin D, since low levels decrease calcium absorption.
· Consider supplementing with magnesium.
· Avoid excess protein intake.
· Use caution with vitamin C supplementation.
Why not implement the evidence-based recommendations
first and keep eating your spinach, Popeye?
Warfarin Is Not a Reason to Avoid Greens.
The "patient counseling" section of the drug label for
warfarin reads as follows: "Inform that vitamin K in diet may
affect medication. Instruct to eat normal balanced diet; avoid drastic
changes in diet such as eating large amounts of leafy green vegetables."
Warfarin is among the most commonly prescribed medications, and
risk of hemorrhage is significant. Adhering to the label recommendation
is therefore important. The label does not recommend avoiding leafy
green vegetables. Yet, I hear from patients with concerning frequency
that they do not eat green leafy vegetables because they are on
a blood-thinner. Misreading the label prevents the body from getting
the nutrients it needs from a normal balanced diet, which includes
green leafy vegetables. Avoiding leafy green vegetables does not
make warfarin safer. In addition to increasing the risk of a growing
number of chronic diseases, avoiding greens can make warfarin more
difficult to dose. This may be because people who avoid greens still
use the oregano shaker from time to time, providing them with vitamin
K not recorded in the diet log.
Fat Malabsorption Increases
the Body's Need for Greens.
Some medical conditions such as inflammatory bowel disease, surgeries
such as gastric bypass surgery, medications such as orlistat, and
fake foods such as Olestra reduce the ability of the intestines
to absorb fat-soluble nutrients. Taking a vitamin supplement with
vitamins A, D, E, and K does not cover all the bases. The carotenoids
essential for eye health are also malabsorbed. I believe that patients
should be informed of the consequences of malabsorption and reminded
to eat extra greens.
A detailed presentation of nutrient interventions for the prevention
and delay of progression of macular degeneration is available. See
Harris, Geoffrey R; Steven G. Pratt, and Stuart Richer, "Chapter
1. Age-related Macular Degeneration," in Food
and Nutrients in Disease Management, edited by I. Kohlstadt.
CRC Press, Boca Raton, Florida; Jan 2009.
Ingrid Kohlstadt, MD, MPH, is an FDA
Commissioner's Fellow, using diet to improve drug safety. She has
been elected a Fellow of the American College of Nutrition and is
an associate at the Johns Hopkins School of Public Health. She is
the founder and chief medical officer of INGRIDients Inc., editing
Food and Nutrients in Disease Management
(CRC Press, Jan 2009) and Scientific
Evidence for Musculoskeletal, Bariatric and Sports Nutrition
(CRC Press, 2006). Disclaimer: The views expressed in this article
are the author's and do not reflect the views of the FDA.