It’s crazy when you think about all of the different kinds of food we eat.
We just swallow and hope it all works out for the best.
Well, it turns out there are better ways
to think about keeping our bodies humming healthfully along.
Welcome to Nutrition Facts.
I’m your host Dr. Michael Greger.
Today we discover the powerful properties of citrus.
I’m talking lemons, limes, citrons, bitter orange,
grapefruit, pomelo, mandarine, grapefruits, clementine, kumquats.
Actually one of my favorite citrus fruits is the kumquat
because you can eat the whole fruit - peel and all!
Which is ideal because the DNA repairing enzyme-boosting powers
of citrus appear to be concentrated in the peel.
New data demonstrating a DNA protective agent
was present in at least some fruits and vegetables
found that it was heat sensitive
and determined it was not vitamin C,
confirmed in a study that tried vitamin C directly
and found no effect on DNA protection
and repair of DNA strand breaks.
The carotenoid beta cryptoxanthin,
found primarily in citrus,
seems at least one candidate.
If you expose cells to a mutagenic chemical,
you can cause physical breaks
in the strands of DNA,
but in less than an hour
our DNA repair enzymes can weld most
of our DNA back together.
But if you add some of that citrus phytonutrient,
you can effectively double the speed
at which DNA is repaired.
But this is all just cells in a petri dish,
what about in a person?
If you have people drink a glass of orange juice
and draw their blood two hours later,
the DNA damage you can induce
with an oxidizing chemical drops,
whereas if they just had like orange koolaid,
it didn’t help.
So do people who eat more fruit
walk around with less DNA damage?
Yes, particularly in women.
Does this actually translate into lower cancer rates?
It appears so. Citrus alone associated with a 10% reduction
in odds of breast cancer.
Given to newly diagnosed breast cancer patients,
citrus phytonutrients were found to concentrate
in breast tissue,
though many complained of “citrus burps”
due to the concentrated extract they were given
so researchers evaluated topical application
as an alternative dosing strategy,
recruiting women to apply orange flavored massage oil
to their breasts daily.
This request was met with excellent compliance,
but it didn’t work.
We actually have to eat our food.
Why not just take carotenoid supplements
to boost our DNA repair?
Because it doesn’t work.
Although dietary supplements did not provoke
any alteration in DNA repair,
dietary supplementation with carrots did.
This suggests that the whole food
may be important in modulating DNA repair processes.
Though orange juice consumption was found protective
against childhood leukemia,
it was not found protective against skin cancer.
However, the most striking feature
was the protection purported by citrus peel consumption.
Who eats orange peels?
Lots of people evidently.
Just drinking orange juice may increase the risk
of the most serious type of skin cancer.
Daily consumption was associated with a 60% increase in risk.
So again, better to stick with the whole fruit.
And you can eat citrus extra-whole
by zesting peel into your dishes.
Next, we look at how phytonutrients in citrus,
such as hesperidin,
may increase blood flow sufficient to warm the hands and feet
of those with cold sensitivity.
In 1936, Albert "tsen-yurgi", who won the Nobel prize for discovering vitamin C,
described a vitamin "P,"
which we now know encompasses a class of thousands of phytonutrients called flavonoids.
Some like quercitin, are widespread in plant-based foods.
You can tell something is widespread in the plant kingdom
when you can even find it in iceberg lettuce.
Others, however, are only found in specific plant families.
For example, hesperidin is found primarily in citrus fruits.
This may be one of the reasons, out of all the different types of fruits
that have been looked at, citrus may help cut our risk of stroke the most.
The citrus phytonutrient hesperidin increases blood flow.
Using a machine called a Doppler fluximeter
you can measure blood flow through the skin using a laser beam,
a laser Doppler fluximeter;
sounds like something from "Back to the Future".
And if you give people the amount of hesperidin found in 2 cups of orange juice,
blood flow goes up, though if you instead just give them the orange juice itself,
that works even better.
So there's other beneficial stuff besides just the hesperidin in citrus.
For example, if you measure the changes in genetic expression,
orange juice consumption induces changes in the expression in 3000 of our genes,
whereas hesperidin alone only modulated the expression of about 2,000.
Still, nearly 2000 stretches of our DNA expressed differently
because we consumed just one of the thousands of phytonutrients in plants?
Pretty mind-blowing!
And these changes in blood flow are not just kind of in theory.
Researchers have taken volunteers with cold sensitivity- cold hands, cold feet.
Put them in an air-conditioned room and measure the temperature
of their finger tips after drinking a placebo drink—like orange koolaid,
versus drinks with two doses of actual citrus phytonutrients.
In the koolaid group their fingers got colder and colder,
dropping nearly 9 degrees Fahrenheit.
But the fingers of those consuming low, or high doses of citrus didn't as much.
That's because their blood flow remained steady.
Here's that laser test again.
When we're exposed to cold temperature our body starts to clamp off
peripheral blood flow to keep your core warm,
but if you eat a bunch of oranges before you go skiing
your risk of frostbite may go down
since you're keeping up your blood flow to your fingers and toes.
They even took these poor women and plunged their hands into some chilly water,
and as you can see their finger temperature
rebounded faster towards normal in the citrus group.
Of course, having warm hands is nice,
but maintaining blood flow to your fingers is not as important
as maintaining blood flow to your brain.
Finally today, we look at how daily citrus fruit consumption
during athletic training may reduce muscle fatigue,
as evidenced by lower blood lactate concentrations.
The same lactic acid that makes yoghurt tangy
is the same lactic acid that builds up in our muscles
when we exercise strenuously.
Instead of bacteria fermenting the sugar in milk
to make energy for themselves,
our muscles ferment sugar in our diet
to produce energy to contract.
If, like when we're sprinting, lactic acid builds up
in our muscles faster than it can be removed
we can end up with a burning sensation in our muscles,
forcing us to stop.
Now, if we train we can increase
the number of blood vessels in our muscles
and clear out the lactate faster.
For example, if you take some overweight sedentary women
and start them on an aerobic training program
of running and walking,
at the end of three months their lactate levels
during exercise decreased 17%,
but those on the same program
who drank 2 cups of orange juice a day
decreased their levels 27%.
They did the same exercise program,
but the citrus group experienced a significant decrease
in blood lactate concentration,
signifying an improvement in physical performance
with less muscle fatigue.
I don't recommend drinking juice,
because you're losing all that wonderful fiber
that slows the rate of fruit sugar absorption into our system.
So the whole fruit is nearly always better than fruit juice.
Now this is not to say OJ isn't better than coke.
OJ has those citrus phytonutrients like hesperidin,
which may be why the women's triglycerides didn't go up
even though they were drinking 2 cups of fruit juice every day.
Hesperidin may actually help lower our digestion of fats,
but once you get up to 3 cups a day of juice
you can really start bumping up your triglycerides.
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