Optimize Your Diet with Walter Willett Part 1
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>> Here at Integrative Nutrition,
we strive to give you the most up-to-date information
on health and nutrition in the most unbiased way.
Nutrition is a unique field
as there are always going to be
a lot of opposing views.
Although you may not agree with everything
that you're exposed to in this field,
we encourage you to hear all the facts
and then make your own judgment to determine
what works best for you.
In this class, Walter Willett aims to show you
the importance of preventive nutrition.
He highlights a lot of important research
gathered over the last few decades
to show you what we have learned about diet and health.
We understand that all of this information
can be overwhelming.
As you watch, focus on the underlying message,
the important role that diet has
in both development and prevention of disease.
Keep in mind, you do not need to know everything
to get out there and coach clients.
It's about understanding and awareness,
and it's up to you to decide
how you may want to use this information
and put it into action in your life and your clients'.
>> I'm going to try to cover
a few of the highlights of things
we've learned about in the last 10, 20 years
that are most important for people to understand
if they want to be healthier
and also to weave into this,
a little bit about how we learn about diet and health.
And that I think is really important,
how do we gather the evidence
that we need to understand,
what is really the smartest best choice
when we have so many things
we could choose in our daily eating habits.
The problem is of course for many people
and you'll hear this, "I'm confused,"
that if you look at the web
or pick up almost anything to read
about health and nutrition, you can find for any food
or any meal positions that this is the most toxic thing
you could possibly eat all the way to the other end
that this will save you from cancer, heart disease,
and you'll live forever and be happy all the way.
So how do you sort out this
huge amount of mixed information
and somehow come up to understand
what are the healthiest choices?
So I'm going to look at the kinds of evidence
that we really do need
if we want to put the odds in our favor
when we sit down at a meal in terms of our likelihood
of being healthy over the years.
I think it's helpful to go back in time,
about 50 or 60 years,
to look at one of the early kinds of studies
that provided powerful evidence
that most of the diseases
of western civilization are not inevitable.
And this was the Seven Countries Study
lead by Ancel Keys,
we call this an ecological or correlational study.
Pretty simple,
he basically looked at 14 different populations
in 7 different countries, about 1000 men each,
and then over a decade,
carefully monitored their rates
of coronary heart disease or heart attacks,
the number one cause of death in United States
and now the number one cause of death
in almost every country in the world.
And what he found was this
that there was about a tenfold gradient and risk
from the highest country,
which was Finland at that time,
to the lowest region, which was Crete in Greece.
And other epidemiologists, about the same time,
were doing what we call migrant studies.
They were looking at people
who moved from low incidence countries
like Crete or the Japanese villages
that are in the lower left-hand corner
and they found that those migrants
who moved to the United States
after not too many years
adopted the rates of heart disease
as European Americans living in the United States.
And so that said very powerfully
that these very large differences
in heart disease rates
were not due to genetic factors.
And I think if you read the news now,
you'll hear all about genetics, genetics, genetics.
They play a minor role
actually in determining who will get
and who will not get heart disease
if you look around the world.
This says that something about diet
or lifestyle is much more important,
much more powerful than genetics.
And of course, the next step is
if we could really understand what it was,
then we could maybe modify our risk,
so everybody could be at low risk
like people living in Crete.
There were some clues from this study
that saturated fat
might be an important part of the problem
because of this correlation that you see there.
But we know that many other things are different
in the high-risk versus the low-risk countries,
differences in physical activity,
other aspects of diet, maybe sleep,
see that people in Crete took a siesta for example,
and that has been shown to be
related to lower risk of heart disease.
Smoking, lots of things could be
alternative explanations for these differences in rates
and therefore what we would call confounding variables.
So this was a clue,
but we couldn't really conclude cause and effect
that saturated fat was a major determinant
of heart disease.
There were other epidemiologists at that time
looking at cancer rates around the world.
And they found a similar picture,
large differences in rates of breast cancer,
in colon cancer around the world.
And if we looked at people who moved after some time,
they adopted the rates of the new environment.
Again, playing into something
that was potentially modifiable,
you know, might be diet,
might be animal fat in the diet,
but we shouldn't really conclude that this was causal,
in terms of breast cancer, shown here,
reproductive factors play a very powerful role.
And we know that that might explain
some of these differences,
breast feeding, things like that.
So you really again should not draw conclusions from that.
But those correlations were so tempting
that many people did draw the conclusion
that fat was the major determinant of cancer,
breast cancer, colon cancer,
and many other cancers in western countries,
even though the evidence in fact was very shaky.
So this conclusion really did
permeate dietary guidelines
in the late 1980s, 1990s, up until quite recently.
And this is the 1992 US Food Guide Pyramid.
Right at the top, it says
all types of fats and oil should be used sparingly.
And then of course, you have to eat something,
so if you're not gonna eat fat, by default,
you will end up eating large amounts of carbohydrate,
which they put at the base of the pyramid.
We should have up to 11 servings a day of things like
Rice Krispies, and Wonder Bread,
and crackers, and things like that.
That was supposed to be good for us,
even though there was not a shred of information
that eating large amounts of those foods
was actually good for us.
And if that wasn't enough,
carbohydrate in the diet,
they put potatoes there in the vegetables,
so you could have up to 13 servings
of starchy foods per day.
And there are some other curious things in this pyramid
that they put together red meat,
and chicken, and fish, and nuts,
and legumes all into one group
and said you should have two to three servings a day,
even though there was some suggestion
at that time that it made a big difference
which of those you were choosing
and they didn't distinguish amongst them.
And then of course,
dairy has an interesting position
that it's the only food or milk is the only food
that is said to be essential.
There's lot of options in these other categories.
I grew up in Wisconsin and Michigan,
so I knew that you were supposed to have
three or four servings a day.
But curiously, if you look around the world,
most people don't drink milk as an adult
and their bones are not falling apart.
And we'll come back and talk about that.
Well, I began to be a bit worried
that this push to reduce all types of fat in the diet
and eat more carbohydrate
might not be such a good thing.
And this was,
I think, first suggested by another kind of study.
What we call the controlled feeding study
done by some colleagues in the Netherlands.
And this is where you take a few dozen people
and you actually give them food to eat,
so you totally control their diet
for a couple of weeks.
You just need a few people, a few dozen people
and a few weeks to do this kind of study.
And you look at things
like changes in blood cholesterol level
or changes in blood pressure.
And what they showed was the lower fat,
higher carbohydrate diet,
which was like the diet being recommended,
HDL-cholesterol went down
and in the bottom part of the panel,
triglycerides in the blood go up.
And we know from lots of other studies
that low HDL and high triglycerides
are related to higher
and not lower risk of heart disease.
So this was a bit of a red flag
that you would think all of us being equal,
you might actually be better off on the higher fat diet
where they used olive oil
compared to the lower fat diet
which was being recommended.
And this study was repeated over and over again
and it's very clear that if you do replace fat,
pretty much any type of fat with carbohydrate,
HDL goes down, triglycerides go up,
and that is a little bit worrisome.
Now another player came on the scene,
although it had been there for about 100 years
and almost nobody was paying attention to it,
and that's trans fat in the diet.
These are 60 pound blocks
of partially hydrogenated soybean oil
that I bought at a restaurant supply store
just a mile or two
from our School of Public Health in Boston,
and this is what our fast food industry was using.
They were putting it in their fryer,
later just turning up to 400 degrees
and saying cooked in vegetable oil,
but here at room temperature,
you can do lots of things,
interesting things with these blocks of trans fat.
You can build buildings, you can do sculpture with it.
But of course, we were interested in what it might do
for our coronary arteries.
And again, my colleagues in Netherlands,
doctors Mensink and Katan
led this line of investigation with trans fat.
And what they found was
if they compared saturated fat to trans fat,
it looked like you actually got more of an elevation
in total cholesterol levels
with saturated fat in the diet.
But we've also come to understand
that total cholesterol doesn't mean too much.
It's really the cholesterol fractions
that are important and we want to lower our LDL
and raise our HDL cholesterol
and the ratio of LDL to HDL gives the best prediction
for heart disease.
And as you can see on the bottom,
trans fat was almost twice as bad
on a gram for gram basis
as well as saturated fat in the diet.
Again, many people repeated this study,
found the same thing.
And replication is an important part
of a scientific process.
I'm sure most of you know.
And so this did suggest that
trans fat could be a serious problem
even though people had been eating it
and people were in fact being told
it was good for them.
They didn't say trans fat but they were told to be
consuming Crisco instead of lard
and margarine instead of butter.
And especially in the 1960s, '70s, '80s,
the amount of trans fat was very high
in those products.
However, one of the other concepts
that we've come to appreciate over the last decade
or two is that there are many pathways
leading from diet
to coronary heart disease or CHD here.
And I've only talked about
how a diet can lead to changes in blood lipids
and then on to coronary heart disease,
but we've come to appreciate
that diet can act through affects on blood pressure,
thrombotic tendency, meaning tendency for clots
to form in the coronary arteries,
it can operate through affecting
insulin resistance, oxidation,
homocysteine levels in the blood, and very importantly,
inflammation and endothelial dysfunction,
and ventricular irritability and arrhythmia,
And actually that last is really important
because people usually die of a heart attack
because of not just enough blood,
but the thing that precipitates death
is sudden cardiac death,
an acute arrhythmia,
and diet can influence the likelihood
of that happening.
So the point is
that if you look just at the effect of diet,
like cholesterol fractions
like we've talked about already.
You could be misled
because there could be counterbalancing benefits
through other pathways or there could be effects
in the same direction or synergy
among these various pathways.
And for example, we've come to understand
that trans fat can make inflammation increase.
And that's been documented
in many controlled feeding studies now.
So probably trans fat would be even worse
than we might have expected looking
just at the effects on blood cholesterol fractions.
The important point is that we want to look
directly at heart disease
as well as looking at the effects
on just one pathway at a time
because by looking at heart disease directly,
we integrate all these possible pathways.
So our group has, for the last 40 years,
spent most of our effort
conducting a large prospective studies
where we look at large populations of people,
we have three large studies
that include almost 300,000 men and women
among whom we had been collecting diet,
physical activity, smoking,
other lifestyle factors in detail
and updating that every two to four years
as we go along and then carefully documenting
who gets breast cancer, who gets a heart attack,
who gets diabetes, etcetera.
We were looking at almost every outcome.
And then if we wanted to focus in
on one dietary factor,
we can control statistically for other aspects in diet
and lifestyle and focus in
on our particular research question.
So these studies are rather complex, but as an example,
this is what we saw
when we looked at types of fat in the diet
and risk of coronary heart disease.
This is after about 10 years of follow up,
almost 1,000 of them had died of a heart attack
or been hospitalized
for an acute myocardial infraction.
And here we're looking at
specific types of fat in the diet,
each compared to the same number of calories
and carbohydrates and controlling one for each other,
and in everything else, I'll show you,
we're adjusting for smoking and physical activity
and these other potential confounding factors.
And what we saw was, maybe not surprisingly given
what I've said already,
trans fat was by far the most strongly related
to risk of coronary heart disease.
Saturated fat was very weakly related to heart disease
compared to carbohydrate
but mono and polyunsaturated
especially were related to lower risk of heart disease.
So total fat was not related to heart disease,
it was really the type of fat that was important.
And again, these findings have been replicated
in multiple other studies.
Now in principle, the ideal study
is a randomized controlled trial
where you randomly assign people to a different diet,
a different dietary factor,
it might be high trans fat or low trans fat,
and then you follow them to see
who gets a heart attack and who doesn't
and you evaluate your hypothesis in that way.
By randomization, you guarantee
that the groups are virtually identical.
The problem is that it's really hard to keep
thousands of people on a diet for many years.
And this is one study that did try to do that,
the Women's Health Initiative,
most expensive study ever done,
and this is looking at the cumulative incidence
of cardiovascular disease.
As you can see the two groups,
the low-fat and the high-fat groups
are essentially identical there.
There was no difference in heart disease rates
between low-fat and high-fat groups.
Now you might say that was consistent with the data
I've shown you already from the Nurse's Health Study
in our cohorts, but the problem was,
in this study, several years later,
they published data on the cholesterol fractions
in the two groups and there wasn't any difference.
And we know that if you go on a low-fat diet,
it does change your cholesterol fractions,
HDL goes down, triglycerides go up.
Again, there wasn't any difference.
So it really meant that they didn't test the hypothesis
that people, there was virtually no difference
in low-fat or high-fat groups
in terms of their fat content
and really shows how difficult it is
to do that kind of study.
There was one study though, a randomized trial,
that did show a difference in the treatment groups.
And this was a randomized trial
of a Mediterranean diet conducted in Spain.
They had a low-fat controlled diet
and then a Mediterranean diet that was higher in fat
where they gave people nuts.
And then in the third group, Mediterranean diet
where they give them extra virgin olive oil.
And as you can see, the rates of heart disease
were lower in the two Mediterranean diet groups
compared to the controlled group.
So why they were more successful
in keeping people under diets
is an interesting question in itself here.
It did show all the benefits of the Mediterranean diet
and of the nuts and olive oil, and probably,
there was a greater degree of motivation
because they actually gave people, on a regular basis,
nuts and olive oil, which made it easier
and provided some incentive to stay in the study.
So to summarize this little section on types of fat
and heart disease,
coronary heart disease rates
can be dramatically reduced by nutritional means,
but this will not be achieved
by replacing saturated fat with carbohydrate.
That's pretty much a wash.
We should avoid recommendations
regarding percent of energy from fat
and avoid pejorative references to fat or fatty foods.
Fat is not bad.
You really have to focus on the type of fat.
And advice about dietary fat
should focus on replacement of saturated fat
and trans fats.
Try to eliminate the phrase low-fat
from your vocabulary
because it really is scientifically meaningless
and actually can be confusing
and misleading to many people's detriment.
Now back to cancer and breast cancer in particular.
There was another randomized trail
that tried to look at low-fat diets
and breast cancer risk.
And this one did show some change in HDL cholesterol.
And if anything, the breast cancer rates
were a little bit higher on the low-fat diet.
There was not a statistically significant difference
but it was running in the opposite direction.
So the data for breast cancer and fat in the diet
are also not supported by randomized trials.
Now one major additional problem
with randomized trials,
when we were looking at cancer or heart disease,
is that no-one's quite sure
how long you would really need to run the study
before you should see, in effect,
if there is a benefit or harm.
And the randomized trials,
again, are really challenged
by maintaining people on separate diets.
So we've looked at this and this is one advantage
of long-term prospective studies
where we, we're not telling people to change their diet
but we're tracking their diet so we can look at people
who have been consistently high-fat
or low-fat over a long period.
So this is after 20 years.
And looking at different intakes of fat
in the Nurse's Health Study, by that time,
there were over 3,500 cases among postmenopausal women,
and as you can see,
just no difference in breast cancer incidence
across a very wide range of fat intake.
Now that's fat in the diet, and of course,
that's totally different than fat in the body.
And obesity and overweight are huge problems,
I think you are totally aware of that
and also very much aware
that this is an epidemic in United States
and in most countries around the world
like Mexico going up faster
than we are and actually surpassing us in obesity.
It's really a tragedy seeing
what's unfolding before our eyes in so many countries.
There has been some confusing literature in this area,
claiming that it's actually better to be overweight.
Have some of you heard that?
Yeah, and if you read the New York Times,
don't read the New York Times
if you're interested in learning
anything about nutrition or science,
unfortunately, they have been pushing,
Gina Kolata in the New York Times have been pushing
this story that it's good to be overweight.
And it just doesn't make any sense,
you know, blood pressure goes up,
your lipids deteriorate, glucose tolerance deteriorates
if you're overweight.
And why should that be that good for you?
There would have to be some magic going on.
The problem is, of course, is I think anyone of you
who is talking care of patients
is that we don't just go along
at our weight and drop dead,
most people get sick, lose weight, and then die.
And sometimes they can, for many conditions,
lose weight for quite a while before they actually die.
And also, as we get into our, you know, 80s and 90s,
many people develop frailty, meaning we lose weight,
especially lean mass, and that's a vicious circle
because then we exercise less,
and then we lose more lean mass and then we...
There's a high probability.
It's really a downward spiral
that physicians have appreciated for hundreds of years.
And basic data are that
there is increased risk of total mortality,
diabetes, heart disease, many other conditions,
anything above a BMI of 25 and definitely
when you get to the obese range of BMI above 30,
therefore individuals, there will be some differences
in a person's optimal weight.
And that's one reason why I like
to keep an eye on three numbers,
waist circumference, which your fat's growing,
that tells you that's not a big muscle
we're building up down around our waist,
so that's unfortunately...
And we need to do something about it.
And also keep in mind
what we weighed at an age about 20
because most people were at a pretty good weight then.
Of course, that's changing now
and a lot of people are arriving
at age 20 already overweight
but gains in weight after age 20
are almost entirely going to be fat mass,
unless somebody is doing
a really unusual muscle building program.
And of course, that's obvious
that they've been doing that if that's the case.
So looking at weight gain, waist circumference
and BMI gives you three numbers
that will help an individual know
when they need to be paying attention to weight,
most of us do in reality.
So it is really important to maintain a healthy weight.
And for most people that means not gaining
or gaining as little weight as possible
as we go through our adult life.
Now what is the best diet to help maintain weight?
Until fairly recently,
there was surprisingly little good evidence
on that topic and it's so important,
it was really surprising.
But in the last 15 years, there have been many studies
that have looked at different dietary factors
in weight control.
I just don't have time to go into those.
That's a big topic in itself.
You can study this by randomized trials
because you need just a few 100 people
and following people for a year or two
will give you good information,
less than a year is just too short
because people on almost any diet
lose a few pounds and then regain it.
Just a change in the diet
will usually be worth a few pounds of weight loss.
So to, I think, summarize this quickly,
the bottom-line is that the percentage of calories
from fat in the diet is,
again, not an important factor.
If anything, the data in some studies
tend to show low carbohydrate diets,
and under some circumstances,
being a little more effective for weight loss.
This was probably the best study,
the POUNDS LOST study showing no difference
for a high-protein, low-protein,
high-fat, low-fat, or high-fat,
low-carbohydrate diet.
This was done in about 800 people
followed for two years.
And the fat or macronutrient composition of the diet
really made little difference.
Now some people took away from that,
"Oh, diet isn't effective and your dietary choices
are ineffective in controlling weight."
And that is the wrong conclusion.
It's just that the macronutrient mix
is not very important
but other aspects of diet quality do seem
to be importantly related to weight control.
And there is no single factor,
there is no magic bullet out there, or some, you know,
you can't find a new magic bullet of the month
almost out there for weight control.
There is no single factor
but adding together the elements of a healthy diet
can make an important difference.
So this is an analysis we did
and published a couple of years ago
in the New England Journal of Medicine,
Dariush Mozaffarian led this work.
The three different colors stand
for three different cohorts.
And without going into all of the details,
this produced a massive amount of data
because we started with about 80,000 people
who were not obese and were healthy basically.
And we're looking at weight gain
over a 20-year period in 4-year segments.
And the picture here is,
actually if you look at the right,
the biggest problem is sugar-sweetened beverages.
And this is showing the estimated effect per serving.
So this would be per one 12 ounce
serving of a sugar-sweetened beverage,
the problem is that many people take
many servings a day of sugar-sweetened beverages.
In low-income American groups, we just analyzed,
the average was three servings
of sugar-sweetened beverages per day.
And many people, about 10%,
were taking five or six servings
of sugar-sweetened beverages per day.
This is a huge metabolic problem
and a threat to health.
This I'll talk about a little more.
Fruit juice also is related to weight gain
but dairy products, on the right, were pretty neutral.
If we look at foods on the left,
potatoes, red meat showed up,
refined grains is being related to more weight gain.
Again, dairy products were sort of neutral.
And then at the left, fruits, vegetables,
whole grains, and interestingly,
yogurt in all three cohorts
was related to the least weight gain.
And there's a lot of interest in the microbiome
and all of the bacteria in yogurt being beneficial.
So it is interesting if you look at the fluids
that are related to less weight gain
that pretty much describes the Mediterranean type diet.
And quite, also, interestingly,
one of our colleagues in Israel did
what I think is one of the best studies in the diet
and weight control field.
They randomized three groups
and they did this at a work site
where they had a more control of diet
than just anybody off the street
because many of the foods were prepared
and eaten at work and they could control that.
So the shaded part shows
the first two years of the study,
they had a low-fat group
and a relatively high-fat group
in a Mediterranean type diet
that also had about the same fat composition,
fat content as the higher fat group.
And all three groups
lost weight over the first two years.
The low-fat group lost the least weight,
but then the study stopped
and everyone went back and worked on other things.
But after another four years,
the investigators went back and weighed people
and collect their blood samples,
so six years into the study,
four years without any dietary intervention.
And the Mediterranean diet group
had maintained most of the weight loss
and they were better off metabolically.
The low-fat group had essentially regained everything
and the higher fat group were sort of in between.
But definitely, I think
people were able to stay with the Mediterranean diet
because there was a lot of variety,
it was foods that were enjoyable
and metabolically had an important benefit.
So I think that's sort of the bottom-line
of what we know about diet and weight control
that what's really important is the long-term,
not what you weigh after a couple of months.
Yes, that may get you into the swimming suit in the summer,
but if you're thinking about health,
that's a year-round issue.