《可持续发展的时代》旨在让你了解可持续发展 所面临的关键挑战和实践途径 即兼顾社会包容性和环境可持续性的经济发展
Malnutrition
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来自 Columbia University 的课程
可持续发展的时代
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从本节课中
Sustainable Food Supply and the End of Hunger
Professor Sachs provides an overview of food security, farm systems, and ecology and reviews what can be done to achieve a sustainable global food supply.
与讲师见面
Jeffrey Sachs
Director, Earth Institute; Quetelet Professor of Sustainable Development; Professor of Health Policy and Management
[MUSIC]
We need to consider one of the most complicated and
unsolved problems of sustainable development.
How are we going to feed ourselves?
It's an age old problem.
It's been with humanity for a long time.
But for quite a few decades, this is a problem that many people
thought was already solved with the great breakthroughs in food productivity,
in increasing farmland, increasing yields, it seems that
food production would inevitably stay ahead of the growing world population.
Now we have some serious doubts.
Not only are we coming to realize how badly fed the world population is,
in certain ways, but how many real threats there are ahead.
That is our challenge.
We can't say we haven't been warned.
The warnings have been with us for more than two centuries.
They started, as I've mentioned, with Thomas Robert Malthus who, in 1798,
in his Principle of Population, proposed the base question of
how food production can stay ahead of a growing population.
When Malthus wrote, there were around 900 million people on the planet.
Now with 7.2 billion people, an eight fold increase, the challenge is with us again.
In fact, perhaps in an even more complicated way than Malthus imagined.
Because now, we come to understand that not only
is the world not feeding itself in a healthy and
fair manner, but that there are many, many obstacles that lie ahead.
Let's start with the question of,
what does it mean to feed ourselves in a healthy way?
And, we can ask that by looking at the question of malnutrition.
Malnutrition is a pervasive problem on the planet.
One can argue, I think convincingly, that perhaps 40% of the world's population,
40% is malnourished in one way or another.
But to understand that, we have to understand what we mean by malnutrition.
Now, one thing that jumps to mind, of course, is hunger and undernourishment.
Undernourishment in its most direct sense is simply not taking in
the calories that are needed for daily activity and daily survival.
Hungry people feeling the pangs of hunger, and not having enough energy for
more than mere survival, and in some desperate cases, not even that,
remains a problem afflicting hundreds of millions of people in the world.
There's another kind of undernourishment that is a bit less visible,
and that is a category sometimes called hidden hunger.
The calories may be there, but the micronutrients,
nutrients such as vitamins and particular fatty acids and
other components of food are not present in an adequate supply,
so that people are unhealthy and, perhaps,
are chronically disabled as a result of bouts of micronutrient deficiency.
There's a third kind of malnutrition which has become an epidemic
in many parts of the world,
especially the richest countries, but also many middle income countries.
And that is malnourishment in excessive consumption of calories.
We have an obesity epidemic underway in the world.
And, it's estimated that roughly one third of all adults in the world are overweight
and perhaps, around 10 to 15% are obese.
When you add it up, the numbers are staggering.
Roughly speaking, we can say that between 800 million and
a billion people on the planet are chronically undernourished in
the sense that they do not get the daily energy intake in their diets
to be healthy and to be satisfied with what they're eating.
But another billion people who are not counted in the hunger category are in
the hidden hunger category.
So, roughly 1.8 to 2 billion people are undernourished
either in the direct sense of not enough energy intake or
in the sense of micronutrient deficiencies, and
then the estimates vary on obesity.
But it is certainly well over a billion people who are overweight and
several hundred million, perhaps 7 or 800 million adults, who are obese.
You add it up, it's plausible to think that around 2.8
billion people on a planet of 7.2 billion people
are malnourished, about 40% of the population.
We have a food crisis.
It varies in different parts of the world.
Sometimes it's hidden, sometimes it's the wrong kinds of food,
sometimes it's simply not enough food.
But any serious focus on a sustainable and
secure food supply for the world has to view the crisis in all its dimensions,
from those who lack the basic caloric intake to those who
ingrate unhappiness often are suffering from obesity, and
from all of the massive ill effects that come from that.
Let's have a look at where these problems are distributed.
Undernourishment is concentrated in tropical Africa, and in South Asia.
So we see in tropical Africa, especially in central and southern Africa,
that more than a third of the population is undernourished.
This means simply not enough calories or
by some measurements not enough calories and proteins needed for basic sustenance.
And in South Asia, we see the proportions
chronically undernourished are between a fifth,
20%, and a third, around 33%.
Serious levels of undernutrition, and fortunately,
in the rest of the world, lower levels than that in the high income countries,
very little undernutrition, in that sense though, massive problems
of malnourishment when one considers the problems at the other end of the spectrum.
When children are undernourished, of course,
they suffer a massive disability in their growth that lasts
a lifetime if the undernourishment affects them at
the critical growing stage in the early years of life.
And we measure that undernutrition with several
different concepts, but two are especially important.
One is stunting.
Stunting means that a child is undernourished to the extent
that the child is very short, Low height, that is, for age.
And the standard is measured against a regular distribution for
a normal population of height by age.
And then children who are far to the low end of that scale,
more than two standard deviations below the norm, are considered stunted.
And stunting, of course, reflects the inadequacy of dietary intake.
But it often also reflects chronic infection, worm infections for example
that where the worms take the nutrients that should be going to the young child.
Or other kinds of infections that the child is shedding nutrients,
maybe through bouts of diarrhea or
that make the nutrients not bioavailable to the child.
They can't be metabolized while the child is sick.
So when we see stunting, we usually are looking at
circumstances of chronic dietary undernourishment,
combined, very often, with repeated bouts of illness.
And the stunting we see is most severe where we normally find in tropical Africa.
And the highest stunting rates in the world in South Asia, especially in
India which overwhelmingly has the largest numbers of young children who are stunted.
The second concept for children is even more urgent.
And that is wasting.
Wasting is low weight for height, so
stunting is a chronic condition that means that the child doesn't grow.
Wasting is when the weight is even less than it would be for that low stature.
It's often a sign of acute, undernutrition,
life threatening under nutrition.
The kind of undernourishment that one sees in a famine, in a mega drought.
And then one sees children wasting and
there needs to be an urgent rescue through therapeutic foods and
often emergency procedures to help keep the children alive in those circumstances.
When we talk about undernourishment in general, we tend to separate,
and need to separate analytically, the chronic undernutrition.
Which is the day-in, day-out hunger that does lead to the stunting
from the acute episode of undernutrition that comes from disasters,
from displacement of populations, from drought.
And when those acute episodes occur, not only is the massive
suffering there can be massive death from the undernutrition.
In the worst cases, from starvation itself.
In other cases, from diseases which take advantage of the under nutrition and
the immunosuppression that comes along with the undernourishment.
There's also another massive reason for suffering that comes with acute episodes
of hunger that follow droughts and other disasters.
And that is the conflict often follows on.
Have a look at a map for the spring of 2012 when there were
two regions of Africa both battling drought.
Looking at the map which is a map that is used to measure emergency situations,
we see the acute food and security both in West Africa and in East Africa.
There were indeed large population movements,
resurgent violence, a civil war broke out in Mali, not only for
the reasons of hunger, but hunger stokes these conflicts.
And so this is another scourge that accompanies food crises.
When we turn to hidden hunger, it of course also is
lurking in populations where the visible hunger is also seen.
Now you're looking at a map of an estimate of the hidden
hunger of micronutrient deficiency.
Which kinds of nutrients are we talking about?
Vitamins such as vitamin A, or vitamin B in several of its forms,
iron, iodine, zinc, folates.
All crucial micronutrients that when not adequate in the diet,
can lead to terrible health disabilities, death in extreme cases,
and also very great dangers for child birth.
Mothers who don't have enough folates during pregnancy often
give birth to children with devastating defects.
And this is a pervasive condition that afflicts the poorest countries.
We see again, India and South Asia, much of tropical Africa,
the Andean region, some of the other countries of Western Asia and
of Southeast Asia, where there is considerable micronutrient deficiency.
Unfortunately, the knowledge and
the data of the hidden hunger are themselves hidden.
There are not precise estimates known for many of these, [COUGH],
micro nutrients in terms of where they really are seriously lacking in diets.
The next map shows you an estimate for vitamin A deficiency.
Again, regions of the world that you would expect, but a larger area of the world
even including many middle-income countries in Latin America and also China.
Now, let's look at the other end of the malnourishment spectrum.
One that also is causing a tremendous amount of morbidity,
in other words, disease and premature mortality.
And that is the obesity epidemic that is sweeping much of the world.
There have been enormous increases of obesity in the last 30 years.
What is obesity?
Obesity is a specific measure,
the typical definition is to use the so-called body mass index.
A person's weight in kilograms is divided by
the square of the person's height measured in meters.
And that BMI, the body mass index, if it's over 30,
is considered obese, if it's over 25, it's considered overweight.
And by that measurement we have a massive
epidemic of adult obesity in many of the high-income countries, 30% or
more in the United States and in some other high-income countries.
Why? Partly,
it is the total amount of caloric intake.
Partly, it's the type of calories being consumed, often carbohydrates,
trans fats, and other foods that are known as having high
glycemic indexes that they're easily, the sugars are easily metabolized.
Part of is the relative inactivity, In our new urbanized
environment where people sit, maybe watching television for hours at a time.
A combination of too many calories, the wrong kinds of calories.
And physical inactivity.
What to do?
A starting point is to combine
the food growing challenges with the nutritional science.
What should be grown?
What should people eat?
And here breakthroughs in nutrition science are giving us better indicators.
One of the leaders of modern nutrition and
rethinking what is wrong with our diet is Professor Walter Willett,
chairman of nutrition at Harvard University.
And he has proposed the right kind of food pyramid as it's called
shown here which depicts the kinds of food and
the relative frequency and amounts of those foods that should be eaten.
And just to indicate very briefly,
what the findings of modern nutrition are, because they're important.
It tells us that our diets as they evolved with the fast foods
of the high income countries, have become very imbalanced.
The source of this pandemic of obesity and over eating.
And what is needed is diets that are rich in vegetables, in fruits,
in vegetable oils, so-called unsaturated fats,
which are healthy as opposed to the animal fats and the industrial fats,
the so-called trans fats which can be very dangerous for health.
And when grains are eaten, they should be eaten as whole grains.
And so the dietary mix is quite different from the diet of the high income world
which is heavily concentrated in the wrong kinds of fats,
in refined grains rather than in whole grains, and
in a very heavy meat based diet, which has its own
great difficulties for health especially a large amount of beef eating.
I mentioned this because it's going to have a big consequence when we
discuss what kind of agricultural system
should be consistent with the kind of diet that is healthy for people.
Of course, this kind of food pyramid viewed from the perspective of
the poorest countries is a dream.
How can we get from where we are not even enough calories in the day to this kind
of balanced diet that can be healthy and
provide not only the macro caloric intake in proteins but also the micro
nutrients and the balance of different food components conducive to health.
The world is in increasing stress when it comes to the food system.
More mouths to feed, a rising demand for
meat products which amplifies the demand for the grains to feed
the animals that are being consumed in larger number.
All combined with environmental threats that are undermining
the stability of the food production itself in many parts of the world.
We've already gotten a taste of it, if I could put it that way in rising
food prices that are a major challenge for poor people in the world.
If you look at this graph of food prices since the late 1970s,
you see that for all of the major grains,
the staple grains, maize rice, wheat and the soy beans.
Prices were falling from the 70s until the end of the 20th century.
But since the beginning of the 21st century,
the price of food has been rising and rising sharply.
For wealthy people this is an inconvenience, a discomfort.
For poor people whose diets consume a much larger part
of the family income, this is more than just an annoyance or
a hindrance, it is a profound threat to their well being.
We see Engel's Law in operation here.
The idea that for poor people, the food consumption
occupies a much larger share of the total household income,
and therefore, rises in food prices can be very devastating for
households that buy their food from the marketplace.
So, here we have it.
40% of the world still not properly nourished and
a food supply under threat yet facing rising demands.
From growing populations and from parts of the world with
higher incomes putting even more intensive demands on the food supply.
Huge puzzles, what can we do about it?
We have to look closely now at how food is grown.
Where it's grown.
What the threats are.
What can be done about it.
