We've seen in this MOOC that a lot of progress has been made in understanding
many aspects of how diet and other lifestyle factors contribute to health and disease.
And yet, some urgent nutritional challenges that
we face in the modern world have not been solved,
including the epidemic of obesity,
diabetes, and heart disease.
Why have we not stopped to reverse the spread of these diseases?
The main limitation is not a lack of information,
rather we need new ways to think about the problem,
new approaches for interpreting the huge amounts of
information that we already have about the causes of these diseases,
and of identifying the most important unanswered questions
at which to direct new research.
The approach that we're using for this in
the Charles Perkins Center is nutritional ecology.
Nutritional ecology is the branch of biology that uses theory from the
ecological and the evolutionary sciences to understand nutrition.
It was developed to explore the diversity of
nutritional strategies in animals and we're now applying it to humans.
Why is ecological and evolutionary theory important in human health?
The reason is that chronic disease is
caused by the ways that people interact with their environments.
For example, which foods we choose to buy,
how much of them we eat,
and how our bodies respond to eating those foods.
Ecology and evolution are both sciences that specialize
in understanding the interactions of animals with their environments.
Ecology deals with the short term interactions, for example,
within a lifetime, and how these influence animals and their environments.
Evolution takes a longer view to understand how
the consequences of these ecological interactions accumulate over
many generations to cause evolutionary changes that make
animals better adapted to some environments and poorly adapted to others.
Through nutritional ecology the powerful theory
from ecology and evolution which has developed over
the past century and a half can help us to think more
clearly about the relationships between diet and health.
So what has nutritional ecology told us about why problems such as obesity,
diabetes, and heart disease have not been solved?
So there's many things of which I'm going to discuss two.
There's too much emphasis on linking a specific nutrient to a particular health problem.
So take, for example,
the argument over whether fats or carbs causes obesity.
It began over half a century ago and despite the best that science has thrown at it,
the debate remains unresolved.
Some people argue that fats are to blame,
others that carbs are to blame,
and the research has not managed to produce answers to settle the debate.
Nutritional ecology research on a wide variety of animals,
and now on humans, suggests that the problem is
not with the answers but with the question.
The confusion that has resulted from trying to pin the blame for specific diseases on
single nutrients is leading some scientists to
conclude that nutrients are the wrong level at which to approach the problem.
We should rather be directing our efforts at
the roles of foods or diets in health and disease.
Nutritional ecology tells us that nutrients,
foods, and diets are all important,
each provides the best level for understanding particular parts of the problem.
For example, the strong associations
between obesity and eating junk foods such as donuts.
But foods like donuts don't themselves interact with our physiology to make us obese;
rather it's the nutrients within donuts that
are absorbed into our blood and stored as fat.
Nutrients, and not foods,
are therefore the right level at which to think about
the physiological causes of obesity.
But to understand how those nutrients actually
get into our bodies to affect our physiology,
we need to understand why we eat donuts.
This can involve nutrients.
We might, for example,
eat donuts because we like the sweetness from
the high sugar content. But it will also involve other things including price,
advertising, availability, and so forth.
If donuts were more expensive or more difficult to find, we might eat less of them.
Foods are, therefore, an important level at which to understand
what fills our shopping carts and in turn enters our mouths.
The issue doesn't stop at foods.
Even though donuts could make us fat,
they won't necessarily do so.
In some circumstances they might have no effect, for example,
if eaten only occasionally as a treat or they might even
prevent diseases if fat and carbohydrate are lacking in the diet.
To understand the role of particular foods in health,
we therefore need to know how they combine with other foods to form the overall diet.
Are they a disproportionate part of the diet?
Are they an occasional treat with no health consequences?
Or are they necessary to help balance an otherwise imbalanced diet?
We should not, therefore, be debating whether nutrients, foods,
or diets are the right level for understanding the links between eating and health.
Rather they should all be included in our thinking so that we
can relate each to its specific roles in the problem.
Drawing on ecological and evolutionary theory
and on studies in a wide range of other species,
nutritional ecology therefore provides a systems approach for
understanding the links between human nutrition and health.
This considers the ways that nutrients are packaged into mixtures, foods, meals,
and diets, and how each of these levels links
our biology to the broader environment to influence our health.