Genes
and
lifestyle:
Are we victims of our own
success?
Source: Harvard Men's Health Watch
Publication Date: 12/01/2006
"What a piece of work is
a man."
As usual, Shakespeare got it right. At their best, humans appear to
have a
limitless ability to imagine and create, to innovate and build, to
aspire and
achieve. As man's dreams in the 20th century became realities, he
established a
way of life that is beyond the wildest imagination of his grandparents.
Yet for
all its advantages, life in the information age presents potential
perils as
well as unparalleled opportunities. Unfortunately, some of those perils
contribute to diseases that were rare a few generations ago but
approach
epidemic proportions today.
A scientist speculates
Writing in the August 2004 American Journal of Medicine, Dr. George P.
Chrousos
of the National Institutes of Health explains the potential hazards of
a
mismatch between human genetics and human behavior. At the core is the
body's
stress response. It involves the brain, especially the hypothalamus,
the
pituitary (or "master") gland, the sympathetic nervous system, and
the adrenal glands. In response to stress, this intricate network pours
out
several hormones such as cortisol and other glucocorticoids, adrenaline
and
other sympathomimetic amines, vasopressin, and interleukin 6 and other
cytokines that mediate inflammation and immunity.
You don't have to be a scientist to know how the stress reaction feels
and
looks. Your heart beats faster and harder, and your blood pressure
soars. Your
breathing gets faster and deeper, and your pupils widen. Your muscles
tense up,
and your hair may bristle a bit. Your skin becomes cool and clammy,
your mouth
gets dry, and your stomach may churn with tension. You feel alert and
awake but
tense and nervous.
The changes that go on inside your body are just as impressive. Stress
activates your clotting mechanisms and turns up the immune system.
Blood sugar levels
rise, white blood cells pour into circulation, and urine production
slows.
These changes prepare humans to cope with danger. But they evolved when
the
dangers were predators, privation, and physical dangers. Today, most
Americans
live in a protected world of plenty. Our world has changed, but the
stress
response has not.
In his essay, Dr. Chrousos reviews how the mismatch between our genes
and our
lifestyle may contribute to some important contemporary diseases; a
modified
version of his table is below.
Genes for survival, genes for disease
Threats
to survival |
Genetically determined survival responses |
Contemporary diseases that may result |
Starvation |
Energy conservation |
Obesity and diabetes |
Dehydration |
Retention of salt and fluids |
High blood pressure |
Infection |
Potent
immune system |
Autoimmune and allergic diseases; septic shock
syndrome |
Adversaries |
Arousal and fear |
Anxiety and insomnia |
Dangerous
situations |
Withdrawal from danger, escape |
Depression
and social isolation |
Tissue strain and injury |
Preservation of tissue integrity |
Pain and fatigue syndrome |
Bleeding |
Promotion of clotting |
Heart attack and stroke |
Source:
American Journal of Medicine 2004; 117:205.
As an endocrinologist and
geneticist, Dr. Chrousos calls for more
research into
the survival genes that were once adaptive but are now harmful. He
hopes this
knowledge will lead to preventive measures and identify targets for
drug
development. It's a hope we all share -- but we don't have to wait for
breakthroughs in genetic engineering to correct this imbalance between
our
genes and our lifestyle. We should adapt to the dietary patterns and
exercise
habits that will keep our genes happy and our lives healthy and
enjoyable.
On the run
Think about it. Our earliest ancestors depended on their physical
prowess for
survival. Life itself hinged on obtaining food by hunting and
gathering, both
strenuous activities. Finding shelter, evading predators, and coping
with the
whims of Mother Nature also required strength and endurance along with
a quick
wit.
Anthropologists tell us that at the dawn of humankind, in the late
Paleolithic
era, people lived in small bands that roamed over large areas to find
food and
shelter. Human population was sparse; scant resources, low fertility,
and a
hostile environment limited population to a density of just one person
per
square mile. Society was simple, with most of the people performing
identical
tasks. The most important task was obtaining food. Typically, it was a
question
of feast or famine. One to two days of virtually continuous physical
activity
were required to obtain sustenance. These bursts of exercise were
followed by
several days of feasting and celebration -- but even during these
primitive
holidays, our ancestors were amazingly active, dancing, playing, and
traveling
up to 20 miles on foot in a single day to visit and trade with other
clans. All
in all, an average day's physical activity burned up about twice as
many
calories as a typical American uses today.
The "all-natural" diet
Stone Age people hunted wild game, trapped fish, and gathered fruit,
nuts,
seeds, and tubers. They weren't able to store food, so they ate what
they could
when they could. The result was feast or famine; even today, the human
metabolism remains dedicated to storing calories in body fat to provide
fuel in
time of need.
The Stone Age diet was high in protein but very low in fat. Meat was a
major
source of protein, but wild game was lean and low in fat because the
animals
ran free and eked out a subsistence living on vegetation -- no pens,
grain
bags, antibiotics, or hormones for them! Dairy products were unknown,
and
carbohydrate consumption varied, but the primitive diet was very high
in fiber
and had plenty of vitamins, iron, and minerals -- except for salt,
which was
scarce. Caloric consumption was up and down, probably averaging about
3,000
calories a day.
Cultivating change
Change came slowly in the Stone Age. Hunting and gathering remained the
dominant way of life for about 30,000 years. But about 10,000 years
ago, humans
learned how to cultivate crops and domesticate animals, making life
easier and
more predictable. The population density increased, creating the need
for
specialized occupations and creating social hierarchies, so people
became a
source of stress. For most folks, farming and herding required nearly
as much
physical work as hunting and gathering, but farming produced a new way
of
eating.
Grains, cereals, and tubers became the main vegetable foods, and wild
game was
replaced by dairy products and meat from farm animals. As man became
dependent
on a few crops, dietary diversity suffered and nutritional deficiency
diseases
arose. Periodic crop failures produced epidemics of malnutrition and
starvation. Stored food often spoiled, and microbes passed freely from
animals
to humans and from person to person in the new villages and towns. New
diseases
replaced old problems, keeping the average Agricultural era lifespan at
about
30 years, a minimal improvement over the hunter-gatherer's life.
The industrial revolution
The agricultural way of life still prevails in much of the developing
world,
but in the 19th century, the industrial revolution produced incredible
changes
in the United States
and Europe. Labor-saving devices
made life much easier,
replacing physical labor with mental work. New agricultural methods
made food
cheap and plentiful. Technology and mass production made refined
grains, sugar,
and salt -- to say nothing of tobacco and alcohol -- readily available.
Our
brave new world was born.
The information age
Modern science has accelerated the pace of change and has spread
technological
advances to the far corners of the globe. Life is much better (and much
longer)
today then ever before, but some good things have been lost. Exercise
is one,
dietary diversity another. We've replaced hoes with tractors, brooms
with
vacuums, and stairs with elevators. Fresh foods are out, refined,
processed
foods in; that means less fiber and vitamins but more salt, sugar, fat,
and
calories. Freed from physical labor, people have used their heads to
carry
science and technology to new heights, creating a society of
unprecedented
affluence and convenience. But progress has its price. Mental stress is
one
example, environmental pollution another.
Sedentary living and processed foods extract a price both in health and
in
dollars. Our genes retain most of the Stone Age imperatives, but life
in the
fast lane does not. Human DNA cannot provide a substitute for the
exercise that
has all but vanished from contemporary work stations. The human
metabolism is
still programmed to cope with the Stone Age threat of starvation, not
the
burden of overabundance. Evolution is too slow to have yet produced
ways to
manage today's high-calorie, high-salt, high-fat, low-fiber diet. The
body has
no new enzymes to fight the effects of tobacco, excess alcohol, and
illicit
drugs. The nervous system remembers how to respond to the threat of a
saber-toothed tiger but has not figured out how to cope with a raging
boss or
rush-hour traffic. And as industrial pollution changes the environment,
a sea
of toxins presents new challenges to human genes and human health.
Good genes, bad genes, old genes, new
genes
Most of us are lucky enough to have a perfectly healthy set of genes.
But some
of us have inherited abnormal genes that cause disease. In some cases,
just one
or two abnormal genes among the human complement of some 30,000 genes
can wreak
havoc; cystic fibrosis and sickle cell anemia are examples. And in the
final
analysis, all cancers arise from flaws in the genes that regulate cell
growth.
Gene therapy is an experimental attempt to treat disease by introducing
healthy
genes into patients' cells. It's a tricky business. "Naked" DNA, the
genetic material, is not suitable, so scientists attach the DNA to a
delivery
device, or vector. In one approach, the DNA is attached to a chemical
vector,
such as a form of fat called a liposome. In the other, more promising,
technique, the DNA is injected into a virus, which is then allowed to
infect
the patient's cells, carrying the new gene along with it.
Does it work? Not yet. Hundreds of gene therapy trials have been
performed
during the past 15 years, including several dozen attempts to treat
prostate
cancer. Some partial successes have been reported -- but so have some
major
side effects.
Scientists at the forefront of gene therapy research remain optimistic.
Still,
clinical applications are a long way off. For now, we'll have to settle
for the
genes we have -- and that means adopting the lifestyle suited to our
healthy
genes. It's a shame to squander good genes with bad habits.
Back to the future
Molecular medicine is on the verge of making genetic engineering a
clinical
reality, but it can't possibly bring Stone Age genes up to Space Age
standards.
Since science can't reshuffle your genes, the only way for you to
restore
nature's balance is to adopt a more natural lifestyle.
Fortunately, you can get back to basics without returning to the farm,
much
less the savannah. Here's how:
Eat well. Consume a variety of foods to restore nutritional diversity.
Favor
vegetable-based foods that provide essential vitamins and minerals. Eat
whole-grain products that contain the fiber you need. Avoid animal fat;
get
your protein from fish, poultry, beans, and legumes. Reduce your
dependence on
processed foods, salt, and simple sugars. Eat smaller meals on a
regular
schedule, balancing your caloric intake with your expenditure of
energy.
Exercise regularly. Add physical activity to your daily life by
climbing
stairs, walking instead of driving when possible, and carrying your own
parcels. Set aside 30-45 minutes nearly every day for moderate
exercise;
walking, jogging, biking, swimming, dancing, gardening, and tennis are
good
examples. For best results, add exercises for balance, stretching
exercises,
and prudent resistance training.
Control stress. Balance work and play, stimulation and relaxation,
companionship and solitude. Achieve all you can, but take time to enjoy
every
day.
You don't need a spear or loincloth to get back to basics. You can
incorporate
the best aspects of modern life to live naturally, enjoyably, and
healthfully.
It's all in your genes.
Copyright ©
2006 by President and Fellows of Harvard
College.
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