杏吧原创

FEEDING and fasting have dramatically different effects on the immune
system.

Until now, most doctors and nutritionists have rejected the idea of feeding a
cold and starving a fever as an old wives鈥� tale. But Dutch scientists have found
that eating a meal boosts the immune response that destroys viruses like those
that cause colds, while fasting stimulates the response that tackles the
bacteria to blame for most fevers.

鈥淭o our knowledge, this is the first time that such a direct effect has been
demonstrated,鈥� says Gijs van den Brink of the Academic Medical Center in
Amsterdam. At a Christmas dinner, he and his colleagues decided to take blood
samples to see if alcohol affected the immune system.

To their surprise, later analysis suggested that alcohol had no effect but
food did. So the team asked six volunteers to fast overnight and then come into
the lab for tests. On one occasion they were given a liquid meal, on the second
just water to distend the stomach.

The results were striking. Six hours after the liquid meal, the volunteers鈥�
levels of gamma interferon had more than quadrupled. Gamma interferon is a
hallmark of the cell-mediated immune response, in which killer T cells destroy
any cells that have been invaded by pathogens. 鈥淭his type of immunity is mainly
directed against viral infections,鈥� van den Brink says. 鈥淚t seems to be
stimulated by food.鈥�

But when the volunteers only drank water, levels of gamma interferon fell
slightly over the next six hours, while levels of another chemical messenger,
interleukin-4, nearly quadrupled. Interleukin-4 is characteristic of the humoral
immune response, in which B cells produce antibodies that attack pathogens
lurking outside our cells. This response is needed to tackle most bacterial
infections, van den Brink says.

This fits neatly with recent findings by Paul van Leeuwen of the Free
University Hospital, also in Amsterdam. Leeuwen鈥檚 team has discovered that
glutamine, an amino acid common in milk, meat and some nuts, boosts the
cell-mediated immune response, his colleague Petra Boelens told a recent
conference in Australia.

The work followed an earlier study published in The Lancet (vol 352,
p 772) showing that patients in intensive care are less likely to succumb to
infections if given glutamine supplements.

Van den Brink speculates that the immune response that follows eating evolved
as an energy-saving ploy. Whereas most bacterial infections need an immediate
response, he says, tackling a virus can wait until we have more energy, since
most viruses we encounter are ones we鈥檝e already been exposed to and are not a
serious danger.

He cautions that people should not change their behaviour after such a small
study. But he thinks finding out exactly what stimulates the different responses
will be useful: 鈥淐ertain foods could be given to critically ill patients to
stimulate the right immune response.鈥�