快猫短视频

THERE鈥橲 a carnival atmosphere in the main exhibition hall. Colourful banners hang from the ceiling and below them the stands advertise their wares with elaborate displays, upbeat music and free souvenirs. Like barkers, attractive sales people use big smiles and warm handshakes to entice conference delegates into their booths. Underneath a thin veneer of camaraderie, the competition is intense. Most are hawking a single class of drugs 鈥� antidepressants with familiar names such as Prozac, Zoloft, Wellbutrin, Paxil and Celexa. Luckily for them, there seems to be an insatiable appetite for their products.

In a quiet corner, far from the banners and videos, Joseph Hibbeln is peddling an alternative. Unlike the other exhibitors at the American Psychiatric Association meeting, Hibbeln has no drugs to offer. Instead, the psychiatrist and biochemist from the National Institutes of Health near Washington DC is selling his idea that we are eating ourselves into a collective depression by consuming the wrong sorts of fats. If he鈥檚 right, the cure could be as simple as a change in diet. It鈥檚 a radical idea but a growing number of nutritionists, psychiatrists and biochemists are buying it.

The stakes are incredibly high. Globally, more working days are lost through depression than any other illness and it is one of the most serious health threats worldwide. Affluent countries are the worst affected. In Britain, 1 in 10 people are depressed, and possibly anxious too. For 1 in 20 it鈥檚 a chronic, lifelong condition. In the US, people born after the Second World War are twice as likely to develop the illness as their parents, and the age at which it first strikes is falling.

As well as being a threat to health, depression is hugely expensive. Medication is the treatment favoured by doctors and patients alike: over 22 million prescriptions were written for antidepressants in England in 2000, a rise of a third in only 10 years. In Britain as a whole, the bill for these drugs stands at 拢296 million a year, while the cost associated with loss of production and invalidity benefits is as high as 拢8 billion each year. It needn鈥檛 be like this, believes Hibbeln.

Drugs may have a place in treating depression but, he points out, despite decades of research, our understanding of the illness is still very sketchy. Everyone accepts that its causes are many and complex, with both genes and environment playing a role. While it is convenient to lump together people with similar symptoms, depression probably isn鈥檛 a single condition, which may help explain why it鈥檚 sometimes difficult to find the right drugs regimen for patients and why some people never respond to medication. For Hibbeln, the upsurge in the number of people diagnosed as depressed over the past few decades suggests that there may also be some common factor affecting a large proportion of the population. Find out what that is, and you can tackle the modern epidemic of depression at its root.

Hibbeln distinctly remembers when he first realised that fats might be the key. 鈥淥ne day I was standing in a lab, holding a human brain in my hand, and it suddenly hit me 鈥� the brain is all fat,鈥� he recalls. 鈥淭here is no difference between a stick of butter and your brain.鈥�

He knew that fats in the brain could easily be altered by diet, and wondered if the composition of brain fat might influence our mental health. After all, dietary fats can affect our health in other ways. Saturated fats, mostly from animal-based foods, have been blamed for various forms of cancer, including breast and colon tumours, as well as heart disease. Fats can have beneficial effects, too. One type of polyunsaturated fatty acid called omega-3 can dramatically improve the prospects of patients with cardiac problems. Hibbeln began to wonder whether omega-3 might also be important in the brain.

Looking at the changing patterns of omega-3 consumption persuaded him he might be onto something. For a start our modern intake is very different to what our ancestors were eating when the human brain evolved. They roamed the savannahs hunting for wild game, ate lots of leafy greens and seem to have had a taste for fish and seafood, all of which are high in omega-3s. With settled agriculture, which began about 10,000 years ago, people started to rely on cultivated foods, and the consumption of fish and wild game declined. The result was a decrease in omega-3 intake and an increase in the alternative type of polyunsaturated fatty acid, omega-6 (see Diagram).

But the most dramatic change in what we eat has happened in the past century, with industrialisation and the development of the food industry. Manufacturers favour foods with long shelf lives, so they mostly use soy, corn, palm and cottonseed oil. All contain high amounts of omega-6 fatty acids and very little omega-3, a balance that is further skewed when the oils are hydrogenated to make them keep even longer. According to Hibbeln, the average annual consumption of soy oil in the US stands at 11 kilograms, a thousandfold increase in less than 100 years. It accounts for 83 per cent of all the fats we eat. And while we ladle on the omega-6s, most of us eat few of the foods that are high in omega-3s such as fatty fish, walnuts, flax seed and olive oil. As a result, our diets now contain 16 times as much omega-6 as omega-3, whereas a century ago we would have been getting about equal amounts of each. 鈥淣o body could adjust that fast,鈥� says Hibbeln.

But could this highly unbalanced intake of essential fatty acids actually change the composition of the brain and alter mental health? There are several lines of evidence that suggest diet may indeed play a major role in depression and other mental conditions.

First, fats could influence brain signalling. 鈥淎ll chemical and electrical signals must pass through the outside walls of brain cells,鈥� says Hibbeln. 鈥淭his membrane is composed almost entirely of fats. Neuronal cell membranes are, in fact, 20 per cent essential fatty acids.鈥� Embedded in the membranes are ion channels, through which electrically charged particles must pass if a signal is to be sent. These channels are folded into complex and delicate shapes which are crucial to the way they work. 鈥淎s they change shape, they either allow the flow of the signals, or stop them,鈥� says Hibbeln. He believes that the composition of the fats holding the ion channels affects their shape and so influences their function. Fatty acids affect cell flexibility in other tissues, so Hibbeln thinks the balance between omega-3 and omega-6 is equally important in the brain.

Fatty acids have also been linked to the neurotransmitter serotonin, which inhibits the transmission of nerve impulses across brain synapses. Antidepressants boost serotonin levels. Hibbeln has found that people with little omega-3 in their spinal fluid seem to have low levels of serotonin. And in 1999 researchers Sylvia de la Presa Owens and Sheila Innes at the University of British Columbia found that 18-day-old piglets whose feed contained omega-3 fatty acids had twice as much serotonin in their brain frontal cortices as those on standard feed. 鈥淓arly in development, serotonin acts as a signal to guide migrating neurons to their correct locations,鈥� says Hibbeln. 鈥淪erotonin also assists the correct growth of axons and dendrites.鈥� So lack of omega-3 fatty acids early in life may forever alter the way the brain develops and operates. This much has been widely recognised with the move to add the omega-3 fatty acid docosahexaenoic acid (DHA) to infant formula milk.

But no one is sure exactly how DHA and other omega-3s might boost serotonin and affect mood. Perhaps brains containing more omega-3s are more efficient at producing serotonin and other neurotransmitters. That鈥檚 because the metabolism of these brain chemicals is catalysed by enzymes within the cell membranes of neurons. And the composition of fats in the membranes may affect the efficiency of these enzymes just as it affects the ion channels.

Fishy business

DHA may also improve mood in other ways. Researchers know that supplements of DHA promote brain cell and synapse growth and seem to protect those cells from dying. Hibbeln points out that neuronal damage caused by stress seems to be linked with depression. Also, recent research with brain scans shows that overall blood flow improves with DHA intake. Some researchers have suggested that poor blood flow within the brain might trigger depression.

More remarkably, cross-cultural studies demonstrate a strong relationship between a nation鈥檚 consumption of fatty acids and its level of depression. Hibbeln has found that in countries where people eat the least fish the rate of depression is highest, and vice versa. The average New Zealander, for example, eats only 18 kilograms of fish a year and 6 per cent of the population suffers from depression. In Japan, where they eat 64 kilograms of fish a year, depression strikes fewer than 1 per cent of people. This correlation holds true across the world. Intriguingly, when a Western diet full of processed and fried food infiltrates a culture, as it has in places like Greenland, the rate of depression rises accordingly.

There may, however, be confounding cultural reasons why rates of depression fluctuate between countries. 鈥淭he cross-cultural work is always dicey because so much is different. What else is the same about cultures that eat a lot of fish?鈥� asks Peter Kramer, author of Listening to Prozac. He says that in many Asian countries depression is considered shameful and so is probably under-reported. In other cultures, it may go unreported because it is not seen as abnormal.

But Hibbeln is convinced there鈥檚 a real correlation between depression and low omega-3/high omega-6 consumption. What鈥檚 more, he says, the imbalance leads to other mental disorders. As evidence he has chart after chart with the same high-to-low right-sweeping curve: countries where people eat lots of fish have lower rates of homicide, bipolar disorder and suicide. Hibbeln has also found varying omega-3 fatty acid levels in breast milk across countries, with low levels in women from non fish-eating cultures. Those same women have most post-natal depression. So we have unhappy mothers with little omega-3 to pass along to babies who are in the middle of rapid brain growth.

Taken together, all this has been enough to persuade some doctors to try altering their patients鈥� fatty acid consumption. In the late 1990s, Andrew Stoll of Harvard University conducted a study on 30 patients with bipolar disorder. After four months, those given high doses of fish oil capsules had significantly longer breaks from their depression than those on a placebo. 鈥淲e found that the controls were much more likely to cycle back into mania or depression while those on fish oil remained stable for a long time,鈥� says Stoll. 鈥淚 think these compounds have more of a positive effect on depression, but it鈥檚 the mood cycling that was really affected.鈥�

In another study, Malcolm Peet鈥檚 team from Sheffield University gave large omega-3 doses to 70 depressed patients who hadn鈥檛 been helped by drugs such as Prozac. At 12 weeks, 69 per cent of these patients showed marked improvement compared with 25 per cent given placebos. And this spring, Boris Nemets and colleagues from Ben Gurion University in Israel reported that depressed patients who weren鈥檛 responding to drugs showed significant progress within two weeks of taking fish oil high in the omega-3 fatty acid eicosapentaenoic acid, (The American Journal of Psychiatry, vol 159, p 477). By week four, six of the 10 taking fish oil had a 50 per cent fall in symptoms such as low mood, insomnia and feeling worthless. Only one of the 10 patients on placebo improved similarly.

The outlook is so promising that there are at least 10 ongoing clinical trials testing omega-3 fatty acids as treatments for depression and other mental disorders such as schizophrenia and attention deficit disorder. And most mental health workers are open to the idea that fatty acids are an intriguing avenue for understanding mental conditions. 鈥淸This is] careful work and it鈥檚 intuitively appealing,鈥� says US psychiatrist Kay Redfield Jameson. Both she and Kramer admit to increasing the amount of omega-3 fatty acids in their own diet. The consensus view is so positive that even the National Institute of Mental Health in the US is taking notice. Acting deputy director Wayne Fenton says he would like to see more studies to test the potential of omega-3s as a treatment for mental disorders.

If these clinical trials prove Hibbeln right, the treatment of depression is in for major revision. So far, the drugs companies don鈥檛 seem to be taking the threat very seriously. 鈥淎ntidepressants are recommended as first line therapy for depression because they are consistent,鈥� says Mike Fleming, spokesperson for GlaxoSmithKline, which makes the antidepressants Paxil and Wellbutrin. 鈥淎lso, medication can be used even when talk therapy is not available.鈥� Other firms such as Eli Lilly, manufacturer of Prozac, and Forest Laboratories, which makes Celexa, did not respond to repeated calls asking for comment on this new research approach.

But the drugs companies ought to be worried. Here is a fix that has no side effects. After all, eating more fish, flax seed and walnuts while using olive oil and cutting down on processed food, can only make you healthier, if not happier. The companies might also note that fish oil and specially manufactured omega-3 fatty acids made from seaweed are available in capsule form over the counter at health food stores. So even those of us who aren鈥檛 strong-willed enough to make radical changes to our diet have a prescription-free alternative. It鈥檚 enough to make anyone smile 鈥� except, perhaps, those in the pharmaceuticals industry.