Want to feel happier? Then smile, eat seaweed, get a new hairstyle, send fewer emails, go dancing, spend less money - and don't just pop pills. Or so says one of the country's most eminent scientists.

In a controversial new book, Professor Jane Plant, a chief scientific adviser to the government, proposes a raft of unorthodox treatments for the millions of Britons who suffer from anxiety, stress and depression.

Instead of just popping 'happy pills' such as Prozac to beat the blues, Plant and her co-author, Janet Stephenson, advise sufferers to take steps such as avoiding dairy products, sending fewer text messages, eating porridge at night and playing card games. They say all their tips are based on hard scientific evidence gathered from studies around the world.

'Smiling is a way of tricking your brain into thinking that everything's OK, even if it's not,' said Plant. 'People who are mildly depressed should do their best to show the world a happy face, as that will improve people's reaction to you and lift your mood.'

In Beating Stress, Anxiety and Depression, Plant and Stephenson urge a radical overhaul of the way the NHS treats the soaring number of people with some form of mood disorder. They advise sufferers to increase their intake of mood-boosting chemicals by eating kippers or poached haddock for breakfast because they contain omega-3 fatty acids, and to be less materialistic, as those who achieve success may do so at the expense of personal relationships, which are a better guarantee of happiness.

The authors are serious figures. Plant, a professor of environmental geochemistry at Imperial College in London, is the government's chief adviser on toxic chemicals and a trustee of Prince Charles's Foundation for Integrated Medicine, while Stephenson is an NHS psychologist.

'We do not agree with the usual advice to "keep taking your medication and eventually all will be well, because doctor knows best",' they write. 'We challenge many of the conventions in the treatment of mental illness.' The authors say their aim is to empower people suffering with a mental disorder.

They say that anyone with low self-esteem should ignore celebrity culture as much as possible because it may make them feel even worse when they don't match up to pop stars or TV presenters.

They also recommend improving your appearance through a new hairstyle, clothes or make-up because this can improve self-confidence. And people should definitely smile, even if they are feeling down.

One in six people can expect to experience depression, however briefly, at some point in their lives, and around 2.4 million are affected by an anxiety disorder. A large-scale study recently suggested that Prozac and similar drugs may have little value.

The National Institute of Clinical Excellence already says that psychological 'talking therapies', involving one-on-one sessions, can be just as effective as giving someone drugs. Antidepressants alone cost the health service £300m a year and most family doctors admit that they prescribe too many.

Plant and Stephenson argue that human contact, face-to-face or over the telephone, and the 'people skills' to both talk and listen meaningfully are useful. However, emailing and texting are individualistic and isolating processes which people should do less.

The distinguished neurologist Lord Walton of Detchant, a former president of the British Medical Association and the Royal Society of Medicine, praised their work. In the latest issue of the journal Science in Parliament, he writes that it is an 'admirable book, which would do much to alleviate the fear, helplessness and hopelessness which many feel when suffering from mental ill-health. Many sufferers from stress, anxiety and depression will find invaluable information, guidance and comfort.'

Paul Corry, of the mental health charity Rethink, said the authors were right to stress that some patients could be successfully helped with non-drug treatments, such as talking therapies and lifestyle changes.

And sufferers should always receive a personally tailored treatment plan rather than routinely being given antidepressants. But he argued that there was less evidence to back claims that certain foods could help alleviate the symptoms of mental health disorders.

'The evidence base for food's claimed benefits to mental health - for example, the idea that consuming omega-3 fatty acids will improve the flow of chemicals in the brain - is really, really weak,' said Corry. 'We certainly wouldn't recommend that you could eat or drink your way out of depression, anxiety or schizophrenia, although they do have a role to play.

'[But] long-term unemployment, poor housing, lack of money and limited social contact are more important non-drug determinants of mental illness than food and drink.'

How to beat the blues

· Smile more, spend less and be less materialistic.

· Get a taste for seaweed - and sushi. Breakfast on a grilled kipper or poached haddock topped with an egg. Eat porridge, but only last thing at night.

· Chocolate should have at least 70 per cent cocoa. Drink filtered water - and treat yourself to a smoothie.

· Get a new hairstyle, put on your make-up and go dancing. Or play darts, cards or dominoes.