There is no one answer to treating depression and anxiety. A recent visit to MQ, a new charity funded by the Wellcome Trust to assess different approaches to treating mental illness such as depression, convinced me that my best bet is to combine multiple approaches: drugs if need be, mindfulness, exercise, therapy, but also to be careful with the food I eat.

I have never considered myself a bad eater. It wasn't as though I ate poorly before I became ill. At the height of my depressive episodes I couldn't eat at all but as I recovered, instinctively, I felt I could no longer take food for granted. If food is fuel, depressives need premium-grade help.

But it is hard to rigorously overhaul your diet during the worst of a mental illness. It is nonsense to tell someone suffering from acute depression to choose the fruit, vegetables and fish that might help them to feel better. When you're that ill you are in no position to decide what you eat, let alone find the right shops to buy the right ingredients. You are no different to someone suffering any other serious illness who struggles to eat anything at all; your best hope is to be fed soups, smoothies or soft foods that can be eaten easily.

Few pleasures with depression

Even as you get better, it is still hard to change your diet. There seem to be few enough pleasures in life when you are feeling low. Our emotional brains can associate eating sweet food with reward, reminding us of being comforted as a child. If eating a chocolate biscuit cheers you up, finding a healthier substitute when life is bleak is going to be difficult.

Anxiety can affect digestion, too. Our stomachs are often referred to as our second brain. When I was especially nervous, I found it hard to digest anything solid, just as I had when I was first ill.You also need to find a diet that fits into your life: in my case, a busy one with five children.

The answer for me has been to draw on the expertise of the nutritionist Alice Mackintosh at The Food Doctor, who has helped me switch from a typically English, meat and two veg diet to a Mediterranean-style one, full of tasty things cooked simply. Studies suggest that our brains are developed for a diet many of us no longer eat, but which sustained us for about 99 per cent of human history and 30 million years. The Mediterranean-style diet balances healthy sources of protein with complex carbohydrates.

In practice, this means lots of pulses, fruits, fish, nuts, cereals and olive oil. Sweetened desserts, fried foods, processed meats, refined grains and high-fat dairy products are to be avoided. This helps in two ways. The nutritional needs of your brain cells are satisfied by the antioxidants, vitamins, minerals, enzymes and phytochemicals that a Mediterranean-style diet provides. Secondly, this diet helps increase the amount of tryptophan in your system, the molecule from which serotonin, the brain's chemical messenger, is synthesised.

Post-alcohol low

I cut out alcohol. It can appear to help with anxiety in the short term by raising the levels of certain neurotransmitters in the brain (though the research is inconclusive). On a day-to-day basis, we need those chemical messengers to be busy sending messages brain cell to brain cell saying 'I feel happy.' Chemical receptors can also be affected by low iron levels. But after drinking, these neurotransmitters are broken down and excreted, which may make people feel low afterwards.

It is especially dangerous for those like me who feel most anxious in the mornings, since hangovers create a cycle of waking up feeling even more nervous and ill. I hardly drank before and certainly had not done so when ill; now I have stopped altogether.

There is strong evidence linking depression with good and bad fats. Fat is essential to the brain, which is itself 60 per cent fat. We want our brains to be made up of the good, unsaturated fats known as omega-6 and omega-3 essential fatty acids, rather than animal-based fats. We also need the correct ratio of omega-6 to omega-3 oils: most of us eat too little of the omega-3s.

Foods to add and subtract

I found the easiest way to put my research into practice was to make lists of what to eat more of and what to avoid, meal by meal.

At breakfast I go for sugar-free muesli with berries, porridge, wholegrain or sourdough toast spread with peanut butter, oatcakes with goat's cheese, eggs or other protein. Breakfasting well, combining protein and complex carbohydrates, is a good way to balance your brain chemistry for the rest of the day.

At lunch I eat protein-rich food such as chicken, turkey, fish or pulses with vegetables and salad are good. I avoid sandwiches, instead sprinkling nuts and sesame seeds on to salads to better combat anxiety.

In the afternoons I've found the best snacks are fruit and nuts, Brazil nuts in particular. If you can't resist chocolate (and I can't), at least make sure it is dark chocolate. It's never worth going hungry, as the brain needs that steady supply of nutrients to keep your mood on an even keel.

At supper I find that a meal rich in carbohydrates with the addition of some protein helps me to sleep better and improves my mood. Protein is important to help balance blood sugar before bed. Wholegrain pasta with a tomato and prawn sauce, a stir-fry with brown rice and chicken, or a baked or sweet potato with some cheese, even porridge sprinkled with nuts, are all good choices.