Although all of us experience periods of intense sadness, true depression can range from mourning to chronic and complete disability, characterized by overwhelming feelings of hopelessness and suicidal thoughts. People who are depressed also find it difficult to function; they may have disturbed eating and sleeping and bowel habits, they can't concentrate, they can't enjoy anything in life and they frequently suffer low self-esteem.

What most people don't realize is how closely depression is tied in with diet. Although a lack of appetite can cause malnutrition and therefore depression, the reverse is also true: poor eating habits can cause depression by failing to provide the adequate nutrition necessary for proper functioning.

Many cases of depression may be due to too high or low levels of dietary fat. In the Italian study WDDTY reported on last month, virtually every single person who'd tried to kill himself had too low levels of cholesterol. Many other studies show that a very low fat diet also causes depression (see WDDTY Guide to Your Heart).

An earlier study which examined the suicide rates of 16 Western European countries found that suicide rates corresponded with the average intake of fat, particularly from animal products, but were unrelated to intake of total calories, protein, stimulants or alcohol (J Orthomol Med, 1990; 5 (1): 20-21.

Besides too much or too little fat, caffeine and sugar can make you depressed. Drinking more than 700 mg of caffeine a day (which translates into four or five cups of coffee a day) can cause depression, as can a diet with a large amount of refined sugar. Studies have shown that cutting out caffeine and sugar for as little as one week can lift depression, while adding them back to the diet can cause symptoms to resume. In one study, those patients who felt better were challenged with Kool-Aid, a sugary American drink, and daily doses of caffeine. About half showed a significant and sustained deterioration in mood right after the challenge (Behav Thera, 1988; 19: 4593-604).

Besides caffeine and sugar, food allergies and moulds have been proven to provoke depression. In fact, one study showed that the nearly a third of a group of depressed patients suffered from allergies, compared to only 2 per cent of schizophrenics (J Affective Disord, 1981: 3: 291); another found that 85 per cent of depressed children and adults were atopic that is, were inherently allergic (Compr Psychiatry, 1976; 17: 335).

One 67-year-old woman suffered from depression for many years. She also had a long history of diarrhea with abdominal pain and bloating. Once she was placed on an elimination diet, not only did her gut problems improve but she reported feeling much more cheerful, alert and confident. It was then discovered that milk was behind her bowel problems, and she eliminated it from her diet. Both her irritable bowel and depressive episodes disappeared.

The most usual deficiency in patients with depression is one of the B vitamins, which are powerful regulators of mood. Of all vitamin deficiencies, folic acid tends to be the most common; the average American only manages to consume 60 per cent of the US Recommended Daily Allowance for folic acid every day.

Depression is a common symptom of folic acid deficiency; at least eight studies have shown that patients with depression have lower levels of folic acid than other populations. The worse the depression, usually the lower the level of folic acid in the blood. The most common problem is affective disorder (BMJ, 1980; 281: 1036-42). Depressive illness has been shown to begin at the point where patients become deficient in folic acid (Biol Psychiatry, 1989; 25 (7): 867-72).