Although some research has produced mixed results,1 double-blind trials have shown that food allergies can trigger mental symptoms, including depression.2 3 People with depression who do not respond to other natural or conventional approaches should consult a nutritionist, like myself to diagnose possible food sensitivities and avoid offending foods.
Restricting sugar and caffeine in people with depression has been reported to elevate mood in preliminary research.4 How much of this effect resulted from sugar and how much from caffeine remains unknown. Researchers have reported that psychiatric patients who are heavy coffee drinkers are more likely to be depressed than other such patients.
However, it remains unclear whether caffeine can cause depression or whether depressed people were more likely to want the “lift” associated with drinking a cup of coffee. In fact, “improvement in mood” is considered an effect of long-term coffee consumption by some researchers, a concept supported by the fact that people who drink coffee have been reported to have a 58–66% decreased risk of committing suicide compared with non-coffee drinkers.
Nonetheless, a symptom of caffeine addiction can be depression.7 Thus, consumption of caffeine (mostly from coffee) has paradoxically been linked with both improvement in mood and depression by different researchers. People with depression may want to avoid caffeine as well as sugar for one week to see how it affects their mood.
There is evidence that people with major depression may have insensitivity to insulin and impaired glucose tolerance.8 Whether treatment of impaired glucose tolerance helps depression is unknown, but a doctor can order laboratory tests to detect such abnormalities, and initiate treatment as appropriate.
The amount and type of dietary fat consumed may influence the incidence of depression. Previous studies have found that diet regimens designed to lower cholesterol levels may reduce death from cardiovascular disease, but may also heighten the incidence of depression.9 Does low cholesterol cause depression? It appears not, since studies have shown no adverse effect on mood in people taking cholesterol-lowering drugs.10 11 The connection more likely has to do with the balance of fats in the diet. Diets to lower blood cholesterol usually focus on restricting total fat intake while increasing the intake of polyunsaturated fats (e.g., corn and soybean oils). These oils are very high in omega-6 fatty acids, but the recommended diets otherwise lack important omega-3 fatty acids (EPA and DHA). A high intake of omega-6 fatty acids relative to omega-3 fatty acids and an inadequate intake of omega-3 fatty acids (e.g., from fish and fish oils) have been associated with increased levels of depression.12 People who eat diets high in omega-3 fatty acids from fish have a lower incidence of depression and suicide.