Serotonin is an important neurotransmitter in the brain, particularly in the frontal lobe. This is an area that needs to be vitally enhanced in depressed patients. The brain can make no serotonin unless tryptophan is first present. Most depressed patients have a loss of appetite (appetite increase occurs in only a minority of the depressed).ⁱ Thus, the foods that they do eat should have an abundance of tryptophan. Foods that are high in tryptophan are listed in Figure 1.ⁱⁱ

Note that whole milk has the lowest amount of tryptophan on the list, though many people believe that milk is one of the best sources of tryptophan. Fortunately, there are better sources, with tofu (soybean curd) being the best source on this list.

Some depressed individuals are very sensitive to even a small, temporary reduction in tryptophan, and missing just one day of the moderate to high tryptophan intake can send them into a relapse of depression.

Getting enough tryptophan is not the only nutritional factor in serotonin production. As standard in the preceding chapter, five large amino acids complete against tryptophan in traveling to the brain. A food that contains a large total amount of these five amino acids will reduce the flow of tryptophan to the brain.ⁱⁱⁱ

Thus, if our diet is moderate in tryptophan but high in those five amino acids, we may still develop a tryptophan deficiency in the frontal lobe of the brain. The amount of tryptophan compared to the amount of the five amino acids is the critical yardstick.

Foods with high ratios of tryptophan to these five competitors are shown in Figure 2.^iv

Figure 2 shows that whole milk has a low amount of tryptophan compared to the five amino acids. It also contains a very little quantity of tryptophan, as shown in Figure 1. These factors work together to render milk of less value in supplying the brain with tryptophan.

Tofu, however, is in sharp contrast to whole milk. It has a high amount of tryptophan relative to the five amino acids, and high quantity of tryptophan. This makes it an excellent food for supplying a high quantity of tryptophan to the brain, which enhances the production of serotonin, which in turn combats depression.

Once sufficient tryptophan is in the brain, other lifestyle issues are crucial in the production of serotonin.

Omega-3 fats are emerging as an important nutritional element in the brain science.^v There are actually two types of fat that are absolutely essential in our diets- omega-6 and omega-3 fats. The omega-6 fats are abundant in many foods, so it is extremely rare to see mental or physical problems develop due to a shortage of omega-6. Omega-3 fats are not so abundant, so it is more common to see adverse effects from a diet to low in omega-3.

Tryptophan tends to be low in the diet when calorie intakes are low, but omega-3 can be too low in the diet even if calorie intakes are more than adequate.^vi Even a high fat diet can be too low in omega-3, particularly when the ratio of omega-3 to omega-6 in the diet is low. Interestingly, the ratios of these two fats in the blood do have a direct relationship to rates of depression.^vii

The lower the omega-3 to omega-6 ratio, the higher the rate of depression. Recent research demonstrates that bipolar disorder (manic-depression) in addition to major depression (unipolar disorder) can be helped by a diet high in omega-3.^vii

Most people increase their omega-3 fat intake by eating fist. Most fish, however, are not good sources of omega-3 fats. Cold water fish are good sources, not because their bodies manufacture omega-3, but because they eat a lot of cold saltwater seaweed, which is very high in omega-3 fats. It is important to note that the original sources of omega-3 fats are plant sources, and when we obtain our omega-3 from fish we are getting the nutrients second-hand. The omega-3 content of certain fish is listed in Figure 3.^ix

Note that wide variation in omega-3 content from one kind of fist to another. For example, drum fist, which has the lowest omega-3 content, has only 25 percent as much as Atlantic mackerel.

There are many benefits of a diet with adequate omega-3 fat, but there is a downside in getting it from fish: many fish have unnatural toxins in their bodies due to pollution. 

Folic acid (or folate) deficiencies can be a direct cause of depression.^x I have found this a much more common cause of depression in meat-eaters than in vegetarians. People with an omega-3 deficiency seem to have similar depression rates whether they are meat-eaters or vegetarians.

The RDA (recommended daily allowance) for folate is 400 micrograms. As you can see in Figure 4, which list the folate content of foods, it would require an enormous quantity of meat to obtain 400 micrograms. On the other hand, it is very easy to obtain a minimum of 400 micrograms with a diet based on plant foods, as the figure demonstrates.^xi

Patients who are depressed due to a folate deficiency tend not to improve at all with standard antidepressants. The real treatment is simple—foods high in folate.

Another nutrient that is vital for optimal brain functions, including avoidance of depressed mood, is Vitamin B12.^xii Plant sources that are not fortified do not contain B12 unless they are brown in I recommend the fortified plant sources of B12 as the best way to obtain B12. If a vegetarian does not have access to regular use of the fortified plant sources or B12 supplements, then I recommend the regular use of skim milk.

When Dr. Dean Ornish began to study how coronary artery disease (the disease that leads to the leading cause of death in America) can be reversed by a healthy vegetarian diet, many people though that such a diet could easily bring about depression or anxiety. Since only a minority of Americans are vegetarian, it was thought that adherence to such a diet would decrease social affiliations, increase anxiety over a “strict regimen,” and be less tasty or satisfying.

To help determine whether these assumptions were valid, Dr. Ornish’s research group surveyed both the vegetarian-treatment group as well as the non-vegetarian control group. Each participant was asked to fill out a questionnaire before and after the study regarding his or her psychological distresses. They were asked to rate their degree of anxiety, depression, insomnia, and their inability to experience pleasure (anhedonia). These four distresses were totalled to yield a distress index level for each participant.

It came as a surprise too many that after one year it was the vegetarian group that not only felt better physically, but mentally as well. They had a decrease in depression and anxiety, fewer problems with stress, and improved interpersonal relationships.^xiii Many mistakenly believe that their overall enjoyment of life will deteriorate if they change to a healthy lifestyle, especially if they become vegetarians.

To the contrary, evidence continues to accumulate showing that vegetarians tend to enjoy life more and even have a better social life than before becoming vegetarians. Moreover, the incidence of both depression and anxiety has been found to be lower in vegetarians when compared to non-vegetarians.^xiv