Hello and welcome to Nutrition Facts – the podcast that brings you the latest in evidence-based nutrition research. I’m your host Dr. Michael Greger.
I’m often asked what my opinion is about one food or another. I know what people are asking but, you know, I’m not interested in opinions. I’m not interested in beliefs. I’m interested in the science. What does the best available balance of evidence published in the peer-reviewed medical literature show right now? That’s why I wrote my book, “How Not to Die”, and why I created my nonprofit site NutritionFacts.org and, now, this podcast.
Today we’re going to talk about depression, what contributes to it and what steps we can take to try to prevent it.
Our first story reveals the findings of one of the most comprehensive controlled trials of diet and mood. This study found that a plant-based nutrition program in a workplace setting across ten corporate sites significantly improves depression, anxiety, and productivity.
A 2014 systematic review and meta-analysis of dietary patterns and depression concluded that a healthy diet pattern was significantly associated with reduced odds of depression, but out of the 21 studies they could find in the medical literature, they were only able to find only one randomized controlled trial, considered the study design that provides the highest level of evidence and it was the study I profiled in Improving Mood Through Diet, which removing meat, fish, poultry, and eggs improved several mood scores in just two weeks.
We’ve known that those eating plant-based tend to have healthier mood states, less tension, anxiety, depression, anger, hostility, and fatigue. But you couldn’t tell if it was cause and effect until you put it to the test, which they finally did, but what could account for such rapid results? Well, eating vegetarian does give you a better antioxidant status, which may help with depression.
Also, as I’ve previously addressed, how consumption of even a single carbohydrate-rich meal can improve depression, tension, anger, confusion, sadness, fatigue, alert, and calmness scores among patients with PMS, but what about long term?
Overweight men and women were randomized into a low-carb high-fat diet, or a high-carb low-fat diet for a year. By the end of the year, who had less depression, anxiety, anger, and hostility, feelings of dejection, tension, fatigue, better vigor, less confusion, mood disturbances? The low-carb dieters are represented by the black circles and the low-fat dieters are represented in the white. These sustained improvements in mood in the low-fat group compared with the low-carb group are consistent with results from epidemiological studies showing that diets high in carbohydrates, low in fat and protein are associated with lower levels of anxiety and depression, and have beneficial effects on psychological wellbeing.
But the overall amount of fat in their diet didn’t change in this study though, but the type of fat did. Their arachidonic acid intake fell to zero.
Arachidonic acid is an inflammatory omega-6 fatty acid that can adversely impact mental health via a cascade of neuroinflammation. It may inflame our brain. High blood levels in the bloodstream have been associated with a greater likelihood of suicide risk, for example, and major depressive episodes. How can we stay away from the stuff?
Well, Americans are exposed to arachidonic acid primarily through chicken and eggs but, when you remove chicken and eggs, and other meat, we can eliminate preformed arachidonic acid from our diet.
So, while high-quality treatment studies investigating the impact of diet on depression are scarce, there is that successful two-week trial, but even better, how about 22 weeks?
Overweight or diabetic employees of a major insurance corporation received either weekly group instruction on a whole food plant-based diet or no diet instruction for five and a half months. There was no portion size restriction, no calorie counting, no carb counting, no change in exercise. No meals were provided, but the company cafeteria did start offering daily options such as lentil soup, minestrone, bean burritos.
No meat, eggs, dairy, oil, or junk, yet they reported greater diet satisfaction compared with the control group participants who had no diet restrictions. How’d they do though? More participants in the plant-based intervention group reported improved digestion, increased energy, better sleep than usual at week 22 compared with the control group. They also reported a significant increase in physical functioning, general health, vitality, and mental health. Here’s this all kind of represented graphically, where the plant-based group beat out controls on nearly every measure.
There were also significant improvements in work productivity, thought to be due, in large part, to their improvements in health. So, what this study demonstrated was that a cholesterol-free diet is acceptable, not only in research settings, but a typical corporate environment, improving quality of life and productivity at little cost. All we need now is a large, randomized trial for confirmation, but we didn’t have such a thing, until now.
Ten corporate sites across the country from San Diego to Macon, Georgia, same kind of setup as before. Can a plant-based nutrition program in a multicenter corporate setting improve depression, anxiety, and productivity? Yes. Significant improvements in depression, anxiety, fatigue, emotional wellbeing, and daily functioning. Lifestyle interventions have an increasingly apparent role in physical and mental health, and among the most effective of these is the use of plant-based diets.
Aerobic exercise may also help in the treatment of depression. In fact, exercise was found to be comparable to antidepressant medication in the treatment of patients with major depression.
We’ve known for decades that even a single bout of exercise can elevate our mood, but enough to be used as a treatment for major depression? Well, we know physical activity has been associated with decreased symptoms of depression. For example, if you look at a cross section of 8,000 people across the country, those that exercised regularly were less likely to have a major depression diagnosis.
That’s just a snapshot in time, though. If you look at that study, the researcher openly admits this may be a case of reverse causation. Maybe exercise didn’t cut down on depression; maybe depression cut down on exercise. The reason depression may be associated with low physical activity is that people feel too lousy to get out of bed. What we need is an interventional study, where you take people who already have depression, randomize them into an exercise intervention and see if they get better and that’s what we got.
Men and women over 50, major depression, were randomized to either do an aerobic exercise program for four months, or take an antidepressant drug called Zoloft. This is where they started out before, with Hamilton Depression scores up around 18 (anything over seven is considered depressed), but within four months, the drug group came down to normal, which is exactly what the drugs are supposed to do. What about the exercise-only group, no drugs? Same powerful effect.
They conclude that an exercise training program may be considered an alternative to antidepressants for treatment of depression in older persons, given that they’ve shown that a group program of aerobic exercise is a feasible and effective treatment for depression, at least for older people.
Not so fast, though. A group program? They had the exercise group folks come in three times a week for a group class. Maybe the only reason the exercise group got better is because they were forced to get out of bed, interact with people, maybe it was the social stimulation and had nothing to do with the actual exercise. Before you could definitively say that exercise can work just as good as drugs, what you’d like to see is the same study but with like an additional group, the same two plus a home exercise group, where they were just told to exercise on their own at home, no extra social interaction. But nothing like that had ever been done, until it was. The largest exercise trial of patients with major depression conducted to date, and not just including older persons, but other adults as well, and three different treatment groups this time: a home exercise group, in addition to the supervised group exercise, and the drug group, as before, and they all worked about just as well in terms of forcing the depression into remission.
So, we can say with confidence that exercise is comparable to antidepressant medication in the treatment of patients with major depressive disorder.
Putting all the best studies together, the evidence indicates that exercise, at least, has a moderate antidepressant effect and, at best, exercise has a large effect on reductions in depression symptoms and could be categorized as a very useful and powerful intervention. Unfortunately, while studies support the use of exercise as a treatment for depression, exercise is rarely prescribed as a treatment for this common and debilitating problem.
Neither antioxidant or folic acid supplements seem to help with mood, but the consumption of antioxidant-rich fruits and vegetables and folate-rich beans and greens may lower the risk for depression. Here’s that research.
According to the latest from the CDC, the rates of all of our top ten killers have fallen or stabilized except for one–suicide. Accumulating evidence indicates that oxidative free radicals may play important roles in the development of various neuropsychiatric disorders, including major depression.
For example, in a study of nearly 300,000 Canadians, greater fruit and vegetable consumption was associated with lower odds of depression, psychological distress, self-reported mood and anxiety disorders, and poor perceived mental health. They conclude that since a healthy diet comprised of a high intake of fruits and vegetables is rich in antioxidants, it may consequently, you know, dampen the detrimental effects of oxidative stress on mental health.
But that was just based on asking how many fruits and veggies people ate. If you measure the levels of carotenoid phytonutrients in nearly 2,000 people across the country, a higher total blood carotenoid level was associated with a lower likelihood of elevated depressive symptoms, and there appeared to be a dose-response relationship, meaning the higher the levels, the better people felt.
Lycopene, the red pigment predominantly found in tomatoes, but also present in watermelon, pink grapefruit, guava, papaya, is the most powerful antioxidant among the carotenoid family. In a test tube, it’s about 100 times more effective at quenching these free radicals than vitamin E, for example and in a study of about a thousand older men and women, those who ate the most tomato products had about half the odds of depression. The researchers conclude that a tomato-rich diet may have a beneficial effect on the prevention of depressive symptoms.
Higher intake of fruits and vegetables has been found to lead to a lower risk of developing depression, but if it’s the antioxidants, can’t we just take an antioxidant pill? No. Only food sources of antioxidants were protectively associated with depression, not antioxidants from dietary supplements. Although plant foods and food-derived phytochemicals have been associated with health benefits, antioxidants from dietary supplements appear to be less beneficial and may, in fact, be detrimental to health. This may indicate that the form and delivery of the antioxidants are important. Alternatively, the observed association may be due not to antioxidants at all, but rather to other dietary factors, such as folate, that also occur in fruit, vegetables, and plant-rich diets.
In a study of thousands of middle-aged office workers, eating lots of processed food was found to be a risk factor for at least mild to moderate depression five years later, whereas a whole-food pattern was found to be protective. Yes, it could be because of the high content of antioxidants in fruits and vegetables but could also be the folate in greens and beans, as some studies have suggested an increased risk of depression in folks who may not have been getting enough.
Low folate levels in the blood are associated with depression, but since most of the early studies were cross-sectional, meaning a snapshot in time, we didn’t know if the low folate led to depression or the depression led to low folate. Maybe when you have the blues, you don’t want to eat the greens.
But since then, a number of cohort studies were published following people over time and low dietary intake of folate may, indeed, be a risk factor for severe depression–as much as a threefold higher risk. Note this is dietary folate intake, not folic acid supplements, so they were actually eating healthy foods. If you give people folic acid pills they don’t seem to work. This may be because folate is found in dark green leafy vegetables like spinach, whereas folic acid is the oxidized synthetic compound used in food fortification and dietary supplements because it’s more shelf-stable, but may have different effects on the body, as I explored previously.
These kinds of findings point to the importance of antioxidant food sources rather than dietary supplements. But there was an interesting study giving people high-dose vitamin C, also known as ascorbic acid. The vitamin C, but not placebo, group experienced a decrease in depression scores and also greater FSI. What is FSI? FSI evidently stands for penile-vaginal intercourse, an acronym that makes no sense to me.
But evidently, high-dose vitamin C improves mood and intercourse frequency, but only in sexual partners that don’t live with one another. In the placebo group, those not living together had sex about once a week, and those living together a little higher, once every five days, but no big change on vitamin C, but those not living together, on vitamin C, every other day! The differential effect on non-cohabitants suggests that the mechanism is not a peripheral one, meaning outside the brain, but a central one–some psychological change which motivates the person to venture forth to have intercourse. The mild antidepressant effect they found was unrelated to cohabitation or frequency, so it does not appear that the depression scores improved just because of the improved FSI.
If the amino acid tryptophan is the precursor to the so-called happiness hormone, serotonin, why not just take tryptophan supplements to improve mood and relieve symptoms of depression? Here’s your answer.
Recent studies suggest that dietary patterns characterized by high intakes of vegetables, fruit, mushrooms, and soy products are associated with fewer depressive symptoms.
The year before, it was this study: The Association between Dietary Patterns and Mental Health in Early Adolescence, showing improved behavioral scores significantly associated with higher intakes of leafy green vegetables and fresh fruit.
Could any of this be because of the psychoactive substances found in plant foods?
The neurotransmitter serotonin, often referred to as the happiness hormone, is found in plant foods but serotonin doesn’t cross the blood-brain barrier. So, it shouldn’t affect our mood, no matter how much we eat.
The precursor to serotonin, however, what your body makes serotonin out of, is an amino acid called tryptophan and there’s a transport protein in the brain that plucks tryptophan out of the bloodstream and, so, what you eat can end up affecting our mood.
Back in the 1970s, they did tryptophan-depletion experiments, where you give people specially concocted tryptophan-deficient diets and, indeed, their mood suffers. They get irritable, annoyed, angry, depressed, right? Their body just can’t make enough serotonin.
Likewise, you can give people tryptophan pills to improve their mood and, indeed, it became a popular dietary supplement, until people started dying from something called eosinophilia myalgia syndrome, an incurable, debilitating, and sometimes fatal, flu-like neurological condition, caused by the ingestion of tryptophan supplements. May have been due to some unknown impurity, but, better safe than sorry.
Thanks for listening to this episode of Nutrition Facts. To see any graphs, charts, graphics, images, or studies mentioned here, please go to the Nutrition Facts podcast landing page. There, you’ll find all the videos I highlighted with links to all the sources cited.
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Thanks for listening to Nutrition Facts. I’m Dr. Michael Greger.