Hello and welcome to the Nutrition Facts podcast, I’m your host Dr. Michael Greger.
Now, I know I’ve made a name for myself in explaining how not to do certain things – just look at my books – How NOT to Die – and my upcoming book, How NOT to Diet. But what I want to share with you is actually quite positive: what’s the best way to live a healthy life? Here are some answers.
Today we look at research that shows the effects of certain foods and nutrients on mental illnesses. And we begin with the question: If depression can be induced with pro-inflammatory drugs, might an anti-inflammatory diet be effective in preventing and treating mood disorders? Let’s look at the facts.
Depression affects more than 150 million people worldwide, making it a leading cause of losing healthy years of life as a result of disability. In fact, by 2020, depression may be the second leading cause of healthy years of life lost, second only to heart disease. Why is depression so common? Well, it is said, “Nothing in biology makes sense except in the light of evolution.” But, why would we evolve to get depressed?
Depression poses a baffling evolutionary puzzle. It has such negative effects, but remains so common and heritable, meaning a big chunk of risk is passed through our genes. So, there must be some kind of adaptive benefit. Otherwise, presumably, it would have been naturally selected against. Maybe, depression is an evolutionary strategy for defense against infection.
Infection has been the leading cause of mortality throughout human history. The average life expectancy was 25, and it was not uncommon for half our kids to die. With such stark capabilities, infection has been a critical and potent driving force in natural selection.
When we become infected, there is a surge of inflammation as our body mounts a counterattack, and then what happens? We feel lousy. We feel sick. We get weak, tired, slow, and sleepy. We don’t see anyone; we don’t want to do anything; all we want to do is sleep. It’s like we’re depressed—and that’s great for fighting infection. Not only does that help us conserve energy so we can put up a good fight, but it reduces social contact. We’re not running around infecting everyone.
It’s the same reason we evolved to think poop doesn’t smell good, or decaying flesh. That keeps us safe from infection. In fact, we see this phenomenon with other social animals, like honeybees and mole rats, who feel impelled to crawl off and die alone when they get sick, which reduces the risk to the rest of the community.
The relationship between mental health and inflammation was first noted in 1887, for which the only psychiatrist to ever win the award got a Nobel Prize. But what evidence have we accumulated in the century since that inflammation causes depression? Well, people who are depressed have raised inflammatory markers, such as C-reactive protein, and inflammatory illnesses are associated with greater rates of major depression. Indeed, that’s what’s found in a variety of inflammatory conditions including more benign inflammatory conditions, like asthma and allergies. And, that’s important, suggesting the mood symptoms are not simply ‘feeling bad about having a terrible disease,’ but may be directly tied to the inflammation. Most powerfully, you can actually induce depression by inducing inflammation, like when we give interferon for certain cancers or chronic infections—up to 50% go on to suffer major depression. Even just giving a vaccine can cause enough inflammation to trigger depressive symptoms. Taken together, these studies are strongly suggestive of inflammation being a causative factor of mood symptoms.
So, can an anti-inflammatory diet help prevent depression? We didn’t know, until about 43,000 women without depression were followed, along with their diets, for about a dozen years to see who became depressed, and it was those who ate a more inflammatory dietary pattern, characterized by more soda, refined grains and meat, suggesting that chronic inflammation may underlie the association between diet and depression. Normally, we think of omega-3’s as anti-inflammatory, but they found fish to be pro-inflammatory, associated with increased C-reactive protein levels consistent with recent findings that omega-3’s don’t seem to help with either depression or inflammation. The most anti-inflammatory diet is plant-based diet, which can cut C-reactive protein levels by 30% within two weeks, perhaps because of the anti-inflammatory properties of antioxidants.
I’ve talked about this before, but never really explained why antioxidants are anti-inflammatory. See, oxidative damage caused by free radicals may cause an autoimmune response in the body by changing the chemical structure of otherwise ubiquitous molecules to generate new structures that the body attacks as foreign. For example, when LDL cholesterol gets oxidized, our body creates antibodies against it and attacks it. And, so, clinical depression can be accompanied by increased oxidative stress and the autoimmune inflammatory responses it creates. Free radicals lead to autoimmune inflammation.
Where else does inflammation come from in our diet? Endotoxins. It’s worth reviewing how the endotoxins in animal products can cause a burst of inflammation within hours of consumption. What does that do to our mood? If you inject endotoxin into people, within a few hours, inflammation shoots up, and so does feelings of depression, as well as feelings of social disconnection between people.
Although previous research has demonstrated that inflammatory activity contributes to depressive symptoms, no work in humans has examined the effect of experimentally induced inflammation on anhedonia, the lack of reaction to pleasurable stimuli, this is an important symptom of depression. No work has been done, that is, until now. Within hours of endotoxin hitting their bloodstream, these experimental subjects not only started to feel depressed, but they had significant reductions in activity in the reward center of the brain. They were less excited about winning money playing video games, for example, in the study.
But by eliminating animal products, and eating antioxidant rich diets, we may be able to prevent or treat depression.
In our next story we hear about the results of one of the most comprehensive controlled trials ever undertaken of diet and mood.
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. It was the study, Improving Mood Through Diet, in 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. 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, consumption of even a single carbohydrate-rich meal can improve depression, tension, anger, confusion, sadness, fatigue, alertness, 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 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, or mood disturbances? 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 carbohydrate and low in fat and protein are associated with lower levels of anxiety and depression, and have beneficial effects on psychological well being.
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?
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, and 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, and 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. 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 in 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 well-being, 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.
For our final story today–we ask the question –are happier people actually healthier?
More than 60 years ago, the World Health Organization defined health as a “state of complete physical, mental, and social well-being and not merely the absence of disease or infirmity.” Just because you’re not depressed doesn’t necessarily mean you’re happy. But if you look in the medical literature, there are 20 times more studies published on health and depression than there are on health and happiness.
In recent years, though, research on positive psychology has emerged: what we can do to increase our success, functioning, and happiness; all inherently good in themselves, but are happier people, healthier people?
There is growing evidence that positive psychological well-being is associated with reduced risk of physical illness. But it’s not surprising that healthier people are happier than sick people. The intriguing issue is whether psychological well-being protects against future illness or inhibits the progression of chronic disease. To figure out which came first, you’d have to get more than just a snapshot in time; you’d need prospective studies, meaning studies that go forward in time, to see if people that start out happier do indeed live longer. And yes, a review of such studies suggests that positive psychological well-being has a favorable effect on survival in both healthy and diseased populations.
But not so fast. Yes, positive states may be associated with less stress, and inflammation, and more resilience to infection, but positive well-being may also be accompanied by a healthy lifestyle that itself reduces the risk of disease. Happy people tend to smoke less, exercise more, drink less, and sleep better. So, maybe happiness leads to health only indirectly. However, the apparent protective effect of positive psychological well-being persisted even after controlling for all these healthy behaviors. Meaning effectively, even at the same level of smoking, drinking, exercise, and sleep, happier people seem to live longer.
Ideally, to definitively establish cause-and-effect, we’d do an interventional trial, in which participants are assigned at random to different mood levels and tracked for health outcomes. It’s rarely feasible or ethical to randomly make some people’s lives miserable to see what happens, but if you pay people enough you can do experiments like this.
It’s been thought that people who typically report experiencing negative emotions are at greater risk for disease, and those who typically report positive emotions are at less risk; so, they decided to test this using the common cold virus. Three hundred thirty-four healthy volunteers were assessed for how happy, pleased, and relaxed they were, or how anxious, hostile, and depressed. Subsequently, they were given nasal drops containing cold rhinoviruses to see who would be more likely to come down with the cold. Who would let someone drip viruses in their nose? Someone paid $800, that’s who.
Now, just because we get exposed to a cold virus doesn’t mean we automatically get sick, because we have an immune system that can fight it off, even if it’s dripped right into our nose. The question is whose immune system fights better?
In a third of the bummed out folks, their immune systems failed to fight off the virus and they came down with a cold, but only about one in five got a cold in the happy group. Maybe it’s because those with positive emotions slept better, got more exercise, had lower stress? No, it appears even after controlling for the healthy practices and levels of stress hormones, happier people still appear to have healthier immune systems, a greater resistance to developing the common cold.
Works with the flu too—they repeated the study with the flu virus, and like in their earlier study, increased positive emotions were associated with decreased verified illness rates. These results indicate that feeling vigorous, calm, and happy may play a more important role in health than previously thought.
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NutritionFacts.org is a nonprofit, science-based public service, where you can sign up for free daily updates on the latest in nutrition research via bite-sized videos and articles. Everything on the website is free. There’s no ads, no corporate sponsorship. It’s strictly non-commercial. I’m not selling anything. I just put it up as a public service, as a labor of love, as a tribute to my grandmother – whose own life was saved with evidence-based nutrition. Thanks for listening to Nutrition Facts. I’m your host, Dr. Michael Greger.