Who benefits most from a healthy diet?
First off, diet programs tended to work better for women. Why? Besides differences in hormones and metabolism, Firth conjectured, women seem to be in a better position to benefit. They’re more likely to be depressed, and, he says, they might have more discipline at following diets than men.
Also, the diet programs worked better if a dietary professional administered them—probably because the recommendations were sounder and the participants (believing in the dietitian’s authority) were more apt to follow them, Firth says. An earlier review of diet studies came to a similar conclusion.
One of the strongest studies in the collection suggested that diet could help people who were right in the midst of a major depressive episode. Researchers recruited 67 depressed people with poor diets, half of whom were instructed to follow a healthy, Mediterranean-style diet favoring whole grains, fruit and vegetables, legumes, low-fat dairy, nuts, fish, lean red meat, chicken, eggs, and olive oil while reducing sweets, refined grains, fried and fast food, processed meats, and sugary drinks. Across 12 weeks, they attended seven sessions with a dietitian who helped them set diet goals and stay motivated; they also received recipes, meal plans, and a hamper of food.
The other half attended sessions on a similar schedule. But rather than getting diet advice, they simply spent time with a research assistant who was trained to be supportive of them—talking about topics they were interested in, like sports and hobbies, or playing games with them for an hour.
Despite how beneficial social interaction is, the diet group fared better than the social support group. After 12 weeks, they had reduced their depression and anxiety more—and they were about four times more likely to experience a remission from their depression. The more they improved their diet, the more their depression lifted.

What about anxiety? In that particular study, anxiety did go down—but on average, across all 16 studies, healthier diets didn’t seem to make people less anxious. That actually strengthens the case that diet can directly affect depression, says Firth. If the results were simply due to people feeling proud and accomplished with their new healthy habits, you would expect them to feel better all around, including less anxious. The fact that only their symptoms of depression shifted means that something deeper may be going on. 

What could that be? We don’t know for sure yet, but there are a variety of biological processes that seem to be both influenced by diet and involved in mental health. It’s possible that certain diets may increase inflammation and oxidative stress, and disrupt our mitochondrial function and neuron production, in ways that could put us at risk for psychological problems. Our gut microbiome—the colony of microorganisms in our intestines that is increasingly being studied as a contributor to mental health—may interact with many of these processes. Also, says Firth, following a diet can bring us a sense of self-esteem and self-efficacy, as well as potential weight loss—which can influence our minds, too.
But there are still a lot of unknowns. As Professor Almudena Sanchez-Villegas of the University of Las Palmas de Gran Canaria points out, the findings from diet experiments are not consistent. Many of the diet programs in Firth’s review didn’t help alleviate depression, nor did a newer one that also included multivitamins. Researchers have much more to explore.
Who benefits most from a healthy diet?
First off, diet programs tended to work better for women. Why? Besides differences in hormones and metabolism, Firth conjectured, women seem to be in a better position to benefit. They’re more likely to be depressed, and, he says, they might have more discipline at following diets than men.
Also, the diet programs worked better if a dietary professional administered them—probably because the recommendations were sounder and the participants (believing in the dietitian’s authority) were more apt to follow them, Firth says. An earlier review of diet studies came to a similar conclusion.
One of the strongest studies in the collection suggested that diet could help people who were right in the midst of a major depressive episode. Researchers recruited 67 depressed people with poor diets, half of whom were instructed to follow a healthy, Mediterranean-style diet favoring whole grains, fruit and vegetables, legumes, low-fat dairy, nuts, fish, lean red meat, chicken, eggs, and olive oil while reducing sweets, refined grains, fried and fast food, processed meats, and sugary drinks. Across 12 weeks, they attended seven sessions with a dietitian who helped them set diet goals and stay motivated; they also received recipes, meal plans, and a hamper of food.
The other half attended sessions on a similar schedule. But rather than getting diet advice, they simply spent time with a research assistant who was trained to be supportive of them—talking about topics they were interested in, like sports and hobbies, or playing games with them for an hour.
Despite how beneficial social interaction is, the diet group fared better than the social support group. After 12 weeks, they had reduced their depression and anxiety more—and they were about four times more likely to experience a remission from their depression. The more they improved their diet, the more their depression lifted.

What about anxiety? In that particular study, anxiety did go down—but on average, across all 16 studies, healthier diets didn’t seem to make people less anxious. That actually strengthens the case that diet can directly affect depression, says Firth. If the results were simply due to people feeling proud and accomplished with their new healthy habits, you would expect them to feel better all around, including less anxious. The fact that only their symptoms of depression shifted means that something deeper may be going on. 

What could that be? We don’t know for sure yet, but there are a variety of biological processes that seem to be both influenced by diet and involved in mental health. It’s possible that certain diets may increase inflammation and oxidative stress, and disrupt our mitochondrial function and neuron production, in ways that could put us at risk for psychological problems. Our gut microbiome—the colony of microorganisms in our intestines that is increasingly being studied as a contributor to mental health—may interact with many of these processes. Also, says Firth, following a diet can bring us a sense of self-esteem and self-efficacy, as well as potential weight loss—which can influence our minds, too.
But there are still a lot of unknowns. As Professor Almudena Sanchez-Villegas of the University of Las Palmas de Gran Canaria points out, the findings from diet experiments are not consistent. Many of the diet programs in Firth’s review didn’t help alleviate depression, nor did a newer one that also included multivitamins. Researchers have much more to explore.
