October 09, 2019
A simple dietary intervention that emphasizes lean meat, fish, and fresh fruits and vegetables appears to improve depressive symptoms within 3 weeks in young adults with unhealthy eating habits, new research shows.
The results of the randomized control trial demonstrate that a simple dietary intervention is effective and feasible, even among young people with depressive symptoms that can frequently affect motivation, study investigator Heather M. Francis, PhD, Psychology Department, Macquarie University, Sydney, New South Wales, Australia, told Medscape Medical News.
"Just by giving some simple, succinct diet recommendations that are easy to follow, people with depression can make changes to their diet and, if they do, they may observe improvements in their depressive symptoms," she said.
The study was published online October 9 in PLOS One.
Moderate to Severe Symptoms
The analysis included 76 normal weight university students with a mean age of about 20 years and 63% were women. Participants had a score of 7 or more on the Depression, Anxiety and Stress Scale-21 Depression subscale (DASS-21-D), which corresponds with moderate depression symptoms, and a score of more than 57 on the Dietary Fat and Sugar Screener (DFS), which suggests a poor diet.
If receiving antidepressant therapy, participants were required to be on the same treatment for at least 2 weeks before the study began.
Participants were randomized to the diet change (DC) intervention or continuation of their habitual diet (HD).
Those in the intervention group received diet instructions via a short video. The diet was based on the Australian Guide to Healthy Eating plus additional dietary recommendations related to reduced risk of depression (for example, omega-3 fatty acids, cinnamon, and turmeric).
"We included those two spices because they are known to reduce inflammation," said Francis. She added that experts theorize that reducing inflammation through diet can improve depression symptoms.
Intervention group participants were given specific instructions on increasing intake of vegetables, fruits, wholegrain cereals, protein (lean meat, poultry, eggs, tofu, legumes), unsweetened dairy, fish, nuts and seeds, olive oil, and spices (turmeric and cinnamon). They were told to decrease intake of refined carbohydrate, sugar, fatty or processed meats, and soft drinks.
Researchers provided easy, low-cost recipes and time-saving tips, for example, using tinned tuna, and frozen instead of fresh fruits and vegetables. Participants also received a healthy food hamper and some funds towards groceries.
Investigators called these participants twice during the study to ask if they had difficulties adhering to the diet and troubleshoot problems.
Less Stress, Anxiety
Participants in the usual diet group received no instructions regarding diet and were simply asked to return after 3 weeks for follow-up.
The primary outcome was based on the 20-item Centre for Epidemiological Studies Depression scale-Revised (CESD-R). The secondary outcome was based on the DASS, which in addition to assessing depression symptoms includes an anxiety and stress subscale.
Using a questionnaire developed for the study, participants in the intervention group reported consuming fewer processed foods and more fruits and vegetables.
This observation was objectively supported by data from a spectrophotometer, which measures skin coloration, an indication of flavonoid consumption.
At 3 weeks, the average CESD-R score in the intervention group had improved from the elevated range (> 16) to the nonclinically significant range, but scores remained elevated in the HD group. The DC group had significantly lower CESD-R scores compared with the HD group, controlling for baseline CESD-R scores (P = .007).
When researchers also controlled for age, gender, physical activity, and baseline body mass index (BMI), the significant group difference remained (P = .01).
As for the DASS scale, the average score for the intervention group improved from the moderate severity range (7-10) to the normal range (0-4), but remained in the moderate severity range for the HD group.
The DC group had significantly lower scores compared with the HD group, controlling for baseline DASS scores, and then additionally controlling for age, gender, physical activity, and baseline BMI. Stress and anxiety levels were reduced in the intervention group.
The Role of Processed Foods
Eating less processed foods appeared to "correlate more strongly" with improved depression scores than other elements of the diet, although it is difficult "to tease out" whether eliminating processed foods alone would be enough to reduce depressive symptoms, said Francis.
Researchers were able to reach 33 participants for a 3-month telephone follow-up. Of those contacted, 21.2% said they had stuck to the diet, and these participants maintained improvements in mood.
Francis noted that the diet intervention was not restrictive or geared towards weight loss.
"We wanted these findings to be independent of weight loss," she said.
Although the study was too small to determine whether the intervention worked better in those with more severe depression, Francis believes that "even someone who is severely depressed could stand to benefit from making changes to their diet."
However, Francis emphasized that she and her team do not recommend replacing antidepressants and psychological therapies with a healthy diet.
Studying a dietary intervention in young adults is important as this population is at particularly high risk of depression and is still forming life-long dietary habits, she noted.
"If we can assist them in making those positive dietary changes earlier in life, not only does it potentially attenuate their current depressive symptoms, but also the future risk of both depression and a host of other diseases that are associated with poor diet," she said.
Remarkable, Encouraging, Powerful
Commenting on the study for Medscape Medical News, Drew Ramsey, MD, assistant clinical professor of psychiatry, Columbia University, New York City, described it as "remarkable, encouraging, and powerful."
"As a nutritional psychiatrist, I'm thrilled to see these new data," said Ramsey. "To date, this is by far the shortest, most effective intervention" to help reduce depression.
However, he noted that this and similar studies of diet-related interventions for depression "are small trials" and that "many factors influence depression."
Also commenting for Medscape Medical News, Felice Jacka, PhD, director, Food and Mood Centre, Deakin University, Geelong, Australia, and president, International Society for Nutritional Psychiatry Research, agreed the results are "very encouraging."
They are "highly concordant" with the findings of the SMILES trial, said Jacka. That trial, which she led, showed that in adults with a mean age of 40 years, a 12-week healthy diet intervention improved depression scores on a clinical rating scale compared with a social support control group.
The new results are also in line with a recent meta-analysis showing that dietary interventions improve depressive symptoms in many different patient populations, said Jacka.
As with Ramsey, Jacka was impressed with how "inexpensive and minimal" the intervention in the new study was.
Although many health practitioners are pessimistic about interventions successfully getting young people to improve their diet, the new results show that some people are "very keen" to alter their diets if they believe it will improve their mood, said Jacka.
Ramsay and Jacka have reported no relevant financial relationships.