Obesity versus Depression

Is depression the cause of obesity or is obesity the cause of depression? Although depression and obesity often come hand in hand, the relationship between the two is difficult to tease apart. A new, large-scale genomic study adds new evidence.

Pensive woman ponders obesity
The relationship between depression and obesity is complex.

Both excessive weight and depression are significant global health problems. According to the authors of the latest research, they cost the global economy trillions of dollars every year.

Previous studies have noted that depression often appears in individuals who are overweight or obese.

However, observational studies have not been able to demonstrate whether obesity causes depression, as there are many competing factors to consider.

For instance, being grossly overweight is a risk factor for a number of conditions, and so it might be that dealing with other health issues increases the likelihood of becoming depressed, rather than the obesity being the cause.

Some researchers have argued that the relationship might be the other way around: depression is a risk for obesity.

Others believe that depression and obesity exacerbate each other. For instance, obesity might make depression more likely to occur initially, but once depressive symptoms arise, they might compound the condition by making it harder for the individual to exercise. In these cases motivation of the individual would be a great place to start.

Obesity and depression revisited

To gain a better understanding of this complicated relationship, researchers from the University of Exeter in the United Kingdom joined forces with scientists from the University of South Australia. They published their results in the International Journal of Epidemiology this week.

“Obesity and depression are both global health problems that have a major impact on lives and are costly to health services,” explains lead author Dr. Jess Tyrrell. “We’ve long known there’s a link between the two, yet it’s unclear whether obesity causes depression or vice versa, and also whether it’s being overweight in itself or the associated health problems that can cause depression.”

The study used genetic data to inspect the causal relationship between excessive weight and depression. The team wanted to understand whether a higher body mass index (BMI) was related to an increased risk of depression without the presence of other health conditions.

The researchers used genetic and medical data from 48,000 people with depression and compared it with in excess of 290,000 controls, making it the largest study to address this question to date.

Psychological impact to blame?

Overall, as expected, a higher BMI was associated with higher odds of depression. This association was stronger in women than men, confirming earlier findings. Women with a high BMI had a 21 percent increase in risk, compared with 8 percent in men.

By investigating individuals with genes predisposing them to obesity but without ones that predispose them to metabolic conditions, such as diabetes — referred to as a “favorable metabolic profile” — the researchers could separate out the psychological component of obesity.

In their analysis, they accounted for a range of variables that could influence the results, including socioeconomic position, alcohol consumption, smoking, and physical activity.

They found that individuals with a favorable metabolic profile were just as likely to develop depression as individuals with obesity that carried genes predisposing them to develop metabolic conditions. This effect was most pronounced in women.

To double-check their findings, they also took data from the Psychiatric Genomics Consortium. And their second analysis returned similar results, adding further weight to their conclusions.

“Our robust genetic analysis concludes that the psychological impact of being obese is likely to cause depression.” Dr. Jess Tyrrell

These results provide vital insight, as Dr. Tyrrell explains, “This is important to help target efforts to reduce depression, which makes it much harder for people to adopt [healthful] lifestyle habits.”

However, the relationship between the two is convoluted, and questions remain. As the authors write, “we have not ruled [out] a possible bidirectional causal relationship between higher BMI and depression […] Further research is required to explore the causal role of depression on body mass index and obesity.”

Because depression and obesity can have profound impacts on individuals and society at large, scientific attention is likely to continue to look at their links.

Nuts and your health

Two new studies suggest that a small daily serving of nuts may benefit overall metabolic health and keep off the weight we tend to gain as we enter adulthood.
serving of nuts
A daily serving may prevent weight gain and improve metabolic health in the long run, two new studies suggest.

From providing cardiovascular benefits to potentially improving fertility, and even boosting memory and intelligence, the health benefits of nuts are numerous — and no wonder.  They are packed with unsaturated fatty acids, fiber, protein, and other beneficial chemicals, which may all contribute to good health.

However, can these dried seeds aid weight loss? Are certain types better able to support good metabolism?

Two new studies delved deeper into these questions. The authors will present the findings at Scientific Sessions 2018, a conference to be held by the American Heart Association (AHA) in Chicago, IL.

The first study — led by Xiaoran Liu, Ph.D., a research associate in the nutrition department of the Harvard T.H. Chan School of Public Health in Boston, MA — looked at the long-term effects of nuts and peanuts on body weight.

The second study examined the effects of Brazil nuts on satiety, blood sugar, and insulin response.

It was supervised by Mee Young Hong, Ph.D., a registered dietician and a professor in the School of Exercise & Nutritional Sciences at San Diego State University in California.

Nuts prevent weight gain in adulthood

The first study explored consumption in:

  • 25,394 healthy men who had taken part in the Health Professionals Follow-up Study
  • 53,541 women who had participated in the Nurses’ Health Study
  • 47,255 women who had taken part in the Nurses’ Health Study II

The three groups had filled in food frequency questionnaires once every 4 years.

The researchers discovered that replacing foods that had less nutritional value with a 1-ounce serving of nuts and peanuts lowered the risk of weight gain and obesity over the 4-year follow-up intervals.

More specifically, replacing a serving of red meat, processed meat, french fries, desserts, or potato chips with a serving of nuts correlated with significantly less weight gain in the long run.

The study’s first author comments on the findings, saying, “People often see nuts as food items high in fat and calories, so they hesitate to consider them as healthy snacks, but they are in fact associated with less weight gain and wellness.”

“Once people reach adulthood, they start to gradually gain about 1 pound a year of weight, which seems small. But if you consider gaining one pound over 20 years, it accumulates to a lot of weight gain,” Liu notes.

Adding 1 ounce of nuts to your diet in place of less healthy foods — such as red or processed meat, french fries or sugary snacks — may help prevent that slow, gradual weight gain after you enter adulthood and reduce the risk of obesity-related cardiovascular diseases.”

Xiaoran Liu, Ph.D.

Brazil nuts benefit insulin, glucose responses

In the second study, researchers examined the effects of consuming the Brazil variety in 22 healthy adult participants, 20 of whom were women.

The participants added either 36 grams of pretzels or 20 grams of Brazil nuts to their normal diet in two trials. At least 48 hours passed between trials.

The Brazil nuts and pretzels contained about the same number of calories and the same amount of sodium. Both triggered a sense of fullness, but the Brazil type contributed to an increased feeling of satiety.

Forty minutes after the participants had consumed their snacks, the researchers found that the pretzels had caused significant increases in blood sugar and insulin levels, whereas the Brazil nuts had not.

The study’s senior author explains, “While both Brazil nuts and pretzels increased a sense of fullness after they were eaten, eating Brazil nuts stabilized postprandial (after eating) blood glucose and insulin levels, which may be beneficial in preventing diabetes and weight gain.”

Although the study was observational, the researchers speculate that selenium may explain the benefits of Brazil nuts. Prior studies had linked the mineral with better insulin and blood sugar responses, and Brazil nuts are rich in selenium.

However, the researchers caution that because only 9 percent of participants were men, the study’s findings may not apply to all.

Our study allows researchers and clinicians to consider the possible beneficial role of Brazil nuts to help people feel full and maintain a healthy level of glucose, reducing the risk of obesity and diabetes.”

Mee Young Hong, Ph.D.