Gender Differences in Brain Serotonin Activity

Is there a connection to emotional overeating?

Posted Aug 27, 2019

Despite diet plans too numerous to remember, and interventions ranging from psychotherapy to exposure to cold showers, overeating in response to emotional turmoil has not been vanquished. Control over food intake works until life goes out of control. Then the self- imposed discipline of limiting food choices to healthy, portion-controlled, food items at predetermined times of day (mealtime) is overwhelmed by emotional turmoil. At such times salads and lean protein are discarded in favor of sweet or salty foods, often high in carbohydrates and fat. Quantities are rarely measured, and the eating may stop only when there is no more to be eaten.

A friend whose weight has been an issue since she was in elementary school told me she is able to adhere, easily, to a diet until one of her now adult children has a problem. “When their lives go out of control, my eating does the same.”

Many studies affirm what any failed dieter knows well: stress, in all of its manifestations, is a trigger for the consumption and overconsumption of calorie-dense, usually nutrient-weak foods.

Although stress does not discriminate among those it affects, the tendency to overeat in response to stress is more likely to occur among women than men. In her review of gender and eating behaviors, Beydoun cites several articles showing a relationship between stress and or/depression and the consumption of energy-rich snacks among women, but not men. A much earlier study looking at gender differences in binge eating disorder found the same relationship. Women, but not men, overate when experiencing negative emotions such as anxiety, anger, and depression.

The reasons people give for overeating are typically: “to feel better” “food soothes me,” “eating calms me down,” “food decreases my anger,” “food takes the edge off my stress,” or “it numbs me.” Anyone who has engaged in emotional overeating has experienced these feelings and thus may be unlikely to substitute non-eating behaviors, such as taking a walk or listening to music when upset. Such alternate behaviors may not bring about the same sense of emotional relief.

What is rarely discussed is how food decreases emotional distress, and why are women more likely than men to use food to bring about this effect.

Is it because eating junk food soothes women’s taste buds? Or do women find emotional relief by chewing and munching? Is it a social phenomenon? Are men embarrassed by desiring a brownie rather than a glass of Scotch when stressed? Certainly in the past, the media has had males tell each other that they, “need a drink!” when confronting a stressful situation. Rarely do they clap each other on the shoulder, and go off to eat a croissant.

The answer may be found in the brain.

Stress seems to be relieved, and the edge is taken off of the intense emotions when serotonin is released. The synthesis and activation of serotonin occur when sweet and/or starchy carbohydrates are eaten.  The process of making and activating serotonin is slowed by fat because digestion of the carbohydrate food is slowed. Protein prevents serotonin from being made altogether. (Even though fructose is a carbohydrate, it has no effect on increasing serotonin synthesis.) Thus eating carbohydrate-rich snacks like cookies or cereal is a form of self-medication; it may make the stress more bearable by making serotonin.

But why are women more likely to turn to food than men? Wouldn’t men also need to make more serotonin to relieve their stress?

Perhaps not. It turns out that male brains may contain more serotonin than female brains.  In a study done about 25 years ago, researchers temporarily decreased the ability of the brains of women and men to make serotonin. They restricted the brain’s access to tryptophan, the amino acid from which serotonin is made. When they made tryptophan available again, they found that the rate of serotonin synthesis was 52% faster in men’s brains. 

In a more recent study using PET scans to detect differences in brain markers of serotonin activity between men and women, women’s brains showed lower serotonin activity. 

The differences in male-female serotonin levels have been used to explain the higher incidence of depression in women, but it also may explain their drive to consume carbohydrates when stressed. If their serotonin levels are lower than in male brains, they may be more sensitive to the emotional relief brought about when their serotonin levels are increased.

The problem, of course, is that the emotional overeater eats much more carbohydrate than needed to increase serotonin. She also eats carbohydrate snacks that usually contain fat (rice cakes and shredded wheat squares are not usually the “go-to” comfort foods). If she is eating the carbohydrate along with (or just after) consuming protein, no serotonin will be made, but she may continue to eat anyway.  If she is following a carbohydrate-free or restricted diet, she has no hope of increasing brain serotonin and relieving her stress.  What she is rarely, if ever, told to do is to eat about 25 grams of a starchy carbohydrate like pretzels, wait 30 minutes and then see if she feels less stressed. The crackers and ultimately, the serotonin will not make the stress go away but should make bearing it easier.

References

“The Interplay of Gender, Mood, and Stress Hormones in the Association between Emotional Eating and Dietary behavior,” Beydoun M, The Journal of Nutrition, 2014; 144: 1139-1141.

“Comparison of men and women with binge eating disorder,” Tanofsky M1, Wilfley D, Spurrell E et al, Int J Eat Disord.1997; 21:49-54.

“Differences between males and females in rates of serotonin synthesis in human brain,” Nishizawa S, Benkelfat C, Young S et al, Proc Natl Acad Sci USA 1997; 94:5308-5313.

“Sex differences in the serotonin 1A receptor and serotonin transporter binding in the human brain measured by PET,” Jovanovic H, Lundberg, J, Karlsson P, et al, NeuroImage 2008; 39:1408–1419.