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Of Hunger & Happiness

Carbs' Role in the Food-Mood Connection

by Karolina Lempert

Don't worry. Come exam time, you're not the only one eating more pizza, chips, and chocolate than your body could possibly need. Unfortunately for our waistlines, the urge to gorge can have little to do with the kind and quantity of food we eat, especially when we're stressed or upset. The hunger is all in your head—literally.

Behind the nearly universal love for carbohydrates lies a basic need for something that sounds slightly less delectable—the neurotransmitter serotonin. This signaling molecule happens to be particularly important for efficient brain functioning. Low levels of serotonin have been linked to reduced verbal memory, impaired decision-making, and even depression.1 As carbohydrates can ultimately increase the production of serotonin, this commonplace nutrient proves more than just a source of calories.2

The process begins with the release of insulin, triggered by the consumption of carbohydrates. This event suppresses circulating levels of most large amino acids except for tryptophan, which remains relatively unaffected. With fewer competing amino acids in the bloodstream, more tryptophan is transported to the brain. Inside certain neurons, enzymes convert tryptophan into serotonin, potentiating its future release.2 In susceptible individuals, the serotonin boost fuelled by carbohydrates can improve mood, analogous to (though less potent than) the effect of selective serotonin reuptake inhibitors (SSRIs), popular antidepressants. A recent study reported that individuals with periodic mood perturbations experience frequent carbohydrate cravings while depressed.2 Similarly, women experiencing PMS and people with major depression (both conditions associated with low levels of synaptic serotonin) appear especially vulnerable to binging on carbs.3

This connection between carbohydrates and mood helps explain a particular gastronomical puzzle that you might have observed during Thanksgiving dinner. After eating unfathomable helpings of mashed potatoes, turkey, and cranberry sauce, you're still game for that slice of pumpkin pie. Hunger persists because following the ingestion of carbohydrate-rich foods alongside considerable protein, large neutral amino acids block the uptake of tryptophan into the brain. Consequently, the eater does not experience the expected neurochemical effects as promptly as anticipated, causing her to seek more carbohydrates than would usually do the trick.2 The signaling interference produced by certain combinations of foods can no doubt result in weight gain, especially in those highly responsive to the mood altering effects of carbohydrates.

But if undesirable weight gain has occurred, don't jettison carbs completely. It seems that some pasta or popcorn may actually be crucial to a diet's success, as frequent small feedings can bolster a dieter's willpower. Such noshing helps maintain normal blood glucose levels, which stabilize levels of circulating insulin.4 In turn, with a steady supply of tryptophan to neurons, the production of serotonin also remains constant—helping to stave off those runaway cravings. So if you feel a sudden desire for something sweet, don't expect a Diet Coke to quell your longing, because sugar substitutes don't elevate serotonin levels. Instead, reach for some fruit or whole grain cereal because the unrefined carbs will replenish blood sugar—and may even restore your capacity for self-control. Recent research has shown that acts of willpower such as dieting drain the body's glucose levels, thereby impairing later acts of self-control.4 Thus, individuals who eat several small meals a day appear more successful at losing weight than those who skip meals in an attempt to accelerate their diet.5 For those less concerned with weight, stable blood glucose could facilitate self-control for other purposes—say, resisting the lure of Facebook while writing that term paper.

As you struggle to focus on your problem set, you're probably justified in indicting serotonin. Not only will you feel up on your neuroscience, but equipped to rectify the situation as well. That brain-break bagel will tackle either of the potential culprits—your metabolic calorie deficit or your brain's jones for tryptophan. Still find your browser straying to NBC.com to watch reruns of the "The Office," despite a stuffed stomach? Exercise appears to heighten serotonin just like that bowl of pasta would, so try sweating off your distraction on the treadmill.6 With those new TVs in the MAC, you might boost your self-control and satisfy that craving for cubicle humor.

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