"Abnormally low levels of serotonin might be found in someone who is suicidal, who is particularly aggressive towards others, or a person who is extremely depressed. High levels of serotonin may be found in a person who is in a constant state of anxiety, has a tendency to be over-exacting in completing tasks, who suffers insomnia, or who has a tendency to feel overly stimulated by their surroundings (overwhelmed)." (Source: something-fishy.org)
Low levels of serotonin, which could contribute to a person's feelings of depression, are increased when high levels of sweets, starches, or carbohydrates are eaten. As serotonin levels rise, a feeling of well-being is created in the brain. But this is only temporary.
The problem then becomes the sugar you've just ingested. Fast burning carbs like sugar or starch are more quickly absorbed by the body. In other words, they burn off fast. From the neck up, anyway...and that emotional high depletes rapidly. For the rest of the body, however, these carbs start a cycle that cannot be stopped! While the chemicals in your brain are doing the happy dance and you're starting to "feel better" for the moment, your pancreas is creating insulin (cue the ominous music). Insulin is like the "traffic cop" that directs the sugars to where they're needed the most. The more sugar you ingest, the more insulin your body makes. If there's too much insulin (from the excess of sugar consumption), it just hangs out, waiting for someone to tell it where it can be best used. If it cannot be used, your body metabolizes it into that nasty, yellow, artery-clogging fat.
An insulin spike will remain in your body for up to 5 hours! This is how someone who is obese can still be malnourished and have vitamin deficiencies. They're creating more fat based on what they're eating and not ingesting the proper amounts of vitamins and minerals.
In fact, the more sugary sweets a person eats, the more outta-whack your serotonin levels can get, creating an actual dependency on the sugar-serotonin relationship to feel better! Just think about the long term effects of sugar consumption. My cheat meal or cheat days NEVER consist of straight sugar sweets. Not even birthday cake. I'm NOT perfect at this, but I try to stay away from straight sugar because of the addictive properties it has on me and how it influences my Seritonan levels negatively.
Keep working on those food journals and think about the effects sugar has on the brain, emotions and health.