When you're dieting and constantly thinking about food, it causes your mood to drop, Frew said. The chronic stress of dieting can cause your body to go into a fight or flight mode, with the body releasing adrenaline and cortisol, making you feel more irritable and anxious. She added, "You lose interest in the things that normally bring you joy, as food preoccupation is predominant."
Registered dietitian Rachel Berman, and general manager of Verywell said, "In my opinion, the emotional and physical elements are very much tied together. If you're not eating enough during the day, particularly carbohydrate-rich foods, you may have decreased levels of serotonin, a hormone that has a calming effect. Therefore, you may feel more anxiety the more you restrict or obsess over the calories you do consume."
Your self-worth quickly becomes linked to your ability to stick to dietary rules. "When you're following the plan, you feel fleetingly good, but when you're not, you can feel as if you're failing and are not good enough," she said.
Meehan added that worrying about weight, dieting, restricting food and calories all contribute to emotional distress. She said, "A hyper-focus on micromanageing our eating and our bodies can zap energy levels and leave us feeling distracted or overwhelmed."
Being physically deprived of food can also cause depression, as seen most clearly in the Minnesota Starvation Experiment, where previously well-adjusted young men experienced depression, anxiety, anger, and even psychosis (in a couple of cases), simply due to food deprivation, Harrison explained. "And this wasn't anywhere near total starvation; in fact, it was a level of deprivation that most dieters have experienced," she added.