There IS a scientific reason for it! It’s called “starvation syndrome,” which is a constellation of psychological and physical changes that result from consuming less energy than your body needs to thrive.
The syndrome was first described by researchers during the Second World War who studied a group of men who ate a reduced-calorie diet of just 1,600 calorie/day for three months. The researchers wanted to document the effects of starvation due to wartime interruptions in food supplies, and this amount of calories was deemed similar to what many war refugees were eating at the time (a fact that is quite disturbing when you consider that most weight-loss diets direct people to voluntarily consume this same small amount of food).
Researchers carefully documented the outcomes of this restrictive eating and this is what they found [all quotes from Junkfood Science]:
As the men lost weight, their physical endurance dropped by half, their strength about 10%, and their reflexes became sluggish… The men’s resting metabolic rates declined by 40%, their heart volume shrank about 20%, their pulses slowed and their body temperatures dropped. They complained of feeling cold, tired and hungry; having trouble concentrating; of impaired judgment and comprehension; dizzy spells; visual disturbances; ringing in their ears; tingling and numbing of their extremities; stomach aches, body aches and headaches; trouble sleeping; hair thinning; and their skin growing dry and thin. Their sexual function and testes size were reduced and they lost all interest in sex. They had every physical indication of accelerated aging.
The psychological changes were just as disturbing, and included nervousness, anxiety, depression, loss of interest in hobbies, and social withdrawal. Most relevant to your Ask, the men’s relationship with food also changed dramatically:
…they became obsessed with food, thinking, talking and reading about it constantly; developed weird eating rituals; began hoarding things; consumed vast amounts of coffee and tea; and chewed gum incessantly (as many as 40 packages a day). Binge eating episodes also became a problem as some of the men were unable to continue to restrict their eating in their hunger.
I am sure this will all sound very familiar to anyone who has dieted to lose weight or suffered from food insecurity or suffered from an eating disorder! The body needs energy to survive and to thrive, and if it doesn’t get it, you are going to “hear” about it.
The ask about obsessing about food when hungry made me think about one of my extremer diets where I’d dream about eating basically every night in such a vivid way that I’d wake up feeling guilty for eating and it took a while for my guilty conscience to accept that it was a dream and I didn’t actually eat. It was so crazy! Anyway, yeah obsessing with food is normal when on a diet. That’s why dieting people talk about it constantly.