Broccoli, spinach, kale, and Brussels sprouts are all considered healthy. Loaded with minerals, vitamins, and fiber, they are a dietician's dream - a dietician that hates you and wants you to be miserable by taking away all the sweet pleasures of life.
On the other hand, stuff that you love, - fries, burgers, desserts, and even red meat - are right at the bottom of the food pyramid. Called junk food, these, the health experts say, should not be consumed more than once a week, that too in moderation. I guess, like me, you are wondering why only the food that is so flavorful is always considered bad!
The reason is that, most 'tasty' foods are high either in fats, sugar, or salt; or some combination of them. And the reason our taste buds prefer them, is that we have evolved to love them. Our ancestors didn't live in the prosperous times that we live in, and back then, these three things weren't so abundant. So, prehistoric man and his body learned to value and preserve them.
They store energy. Fats are very high in calories - they contain twice the calorie content of carbohydrates. But since they take longer to digest, the body likes to store them for use when we don't have enough food.
Our ancestors' food supply was very irregular. The day they killed a mammoth, for example, there was enough food to feed the tribe for several days. But that happened pretty rarely, hence, our ancestors evolved to store as much as they could, and depended on the fat stores in times of food shortage. The person whose body was most equipped to store fat, was, by an evolutionary point of view, the fittest. He/she could survive through the harshest of times, and hence, our brains and taste buds love fat.
For our body, sugar is energy. Always on the lookout for food, ancient man also was an expert at detecting the most energy-rich sources. Usually, this meant ripe fruit, which are sweeter and easier to digest than unripe food. Many scientists speculate that sweetness is also a sign of abundance. Hence, when we eat something sweet, the pleasure receptors in our brain are activated, releasing dopamine. In fact, the effect of sugar is linked to drugs like heroin.
It was not available like how easily it is now. Salt is the best source of sodium, a mineral essential for the muscles and nerve cells to work. Besides table salt, sodium is only found in small quantities in animal blood, meat, and eggs. Hence, it was prized, and actively craved for. Some scientists also speculate that it releases dopamine in the brain, much like sugar.
Kids often get treats - sugary or fatty foods, as a reward for being 'good'. This gets fed to our brains again and again, until we finally associate these foods as something coveted and prized. We often see this happen in adults too - when under stress or emotional distress, a lot many people find comfort in food, and more often than not, food that is tasty and unhealthy.
And, Why Do We Hate Greens?
Most green vegetables - broccoli, kale,Brussels sprouts, etc., are bitter. Again, the unpalatibility of these foods is based on the food available to our ancestors. Most poisonous plants are bitter in taste, and hence, evolution made sure that our brains are simply hardwired to dislike them.