Every animal, including humans, need calories to be alive. In it's most simplistic definition, a calorie is the amount of energy required to heat 1 gram of water 1 degree Celsius. Each person also needs a certain amount of calories to be able to carry out basic functions such as metabolism, movement, and breathing. These calories determine a threshold, which is the minimum amount of calories we should to consume per day. Although this threshold is fairly constant for all people around 2000-2,500 calories, it can vary based on height, current weight, metabolism, physical activity, and other factors.
Because all calories have the same thermodynamic capability in the lab (ie. the same ability to heat the same amount of water), unreliable nutrition studies and news sources have claimed that all calories affect the human body in the same way. This means that a calorie of sugar has the same effect as a calorie of broccoli. However, members of the medical community such as Dr. Hyman have recently shown that a calorie is not simply a calorie. He explains that calories from different food sources play various roles in human metabolism, brain activity, and hormone production, and therefore cannot be compared simply by numbers.
So how exactly are calories different?
According to Dr. Hyman, calories from foods such as soda, candy, and other processed foods tend to fall high on the glycemic scale. These foods are typically full of solid fats and added sugars. Scoring high on the glycemic scale means that the calories will spike the blood sugar and be digested very quickly, which means that many calories enter the body at the same time. This stimulates the body to store the excess energy as stomach fat and makes the body want food again soon after eating. Additionally, Dr. Wang, one of the featured researchers for the film Fed Up, has shown that these "empty calories" tend to rev up inflammatory pathways, promoting disease in the body.
This Harvard study, on the other hand, has shown that the same amount of calories from foods low on the glycemic scale will increase satiety. These minimally processed foods cause blood sugar to slowly increase in the body, preventing a blood sugar crash and hunger. These calories are also typically accompanied by many anti-inflammatory and antioxidant molecules found in plant-based foods, which help fight diabetes, autoimmune diseases, cancer, and more. Additionally, Dr. Hyman explains how some calories in high-fiber foods get trapped in the cells of the food, and aren't actually absorbed. This means that you may be eating more calories than your body is actually using and storing, allowing you to eat more food.
More interesting evidence comes from The China Study, a massive study done by Cornell researcher Dr. T. Colin Campbell and his colleagues. Here Dr. Campbell saw that the people in rural China were consuming 3000 calories or more a day, but were much leaner and healthier than Americans. These people were not exercising enough to justify taking in these many calories. So, how are the rural Chinese eating so much more than us, while sustaining significantly smaller waist-lines? Dr. Campbell concluded that the key was their fruit, vegetable, legume, and whole grain-rich diet. These people barely ate any animal products or processed foods, the opposite of the standard American diet. This distinction is an additional support that calories from plant-based foods are very different from processed foods.
All in all, science has shown that the mere number of calories does not represent the benefits of certain foods or their effects in the human body. By focusing on calories from plant-based foods low on the glycemic scale, minimally processed, and full of antioxidants, we are much more likely to fuel our bodies in a way that will make us be healthy and feel our best.