Here is why
In the 19th century, German physiologists discovered that the stomach is shaped so that liquids can pass right through the center. The German medical word for the “rapid pathway through the stomach” is called, magenstrasse, which means main street. Only water is supposed to go through the mouth and stomach without digestion. Everything else requires processing.
If a person eats an apple or carrot, the eating process is slow. A bite is taken, chewed for a while and swallowed. The sequence is repeated. There are digestive enzymes in the saliva that begin to process the food. The taste and “mouth feel” of the food sends signals to the stomach to make appropriate acid and digestive enzymes to prepare for the first arrival of food. The digestion process continues. Various minerals require stomach acid to be ionized for absorption and many vitamins need to be changed or attached to special proteins for proper absorption.
Rough, fibrous foods (such as apples and carrots) slowly and gradually break down, sending a little at a time into the intestine. Gradually, over many hours, the sugars extracted from these foods will reach the intestine. Because the body is only receiving a little sugar at a time, very little insulin is needed. In contrast, elevated insulin levels stimulate weight gain, hormonal imbalance and can stimulate cancer.
Turning our food into liquids in the form of juices, shakes and smoothies cause the food to speed through the mouth and stomach and go directly into the intestine without any of the proper processing. Without preparation, only the sugars can be well absorbed. That sugar hits the blood rapidly causing a sugar high which might later be followed by a crash as insulin levels rise. Protein powder comes in unnaturally small pieces. Protein can be broken down into sugars if too rapidly absorbed. Fats cannot be turned into sugars but protein can.
At Costco they often have a sales display of a big, heavy blender. The demonstrator declares that you can get all of the vitamins needed with a pound of carrots in one, single drink. Wrong. You will get all the sugar from that pound of carrots but the undigested vitamins and minerals will not be well absorbed. The fiber will be in tiny pieces, not chewed in bigger pieces that the bacteria in our intestine should have. Author Michael Pollen says that there is no healthy meal that fits into the cup holder of your car.
Following a healthy diet is simple: eat mostly whole plant-based foods, some protein from meat or seafood and importantly, always eat calmly and with intention. These are considered Slow Foods, not Fast Foods. Most fast food is very soft and can be gobbled down rapidly, or worse, turned into a liquid drink. Soup and salad is acceptable because salad ingredients slow down the absorption process along with the soup, which is eaten a spoonful at a time. Soft drinks and juices contain huge amounts of sugar, and flow rapidly through the magenstrasse into the intestine. Water is still the best drink to have during a meal and it doesn’t have to be cold. Hot water, tea or coffee is fine (with minimal sugar). The French and Italians have it right. They eat healthy food in a relaxed atmosphere, with good taste and in small portions.