Protein: The Muscle Maker
It's time to give protein the credit it deserves. This nutrient is so much more than what's found in a piece of steak or a block of tofu. Protein from your diet provides the raw materials for the proteins your body builds to execute critical tasks, such as digesting food, building muscle, producing vitamins, and managing energy use. While protein from food and proteins made in the cells are the same substance, they have different functions in the body. Here's a chance to muscle up on protein and its many roles.
Each type of protein in the human body (there are an estimated 20,000 to 25,000) is made of the same 20 building blocks, chemicals called amino acids that consist of carbon, nitrogen, hydrogen, oxygen, and sometimes sulfur atoms. The amino acids that link together to form proteins come either from the diet or are made by the body inside cells for specific purposes. Some proteins work inside cells while others enter the bloodstream or embed themselves in cellular membranes. Proteins are also used as raw material for building muscle. Muscles are mostly made up of fibrous proteins; that's why the meat we eat is so high in protein.
The protein insulin (above)
Protein is pretty complex stuff, chemically speaking. The amino acids that form a protein determine its three-dimensional structure. This is a true biological marvel, as if a strand of cooked spaghetti spontaneously folded itself into a bow. A protein's structure is what makes it able to perform its tasks.
Genes provide the blueprint for building each protein. But gene mutations that create errors in the sequence of amino acids can disable a protein, causing disease.
Not all dietary protein is created equal. Some foods are abundant in certain amino acids that humans need but deficient in others. While the human body can make some amino acids from scratch, nine "essential" ones must come from the diet.
Protein sources that contain roughly the correct proportion of essential and nonessential amino acids for sustaining human life are considered high-quality proteins. Eggs, meat, dairy, and soy are all sources of high-quality protein. Protein from corn, grains, beans, and vegetables tends to be of lower quality. This is why it's important for people, particularly vegetarians and vegans, to get their protein from a variety of sources, ensuring a good mix of amino acids in the diet.
In places where food is plentiful, like the United States, most people don't need to worry about getting enough protein. Adults should consume around 50 grams of high-quality protein each day; pregnant and breast-feeding women need a bit more. Experts recommend that about a quarter of a meal plate be filled with a food that's high in protein but low in saturated fat, like fish.
However, for some people with diabetes, eating excess protein can be harmful. Diabetes can cause kidney damage, which is exacerbated by too much protein in the diet. Doctors may recommend that people with kidney disease follow a lower-protein diet.
Cooking and eating protein break it back down into its basic components, amino acids. As a result, people can't just absorb whole proteins through the diet, but instead must build all their body's proteins from scratch. Whether dietary protein comes from beans, milk, beef, fish, or another source, the body treats it all pretty much the same. Stomach acid "denatures" proteins, causing them to unfold from their pretty structures (box, right) and flop around like boiled spaghetti. Denatured proteins are broken down by enzymes in the stomach and small intestine into their constituent amino acids. That allows the body to absorb them through the walls of the small intestine.
The body needs amino acids for different purposes. They can, of course, be used to make more proteins, like enzymes, hormones, and antibodies, which constantly undergo turnover in the body, being created and destroyed and created again, as needed. Amino acids also serve as a source of nitrogen, for making nonessential amino acids or nucleic acids, the building blocks of DNA. Under extreme conditions, some amino acids can also be converted to glucose or ketones (fat-like molecules) to provide energy should carbohydrates and fats become scarce. If a person is starving, proteins in the body, like those in muscle, may even be dismantled for energy.
People with diabetes have to make careful choices about what to eat. The key with protein is to make it part of a well-balanced diet and ensure that it isn't too fatty. While proteins in the body are complex in their makeup and purposes, it's simple enough with a little planning to get the right amount and kinds of protein for a healthy diet.