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Why do we eat? Energy, Building Blocks and Essential Nutrients
A healthy diet supplies energy (fuel for the cells in the form of glucose) , building blocks and essential nutrients. Our cells
individually work to make us function. When our heart beats, lungs breathe, or muscles contract, it is individual cells that do all that.
They fuel up not on pizza or cheeseburgers, but rather use only the simplest molecules, such as glucose, amino acids or fatty acids.
These simple molecules are called building blocks.
We cannot directly use a pizza in our body -- it just does not serve a function in it's pizza form. But that pizza can be broken down .
The protein in the meat, cheese and crust is broken down in amino acids. The fats in the crust, meat and cheese are broken down to
glycerol and fatty acids. The carbohydrates in the crust, and the vegetables are broken down into simple sugars such as glucose. The
body then uses the glucose, amino acids, fatty acids and glycerol to build the molecules that we do need. Given a source of organic
carbon (such as sugar) and organic nitrogen (such as amino acids from digestion of proteins), an animal can fabricate a great variety of
organic molecules by using enzymes to rearrange the molecular skeletons of precursors. There are some things that the body needs,
however, but cannot make. These are called essential nutrients.
Essential nutrients are amino acids,fatty acids, vitamins and minerals. We can make 11 amino acids, but must ingest other 9 (we
need 20 amino acids in total). Humans can manufacture some, but not all fatty acids. We do make some of the vitamins -- organic
molecules-- we need (actually bacteria in our gut make some), but we have to eat the rest. Finally, we need minerals in very small
quantities, but we obviously cannot make elements. So, we now know we need to eat foods that supply carbohydrates, proteins, fats,
vitamins and minerals. But where do they come from?
Nutrition Labels: Understanding and using them
The nutritional information given on a food label is based on a serving size. It relates this serving size to the % daily value. The daily
value for calories depends on one's sex and age, but the average is considered to be 2000.
When you add up all that you have eaten on a given day, the proportions of the three macromolecules (carbs, proteins and fats) should
be a certain percentage of 2000 kcalories:
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65 grams should come from fat (30% of the kcalories); 20 grams of these 65 grams from saturated fat (10% of the
kcalories);
300 grams should come from carbohydrates (60% fo kcalories);
25 grams of fiber (no kcalories);
50 grams should come from protein (10% of kcalories);
fat yields 9 kcalories/gram
carbohydrates yield 4 kcalories/gram
proteins yield 4 kcalories/gram
9 kcalories/gram * 65 grams = 585 calories from fat
4 kcalories/gram * 300 grams = 1200 calories from carbohydrates
4 kcalories/gram * 50 grams = 200 calories from protein
Food Pyramid
We require three types of macromolecules (macronutrients) to supply energy and building blocks: carbohydrates, proteins and fats.
We also require minerals and vitamins.
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More than half of our diet should come from bread, cereal, rice and pasta, preferably whole-grained (more fiber, vitamins and
minerals). We should have 6-11 servings of these foods each day.
We should have 2-4 servings of fruits and 3-5 servings of vegetables. Fruits and vegetables are a great source of fiber,
vitamins and minerals.
We need 2-3 servings of dairy products and meats.
Fats and sugars should be minimized.
Carbohydrates -- sugar and starch. Principle product of carbohydrate breakdown is glucose. Glucose not immediately needed for
energy is stored as glycogen in the liver and muscles. When we are eating carbs, we are eating from the bottom two levels of the food
pyramid -- grains, bread, cereal, pasta, vegetables and fruit. Sixty percent of our calories each day should come from carbohydrates.
Complex carbohydrates (white flour products) are a good source. They lack fiber, however. Most fiber in complex carbs has been
removed. Fiber is the casing around the grain. Supercomplex carbs are richer in fiber, thus a healthier source for both carbohydrates
and fiber. Eat whole-grain products, such as oatmeal, barley, bulgur wheat, wild and brown rice. They are better than just complex
carbs.
In 1996, Americans ate 152 pounds of sweeteners in products found at the very top of the pyramid -- called fats and sweets. Although
a product label must include all ingredients in the order of greatest to least amount, the large amount of sugar is often hidden because
several kinds of sugar are often used in a given product. Some of them sound quite healthy: high fructose corn syrup, dextrose, corn
syrup, honey, fructose, and finally sugar. Be aware, they are all just sugar!
Proteins give cells their structure and are the components of enzymes, hormones, neurotransmitters, muscles and more. They are
made up of amino acids. We need proteins in our diet because we break them down and use the amino acids to build various proteins
that our bodies need -- hormone, enzyme, muscle fiber. We can use protein as a source of energy, but this is inefficient. Usually the
body does not use proteins as an energy source because proteins are too valuable for muscle, enzymes, antibodies, hair, cartilage,
hormones, etc. The body can break proteins down during starvation, after all available carbohydrates and fats have been used, by
converting amino acids to glucose in the liver. The third level of the food pyramid supplies our protein needs: 10%of our calories
should come from protein each day. Proteins are described as either complete or incomplete.
Complete proteins supply all 20 amino acids. We can make 11 of these amino acids but the other nine are considered essential, which
means that we have to eat them because we cannot make them. Animal proteins such as meat, eggs, milk and cheese supply all 20
amino acids. Plant proteins do not. So, a vegetarian diet has to be carefully planned to include a mixture of corn, beans, rice and
grains.
A vegetarian diet can be healthier than a diet that includes red meat and dairy products, as these contain saturated fats. However, a
vegetarian diet is not recommeded for young children because it is so hard to get all the essential amino acids. Eating meat supplies all
20 amino acids. No plant protein can supply all 20 amino acids, except soy and quinoa. So, the diet must include a combination of
plant proteins. It is no coincidence that many third world diets include corn and beans. Corn and beans together, supply all 20 amino
acids. Amino acids are not stored like sugars are. The liver can hold on to them for a while, but you must eat all 20 every day in order
to keep the body running smoothly. A vegetarian diet, thus, takes a bit more tought and preparation than the diet of carnivores.
Lipids -- fats, oils, cholesterol-- are another source of stored energy. They should make up no more than 30% of our diet and should
include mono- and poly- unsaturated fats instead of saturated fats! Remember that some fats are essential because we cannot make
them in our bodies. We must eat fat to get the essential fatty acids. We need fats to make up new cells. The downside of fat is that it
causes cardiovascular diseas, by clogging the arteries. Fats are found in many of the foods we eat -- usually the foods that taste best.
They are also found at the top of the food pyramid, and should be used with restraint.
Saturated fats are those found in meats, candies, dairy products and pastries, and are associated with cardiovascular disease because
they raise the levels of LDL (or popularly known as "the bad cholesterol") in our blood. Polyunsaturated fats like canola oil lower
the risk of cardiovascular disease, but increase the risk of cancer. What fats are then good for you? Olive and peanut oils are
monosaturated and seem to be best for us because they do not cause heart disease or cancer.
Hydrogenated vegetable oils sounds like a good thing but it is not! They are vegetable, but hydrogenated means that they have been
made saturated and thus contain trans fatty acids.
Cholesterol is made by the body and is necessary because it is the precursor of steroid hormones such as estrogen, progesterone, and
testosterone. It is also found in plasma membranes, and helps keep them fluid at lower temperatures.
The bottom line is that a healthy diet should come from a variety of sources. Furthermore, one should always remember that any food
is healthy food when consumed in moderation! Remember the food pyramid and stick to its model and you will be eating healthy. Add
to that regular exercise -- half an hour of brisk walking daily will do-- and you will live a healthy and happy life! It is not as hard as
many of us may have thought, is it?