The main reason you need to eat is for energy but have you ever noticed awhile after eating a giant piece of cake you feel anything but energized? In fact, you may feel very sleepy and ready for a nap? This is a result of three factors, all of which lead to delayed breathing, and a feeling of sleepiness.
1. Simple Carbohydrates
Starches (white pasta, rice, bread, potato chips, flour tortillas), sugar, or foods high in sugar (cookies, candy, and cakes) have a higher respiratory quotient than protein and healthy fats. Foods that have a higher respiratory quotient metabolize into carbon dioxide quickly. Carbon dioxide is the by-product which escapes your lungs as you exhale. Having high carbon dioxide in the body makes you feel weak and tired. Simpler carbohydrates have a higher respiratory quotient, and therefore will make you feel less energized, weak, and tired. You should still consume complex carbohydrates for the many health benefits such as high fiber, vitamins, and minerals contained in these foods, but when choosing starchy foods always opt for the whole grain, whole wheat, whole oat, or whole corn option.
2. Foods High in Sodium
Foods that are high in salt or are heavily processed increase water retention in the body giving you a heavy, fatigued feeling. Sodium is an electrolyte in your body which attracts water. Having too much sodium in the body causes water to be obtained in places it should not such as your blood stream (causing high blood pressure) and the interstitial tissues of your lungs. Again, this leads to difficulty breathing and a weighty, tired, weak feeling due to excess water weight. Don't worry, you're likely getting all the sodium you need by eating natural foods because all foods including fresh fruits and vegetables contain natural sodium. Read food labels on packed items for sodium and purchase items labeled as "low sodium." By law these foods can only contain 140mg or less per serving. Try to stay under 1800mg sodium for the entire day.
3. Carbonated Foods
Carbonated beverages and chewing gum cause your stomach to retain a lot of air, which can also give you a worn-out feeling. Having a very full stomach actually pushes against your diaphragm, the main muscle helping your lungs breath efficiently. At the same time you need more oxygen to digest a larger meal. Chewing gum causes you to swallow air and carbonated beverages contain a lot of air in the bubbles which fill your stomach causing your stomach to push on your diaphragm, an important muscle needed to breathe efficiently. Carbonated beverages also contain dissolved carbon dioxide helping to increase the carbon dioxide in your body after consumption. Not to mention if the carbonated beverage of your choice is caffeinated, the 'crash' that follows a caffeine energy rush combined with the high carbon dioxide and air content is a double whammy.
To feel energized, eat smaller meals to avoid an overly full stomach and base your diet on lean protein such as beans and tofu, healthy fats like nuts, and complex carbohydrates like non-starchy vegetables. Stay away from sugar, salt, carbonated beverages, and chewing gum.