Although all calories from all foods provide energy, some foods promote stable energy levels and some foods promote energy surges followed by a quick crash. Other foods can make you feel sluggish and tired after eating. For optimal energy, avoid simple sugars from sodas, candy and desserts; refined grains from baked goods, white bread and white pasta; and fatty fried foods.
Cake, candy, cola and fruit drinks are concentrated sources of sugar. Your body breaks down sugar very quickly, sending it immediately into your bloodstream. This gives you the familiar "sugar high." In response to all that sugar, your body produces insulin to usher the sugar into cells. It does this so quickly, however, that you can quickly experience low blood sugar. This is the crash that follows the high. When it happens, you're likely to feel tired and weak.
Refined grains have been stripped of their digestion-slowing fiber during processing. Your body is able to quickly break them down into sugar, which is what all carbs eventually become. However, the speed with which refined carbs enter the bloodstream results in a reaction in your body very similar to what happens after you eat sugary foods. Your insulin rises to clear up all that sugar and then you can experience symptoms of low blood sugar including fatigue.
On the other end of the digestion spectrum are high-fat foods, such as fried chicken and french fries. Fatty foods take your body a long time and a lot of energy to digest. Fat also coats blood cells, reducing their elasticity and their ability to transport oxygen, which you need for energy, throughout your body. In fact, a review published in the journal Sleep in May 2012 reported that a high-fat diet is associated with increased sleepiness.
To keep your energy levels stable, limit your intake of added sugars. Get a sweet fix from fresh fruit, which supplies fiber, vitamins and minerals your body needs for optimal functioning. Replace sugary sodas with water or unsweetened tea. Choose healthy sources of complex carbs at each meal including brown rice, leafy greens, beans and whole-grain bread and pasta. Your body digests these more slowly, which promotes stable energy levels. Eat smaller amounts of fats at one sitting, and choose healthy fats from fish, nuts and olive and canola oils over trans and saturated fats found in greasy fried foods.