Sugar and caffeine are often found in coffee, energy drinks and sodas. Although they are stimulants, both products can make you feel sleepy after the initial surge of energy they can provide. The way the body processes sugar and caffeine leads to fatigue in some people, a condition sometimes called the "afternoon slump."
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Caffeine stimulates the central nervous system. Short-term effects include increased irritability, restlessness, alertness, rise in body temperature and increased need to urinate. As the day continues, the impact of caffeine can turn to fatigue. Gayle Reichler, a registered dietitian and certified nutritionist, notes in her book "Active Wellness: Feel Good for Life," that within the first five minutes of caffeine consumption, your body releases stress hormones into your bloodstream. "Within the next hour or so, after the stress response dissipates, you will probably feel more tired and hungry," Reichler notes.
Low blood sugar levels may be responsible for fatigue and lethargy. In his blog post, "What Can Be Done to Prevent the ‘Mid-Afternoon Slump’?" Dr. John Briffa notes that when your blood sugar level rises, your body responds by producing insulin. "The higher the rise in blood sugar that follows lunch, the more likely the body is to overcompensate for this, leading to low blood sugar levels about two or three hours later, causing brain and body energies to stall," Briffa states. Bread is a common cause of fatigue because it releases sugar into the bloodstream, he notes.
Recommended Caffeine Limits
Limiting your caffeine intake can reduce the amount of stress hormones your body releases. The National Drug and Alcohol Research Centre in Australia notes that consensus among physicians is that 600 mg or less of caffeine per day carries little risk. If you're anxious, stressed or pregnant, less than 200 mg of caffeine per day is recommended, the organization adds. An 8-oz cup of brewed coffee has 95 to 200 mg of caffeine. A 12-ounce can of cola has about 35 mg of caffeine.
Recommended Sugar Limits
Controlling the amount of sugar you consume during the day might help you regain some energy. The American Heart Association recommends limiting added sugar intake to 6 tsp per day for women and 9 tsp per day for men. That amount of sugar may seem like a lot, but it is surprisingly easy to consume much more than the recommended limit. For example, soda can contain as much as 41 grams of sugar—the equivalent of 10 tsp—in one 12-oz serving, according to the Harvard School of Public Health.