It All Starts With Digestion
The food that we eat is digested and broken down into essential nutrients that the body can use as fuel, including glucose. Insulin, produced by the pancreas, is a hormone that helps glucose enter the cells to be used as energy.
Blood glucose levels generally follow a curved, wave pattern throughout the day. The amount of glucose rises after a meal as the digestive system goes to work, and falls a few hours later before your next meal. Ideally, the curves are moderate -- that is, the peaks and lows stay within a certain range of concentration in the blood. Outside of this ideal range, the highs and lows can cause symptoms like irregular heartbeat, fatigue, trouble concentration, sweating or even loss of consciousness. While these can be corrected quickly with the ingestion of liquid glucose (in the case of low blood sugar) or medication like insulin (in the case of high levels), long term problems can occur if these episodes become frequent. Long-term high spikes in blood sugar can damage the vessels of the heart, kidneys, eyes and nerves.
Which Foods Will Raise Blood Sugar?
Essentially, anything that gets broken down into glucose. This includes grains, dairy, fruit and some vegetables. Fat does not affect blood glucose on its own, and protein has a minimal effect.
One way to compare how foods affect glucose levels is a system of measurement called the glycemic index (or GI) -- you may have heard of foods being marketed as "low GI." The GI measures the effect that a food has on blood sugar levels, comparing the food to the same amount of sugar. The scale measures 0-100, with 100 being the effect that pure sugar has on the blood.
Foods with a low GI (less than 55) cause a slower, lower rise in blood sugar. These include wholegrain breads, high-fiber cereals, beans, most fresh fruit, and milk. Foods with a high GI (greater than 70) cause a faster and higher rise in blood sugar levels. These include white bread, white potatoes, sports drinks, refined cereals like corn flakes, and some fruit candies.
Aiding Slow Digestion
Some dietary components can help slow digestion, which means that the glucose is absorbed into the bloodstream slowly and blood levels do not spike as high. These include fiber, protein and fat. For example, if a fruit is eaten in its whole form instead of juice, the added fiber of eating the whole food will help blunt the rise in blood sugar. This way, you don't have to entirely cut out high GI foods, but it's a good idea to combine them with low GI foods. Some cereals are high GI, but if you add milk to the cereal, for one example, the protein and fat in the milk will help slow the digestion and lower the GI of the meal.
Eating at the Right Times
The timing of meals can also help avoid blood sugar dips and spikes. Make sure you eat breakfast, as your blood sugar will be lowest in the morning. Avoiding breakfast means that your blood sugar will continue to drop, potentially low enough to cause symptoms. Eat regular meals throughout the day, as going too long without food can also cause dips
The only way to lower blood sugar (in a person without diabetes) is to wait. Exercise can speed the process along, as your body uses up the glucose for energy while physically active.
Testing for Glucose Levels
If you're concerned about your blood sugar levels, a fasting glucose test can be included in any yearly monitoring blood tests that your doctor recommends. There is also a test called Hemoglobin A1c, which measures how well your blood sugar is controlled over the previous three months. If you have been diagnosed with diabetes, it's important to speak to your doctor or certified diabetes educator about controlling your blood sugar through medication or insulin if necessary. You can also ask to speak to a dietitian about using the glycemic index of foods to create a meal plan.
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Carolyn McAnlis, RDN, is a Registered Dietitian Nutritionist who has a special interest in preventing chronic disease through nutrition. She graduated from Syracuse University with a Bachelor of Science in Nutrition Science & Dietetics and a minor in Psychology. After completing a full-time dietetic internship at the University of Virginia Health System, she has developed a passion for convincing others that healthy food can be delicious through her blog A Dietitian in the Kitchen.