Out of the three primary macronutrients -- proteins, carbohydrates and fats -- only carbohydrates have a significant effect on a food's glycemic index, or GI. When you eat foods high in carbohydrates, your blood glucose level rises. The GI measures how quickly that increase takes place, and how much your glucose level changes. Though monitoring the GI of the foods you eat may help you maintain a healthy weight, stabilize your blood sugar and prevent diabetes, a high-protein diet may not meet all your nutritional needs.
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The glycemic index measures the fluctuations in a healthy person's blood sugar after eating a food containing carbohydrates. Foods that raise blood sugar quickly have a higher ranking on a scale of 1 to 100 than foods that raise blood sugar slowly. Because foods that contain only protein, or protein and fat, have little or no immediate impact on blood glucose levels, the methods used to test GI from these foods on human subjects do not work.
Protein and Blood Sugar
Although your liver eventually converts protein into glucose, the process happens in such a way that the glucose has little or no immediate impact on your blood sugar. According to Marion J. Franz, M.S., R.D., almost none of the glucose that your liver produces from protein enters your general blood circulation. This may be because the amount of glucose produced is so small that your body uses it immediately if you have adequate insulin. Another theory suggests that the insulin triggered by protein may cause such a rapid conversion of glucose to stored energy that the glucose doesn't register when testing your blood sugar levels.
The age-old pairing of meat and potatoes may make sense if you're trying to lower the overall GI of your diet. Because proteins have little or no effect on your blood sugar, eating meat with a starchy, high-GI food like potatoes may counterbalance the effects of the carbohydrates. The U.S. Department of Agriculture's pyramid for healthy eating devotes a relatively small segment to protein-based foods, emphasizing lean proteins like legumes, fish, tofu and skinless poultry.
Risks of a High-Protein Diet
Even if you're focusing your diet on foods with a low GI, a high-protein diet may not be healthy for you. High-protein diets may lead to weight loss in the short term, but restricting carbohydrates for more than three or four months may lower your fiber intake, cause constipation and increase your risk of colon cancer, says MayoClinic.com. Many high-protein foods, such as beef, cheese and full-fat dairy products, are high in saturated fats, which may raise your cholesterol and increase your risk of heart disease.
When you combine protein with fiber and carbohydrates in the same food or meal, you benefit from the tissue-building amino acids in the protein and the energy released by the carbohydrates. You don't have to eliminate high-GI foods or base your diet on proteins to maintain a healthy weight and stable blood sugar -- just combine these foods with plenty of fiber-rich, low-GI legumes, vegetables, fruits and whole grains.