The effect of cooking upon the blood glucose response to ingested carrots and potatoes

Ten insulin-dependent diabetic subjects were given the following tests in randomized order: 50 g glucose dissolved in water, 250 g raw and cooked potato (equal to 50 g carbohydrate), 270 g raw and cooked carrot (equal to 25 g carbohydrate), and 4 h of fasting. Blood glucose was measured for 4 h following the tests. The postprandial blood glucose responses after pure glucose and cooked potato were almost similar (90-min values: glucose 8.8 mmol/L, cooked potato 8.0 mmol/L), while the response after raw potato was considerably slower and weaker (90-min value: 3.3 mmol/L). There were no differences between the postprandial blood glucose responses after raw and cooked carrot (90-min values: raw carrot 3.2 mmol/L, cooked carrot 2.8 mmol/L), but the responses were statistically different from blood glucose values during fasting alone (90-min value: 0.8 mmol/L). The study shows that cooking is responsible for the rapid increase in blood glucose after ingestion of cooked potato, while no such phenomenon is seen after cooking of carrots.