The effect of varying carbohydrate intake upon plasma insulin and glucagon was tested in five volunteers. One week of carbohydrate restriction lowered fasting insulin from 18 to 11 μU per milliliter, whereas fasting glucagon rose from 100 to 136 pg per milliliter, a decline in insulin-glucagon ratio (I/G) of 3.9 to 1.6. One week of isocaloric restoration of carbohydrate to the diet increased fasting insulin to 14 μU per milliliter, and glucagon declined to 65 pg per milliliter, a return of I/G to 4.4. A week of carbohydrate restriction changed the response of insulin and glucagon to protein, insulin rising only to 15 μU per milliliter, whereas glucagon rose from 126 to 218 pg per milliliter, I/G remaining unchanged. After one week of a carbohydrate-containing diet insulin rose to 38 μU, and glucagon to only 167 pg per milliliter, I/G rising from 4.35 to 8.2. The results support the key glucoregulatory role of the alpha and beta cells in influencing hepatic glucose production from both endogenous and ingested glucose precursors in accordance with need.
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