什么是糖异生？
摘要
糖异生是机体从非碳水化合物来源（如蛋白质和某些脂肪）合成葡萄糖的代谢过程。这一内置系统使机体无需通过饮食摄入碳水化合物即可维持稳定的血糖水平。Berg 博士解释说，正因为存在这一过程，碳水化合物并非必需的膳食营养素。
核心要点
- 糖异生字面意思为”生成新的葡萄糖”——gluco（葡萄糖）+ neo（新）+ genesis（生成）。
- 机体可以从蛋白质和某些脂质（特别是甘油三酯）中产生葡萄糖。
- 糖异生的主要目的是预防hypoglycemia（低血糖）。
- 它有助于在餐间及禁食期间维持稳定的blood sugar水平。
- 机体内几乎所有细胞都可以利用ketones作为替代能量来源。
- 少数例外——眼部某些细胞及大脑的小部分区域仍需要葡萄糖。
- 红细胞同样需要葡萄糖，无法利用酮体。
- 由于机体能够自行合成葡萄糖，饮食中的碳水化合物并非必需。
详细说明
糖异生的机制
Gluconeogenesis是一条代谢通路——即一系列生化反应步骤——将非碳水化合物底物转化为葡萄糖。主要利用的两种来源为：
- 蛋白质（由膳食蛋白质或肌肉组织分解而来的氨基酸）
- 某些脂质，特别是甘油三酯（一种存在于食物中并储存于体脂中的脂肪类型）
这意味着机体拥有一套独立于碳水化合物摄入的内部葡萄糖合成系统。
机体为何需要这一系统
糖异生的主要驱动力是血糖调节。当你长时间不摄入碳水化合物时——例如在**intermittent fasting**、长时间禁食或ketogenic diet期间——血糖可能会降至危险水平。糖异生通过为特定需要葡萄糖的组织提供恰好足量的葡萄糖来防止这一情况发生。
哪些细胞需要葡萄糖，哪些可利用酮体
Berg 博士强调了一个重要区别：
- 机体内大多数细胞具有灵活性，可以用ketones作为主要能量来源代替葡萄糖。
- 仍需要葡萄糖的细胞包括：
- 眼部某些细胞
- 大脑特定的小区域
- 红细胞（红细胞没有线粒体，无法代谢酮体）
对于这些细胞，糖异生确保即使在限制碳水化合物摄入期间，葡萄糖供应也能持续不断。
碳水化合物并非必需营养素
Berg 博士的核心观点是碳水化合物并非必需膳食营养素。与蛋白质（提供必需氨基酸）和脂肪（提供必需脂肪酸）不同，并不存在所谓的”必需碳水化合物”。当机体需要葡萄糖时，可以通过糖异生精确合成所需的量——无需从饮食中摄入碳水化合物。
相关概念
- gluconeogenesis
- hypoglycemia
- blood sugar regulation
- ketones
- ketogenic diet
- intermittent fasting
- triglycerides
- fasting
English Original 英文原文
What Is Gluconeogenesis?
Summary
Gluconeogenesis is the metabolic process by which the body creates glucose from non-carbohydrate sources such as protein and certain fats. This built-in system allows the body to maintain stable blood sugar levels without requiring dietary carbohydrates. Dr. Berg explains that because of this process, carbohydrates are not an essential dietary requirement.
Key Takeaways
- Gluconeogenesis literally means “making new glucose” — gluco (glucose) + neo (new) + genesis (create).
- The body can produce glucose from protein and certain lipids (specifically triglycerides).
- The primary purpose of gluconeogenesis is to prevent hypoglycemia (low blood sugar).
- It helps maintain stable blood sugar levels between meals and during fasting.
- Nearly all cells in the body can run on ketones as an alternative fuel source.
- A few exceptions exist — certain cells in the eye and small regions of the brain still require glucose.
- Red blood cells also require glucose and cannot use ketones.
- Because the body can manufacture its own glucose, dietary carbohydrates are not essential.
Details
The Mechanics of Gluconeogenesis
Gluconeogenesis is a metabolic pathway — a series of biochemical steps — that converts non-carbohydrate substrates into glucose. The two primary sources used are:
- Protein (amino acids broken down from dietary protein or muscle tissue)
- Certain lipids, specifically triglycerides (a type of fat found in food and stored in body fat)
This means the body has an internal glucose manufacturing system that operates independently of carbohydrate intake.
Why the Body Needs This System
The main driver of gluconeogenesis is blood sugar regulation. When you go extended periods without eating carbohydrates — such as during intermittent fasting, prolonged fasting, or a ketogenic diet — blood glucose could drop dangerously low. Gluconeogenesis prevents this by supplying just enough glucose to meet the demands of tissues that specifically require it.
Which Cells Need Glucose vs. Ketones
Dr. Berg highlights an important distinction:
- Most cells in the body are flexible and can use ketones as a primary fuel source instead of glucose.
- Cells that still require glucose include:
- Certain cells in the eye
- Small specific areas of the brain
- Red blood cells (which have no mitochondria and cannot metabolize ketones)
For these cells, gluconeogenesis ensures a continuous glucose supply even during carbohydrate restriction.
Carbohydrates Are Not Essential
The overarching point Dr. Berg makes is that carbohydrates are not a dietary essential. Unlike protein (needed for amino acids) and fat (needed for essential fatty acids), there is no equivalent “essential carbohydrate.” If the body requires glucose, it can synthesize exactly what it needs through gluconeogenesis — no dietary carbs required.
Mentioned Concepts
- gluconeogenesis
- hypoglycemia
- blood sugar regulation
- ketones
- ketogenic diet
- intermittent fasting
- triglycerides
- fasting