研究发现大多糖尿病患者用生酮、地中海等饮食法可有效控制血糖，如何看待这一结论？

在一些糖友论坛上，每当到分享控糖、抗糖的经验时，总有些糖友谈到自己采用了所谓“低碳水饮食”甚至是“生酮饮食”的新饮食模式，短期内就将血糖控制到了比较理想的水平，而且体重也迅速下降，真可谓“控糖”“减肥”一箭双雕。

那么，什么是“低碳水饮食”、“生酮饮食”？连目前的医学都无法治愈、需要终生用药的糖尿病，真的只靠转换一种饮食方式就能完全控制住吗？“低碳水饮食” 就是控制碳水总量的饮食方法；按照碳水化合物所占一天的供能比例又分几种情况：碳水占25%~30%的为“温和低碳水饮食”，20%左右的为“控制型低碳水饮食”，10%左右的为“极低碳水饮食”，5%左右的就是所谓的“生酮饮食”。

“低碳水饮食”是把双刃剑

无论是减肥人士还是需要控制血糖的糖尿病患者，有一条很让人“难以忍受”的要求是，需要严格控制饮食——而这让很多“吃货”们叫苦不迭。而“低碳水饮食”甚至是“生酮饮食”特别吸引人的一点是：只需控制碳水化合物的摄入，对其他食物则无需特别控制。具体到日常饮食中就是少吃甚至不吃谷薯类食物；而蔬菜水果特别是肉类，可以敞开了吃。

那“低碳水饮食”的原理是什么呢？简单说来，正常情形下身体是靠分解碳水化合物形成葡萄糖为机体供能；在碳水化合物不足的情况下，身体就会转而燃烧脂肪来进行供能。不分解碳水化合物就不会形成葡萄糖，血糖就不会有太大的波动：这似乎是“低碳水饮食”对糖友们最有诱惑力的一点。

但是，在脂肪分解的过程中会生成一种不完全的代谢中间产物“酮体”。如果没有酮体，人体在低碳水摄入的状态下就无法正常运转：有些身体组织（主要是大脑和神经系统）不能直接使用脂肪酸作为能源。在它们需要能源的时候，会先找葡萄糖；如果葡萄糖不够用，就得找酮体顶上去。一般来说，只要碳水化合物摄入低于100g，酮体就会开始产生；碳水越低，酮体产生越多。

“低碳水饮食”对糖尿病有效果吗？

尽管有部分研究声称“低碳水饮食可以短期内缓解2型糖尿病”，但无论是结果的显著性还是研究本身的严谨性和全面性都有待商榷。或者说，迄今为止尚没有有效的研究能证明所谓的“低碳水饮食”对糖尿病有明显的作用。

但是，正如上文说到的，这种饮食模式产生的酮体也正是糖尿病并发症“酮症酸中毒”里面的那个“酮体”，而且二者的形成机理基本一致：身体没有足够的葡萄糖作为能量，随即转而消耗脂肪为机体供能。而如果身体内的酮体水平超过了所能代谢的极限，就会诱发酮症中毒反应；由此看来，“低碳水饮食”对于糖友们来说实在是得不偿失。

除了对血糖水平“短暂的”缓解之外，低碳水饮食还会存在其他一些隐患，最主要的就是低血糖以及因为过多摄入脂类食物而造成的高血脂。

总体来说“低碳水饮食”仍然存在争议，实际应用中也存在一些风险。对于中国居民来说，谷类食物作为主食，在饮食结构中占有重要地位；如果贸然追随“低碳水”饮食结构，未必能有较大的健康获益。

回到原点：一旦确诊了糖尿病，就意味着需要终生服药或注射胰岛素进行治疗。很多糖友都希望能有某种“偏方”或者“奇迹”可以不依靠治疗而控制病情；“低碳水饮食”恰好就是迎合了部分糖友的这类心理。但是，我们必须正视现实：以目前的医学水平，糖尿病是无法治愈的，只能在医生的指导下通过正规的手段进行血糖的控制。

盲目迷信所谓的“偏方”，贻害无穷！

EATING PATTERNS

Consensus recommendations

• A variety of eating patterns (combinations of different foods or food groups) are acceptable for the management of diabetes.
• Until the evidence surrounding comparative benefits of different eating patterns in specific individuals strengthens, health care providers should focus on the key factors that are common among the patterns:
  
• ○ Emphasize nonstarchy vegetables.
  ○ Minimize added sugars and refined grains.
  ○ Choose whole foods over highly processed foods to the extent possible.

• Reducing overall carbohydrate intake for individuals with diabetes has demonstrated the most evidence for improving glycemia and may be applied in a variety of eating patterns that meet individual needs and preferences.
• For select adults with type 2 diabetes not meeting glycemic targets or where reducing antiglycemic medications is a priority, reducing overall carbohydrate intake with low- or very low-carbohydrate eating plans is a viable approach.

What is the evidence for specific eating patterns to manage prediabetes and prevent type 2 diabetes?

The most robust research available related to eating patterns for prediabetes or type 2 diabetes prevention are Mediterranean-style, low-fat, or low-carbohydrate eating plans (26,69,74,75). The PREDIMED trial, a large RCT, compared a Mediterranean-style to a low-fat eating pattern for prevention of type 2 diabetes onset, with the Mediterranean-style eating pattern resulting in a 30% lower relative risk (69). Epidemiologic studies correlate Mediterranean-style (76), vegetarian (77–80), and Dietary Approaches to Stop Hypertension (DASH) (76,81) eating patterns with a lower risk of developing type 2 diabetes, with no effect for low-carbohydrate eating patterns (82).
Several large type 2 diabetes prevention RCTs (26,74,83,84) used low-fat eating plans to achieve weight loss and improve glucose tolerance, and some demonstrated decreased incidence of diabetes (26,74,83). Given the limited evidence, it is unclear which of the eating patterns are optimal.

What is the evidence for specific eating patterns to manage type 2 diabetes?

Mediterranean-Style Eating Pattern
The Mediterranean-style pattern has demonstrated a mixed effect on A1C, weight, and lipids in a number of RCTs (85–90). In the Dietary Intervention Randomized Controlled Trial (DIRECT), obese adults with type 2 diabetes were randomized to a calorie-restricted Mediterranean-style, a calorie-restricted lower-fat, or a low-carbohydrate eating pattern (28% of calories from carbohydrate) without emphasis on calorie restriction. A1C was lowest in the low-carbohydrate group after 2 years, whereas fasting plasma glucose was lower in the Mediterranean-style group than in the lower-fat group (90).

One of the largest and longest RCTs, the PREDIMED trial, compared a Mediterranean-style eating pattern with a low-fat eating pattern. After 4 years, glycemic management improved and the need for glucose-lowering medications was lower in the Mediterranean eating pattern group (89). In addition, the PREDIMED trial showed that a Mediterranean-style eating pattern intervention enriched with olive oil or nuts significantly reduced CVD incidence in both people with and without diabetes (91).

Vegetarian or Vegan Eating Patterns
Studies of vegetarian or vegan eating plans ranged in duration from 12 to 74 weeks and showed mixed results on glycemia and CVD risk factors. These eating plans often resulted in weight loss (92–97). Two meta-analyses of controlled trials (98,99) concluded that vegetarian and vegan eating plans can reduce A1C by an average of 0.3–0.4% in people with type 2 diabetes, and the larger meta-analysis (99) also reported that plant-based eating patterns reduced weight (weight reduction of 2 kg), waist circumference, LDL cholesterol (LDL-C), and non–HDL-C with no significant effect on fasting insulin, HDL-C, triglycerides, and blood pressure.

Low-Carbohydrate or Very Low-Carbohydrate Eating Patterns
Low-carbohydrate eating patterns, especially very low-carbohydrate (VLC) eating patterns, have been shown to reduce A1C and the need for antihyperglycemic medications. These eating patterns are among the most studied eating patterns for type 2 diabetes. One meta-analysis of RCTs that compared low-carbohydrate eating patterns (defined as ≤45% of calories from carbohydrate) to high-carbohydrate eating patterns (defined as >45% of calories from carbohydrate) found that A1C benefits were more pronounced in the VLC interventions (where <26% of calories came from carbohydrate) at 3 and 6 months but not at 12 and 24 months (110).
Another meta-analysis of RCTs compared a low-carbohydrate eating pattern (defined as <40% of calories from carbohydrate) to a low-fat eating pattern (defined as <30% of calories from fat). In trials up to 6 months long, the low-carbohydrate eating pattern improved A1C more, and in trials of varying lengths, lowered triglycerides, raised HDL-C, lowered blood pressure, and resulted in greater reductions in diabetes medication (111). Finally, in another meta-analysis comparing low-carbohydrate to high-carbohydrate eating patterns, the larger the carbohydrate restriction, the greater the reduction in A1C, though A1C was similar at durations of 1 year and longer for both eating patterns (112).

Evert, A. B., Dennison, M., Gardner, C. D., Garvey, W. T., Lau, K. H., MacLeod, J., Mitri, J., Pereira, R. F., Rawlings, K., Robinson, S., Saslow, L., Uelmen, S., Urbanski, P. B., & Yancy, W. S. (2019). Nutrition therapy for adults with diabetes or prediabetes: A consensus report. Diabetes Care, 42(5), 731–754. https://doi.org/10.2337/dci19-0014

地中海也好、生酮饮食也好，其实就是糖人们的常识而已：控碳水。

毕竟碳水化合物能直接拉升血糖，你直接不吃碳水，血糖最大的源头（外源性血糖）直接砍了，不能控制血糖就怪了。

另外这两种饮食方法能比较有效地减肥，这是能控制血糖的另一个原因。

我们知道糖尿病患者——无论是一型还是二型——的一个典型症状就是消瘦，而这是因为体内缺乏胰岛素的原因。

一型糖尿病患者由于各种原因，胰岛β细胞被破坏、胰岛素分泌几乎为零；二型糖尿病患者初期表现是肥胖（或者说肥胖导致糖尿病，二者是个恶性循环），但如果不加控制，在糖尿病后期则会迅速消瘦，因为此时患者的胰岛β细胞已经不堪重负衰竭了，体内同样缺乏胰岛素。

那为什么胰岛素缺乏会导致人体消瘦呢？胰岛素的作用是什么？

胰岛素是一种多肽激素，主要由胰岛的胰岛β细胞分泌，通过合成代谢途径发挥作用，调节血液中的葡萄糖水平，将葡萄糖转换为糖原储存到肝脏、肌肉和脂肪组织中，这个过程显然会导致体重增加。所以当人体缺乏胰岛素时会难以利用葡萄糖、无法将其转换为糖原储存到人体组织中[1]。

一型糖尿病患者缺乏胰岛素就不用说了，对于二型糖尿病患者，一开始由于肥胖、缺乏运动、饮食不健康等原因会患上胰岛素抵抗，简单说就是由于上述原因导致人体组织根本不缺乏糖原，而且由于不运动糖原根本用不掉，所以拒绝接收胰岛素传过来的糖原，但这样一来血糖就会居高不下，于是胰腺就会分泌更多胰岛素以对抗胰岛素抵抗，于是血糖就能降下去，但人也会变更胖，可以看到，这其实是一个恶性循环。

如果不加以干预，这个恶性循环会越滚越大，终有一天胰腺会不堪重负衰竭，之后体内就会缺乏胰岛素，然后慢慢消瘦。

其中二型糖尿病患者在胰岛素抵抗这个阶段由于胰岛素超额分泌，所以血糖可以完全正常，但此时血液中胰岛素含量会比正常人高，即高胰岛素血症（Hyperinsulinemia）。

前面说到胰岛素会把糖分储存到肝脏、肌肉和脂肪中，会促进体重增加，还有一个点是血液中胰岛素含量高时，会大幅减少脂肪供能，仅由糖原供能，当糖原消耗完时脂肪供能又跟不上，人就会特别容易饿、且特别饿，甚至出现低血糖现象如心慌手抖，于是又找东西吃，又一个恶性循环。

所以生酮、地中海饮食以及断食都可以减肥，因为这三个方法有个共同点是可以最大程度减少刺激胰岛素的分泌，生酮和地中海饮食的食物促胰岛素分泌指数（FII：food insulin index）很低，可以减轻胰岛素血症，而断食则拉长了空腹间隔，通过延长进食间隔时间强行不让胰岛素分泌，减轻高胰岛素血症，同时进食间隔期间由脂肪供能，加速减肥。

到此其实现代人容易长胖的机制也很清楚了：

由于缺乏运动，温饱不愁的现代人消耗不掉额外的糖分，导致了人体组织的胰岛素抵抗和高胰岛素血症，腹部的内脏器官容易堆积脂肪。

现代食品工业、物流、快递外卖高度发达，大家极容易吃到各种制作精细的食物，但这些食物的促胰岛素分泌指数同样很高，事实上，胰岛素分泌指数最高的那些食物都是工业革命以来才出现的。这些食物能迅速拉高血糖和胰岛素，再加上社交活动、娱乐活动时也会吃东西，而且这些食物还很容易消化，导致过度进食，使人体长期处于高胰岛素血症中，脂肪难以消耗还容易饿，减肥变得难以执行，成为违背身体指令、非常消耗意志力的活动。

而当人体长期处于胰岛素抵抗、高胰岛素血症时和肥胖时，会导致高血糖、多囊卵巢综合症、不孕、高血脂、高血压、高尿酸、动脉硬化等一系列慢性疾病^[2]。

所以，生酮和地中海饮食可以有效减轻高胰岛素血症和肥胖，并因此有效控制血糖。

参考

1. ^https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8232639
2. ^https://my.clevelandclinic.org/health/diseases/24178-hyperinsulinemia