不吃早餐可诱发急性胰岛素抵抗

旧金山——一项小型随机交叉试验显示，不吃早餐可引起急性胰岛素抵抗和游离脂肪酸水平。而且只需1天不吃早餐就能引起这种效应，经常不吃早饭则可能导致更严重的代谢紊乱，如慢性胰岛素抵抗，甚至可能进展至2型糖尿病。

Elizabeth A. Thomas博士

科罗拉多大学内分泌学系的Elizabeth A. Thomas博士在内分泌学会(ES)2013年会上报告称，她与同事招募了9名肥胖的非糖尿病志愿者，在间隔约一个月的两个研究日对这些志愿者进行了研究。这些女性的平均年龄为29岁，平均体重指数(BMI)为31 kg/m²。8名志愿者自称有吃早餐的习惯。

志愿者随机在前一研究日吃或不吃早餐，而在后一研究日则相反。研究者要求志愿者在这两天之前不要锻炼，并且让她们在研究日前一晚吃标准化晚餐。在研究日空腹检测实验室指标，4 h后让志愿者吃标准化午餐。午餐后3 h内每30分钟采1次血，然后吃标准化晚餐。

结果显示，吃早餐日和不吃早餐日的午餐前胰岛素、血糖水平并无显著差异。不吃早餐日的午餐后胰岛素和血糖水平明显高于吃早餐日，提示发生了急性胰岛素抵抗。

与吃早餐日相比，不吃早餐日的早餐时间后1 h内胰岛素水平显著上升，并且在2 h时仍保持高水平。血糖水平也表现出与胰岛素水平相似的情况。

正如研究者预料的，早餐后游离脂肪酸水平受到抑制，因此不吃早餐日的午餐前游离脂肪酸水平高于吃早餐日。午餐后游离脂肪酸曲线下面积(AUC)的总值和增值均在不吃早餐日更高，提示午餐前游离脂肪酸水平并非AUC增加的原因所在。

午餐前甘油三酯水平在不吃早餐日更低。午餐后甘油三酯AUC总值在不吃早餐日更低，不过AUC增值并无明显差异，提示午餐前甘油三酯水平是AUC总值差异的原因所在。

间接测热检查显示，不吃早餐日的能量消耗减少，呼吸商显著降低，提示脂肪氧化更强烈。

既往流行病学和纵向研究显示，不吃早餐与更多的体重增加和更高的2型糖尿病风险相关，但这些研究多为针对苗条受试者的小型研究，而且无一显示出因果关系。仅有数项短期研究评估了不吃早餐对代谢参数和食欲的影响。

在本项研究中，不吃早餐日的胰岛素AUC总值为12,322 mIU/ml×180分钟，而吃早餐日为8,882 mIU/ml×180分钟。

不吃早餐日和吃早餐日的午餐前游离脂肪酸水平分别为705和287 mEq/L；游离脂肪酸AUC总值分别为33,980和25,692 mIU/ml×180分钟，AUC增值分别为–92,980和–26,008 mIU/ml×180分钟；午餐前甘油三酯水平分别为86和121 mg/dl；甘油三酯AUC总值分别为17,352和24,060 mg/dl×180分钟。

医学文献报告显示，大约10%~20%的美国人常常不吃早餐。发布这项研究结果的新闻发布会的主持人、明尼苏达大学的Lisa Fish博士指出，美国人所吃的早餐很多都是高碳水化合物、低蛋白质，应该从今天开始采取更加均衡的饮食以增进健康。

Thomas博士希望将研究对象增加至20名女性，纳入更多习惯不吃早餐的女性。她还计划在今后的研究中校正锻炼因素。

Thomas博士报告称无相关利益冲突。这项研究由内分泌研究员基金会、国立卫生研究院以及科罗拉多营养肥胖研究中心资助。

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By: SHERRY BOSCHERT, Clinical Endocrinology News Digital Network

SAN FRANCISCO – Skipping breakfast triggered acute insulin resistance and elevated levels of free fatty acids in nine obese, nondiabetic women, compared with a day on which they ate breakfast in a randomized crossover trial.

If just 1 day of missing breakfast could do this, then skipping breakfast regularly over time may lead to further metabolic derangements, such as chronic insulin resistance and possible progression to type 2 diabetes mellitus, Dr. Elizabeth A. Thomas suggested.

The findings give clinicians one more tool to try to convince patients to eat a healthy breakfast, she said at the annual meeting of the Endocrine Society.

She and her associates studied the women on two separate days, approximately 1 month apart, and randomized them to receive breakfast or no breakfast at the first visit and the opposite at the second visit. They asked the women not to exercise prior to each visit and gave them a standardized dinner the night before the study day. Fasting laboratory measures were taken the morning of the study day, and 4 hours later, the participants were given a standardized lunch. The investigators took blood samples every 30 minutes after lunch for 3 hours and later gave them a standardized dinner.

Levels of insulin and glucose did not differ significantly between groups before lunch. Insulin and glucose levels were significantly higher after lunch on the days that the women skipped breakfast, representing acute insulin resistance, reported Dr. Thomas, an endocrinology fellow at the University of Colorado, Aurora.

Insulin levels rose significantly higher on the no-breakfast days, compared with after breakfast within 1 hour of the meal, and remained significantly higher at 2 hours. Similarly, the increase in glucose levels was significantly higher on the no-breakfast days within 1 hour of eating and remained significantly elevated, compared with levels on the breakfast days.

Free fatty acid levels were suppressed following breakfast, as would be expected, and thus were higher before lunch on days without breakfast. Both the total and incremental area under the curve (AUC) for free fatty acids after lunch were higher on the no-breakfast days, compared with breakfast days, suggesting that prelunch free fatty acid levels were not the cause of the increased AUC, she said.

Prelunch triglyceride levels were lower on no-breakfast days than on breakfast days. The total AUC for triglyceride levels after lunch was lower on no-breakfast days, compared with breakfast days, but the incremental AUC did not differ significantly between groups, suggesting that the prelunch triglyceride levels were driving the difference in total AUC, Dr. Thomas said.

Indirect calorimetry measures showed decreased energy expenditure on no-breakfast days and a significantly reduced respiratory quotient, which indicates greater fat oxidation, she said.

Previous epidemiologic and longitudinal studies have found associations between breakfast skipping and greater weight gain and risk for type 2 diabetes, but most of these were small studies focused on lean subjects, and none have shown a causal relationship, Dr. Thomas said. Few other short-term studies have assessed the effects of breakfast skipping on metabolic parameters and appetite.

In the study, the insulin total AUC was 12,322 microIU/mL x 180 minutes on no-breakfast days, compared with 8,882 microIU/mL x 180 minutes on breakfast days. The glucose total AUC was 20,775 vs. 18,126 mg/dL x 180 minutes on no-breakfast and breakfast days, respectively.

Prelunch free fatty acid levels on no-breakfast and breakfast days, respectively, were 705 vs. 287 microEq/L, and the total AUC for free fatty acids was 33,980 vs. 25,692 microEq/L x 180 minutes. The incremental AUC for free fatty acids was –92,980 vs. –26,008 microEq/L x 180 minutes. Prelunch triglyceride levels were 86 vs. 121 mg/dL on no-breakfast and breakfast days, respectively. The triglyceride total AUC was 17,352 vs. 24,060 mg/dL x 180 minutes on days without and with breakfast, respectively.

The women had a mean age of 29 years and a mean body mass index of 31 kg/m2. Eight women said that they habitually eat breakfast. Dr. Thomas hopes to expand the study to 20 women and to include more women who habitually skip breakfast. She also plans to control for exercise in a future study.

The medical literature reports that roughly 10%-20% of Americans routinely skip breakfast, she said. Dr. Lisa Fish of the University of Minnesota, Minneapolis, who moderated a press briefing on Dr. Thomas’s study, said that many American breakfasts are high in carbohydrates and low in protein, and that eating a more balanced meal at the start of the day would be healthier.

Dr. Thomas reported having no financial disclosures. The study was funded by the Endocrine Fellows Foundation, the National Institutes of Health, and the Colorado Nutrition Obesity Research Center.