Copyright 2002 American Medical Association. All Rights Reserved. Applicable FARS/DFARS Restrictions Apply to Government Use.
To the Editor: Dr Ludwig reviewed the glycemic index and its possible role in the establishment and maintenance of insulin resistance.1 However, in the section addressing the mechanisms by which a high–glycemic index diet may precipitate cardiovascular disease, he did not address the cardiovascular effects of counterregulatory hormones and fatty acids. Such substances may be related to chronically increased autonomic tone,2 which has many of the same long-term consequences as insulin resistance.
Ludwig notes that consumption of a meal with a high glycemic index results in a postprandial surge of counterregulatory hormones and free fatty acids that "resembles a state of fasting normally reached only after many hours without food." In contrast to insulin, which is vasodilatory, all the counterregulatory hormones (glucocorticoids, catecholamines, glucagon, and growth hormone) increase cardiovascular tone. There is recent evidence that fatty acids do so, as well.3 Thus, this response itself may confer increased risk for cardiovascular disease.
In the metabolic syndrome, urinary norepinephrine levels are elevated, likely reflecting increased sympathetic tone.4 Clinically, this may be responsible for higher resting heart rate, decreased heart rate variability, impaired heart rate recovery after exertion, and increased mortality.2 The recent observation that fatty acid infusion increases blood pressure, norepinephrine levels, and heart rate while decreasing heart rate variability3 suggests that increased circulating free fatty acids may contribute to abnormal sympathetic tone in the metabolic syndrome. Fatty acids may also impair endothelial function directly.5 Similarly, cortisol and growth hormone may increase cardiovascular tone through potentiation of catecholamine effects6 and perhaps by stimulating lipolysis, leading to increased concentrations of circulating fatty acids. Finally, glucagon increases cardiac inotropy and chronotropy.7
Thus, it is possible that any type of hormone-induced carbohydrate insulin resistance might also increase cardiovascular tone, especially when insulin production is compromised and its vasodilatory effects are overwhelmed. If the insulin resistance associated with the consumption of high–glycemic index meals is due in part to a counterregulatory hormone surge, as Ludwig suggests, then the hemodynamic effects of these hormones may be as important as hyperglycemia or oxidative stress in precipitating cardiovascular morbidity and mortality.
Country-Specific Mortality and Growth Failure in Infancy and Yound Children and Association With Material Stature
Use interactive graphics and maps to view and sort country-specific infant and early dhildhood mortality and growth failure data and their association with maternal
Instructions
Comments are moderated and will appear on the site at the discretion of the Journal of American Medical Association editors. Comments should not exceed 500 words of text and 10 references.
Do not submit personal medical questions or information that could identify a specific patient, questions about a particular case, or general inquiries to an author. Only content that has not been published, posted, or submitted elsewhere should be submitted. By submitting this Comment, you and any coauthors transfer copyright to the journal if your Comment is posted.
* = Required Field
Disclosure of Any Conflicts of Interest* Indicate all relevant conflicts of interest of each author below, including all relevant financial interests, activities, and relationships within the past 3 years including, but not limited to, employment, affiliation, grants or funding, consultancies, honoraria or payment, speakers’ bureaus, stock ownership or options, expert testimony, royalties, donation of medical equipment, or patents planned, pending, or issued. If all authors have none, check "No potential conflicts or relevant financial interests" in the box below. Please also indicate any funding received in support of this work. The information will be posted with your response.
Register and get free email Table of Contents alerts, saved searches, PowerPoint downloads, CME quizzes, and more
Subscribe for full-text access to content from 1998 forward and a host of useful features
Activate your current subscription (AMA members and current subscribers)
Some tools below are only available to our subscribers or users with an online account.
Download citation file:
Customize your page view by dragging & repositioning the boxes below.
and access these and other features:
Register Now
Enter your username and email address. We'll send you a reminder to the email address on record.
Athens and Shibboleth are access management services that provide single sign-on to protected resources. They replace the multiple user names and passwords necessary to access subscription-based content with a single user name and password that can be entered once per session. It operates independently of a user's location or IP address. If your institution uses Athens or Shibboleth authentication, please contact your site administrator to receive your user name and password.