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The high cost of high heat cooking

The delicious browning and crusting of steak or chicken could also be harmful. This one-year long randomized trial looked at high-heat cooking versus gentler cooking, and its impact on insulin resistance.

Introduction

Advanced glycation end products (AGEs) are highly reactive compounds that result from a chemical reaction between reducing sugars and amino acids (also known as a Maillard reaction) and from the oxidation of sugars, lipids, and amino acids. Although the formation of AGEs within the body is a part of normal metabolism, a growing body of evidence[1][2][3] suggests that excessive AGE levels promote oxidative stress and inflammation and may therefore increase the risk of developing type 2 diabetes, cardiovascular disease, fatty liver, cancer, Alzheimer’s disease, and infertility.

AGEs were first recognized as being produced within the body under conditions of increased oxidative stress. However, it is now known that dietary AGEs are important contributors[4] to the body’s total AGE concentration, where they become indistinguishable[5] from those AGEs produced within the body itself. The most widely studied AGE is carboxymethyllysine (CML), while another common marker of AGE formation is methyl-glyoxal (MG).

Although the accuracy of AGE measurement is debated within the scientific community, the largest study to date[6] to investigate the AGE content of food showed that AGE content is highly dependent both on the food itself and the preparation method used. Although high fat, high protein foods generally had higher levels of AGEs compared to foods high in carbohydrate, there was considerable variability. By contrast, harsher cooking methods such as frying, broiling, grilling, and roasting consistently led to higher AGE levels than gentler cooking methods such as boiling, poaching, stewing, and steaming, suggesting that high-heat and dry heat cooking lead to higher AGE levels. Some specific levels are shown in Figure 1.

Figure 1: Carboxymethyllysine content of chicken breast by cooking technique

Reference: Uribarri, J, et al. J Am Diet Assoc. 2010 Jun.

A handful of short-term clinical trials have shown that restricting dietary AGEs results in reduced inflammation and increased insulin sensitivity among patients[7] with[8] type 2 diabetes[9], overweight women[10], and healthy adults[11]. Moreover, among individuals with obesity and the metabolic syndrome, both dietary and serum AGEs have been significantly correlated[12] with insulin resistance, oxidative stress, and inflammation. However, no long-term trials have been conducted.

The study under review was designed to test whether prolonged (one year) dietary AGE restriction could improve insulin resistance and other risk factors for type 2 diabetes in people with metabolic syndrome.

Advanced glycation end products (AGEs) are produced both within the body and during the cooking and processing of food. Dietary AGEs contribute to the body’s total AGE concentration. Excessive amounts promote oxidative stress and inflammation. Short-term clinical trials show that reducing dietary AGEs improves insulin sensitivity and reduces inflammation. The current study sought to test if these observations would be apparent over the long term (one year).

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