There is little question that grilling and baking are healthful alternatives to frying, particularly in terms of reducing calories and fats.
But when it comes to meat, these high-temperature, dry-heat cooking methods may not reign supreme for health. Research increasingly suggests that moist-heat methods, such as braising or poaching, in addition to shorter cooking times and lower temperatures, can reduce potentially harmful compounds that may contribute to chronic disease.
Advanced glycation end products, or AGEs, are a group of compounds present in the body as a byproduct of normal metabolism. However, evidence is mounting in favor of the theory that excess AGEs promote oxidation and inflammation — leading to or worsening chronic health problems such as heart disease, Type 2 diabetes, kidney disease and Alzheimer’s disease. AGEs may even contribute to the aging process.
Typical AGE formation within the body occurs very slowly and accumulates over time; thus, older people tend to have higher levels than younger individuals. People with diabetes also may have more AGEs in the body due to higher blood sugar levels and because excretion of AGEs through urine is reduced, the latter of which is true among people with kidney disease as well.
While the backyard barbecue is hardly the sole contributor of added AGEs (tobacco smoking is another source), excess AGE levels typically result from the diet. Higher-protein foods from animal sources are among the richest in AGEs, with beef and cheese topping the list, followed by poultry, pork, fish and eggs. Butter, cream cheese, margarine and mayonnaise serve up higher amounts than oils and nuts. Aged cheeses and cheeses higher in fat contain more AGEs than reduced-fat and non-aged cheeses.
Although carbohydrate-rich foods generally contain fewer AGEs than high-protein or high-fat foods, those processed with dry heat (such as crackers, chips and cookies) may contain more due to the addition of fat. Meanwhile, boiled and steamed grains, legumes, breads, vegetables, fruits and milk are among the foods lowest in AGEs.
In addition to occurring naturally, AGEs are produced in large amounts under certain cooking conditions, especially when animal-derived foods are cooked with high heat. The compounds are formed when sugars combine with proteins, fats or nucleic acids — also known as the colorful and tasty Maillard reaction that is seen in the darkened edges of grilled chicken and seared steaks, or on the crispy surfaces of toasted bread or marshmallows.
Until recently, scientists had little concern regarding AGEs in food because it was believed the body absorbed very few of the compounds. Newer research, however, shows people absorb about 10 percent of AGEs consumed — which could be significant, depending on one’s food choices and preferred cooking methods.
Animal research suggests avoiding dietary AGEs helps delay chronic illnesses and aging. Research involving healthy human volunteers shows mixed results, with some (but not all) studies finding AGE intake linked to insulin resistance, weight gain, inflammation and other health measures. Many studies show that, when AGE consumption is high, inflammatory markers such as C-reactive protein, or CRP, fibrinogen and tumor necrosis factor alpha (a.k.a. TNFalpha) increase in the blood. Likewise, when AGE intake is low, these inflammatory markers drop.
The correlation between diets high in AGEs and inflammatory markers are of particular interest to diabetes researchers exploring the effect of constant, low-grade inflammatory states that are common among people with diabetes and the potential role of AGEs in diabetes complications.
Some research suggests the amount of AGEs present in the retinas of people with diabetes predicts the severity of diabetic eye disease. Additionally, people with diabetes tend to have higher amounts of AGEs in their peripheral nerves, suggesting that AGEs may play a role in the common nerve disorder associated with diabetes.
Still, other studies suggest AGE restriction among people with Type 2 diabetes may improve insulin resistance. For example, in one intervention that modified only cooking methods (not food choices), participants halved their AGE intakes. After four months, this resulted in reduced oxidative stress, insulin resistance and markers of inflammation — and plasma insulin levels fell by 30 percent.
Heart Disease with Diabetes
AGEs also may affect the heart and blood vessels. According to some studies, among people with diabetes, those who consumed the most AGEs had the greatest risk for cardiovascular disease. AGEs may cause damage by linking with some of the proteins in blood vessels, making the blood vessels less elastic and more prone to disease. Additionally, AGEs may modify low-density lipoprotein cholesterol in such a way that it is easily oxidized and deposited within blood vessel walls, triggering the formation of fatty streaks and eventually leading to atherosclerosis or plaque formation.
In older adults, higher levels of AGEs in the bloodstream typically are associated with poorer kidney function. One study showed older women with late-stage kidney disease, diabetes or both had higher levels of circulating AGEs than healthy women. A separate study found kidney function improved in overweight and obese people on a low-AGE diet.
The evidence suggesting a role of AGEs in the development of cancer is less robust, says Karen Collins, MS, RDN, CDN, FAND, nutrition advisor to the American Institute for Cancer Research. However, AGEs may influence cancer risk, Collins says, by increasing chronic low-grade inflammation. They also may increase oxidative stress, resulting in damage to genes that start the cancer process and affect systems responsible for controlling cell growth and destroying abnormal cells. “Limited studies show signs of higher AGEs in tumors of the colon, stomach, pancreas, prostate, breast and ovary, though this research is in very early stages,” Collins says.