Chapter 18
AGE Sources
Our body deploys a range of defense mechanisms to counteract the formation of AGEs, which only underscores their toxicity. But once they are there, they are hard to get rid of again, so they gradually accumulate and cause devastating damage. Over 50 to 60 years, AGEs in tissue roughly double. We know this is not merely a marker of aging but an active driver, because it has been shown that AGE inhibitors extend the lifespan of animal models, whereas increases in AGEs shorten their lives. In experiments with laboratory animals, galactose is preferentially used to accelerate aging (a primary breakdown product of the milk sugar lactose), because it achieves the accumulation of AGEs in fast-forward. Throughout the animal kingdom, the rule is: the longer a species lives, the more slowly AGEs form. The Greenland whale, for example, which lives to over 200 years and is therefore probably the mammal with the longest life expectancy, deposits AGEs extraordinarily slowly. How can we keep our AGE level as low as possible?
The formation of AGEs is heat-dependent. At body temperature, the Maillard reaction proceeds extremely slowly, and it takes weeks, months, or even years for sugar and protein to cross-link. Imagine what would happen in the body if, instead of its internal temperature of about 38 degrees Celsius, it were suddenly 90, 150, or 200 degrees hot. That happens when we put meat in the oven. It is not merely poetic license when the initially yellowish and then brownish discoloration in cataracts is called the “AGE food colors of roasted turkey.” The same AGEs that, over the course of decades, cloud the crystal-clear proteins of the eye lens can form on the stovetop within minutes. For the AGE burden in our tissues, it seems to matter less how much we produce and more how many AGEs we eat.
AGE Sources
About a million years ago, our ancestors began to use fire. When muscle cells are exposed to the high temperatures of flames, they break open, and what oozes out are highly reactive amino acids that join with blood and the body’s own sugar to form AGEs. Just like us, the animals we eat naturally have AGEs in their tissues, but cooking at high temperature can dramatically drive up their production. Different cooking methods expose tissue to different amounts of heat and moisture. Poached or steamed chicken, for example, has not even a quarter of the AGEs of roasted or braised chicken, which was prepared with less water and at higher heat.
In the 1970s, experiments with rats showed that the animals did not absorb AGEs from the diet particularly well, so food was dismissed as an insignificant AGE source—but only until, a quarter century later, researchers finally tested AGE absorption in humans. A groundbreaking article in the Proceedings of the National Academy of Sciences proved that dietary AGEs were indeed absorbed in the human body. Further studies showed that dietary AGEs contribute more to the toxic depot of AGEs in our body than our body’s own production. In other words, exposure to AGEs comes more from what we eat than from what we make. Since then, dietary AGEs have been a burning concern for the food industry. Scientists propose avoiding foods with high AGE content and cooking methods that generate large amounts of AGEs in order to reduce the body’s burden of these toxins.
Researchers got to work and tested AGE amounts in more than 500 foods, from Big Macs and Hot Pockets to Frosties and Pop-Tarts. They found the largest amounts in “highly heated meat” and, more generally, in “foods of animal origin with high fat and protein content,” and found that the fewest AGEs are found in vegetables, fruit, whole grains, and milk (with the exception of a milk-based baby formula, Enfamil, which contains more than 100 times more AGEs than human breast milk). Meat averages 20 times more AGEs than highly processed foods like breakfast cereals and about 150 times more than fresh fruits and vegetables. Poultry came out worst, containing about 20 percent more AGEs than beef.
In the most frequently cited database on AGE, which also includes hundreds of vegetarian products, the Top 15 were mostly poultry products, with oven-baked chicken breast in first place.
Researchers were quite surprised that foods high in fat and protein generated more AGEs than starchy and sugary foods with high carbohydrate content. After all, AGEs are called “glycotoxins” for good reason. They involve glycation reactions like the Maillard reaction mentioned, in which sugar binds to proteins. Sugar can also brown at high heat, so at first glance it may look, smell, and taste similar to a Maillard reaction product, but that is the result of a completely different chemical process: caramelization. By definition, AGEs are produced by a Maillard reaction only when amino acids from protein are involved. For a deeper look at other AGE ratings, see see.nf/agerank.
How to Eat Less Toxic AGEs
The largest AGE databases mostly used a single AGE (carboxymethyllysine) as a marker for total AGE content, but more than 40 individual AGEs have been identified, and not all are toxic. Some are even useful. Melanoidin, for example, a component in roasted coffee beans, acts as an antioxidant. AGEs from foods of animal origin appear to have more toxic effects than those from plant-based foods. Plant-based foods not only produce 30 times fewer AGEs: Even if you expose the same amount of proteins to AGEs from plant versus animal sources, the former results in 25 times fewer cross-links and 40 times fewer compared with AGEs from poultry. Plant-derived AGEs also produce less inflammation and fewer free radicals. The AGEs formed during the curing of tobacco are an exception, since the AGEs from cigarettes are related to the harmful effects of smoking.
If you do not want to limit your meat consumption, you can still sharply reduce your AGE intake by using other cooking methods. Most AGEs are produced at high, dry heat, with oven baking being worse than deep-frying, which is worse than grilling, and that is worse than frying in a pan. There is no threshold temperature, but the general recommendation is: the lower the heat, the better when it comes to producing fewer AGEs. The safest cooking methods for meat use low temperatures and more liquid—so you boil, poach, stew, and steam. Boiled beef has three times fewer AGEs than grilled, boiled chicken has five times fewer AGEs than grilled, and boiled eggs come in at nearly six times fewer AGEs than fried. Microwave preparation is also relatively safe; it is roughly on a par with boiling.
When it comes to reducing dietary AGEs, these changes make a big difference. It really does come down to the cooking method. A raw apple has three times fewer AGEs than a baked one, and a boiled sausage has fewer than a grilled one. But do not lose sight of the bigger picture: A raw apple has 13 AGE units, a baked one 45, but a boiled sausage has 6736 units and a grilled one 10 143. That means the baked apple still has 150 times fewer AGEs than the boiled sausage, and vegetables, even when grilled, have only a fraction of the AGEs of raw meat.
Scientists recommend preparing meat with methods that use moist heat such as steaming or braising, but even boiled fish has more than ten times more AGEs than a sweet potato that was baked for an hour. Even fried potatoes have less than boiled meat. The scientists concluded that daily AGE intake could practically be cut in half if one were to eat a little less meat.