What are Advanced Glycation End-Products (AGEs)?
Advanced Glycation End-products, or AGEs are products of normal dietary metabolism in all animals and to a much lesser extent, plants as well. There are hundreds of different types of AGEs and although this rowdy gang behaves like oxidants with the potential to damage proteins such as collagen, DNA and our cells, our antioxidant system under normal conditions, does a good job of neutralizing and excreting most of them in our urine. Problems occur when there are too many AGEs for our antioxidants to handle. This excess can result from a high rate of endogenous AGE production in our bodies and from excessive exogenous dietary intake. Excess AGEs accumulate in long-lived cells such as nerves, brain cells, the retina and cornea of the eye and pancreatic beta cells and cause a host of problems such as insulin resistance and the stiffening and weakening of collagen in our skin and blood vessels. Everyone young and old is at risk of having too many AGEs in circulation due to the composition of our Western diet. As AGEs accumulate in our tissues, they create inflammation and contribute to chronic disease. Very simply, excess AGEs age us.
Sources of AGEs
Pre-formed AGEs exist in virtually all of the foods we eat however some food groups have a higher concentration than others. For instance, meat is much higher in pre-formed AGEs than plants. We can see this by comparing 3 ounces of raw beef, which has 636 kU (kilo units) of AGEs to an equivalent amount of raw tomato, which has only 23 kU. Does this mean that meat-based diets are destined to result in higher blood AGE levels than plant-based diets? Not necessarily. I’ll explain further in a moment.
Heating food especially by high heat and dry cooking methods induces the Malliard reaction, which increases the amount of AGEs in food that we experience as browning and the development of taste and aroma. If you’ve ever seared a steak, roasted a chicken or baked a loaf of Paleo bread with a nice brown crust, and savored the enticing smell and flavor of these foods, know that you have enjoyed the AGEs’s you’ve created. During the Malliard reaction, heat induces glycation; the interaction of amino acids and simple sugars such as glucose, fructose and galactose. Glycated amino acids, after several additional chemical rearrangements (the formation of a Schiff base and an Amadori product) form AGEs that improve taste, heighten aroma and cause browning.
Food Processing adds greatly to the AGE content of foods from heating, browning, the combining of high fat and sugary ingredients together and/or by adding pre-formed AGEs directly into products to enhance visual appeal, flavor and aroma. If you find highly processed food, including fast food highly palatable, you can give a big thanks to colorful, flavorful, aromatic AGEs.
Endogenous production of AGEs occurs when the Malliard reaction happens inside us. Simple sugars form glycated proteins and fats in our blood and cells. Interestingly, fructose has a very high affinity for this, and as a result, forms many more AGEs within our bodies than other simple sugars.
We know a lot about glycation from the study of the complications of diabetes. If too much sugar is available the rate of glycation increases and this is why AGEs are very problematic for diabetics. In fact, AGEs are strongly associated with all the complications of diabetes: insulin resistance, skin problems, eye problems (retinopathy), nerve damage (neuropathy), high blood pressure, cardiovascular disease, kidney damage (nephropathy), hearing loss and Alzheimer’s disease.
Finally, glycation is not the only way AGEs are formed. All three macronutrients – sugars, proteins and fats when oxidized can produce AGEs as well. In fact, when fats, especially unstable polyunsaturated fats (PUFAs) are oxidized from light, heat and/or air, specific AGEs known as Advanced Lipid Peroxidation End-products (ALEs) are formed. However, for our purposes, they’re all AGEs.
How Many AGEs are Safe and What’s the Deal with Fructose?
Regarding exogenous AGE intake, research shows that the average adult consumes around 15,000 kU of AGEs per day but that some adults consume even more than 40,000 kU/day. An optimal dietary AGE intake has not been established but reducing AGE consumption to anywhere from 5,000 kU to 8,000 kU/day has been shown to keep blood levels low enough to prevent Advanced Glycation End-products related inflammation.
How can we get our blood AGE levels under control? Avoiding high AGE foods and implementing low AGE cooking methods might do it, but perhaps even more effective is avoiding excess fructose. Fructose is 10x more prone towards AGE production than glucose. An interesting study showed that vegetarians eating a diet of plants, dairy products and eggs had more AGEs in their blood than meat eaters! This is surprising since, as we know, meat as a food group has a high pre-formed AGE content. The researchers concluded that vegetarian diets high in vegetables and fruit with a predominance of fructose induces AGE formation to a higher degree than omnivore diets.
What Foods Are Highest in AGEs? What Foods Are Lowest?
As we already know, some foods are relatively high in pre-formed AGEs including meats and refined oils. Butter, (The jury is still out on butter as it has been shown to have less AGEs via alternative testing methods), cream and processed cheeses also end up with high AGE content from pasteurization and processing. Fast foods are very high in AGEs and crispy brown and fatty processed foods especially those sweetened with honey, sugar or high fructose corn syrup are also very high in AGEs. Fruits, vegetables, grains and low-fat dairy tend to be lowest in pre-formed AGEs. Although there is contention over the best method to measure the amount of AGEs in foods, the values of 549 foods on this list in Table 1 are the most widely accepted at this point.
Selected Paleo Foods highest in AGEs:
- Roasted, grilled, or fried beef, pork, poultry
- Grilled hot dog, sausage, bacon
- Broiled, grilled or fried fish
- Roasted nuts
- Butter, oxidized oils
Selected Paleo Foods with very low to moderate AGEs
- Dark Chocolate
- Poached, boiled or steamed chicken
- Poached or steamed fish
- Raw and smoked salmon
- Canned tuna
- Canned salmon
How To Minimize Exogenous AGEs
- Vary your cooking methods and remember that dry heat cooking at high temperatures such as grilling, searing, broiling and frying increases the formation of AGEs. Therefore, to minimize AGE creation, cook with low heat and high moisture such as poaching, steaming, stewing and boiling. For instance, 3 ounces of poached or boiled chicken has 1000 kU (kilo units) AGEs compared to broiled chicken, which has > 5000 kU. Similarly, 3 ounces of stewed beef contains 2,391 kU compared to broiled steak which contains almost 7,000 kU.
- Avoid excessive intake of high AGE foods such as bacon and roasted nuts. Don’t panic Paleo peeps. The operative word here is “excessive.” Just be mindful of how much and how often you’re consuming these foods.
- Marinating meats in an acidic medium for even just one hour can prevent AGE formation by 50%. For 1 pound of meat, use four to six tablespoons lemon juice, lime juice, vinegar plus enough water or other ingredients to cover the food.
- Cook meats to rare or medium rare. If grilling, wrap in foil for the first part of cooking or pre-cook using a low AGE method.
- For ground meat, cover the skillet to retain moisture.
- Don’t heat oils beyond their smoke point.
In conclusion, although more research needs to be done on AGEs and their effects on human health, if you’re following a Paleo diet and eating a variety of foods (don’t gorge on bacon and fructose folks!) that are prepared using a variety of cooking methods and you don’t have diabetes or kidney disease, you probably don’t need to give AGEs a second thought. However, if your Paleo diet doesn’t seem to be quelling inflammation, it may be a good idea to take a closer look at how much fructose and high AGE foods you’re consuming.
The AGE-Less Way by Helena Vlassara, MD