Ever brought home fresh veggies from the farmers market and wondered how to cook them, or looked at the charred ends of a juicy steak and questioned if it was good for you? Luckily, food science has the answers. Read on to learn what the evidence says about various cooking methods, including which retain the most nutrients and which cause the most inflammation.
I’ve written a lot about what to eat, but not as much about the method of preparing a food. Yet the way you cook your food has an enormous impact on the amount of nutrients that will make their way into your mouth and that are subsequently absorbed and available to your body to use.
What if you’re not getting the nutrients you think you are? What if you are unknowingly promoting inflammation with the way you cook? Should we throw out cooking altogether? This article will cover it all.
Do you know which cooking method is the most inflammatory?
Cooking from an Evolutionary Perspective
Raw foodists claim that uncooked food is best for optimal health and boycott cooking altogether. Yet cooking can reduce exposure to foodborne pathogens, and many nutrients become more bioavailable when cooked.
Cooking has long been a part of human history. The first evidence of cooking dates back to 15,000 B.C., when hunter–gatherers are thought to have used stone pots for cooking fish and other marine life (1).
Of course, there are downsides to cooking. In some cases, cooking reduces antioxidant content. It can also increase the levels of carcinogens and oxidized fats in food, depending on the method, temperature, and ingredients used.
The Various Methods of Cooking
Each cooking method has its pros and cons. First, we’ll cover the basics of each method. Then we’ll dive into specific types of foods and what the evidence says the best cooking method is for each.
Grilling and broiling
Grilling and broiling involve using dry heat to cook food. In grilling, the heat source comes from below, while in broiling, the heat source is above the food. Grilling is one of the most popular cooking methods because of the delicious, smoky flavor it produces. This is due to the Maillard reaction, which occurs between amino acids and sugars and results in hundreds of different flavor compounds (3). Unfortunately, the same heat that produces the great flavor also contributes to the formation of toxic compounds. These include:
- Acrylamide: Acrylamide forms from the Maillard reaction itself, and levels rise as food is heated for longer periods of time (4). It is often found in grilled or fried starchy foods like potato chips, and it is not found in boiled foods. Acrylamide has known toxic effects on fertility and the nervous system, though according to the World Health Organization, the intake level required to observe neuropathy is about 500 times what we would likely consume in the diet (5). Whether low levels of acrylamides may contribute to cancer risk is less clear.
- Heterocyclic amines (HCAs): HCAs form when amino acids and creatine in muscle meats react at high temperatures. Researchers have identified 17 unique HCAs that are formed that may pose a cancer risk to humans (6). Several studies in animal models have now shown that HCAs cause genetic mutations and alter gene expression to cause cancer (7). This may be one reason why red meat continues to be associated with increased cancer risk in epidemiological studies.
- Polycyclic aromatic hydrocarbons: The primary dietary sources of PAHs are cereals and vegetables, except when meat is grilled over an open flame (8). PAHs are also present in soil and ambient air, and exposure has been linked with cancer, cardiovascular disease, and poor fetal development (9, 10, 11).
- Advanced glycation end-products (AGEs): AGEs are proteins or lipids that have become glycated (tagged with glucose molecules) as a result of exposure to sugars. These compounds are known for creating oxidative damage and accelerating the aging process. The levels of AGEs that your own body produces are far more significant than anything you consume in the diet. Still, dietary AGEs have been shown to contribute to the body’s burden of AGEs. Dietary AGEs deplete antioxidant stores in mice and can cause insulin resistance, atherosclerosis, and kidney disease (12, 13, 14, 15).
Roasting and baking
Roasting and baking both involve cooking in an oven with dry heat. Roasting typically refers to meat and vegetables, while the term baking is used for cakes, muffins, and cookies.
Vitamin and mineral losses are minimal with moderate-temperature roasting or baking. Some B vitamins may be lost in the meat drippings, but these can be retained by basting often or making the collected meat juices into gravy. These methods do cause formation of some AGEs and acrylamide, though they form fewer PAHs and HCAs than grilling (16).
Stir-frying and sautéing
With stir-frying and sautéing, food is cooked in a saucepan or skillet over medium to high heat in a relatively small amount of oil or other fat. This improves the absorption of fat-soluble vitamins and antioxidants.
Cooking without water and for a shorter time helps retain B vitamins, but watch out for high heat, which can destroy these unstable compounds. High temperature stir-frying and sautéing can also cause formation of AGEs and acrylamide.
Frying involves cooking food at a high temperature in a large amount of fat (usually oil). It’s popular because the skin or bread coating forms a seal, ensuring that the inside remains moist and cooks evenly.
Frying generally preserves B vitamins and vitamin C. However, frying at high heats can turn an otherwise healthy vegetable into an inflammatory nightmare. Frying results in very high levels of AGEs, HCAs, and aldehydes.
Aldehydes: Aldehydes are formed when oil is heated at high temperatures for a long time. They have been linked to an increased risk of cancer, atherosclerosis, and rheumatoid arthritis (17, 18). The type of oil, length of cooking, and temperature will all affect the amount of aldehydes produced.
Repeatedly reheating oil, as is often done in fast-food restaurants, further increases AGEs and aldehyde content (19).
Water-based cooking includes poaching, simmering, and boiling. All three of these methods use water to heat the food, but differ in the temperature used:
- Poaching: less than 180° F
- Simmering: 180–200° F
- Boiling: 212° F
Boiling also results in the least production of AGEs (20).
And don’t forget anti-nutrients. For example, boiling is the best at reducing oxalates, which in high amounts can contribute to the formation of kidney stones (21). The oxalates leach out into the surrounding water, much like the vitamins do.
As a general rule, use as little water as possible for poaching or boiling, and consume the liquid left in the pan after cooking vegetables, unless you are particularly sensitive to oxalates or other anti-nutrients.
Steaming is exactly what it sounds like—using the heat and steam from boiling water to cook food, without actually putting the food in the water. Steaming is superb at preserving nutrients, especially those that are sensitive to heat and loss in water.
The downside is that it doesn’t use any fat, so fat-soluble vitamins and antioxidants won’t be quite as bioavailable, but you can easily get around this by steaming foods and then adding olive oil or butter to them after they are cooked.
Slow cooking & pressure cooking
Slow cooking is typically done in a crockpot and is a gentle method of cooking, since it uses low temperatures below the boiling point of water. Pressure cooking is similar to slow cooking but typically uses a higher temperature for a shorter time. There haven’t been many studies on nutrient retention of food prepared in slow cookers, but it’s reasonable to assume that the nutrient losses would be slightly less than boiling.
Like boiling, slow cooking will leach vitamins and minerals from the food that you’ll lose if you don’t consume the water or liquid leftover. For soups or stews, slow cooking is an easy and excellent choice.
While microwaving typically gets a bad rap in the alternative health community, it’s one of the safest methods of cooking. Microwaves emit radio waves that cause water molecules in the food to resonate. This generates heat, cooking the food from the inside out. The shorter cooking times and more even heating from the inside out help to preserve the nutrients in microwaved food. Plus, it’s just convenient!
The downside is that microwaves can leave food unpleasantly dry, soggy, or rubbery. But there’s no evidence that microwaves are unsafe. Of course, don’t stand directly in front of the microwave while it’s running and always heat food in glass or a similarly safe container. When heated, plasticizers and other chemicals in common Tupperware-like containers can leach into your food.
Of course, fermentation can also increase the histamine content of foods, which may be an issue for some people with histamine intolerance or mast cell activation disorder.
Cooking Different Types of Foods
Meat and other proteins
When we think about meat and other proteins, we are primarily concerned with:
- The digestibility of the protein
- The amount of B vitamins
- The amount of minerals
- The absence of inflammatory compounds
We’ll look at each of these in turn. First, cooking meat and other proteins significantly improves their digestibility. Earlier, I discussed why scientists believe the increased energy and raw protein building blocks extracted from cooked meat was what fueled the development of the human brain as it is today. This is also true with other proteins. For example, the protein in cooked eggs is 180 percent more digestible than the protein in raw eggs (23).
The B vitamin content of meat greatly depends on the cooking method used and the heat applied during cooking. B vitamins are water soluble, meaning they can easily get “washed out” of meat cooked in water. They are also unstable when subjected to heat and will be degraded into compounds that are not necessarily harmful but are not useful to the body.
With long cooking times at high temperatures, B vitamins in roasted, grilled, or broiled meat may decline by as much as 40 percent (24). Roasting is a good option because the meat juices can be collected and consumed. With grilling, these drippings and the nutrients they contain are often lost. Still, these may be better than water-based methods. Simmering has been shown to result in the loss of up to 60 percent of B vitamins (24).
Few studies have been done on minerals in cooked meats, but there is a general consensus that minerals are reasonably well retained. Manganese, copper, iron, and zinc are thought to be the most stable (25). One study found that most minerals in pork loin increased in content with boiling but subsequently decreased if cooking was carried on to higher temperatures (26). Around 160° F (71° C) seemed to be the sweet spot that provided the peak content for most minerals.
Several studies have linked well-done meat with certain diseases, including colorectal cancer, pancreatic cancer, and cancer risk overall (27, 28, 29). Of course, these are just associations and are prone to the healthy-user bias (i.e., are people eating that well-done meat atop a juicy wheat bun with a side of fries?). But as I discussed earlier, there are some concerning compounds formed when meat hits the heat.
Fortunately, the amount of AGEs and HCAs that is formed can be mitigated by marinating the meat in advance. Mark Sisson explained how this works in his excellent article concerning cooking and inflammation. Choose your marinade wisely. Antioxidant-rich fats; acidic mediums like wine, vinegar, or citrus; natural sweeteners like honey; and herbs and spices can all help prevent the formation of toxic compounds (30, 31, 32, 33). One study in China even marinated meat in a tea extract and found that it reduced HCA levels by 75 percent at moderate temperature and 46 percent at high temperatures (34)! At least two studies suggest that pastured meat may have higher antioxidant levels “built in” and thus have better oxidative stability (35, 36). On the other hand, table sugar, soy sauce, and unstable oils will increase toxic compound formation (37).
Cooking temperature also matters, as HCA content closely parallels the degree of doneness of the meat. In other words, rare meat has much lower levels of HCA than well-done meat (38). AGEs follow a similar pattern, as they form when the meat browns, a direct result of the Maillard reaction. Minimizing smoke can reduce the formation of PAHs.
This is thought to be the initiating event in atherosclerosis (39).
Polyunsaturated fats are the most prone to oxidative damage at high temperatures. These can be found in the oils used in cooking or in the food itself, in the case of meat and fish. Omega-3 fatty acids are particularly fragile. Frying tuna has been shown to degrade omega-3s by 70 to 85 percent (40), while baking or boiling fish has been shown to preserve more omega-3 fatty acids than frying (41).
Use heat-stable fats whenever you’re cooking at higher temperatures (frying, roasting, grilling, broiling, or stir-frying). Saturated fats like lard, tallow, and butter are the most heat stable. Coconut oil has also been shown to hold up to oxidative damage (42). High-quality avocado oil and extra-virgin olive oil are also good choices due to their high antioxidant content.
Things get a little trickier with vegetables, as the chemistry is very different from one vegetable to the next. The major factors to consider with cooking vegetables include:
- The amount of vitamin C
- The amount of B vitamins
- The amount and availability of minerals
- The amount and availability of antioxidants and polyphenols
- The amount of antinutrients
- The formation of inflammatory compounds
- Resistant starch formation
Vitamin C is abundant in many vegetables, yet it is very unstable when heated. Boiling causes more loss of vitamin C than any other cooking method. One study found that broccoli, spinach, and lettuce lose up to 40 to 55 percent of their vitamin C when boiled, compared to 21 to 28 percent loss when microwaved and 8 to 14 percent loss when steamed (43). Another study found that stir-frying resulted in about a 60 percent loss of vitamin C from red cabbage (44).
Less is known about the effects of cooking vegetables on B vitamins and minerals. Water-based methods of cooking will cause these to leach out into the surrounding water. For B vitamins, gentler cooking methods or microwaving may be the way to go. One study found that microwaved turnip greens retained more B vitamins than greens blanched in boiling water (45).
As for antioxidants, it really depends on the vegetable. Consider the following findings:
- Microwaving is the best method for retaining antioxidant activity in mushrooms (46)
- Steaming is best at preserving antioxidants and cancer-fighting glucosinolates in broccoli and cabbage (47, 44)
- Boiling increases the antioxidants and carotenoids in carrots and does a better job of preserving them than frying or steaming (48)
Let’s face it, though: microwaved, steamed, or boiled vegetables simply don’t taste as good as stir-fried or grilled vegetables. One solution is to add oil, butter, or meat juice gravy after cooking or to cook the vegetables most of the way before stir-frying for the last few minutes of cooking.
This also reduces the amount of toxic compounds formed. While we typically think of meat as being the major source of PAHs, they can also be formed on vegetables. Yep, sorry, but that charred piece of grilled broccoli that makes your mouth water is likely full of PAHs. Luckily, you can use some of the steps we discussed in the meat section to mitigate HCA mutagenicity (think: marinade and herb seasoning on your veggies).
We’d be remiss to not talk about anti-nutrients, although the evidence for the various cooking methods is limited. One study found that blanching (briefly dropping vegetables in boiling water) significantly reduced levels of phytic acid and tannic acid (49). Another study found that microwaving was most effective at removing tannic acid (50). These anti-nutrients bind to minerals and prevent their absorption. Some, like lectins, can also be hard on the digestive system.
Lastly, let’s talk resistant starch. Cooking and cooling potatoes causes some of their starch to convert into resistant starch. This is one instance where frying may be beneficial, as frying potatoes converts the starch into resistant starch, which feeds good gut bacteria and has a lower glycemic index (51).
In most cases, fruit is best eaten raw. Many fruits are an excellent source of vitamin C, which, as we know, is extremely sensitive to heat. In some cases, though, cooking increases the nutrition of fruit. For example, cooking berries significantly increases their free-radical scavenging activity (52).
Nutrient synergy matters
It’s important to point out that we don’t consume foods in isolation. Rarely do you consume a grilled steak without something else along with it! This is where nutrient synergy comes into play. Cruciferous vegetables, chlorella, omega-3s, and the polyphenols in red wine, tea, and coffee have all been shown to protect against the negative effects of HCAs (53, 54, 55, 56, 57, 58).
Antioxidant absorption is also dramatically enhanced by the addition of fat:
- Absorption of beta-carotene is 75 percent in stir-fried carrots, compared to just 11 percent in raw carrots (59).
- Blood trans and cis-lycopene levels increased by 82 percent and 40 percent, respectively, when tomatoes were consumed sautéed in olive oil, compared to 0 percent and 15 percent when tomatoes were consumed without oil (60).
Putting It All Together
I hope I have provided a lot of food for thought, but it should be taken with a grain of salt. Here are my three key takeaways on this topic:
There is no perfect cooking method that retains all of the nutrients in a food. Err towards using the method that maximizes the nutrient density of the food and minimizes inflammatory compounds, but don’t feel the need to cook it the same way every time.
As a general rule, cooking meat for shorter periods of time at lower temperatures will result in the most nutrient retention and least formation of inflammatory compounds. Take the time to marinate in advance, and pay attention to nutrient synergy.
The best method to cook vegetables is the method where you’ll actually eat them. If that means stir-frying your broccoli in butter instead of steaming it, so be it. At the end of the day, your enjoyment of food matters, and vegetables cooked using any method are better than no vegetables at all.