Grilled & Charred Meat Carcinogens (HCAs/PAHs)

If you want the practical part first, these come straight from NCI's guidance and they are easy to fold into how you already cook.

1. Keep meat off direct flame. Move it to the side of the grill, use indirect heat, or raise the grate. PAHs form in the smoke that rises when fat hits fire.
2. Microwave the meat for a minute or two first and pour off the juices. Less time on high heat means fewer HCAs.
3. Flip often. Turning meat continuously on a hot surface substantially reduces HCA formation compared with letting one side sit.
4. Cook smaller pieces. They spend less time over heat.
5. Cut off the charred parts before eating. That is where the concentrations are highest.
6. Do not make gravy from the drippings. They concentrate the same compounds you have been avoiding.

None of this requires giving up grilling, and that is deliberate, because the human evidence does not justify that.

Two different families of chemicals form when meat meets high heat.

HCAs, heterocyclic amines, form when amino acids, sugars and creatine or creatinine react at high temperatures. Because creatine comes from muscle, HCAs form in meat, poultry and fish but not meaningfully in vegetables. Cooking above roughly 300°F, and cooking for a long time, produces more. Well-done, grilled, pan-fried and barbecued meats carry the highest levels.

PAHs, polycyclic aromatic hydrocarbons, form differently. When fat and juices from meat drip onto a flame or hot surface, the resulting smoke rises and deposits PAHs on the food. Smoking meat produces them too. This is the same chemical family found in tobacco smoke and vehicle exhaust.

This is where it is worth being careful, because the topic is often written up as if it were settled.

In the laboratory, HCAs and PAHs cause changes in DNA that may increase cancer risk. That mechanism is not in doubt.

In animals, rodents fed HCAs developed tumors of the breast, colon, liver, skin, lung and prostate. Rodents fed PAHs developed leukaemia and gastrointestinal tumors. The important caveat, which NCI states directly, is that the doses used in these experiments were thousands of times higher than the amounts people get from food.

In people, the picture is unresolved. NCI's position is that population studies have not established a definitive link between HCA and PAH exposure from cooked meats and cancer in humans. Some studies have found associations between high intake of well-done, fried or barbecued meat and colorectal, pancreatic and prostate cancer. Others have found nothing. Part of the difficulty is that measuring how someone actually cooks their meat, across years, from a questionnaire is genuinely hard.

So the honest summary is: strong mechanism, strong animal evidence at unrealistic doses, and human evidence that has not converged.

There is no IARC classification for "grilled meat" as a category. Individual compounds have been evaluated separately. Benzo[a]pyrene, one of the PAHs, is classified in Group 1, meaning the evidence that it can cause cancer in people is strong. Several HCAs, including PhIP and MeIQx, sit in Group 2B, possibly carcinogenic to humans.

As always with these labels, the Group describes how confident scientists are that a substance can cause cancer, not how much risk it creates at the doses people actually encounter. A Group 1 compound present in trace amounts on the crust of a steak is not the same proposition as a Group 1 exposure you breathe for eight hours a day.

If you are making decisions about meat and cancer risk, the better-established signal is not cooking method. It is how much processed and red meat you eat overall. IARC classifies processed meat as Group 1 and red meat as Group 2A for colorectal cancer, and WCRF and AICR recommend very little processed meat and no more than about three portions of red meat a week.

Cooking technique is a reasonable secondary adjustment on top of that. It is not where the weight of the evidence sits, and treating it as the main event tends to distract from screening, physical activity, alcohol and smoking, all of which have far better-established effects.

• IARC — Agents Classified by the IARC Monographs (benzo[a]pyrene Group 1; PhIP and MeIQx Group 2B)
• WCRF/AICR — Limit red and processed meat