If you read the Daily Mail often enough, you would be forgiven for thinking everything causes cancer.

With the overwhelming number of health warnings we hear every day, it’s easy to become inundated with conflicting information. It’s unsurprising of us just brush it all off and vow to live by the easy “everything in moderation” rule.

Sure, cancer is caused by many things. But by far the biggest cause is through direct carcinogen (cancer-causing substance) exposure. The majority of which enter our body through foods we eat.

Considering cancers are responsible for nearly 1 in 4 deaths in the US and Europe, it’s worth paying at least a little attention to how our eating habits might put us at increased risk.

Five Ways Our Diet Affects Cancer:

1. Directly eating powerful carcinogens in our diet
2. Foods that cause carcinogen formation inside our body
3. Foods that affect how carcinogens are metabolised by our body
4. Foods that affect cancer cell metabolism
5. Calorie Intake affects cancer risk (High-Energy Diet)

Let’s focus first on the easiest category: carcinogens we eat directly in our food. There are 3 main sources of these carcinogens. Some occur naturally, some are created by the way we cook our food, and some originate from the way we store our food:

Eating Carcinogens

1. Carcinogens Occurring Naturally in Our Food

Safrole is a carcinogen that occurs in small amounts in common foods such as thai basil, nutmeg, anise, cinnamon, tamarind and black pepper. Yes, ingested safrole has been shown to be very potent at causing cancer – but should we be worried and avoid these foods? No, the concentrations at which it’s found naturally in these foods is very low, and the risk is negligible compared to other sources of carcinogens we eat.

(Side note: Safrole used to be an ingredient in Coke and other soft drinks until it was banned in the USA in the 70s. It continues to be used in most soft drinks in Asia in concentrations up to 5x the recommended limit. This is vastly different to the low levels of safrole found naturally in food.)

2. Carcinogens Generated Through Cooking

Various ways we heat our food can generate something called polycyclic aromatic hydrocarbons (PAH). PAH are very well-studied carcinogen that mainly causes liver, stomach, lung, bladder, and skin cancers by provoking DNA mutations.

Barbecuing, smoking, deep-frying and flame-grilling, are thought to produce the most PAHs in foods. In particular, the smoke created by fat-dripping onto open flames can coat food in harmful PAHs.

How far do you have to go to minimise these risks? We eat 3 meals a day, so over time small adjustments in how we choose to cook can add up. Everyone loves a flame-grilled burger, but perhaps make it a treat not a habit.

3. Carcinogens from Improper Food Storage

Food stored in warmth and humidity can culture microorganisms that produce cancerous toxins. For example, molds that grow in common foods such as wine, peanuts, corn, rice, wheat, and sunflower seeds, produce Aflatoxin B1.

Aflatoxin B1 is one of the most carcinogenic substances known, and primarily causes liver cancers. Worryingly, even milk, eggs, and meat from animals fed with contaminated feedstocks have been found to contain significant levels of aflatoxins.

There’s little you can do about things further up the food-supply chain, apart from choosing where and how you shop. But in your own home you can make sure food is stored safely and appropriately.

Apart from directly eating carcinogens, there are certain things we eat that aren’t carcinogens in themselves, but cause carcinogens to form within our body once ingested.

Foods that Cause Carcinogen Formation inside our Bodies:

You may have seen a lot of press lately about processed meats causing cancer. This is due to nitrite, which is used as as a food additive to preserve meats, and fairly harmless in itself. You’ll find lots of nitrites in bacon, sausages, ham, salami, and other cured meats. When exposed to acids, like in our stomach, nitrites form nitrosamines, which then cause bowel cancer.

The evidence for this is as strong as the evidence that smoking causes lung cancer, so it should be taken seriously. For this reason the NHS recommends that adults eat 70g or less of red or processed meat a day.

Fat is another substance that’s harmless (in fact essential) in itself, but can cause problems inside our gut. Regularly eating a high-fat diet can increase secondary bile acid secretion in our gut. This increases cancer risk by altering our gut bacterial flora and creating a chemical environment more inductive to developing bowel cancer.

The good news is, a high-fibre diet does the exact opposite. Dietary fibre alters our gut bacterial flora in a good way, and promotes a less carcinogenic environment. Another way in which dietary fibre protects us, is by bulking up our stool. As unsavoury as that sounds, the bulk dilutes the carcinogens and also speeds up passage through our gut, thereby reducing direct contact with our intestinal walls.

Foods that Affect Carcinogen Metabolism

In most simplistic terms, cancer is an overgrowth of cells. In perfect balance, the number of new cells equals the number of dying cells. So anything that interferes with this natural balance, can affect cancer progression. For example, a high-fat diet is thought to enhance cell proliferation: fat cells create more hormones and growth factors that tell our cells to double more often. While garlic and cruciferous vegetables (cauliflower, broccoli, kale, cabbage) are thought to promote natural cell-death.

High-Calorie Diets Increase Cancer Risk

Being overweight or obese, increases your risk of 13 different types of cancers: Breast, bowel, uterine (womb), oesophageal (food pipe), pancreatic, kidney, liver, stomach, gallbladder, ovarian, thyroid, myeloma (a blood cancer), and meningioma (a brain tumour).

On the other hand, energy restriction (to a certain degree) has anti-cancer effects. Extensive studies have been done on the health benefits of prolonged calorie-restriction. But the key here is simply to balance your energy intake to its out-put, so you can also achieve the same effect by increasing physical activity rather than reducing dietary energy intake.

In summary,

Ways we can reduce Cancer Risk through Diet:

A lot of this will sound obvious, or at least like advice you’ve heard over and over again. But maybe there’s a reason you keep hearing….

1. Maintain a healthy body fat percentage (under 30% for women and 24% for men)
2. Increase Plant-based food in your diet
3. Limit energy-dense foods and sugar
4. Limit red meat and avoid processed meat
5. Be aware of how food is stored, and avoid grains or pulses that could harbour mold
6. Limit cooking methods that produce carcinogens