By Conner Middelmann-Whitney and Brian Lawenda M.D.
Fats are the most controversial and misunderstood macronutrients in the human diet.
Vilified for the past four decades as “artery-clogging”, fattening and inflammatory, fat has become a pariah on our plates.
But this view is steadily shifting. While some diet doctors still tell us to limit our fat intake to as little as 10% of total calories, others now say that fats may not be as evil as has long been assumed.
As with many nutritional debates, there are no easy answers. One thing we can say is that there are beneficial fats that may lower our cancer risk, while other commonly-eaten fats can increase it.
In this article we want to clarify some of the misconceptions surrounding fats and show you that it is possible to enjoy dietary fats that can boost your health while avoiding those that can damage it.
Fats are essential to health
Decades of widespread “fat-phobia” have all but obscured the fact that dietary fats are essential components of our diet and are essential for optimal health.
Not only do fats offer a concentrated source of energy and provide the building blocks for cell membranes and a variety of hormones, they also act as carriers for fat-soluble vitamins A, D, E and K, and are needed for the conversion of carotenes to vitamin A, mineral absorption and a host of other vital processes.
Moreover, fats make meals more satisfying and pleasurable: they improve the mouth-feel of our food, increase our flavor perception and make us feel sated for hours after a meal. This means we can go longer without feeling hungry, thus lessening our desire to eat unhealthy snacks.
Before going into detail about “good” and “bad” fats, let’s take a look at dietary fats and their food sources in the table that follows.
| Type of fat | Food source |
| Monounsaturated fats | Olive oil, rapeseed oil, peanut oil, avocados, nuts and seeds |
| Polyunsaturated fats(High in omega-3) | Animal sources: Fatty, cold-water fish (such as sardines, salmon, mackerel, anchovies, herring, sablefish, cod. Smaller fish (i.e. sardines, mackerel, and anchovies) & wild salmon have less mercury and toxic PCBs than bigger fish like tuna, swordfish and shark), krill; eggs, milk and meat from farm animals fed omega-3 rich feed or from wild animalsPlant sources: Walnuts, flax seeds, chia seeds, walnuts, walnut oil, rapeseed oil, green leafy vegetables, purslane, lamb’s lettuce |
| Polyunsaturated fats (High in omega-6) | Most seed oils (safflower, sunflower, corn, soy, cottonseed), nuts and seeds; meat, eggs and milk of animals fed seeds or seed oils (e.g. corn), such as industrially reared chicken or beef. Also, margarines and industrially prepared snacks and baked goods labeled as containing “vegetable fat,” which is often high-omega-6 seed oil |
| Saturated fats (solid at room temperature) | Animal products (such as meat, poultry, seafood, eggs, dairy products, lard, butter and tallow), and coconut, palm and other tropical oils |
| Trans fats | Partially hydrogenated vegetable oils, commercial baked crackers, biscuits and cakes, fried foods (such as donuts and chips), vegetable shortening and margarine |
According to the World Health Organization and the Centers for Disease Control and Prevention, fats should make up anywhere between 20 and 35% of our calorie intake. Of this, roughly a third should come from saturated fats, another third from monounsaturated fats and the rest from polyunsaturated fats.
These are approximate ratios; individual biochemistry, age, sex, physical and mental activity levels, climate and many other variables influence what type of fat, and how much of it, your body needs. For instance, children and adolescents, pregnant or lactating women and physically very active people need closer to 35% of their calories from fat, whereas sedentary adults or elderly people may need significantly less.
Optimizing our omegas
Polyunsaturated fats are our main sources of so-called omega-3 and omega-6 fatty acids and our bodies work best when these two fats are in balance.
Humans need to consume similar amounts of omega-6 and omega-3 fats (the relationship between the two is called the “omega-6-to-3 ratio”): a ratio of 2:1 or 3:1 is considered ideal. However, most people eating a western diet consume significantly more omega-6 fats than omega-3 – in some cases, 30 times more! – and this is problematic.
Omega-6 fatty acids encourage cancer cells to grow and spread through a variety of mechanisms. They can:
- stimulate tumor growth
- inhibit tumor cell death
- increase the formation of blood vessels that feed tumors
- increase the invasiveness of tumors
- suppress immune function
- increase levels of free radicals
- increase the risk of developing breast, prostate, colorectal and lung cancers
- increase the risk of progression and death from breast and prostate cancer
- increase the production of tumor-stimulating growth factors
- and activate a cancer-promoting gene (ras-p21) that leads to tumor growth
Omega-3 fatty acids, on the other hand, can lower our cancer risk in various ways. They are thought to:
- inhibit the production of blood vessels that feed tumors
- decrease free radicals (antioxidant)
- support the immune system
- inhibit tumor cell progression
- enhance the effects of certain types of chemotherapy and radiation treatments
- slow tumor growth, and
- reduce the risk of wasting (cachexia) in cancer patients
(Click here for an excellent selection of scientific articles on omega-3s and cancer.)
The primary source of omega-6 fats in the western diet is seed oils and processed foods made with these. Because they are cheap, food manufacturers like to use corn oil, sunflower oil or safflower oil to make processed food. Baked goods such as cookies and pastries, snack foods like potato chips, ready meals and fast food are almost always made using these oils.
The problem is that corn oil contains 58 more times omega-6 fats than omega-3 – this 58:1 ratio is light years away from the ideal 2:1! Even worse, sunflower oil, grape seed oil and cottonseed oil contain no omega-3 fats at all.
Omega 6’s aren’t just in seed oils
Animal products, too, often contain omega-6 fats. When cows, chickens or pigs are fed a corn-based diet brimming with omega-6 fats, these fats make their way into their milk, meat and eggs. So when we eat animal fats, their omega-6-to-3 ratio reflects what the animals were fed.
Unfortunately, the omega-6-to-3 ratios of meat, dairy and eggs from animals raised on modern feed are far away from the ideal 2:1 balance. For example, while eggs from free-roaming hens feeding on insects and green plants contain an omega-6-to-3 ratio of approximately 2:1, mass-produced commercial eggs can contain as much as 20 times more omega-6 than omega-3 (20:1)!
A study comparing the milks of intensively reared and pastured cows in Denmark showed that pasture-fed cows produced milk with an omega-6- to-omega-3 ratio of 1 (i.e. equal amounts of omega-6 and omega-3). By contrast, conventionally reared cows fed a commercial mix of rapeseed, soybean meal and maize silage produced milk with an omega-6-to-3 ratio of 4.7 (nearly five times more omega-6 fats than omega-3).
The shift to modern feeding methods hasn’t only upset the natural omega-6-to-3 balance in our diets; it has also led to a decline in the conjugated linoleic acid (CLA) available from dairy products.
CLA, a type of fat found mainly in the milk, cheese and butter of grass-fed cows and in eggs, is thought to lower cancer risk. Animal and laboratory investigations indicate that it may reduce the risk of numerous types of cancers, including breast, prostate, colorectal, stomach and brain. In a British study, milk from pasture-fed cows contained up to twice as much CLA as that of conventionally fed cows, 39% more omega-3 fatty acids, 50% more vitamin E and 80% more carotenoids (both important antioxidant nutrients).
It follows that when we consume animal fats they should come animals reared traditionally, spending most of their lives outdoors eating foods they would consume in nature. It’s best to avoid fats from animals that were treated with antibiotics or hormones and ate grains grown with the use of pesticides: hormone and pesticide residues have a tendency to accumulate in an animal’s fat stores.
Alas, genuinely pastured, organic animal products aren’t always easy to find, and stores add to shoppers’ confusion by bandying around terms like “natural,” “organic,” “pastured,” “grass-fed,” “grass-finished,” all of which mean different things but all sound similarly virtuous. Organic, for instance, means the animal was not treated with antibiotics and hormones or fed genetically modified grains, but it does not mean it was grass-fed – it may simply have been eating organic corn instead of chemically grown corn – and even organic corn is chock full of omega-6 fats!
Another way of reducing our intake of omega-6 fats is to avoid processed foods. Because omega-6-rich seed oils like sunflower, safflower and corn oil are cheap to produce, food manufacturers like to use them in baked goods, ready meals and most other convenience foods. Even “healthy” foods such as dried cranberries, canned sardines or granola bars often contain added sunflower oil or other omega-6-rich fats.
Olive oil – Mediterranean nectar
Another ally in our fight against cancer is olive oil. Twenty-five studies on olive oil intake and cancer risk were recently analyzed by a team of researchers in Italy. They found that olive oil reduced the risk of cancers of the breast, respiratory tract, upper digestive tract and, to a lesser extent, lower digestive tract (colorectal cancers).
While it isn’t clear whether the monounsaturated oleic acid that makes up 75% of olive oil is cancer protective (the evidence is mixed), olive oil’s main benefit is derived from its polyphenols: plant chemicals with powerful antioxidant properties.
Olive oil also contains anti-inflammatory compounds – especially the extra virgin olive oils from the first pressing. Inflammation is a key cancer risk factor and foods that help quench it – vegetables and fruits, spices, herbs, red wine and olive oil – can thus have anti-cancer effects. Some compounds in olive oil may even help control certain cancers once they have already developed, for instance by preventing cancerous cells from reproducing or by prompting them to self-destruct (apoptosis).
Trans and saturated fats – more evidence needed
While industrially manufactured trans fats are known to contribute to cardiovascular disease, less is known about their role in cancer. The American Cancer Society states that a relationship between trans fats and cancer “has not been determined” and the evidence is mixed.
One study, for instance, found a positive association between trans fats and prostate cancer. However, a larger study found a correlation between trans fats and a significant decrease in high-grade prostate cancer.
Then again, an increased intake of trans fats may raise the risk of invasive breast cancer by 75%, the results of the French part of the European Prospective Investigation into Cancer and Nutrition suggest. And another recent study found that dietary trans fats were positively associated with the risk of cancers of the colon, the breast (in premenopausal women) and the prostate.
What is known for sure is that trans fats contribute to systemic inflammation, insulin resistance and weight gain – all of which are well-known cancer risk factors. Moreover, when we eat trans fats, it becomes harder for our bodies’ cells to utilize any omega-3 fats in our diets, thus blocking their health benefits. It’s therefore best to avoid trans fats completely, including processed and deep-fried foods.
Saturated fats are another grey area. For a long time they were thought to promote cancer by fuelling inflammation and causing weight gain (two major cancer risk factors). However, more recent investigations have cast doubt on this hypothesis.
For one, saturated fat may not necessarily promote inflammation in the body. In one intervention trial subjects eating a low-carbohydrate diet and consuming three times more saturated fat than those eating a low-fat diet nonetheless had lower inflammatory markers and less circulating saturated fat in their blood than the low-fat dieters.
Moreover, several weight-loss studies have shown that people eating low-fat diets did not lose more weight than subjects eating higher-fat diets. Indeed, some studies have found that when calories were held constant, low-carbohydrate diets were superior to low-fat diets with regard to weight loss.
The only randomized, controlled trial comparing the health effects of vegetable fats against animal fats was the Los Angeles Veterans Administration Hospital Study conducted nearly 50 years ago. Over the course of eight years subjects were randomly assigned to one of two diets that were identical except that one used largely saturated animal fats and the other used largely polyunsaturated, omega-6-rich vegetable fats. After two years, the two groups started diverging: the group consuming vegetable oils had a greater incidence of cancer, and this gap widened over time.
This is not to say that saturated fat is cancer-protective; there is no evidence for such an assumption, and more research is needed to assess the role of saturated fats in the cancer context. However, a modest proportion of saturated fat in a diet that is otherwise rich in plant foods, low-glycemic carbohydrates, omega-3s and olive oil may not be as harmful as has been previously thought.
Indeed, one advantage of saturated fats is that – unlike omega-3s and olive oil – they do not oxidize easily when heated and therefore provide a safer, less carcinogenic fat for cooking.
In summary, our recommendations:
- Regularly eat foods high in omega-3s (i.e. cold-water, deep sea fish, walnuts, flax seeds and green leafy vegetables). Consider taking supplemental omega-3 fatty acids, especially if you do not eat much fish. (Find out how safe your fish-oil supplement is here.)
- Eat olive oil regularly; as little as 1-2 tablespoons of extra virgin olive oil per day can have significant anti-inflammatory benefits. Wherever possible, use unheated olive oil in salad dressings or drizzled over cooked food rather than for cooking, as heat can damage its precious polyphenols.
- Limit foods that are high in omega-6 fatty acids (corn, sunflower and safflower oils, and meat, eggs or dairy products from intensively reared animals fed grains that are high in omega-6 fats).
- When you consume animal fats, they should be from organic, pasture-fed animals wherever possible.
- Completely avoid trans fats, margarines, any processed foods containing these and deep-fried foods.
- Use saturated fats primarily for cooking. When eating saturated animal fats, ensure they come from pastured, organically reared animals (see above).
We hope to have been able to shed some light on the complicated issue of fats and cancer; do contact us with any questions. In a forthcoming post, we will talk more about which fats to use for cooking – another question we get asked frequently.
