Fruits and Vegetables Fight Cancer! Or Do They?

February 21, 2011

The American Cancer Society recommends eating at least five servings of fruits and vegetables per day to help prevent cancer. They have evidence to back this up, right? Um.

I found this study today, which looked for a link between fruit and vegetable consumption and cancer risk in 478,000 European subjects. It’s a prospective epidemiological study, meaning the researchers gathered information about subjects (in this case, how many fruits and vegetables people were eating), waited a few years, and then followed up to see how their subjects fared (in this case, who got cancer). The large number of subjects and the prospective nature of the study made it potentially very informative. Unfortunately for the veggies-prevent-cancer theory, the results were underwhelming at best.

The researchers found that a 200 grams/day increase in fruit and vegetable intake correlated with a statistically significant but minuscule reduction in cancer risk (about a 3% risk reduction). Assuming a cause-and-effect relationship (which is actually a pretty big assumption), this would mean that by increasing intake of fruits and vegetables by 200 grams/day, a person with a 30% probability of getting cancer could reduce that probability to 29.1%. Why am I not running to grocery store to buy more veggies?

Furthermore, even in a large study like this one, such a weak correlation has to be taken with a grain of salt. Other lifestyle factors could be at play that the researchers did not account for. People who eat more fruits and vegetables also tend to smoke less, exercise more, eat fewer french fries, etc. The researchers tried to factor out these variables, but it would be impossible to catch them all. There are probably variables scientists don’t even know about yet that affect cancer risk.

Walter C. Willett, M.D., Dr.P.H., of the Harvard School of Public Health, wrote in an accompanying editorial that “this study strongly confirms” the findings of other prospective epidemiological studies, which show weak or non-existent correlations between produce intake and cancer risk.

The studies that originally sparked the belief in fruits’ and veggies’ cancer-fighting properties were retrospective case-control studies, which tried to obtain dietary information from people who already had cancer and compare it to information from cancer-free controls. The problem is that a cancer diagnosis tends to skew a person’s memories about their dietary habits. Sick people are more likely to remember eating junk food while healthy people are more likely to remember eating nutritious food. Prospective studies, which gather information ahead of time, are free of this 20/40 hindsight bias.

Does this mean people don’t need to eat fruits and vegetables? Well, it certainly disproves the notion that a diet low in fruits and vegetables causes cancer. In later posts I’ll look into the possible connection between fruits and vegetables and heart disease. Either way, they’re not a panacea. But they’re probably good foods to eat because they provide energy and bio-available vitamins and minerals, without any apparent harmful effects on metabolism. Considering the overall quality of our food supply, that’s a pretty big deal.

What’s Wrong With Vegetable Oil?

February 17, 2011

Doctors tout it as a heart-healthy alternative to saturated fat. It’s in everything – packaged food, fast food, gourmet restaurant food, “health” food. But the truth is, vegetable oil is a highly processed, worse-than-empty calorie pseudo-food. And it has nothing to do with vegetables.

“Vegetable” oil is actually made from seeds – corn kernels, soy beans, sunflower seeds, safflower seeds, rapeseeds, cotton seeds – most of which don’t contain much oil to begin with (how much oil is in a kernel of corn?). Forcing oil from non-oily seeds requires intensive processing – either mechanical (using a machine to press the oil from the seed) or chemical (using a solvent such as petroleum-derived hexane). The result of all this crushing and dissolving is a crude oil that must be filtered and deodorized before it is considered edible. Some of the oil is also partially hydrogenated, a process that makes it less susceptible to oxidation (aka going rancid), but also produces trans fat, saturated fat’s evil alter-ego.

This leads to another point, which is that unhydrogenated vegetable oil is not very stable at room temperature, meaning it goes rancid easily. Rancid oils are just as bad as they smell – they contain free radicals which can wreak havoc in human cells and lead to cancer. Heating vegetable oil causes even more oxidation, which is why a lot of the oil used in deep fryers in fast food joints and restaurants is hydrogenated. Why doctors think it’s a good idea to ingest large quantities of oxidized oil, or worse, cook with it, is beyond me.

The energy and technology required to extract oil from non-oily plants and the impossibility of keeping it fresh without refrigeration explains why humans did not start consuming vegetable oil until last century. For the first few million years of human existence, the only types of fat people ate in large quantities were saturated fat (found in animals and some fruits like coconut and palm) and monounsaturated fat (found in animals and some fruits and nuts like olives and almonds). They got a little bit of polyunsaturated fat (the type of fat found abundantly in vegetable oil) from animals, nuts and seeds, but the amounts were tiny in comparison. There is no traditional food that provides anywhere near the amount of polyunsaturated fat found in vegetable oil. This means that humans have had effectively zero time to adapt to its biological effects, the full extent of which researchers don’t yet understand.

Apart from the sheer quantity of polyunsaturated fatty acids, there is the problem of the type of polyunsaturated fat people are eating. Polyunsaturated fat comes in two types, n-6 and n-3 (also call omega 6 and omega 3). Both are essential fatty acids, which means people need to eat them to live, but are required only in small quantities, like a few grams per day. It’s easy (all too easy) to get enough n-6 just by eating normal amounts of meat, poultry, eggs, nuts, seeds, or the tiniest bit of vegetable oil. With a modern diet, getting enough n-3 is a lot trickier, since it’s only found in significant quantities in fish, algae, seafood, fish oil, flax seed and some nuts (which also contain a lot of n-6). This means that a lot of people in industrialized countries are probably n-3 deficient, with a ratio of n-6 to n-3 between 10:1 and 30:1. This ratio is astronomical compared to the ratio consumed by traditional cultures, usually between 2:1 and 1:1.

The ratio is important because n-6 and n-3 perform different and competing functions in the body. They are both used to manufacture eicosanoids, signaling molecules that control inflammation and act as messengers in the central nervous system (according to wikipedia). Very simplistically speaking (eicosanoids are diverse, complex and still poorly understood), eicosanoids made from n-6 are pro-inflammatory (they turn on immune response) while eicosanoids made from n-3 are anti-inflammatory (they turn off or reduce immune response). Inflammation in response to injury or infection is a good thing – it’s how the body quarantines and neutralizes harmful agents. But chronic inflammation, which can be caused by an imbalance between pro-inflammatory and anti-inflammatory eiconasoids, is dangerous, and probably involved in most or all of the non-communicable diseases that plague industrial nations, such as heart disease, cancer, auto-immune diseases, allergies, asthma, metabolic syndrome and mental illness. The ratio of n-6 to n-3 in the diet determines the ratio of n-6- to n-3- derived eicosanoids in the body. Consuming vegetable oil guarantees over-consumption of n-6, creating an imbalance even high dose fish oil supplementation won’t reverse (though fish oil can reverse n-3 deficiency, which is nothing to scoff at).

In summary, vegetable oil is a new-fangled, highly processed substance that humans have not evolved to eat. It goes rancid at the drop of a hat and contributes to chronic inflammation and disease. Unfortunately, it has invaded our food supply, aided and abetted by public health officials terrified of saturated fat, a real food our ancestors evolved to eat. Today it is almost impossible to avoid vegetable oil except by cooking food at home, using traditional animal fat or healthy oils such as olive, palm, avocado or coconut oil (incidentally, all fruit oils). The sudden influx of easily oxidized n-6 polyunsaturated fat into our food supply presents a challenge for which our bodies are completely unprepared. It’s a human experiment of massive proportions with a fast-dwindling control group. We are already seeing the results, in the skyrocketing incidence of degenerative, inflammation-driven diseases.



Abdominal Obesity Correlates With Dementia

February 16, 2011

I’m just going to dive right in with my first post.

Stephan over at Whole Health Source linked to this study on the correlation between abdominal, or central, obesity and dementia risk. Using a sample of 6,583 Kaiser patients who had their sagittal abdominal diameter (distance between the belly button and the back) measured in the 1960’s and early 70’s, the study discovered that the folks with the biggest bellies (the ones in the highest quintile of abdominal fat) were almost three times more likely to end up with dementia than the folks with the leanest midsections (the ones in the lowest quintile). The association remained strong even after the researchers factored in BMI, meaning that overall fatness by itself could not explain the increased risk. Normal weight people with bigger bellies had almost twice the incidence of dementia as normal weight people with lean midsections.

Excess abdominal fat is a bigger danger signal than excess fat on the extremities, even in an otherwise normal-weight person, because it correlates strongly with inflammation and a range of other unhealthy markers such as high triglycerides, low HDL (so-called “good” cholesterol), poor insulin sensitivity and high blood pressure, which are often lumped together under the term “Metabolic Syndrome.” In turn, Metabolic Syndrome is associated with higher rates of heart disease, type two diabetes, non-alcoholic fatty liver disease, and apparently dementia too.

This study doesn’t prove that abdominal obesity causes dementia, but it does provide strong evidence that the two occur hand in hand, and that abdominal obesity in middle age can predict the risk of dementia later in life. This is good news, as it means that reducing or preventing abdominal obesity through diet could have an huge positive impact on quality of life (not to mention medical expenses) as people age. It’s also further support for the idea that disease is largely voluntary – people set themselves up for either disease or health by their lifestyle choices.