Saturday, November 18, 2006

All Fat is Bad

At least that's what Health Canada has consistently told us.

Would you be surprised to learn that the type of fat in your diet is much more important than the amount of fat in your diet?

My guess is probably not - there's been a tremendous amount of very well publicized research that has proven that blindly following a low-fat diet doesn't seem to help with any particular health outcomes and that diets richer in healthy fats are, well, healthier.

You might however be surprised at how much the type of fat you choose in your diet affects your health.

Let's start with the bad fats, the saturated fats and the trans fats - there's no disputing the fact they're not good for you.

Starting with saturated fats, Dr. Ancel Keys back in 1956 with the Seven Countries Study (another very important epidemiological data base) was the first to show that countries with diets higher in saturated fats had higher levels of heart disease. In his studies however, the total amounts of fats in the diet were not linked with heart disease and the country with the highest amount of total fat, Crete, also had the lowest rate of heart disease. Perhaps this is why results of clinical trials looking at simple overall fat reduction are not terribly impressive.

In January of this year, a series of 3 articles came out in the Journal of the American Medical Association detailing the results of the largest dietary fat trial ever conducted. The study they were detailing was the Women's Health Initiative Controlled Dietary Modification Trial where 48,835 women were randomly assigned to a low-fat diet (less than 20% of calories from fat) or to a comparison group and were followed for over 8 years. The papers reported that low-fat diets did not lower the risks of colon cancer, breast cancer or heart disease.

On to trans-fats. Trans fats today constitute roughly 3-7 percent of the calories we consume from fat. Trans fats come from shortenings, fried foods and many commercially baked goods (goods that almost always also use refined flours).

Trans fats have been shown to raise bad cholesterol, raise triglycerides, lower good cholesterol and make our blood stickier increasing the risk of blood clots. Trans fats have also been shown to increase the process of inflammation in our body which in turn has been implicated in heart disease and diabetes and may well also be involved in other disease processes.

Using the Nurses Health Study again, Dr. Walter Willett and colleagues showed that women who ate the most trans fats (3% of total daily calories worth) were 50 percent more likely to develop heart disease over a 14 year period than those who ate the least. Conversely, women who ate the lowest amount of trans fats and the highest amount of healthy fats (we'll get to healthy fats in a moment), were 70 percent less likely to develop heart disease.

The Center for Science in the public interest estimates that removing trans fat from the food supply in North America will prevent between 11,000 and 30,000 deaths per year and save over $50 billion dollars in annual health care expenditures. Interestingly Dr. Willett in his book Eat, Drink and Be Healthy states that he feels these numbers are underestimations as CSPI's report did not take into account the potentially harmful effects trans fats have on diabetes risk.

In June 2006 Health Canada released the findings of their Trans Fat Task Force and made recommendations to our government for the elimination of trans fats from our food supply. Given the strength of the research as well as the degree of damage trans-fats cause, it's hard to fathom why our government is not acting on these recommendations.

Now onto the good fats. The good fats are the unsaturated fats. Monounsaturated fats are found in vegetable oils, avocados and nuts and polyunsaturated fats are found in whole grains and fatty fish. You've probably read a great many claims about these fats and if your eyes have been open you've been seeing food products touting how much of them they contain, especially with regards to omega-3s. Omega-3 fats are unsaturated fats and there are three types of them, ALA, DHA and EPA. ALA is the most common, it's found in a variety of vegetable oils, while EPA and DHA come mainly from fish.

Again using the Nurses Health Study and the Health Professionals Follow Up Study Dr. Walter Willett and colleagues have calculated that replacing just 5 percent of total calories currently consumed from saturated fat with unsaturated fat would reduce the risk of heart attack or death by about 40 percent. In contrast they also showed that replacing saturated fat with carbohydrates (like we're told to do by the Food Guide) showed much smaller reductions in risk.

To summarize the studies on omega-3 fatty acids, they lower levels of LDL or bad cholesterol, they help to prevent the increase in triglycerides in high carbohydrate based diets, they reduce the development of irregular heartbeats (a major cause of sudden cardiac death) and they reduce the tendency for clots to form in our arteries.

A famous study called the GISSI Prevention trial took more than 11,000 men and women who had survived a heart attack and randomly assigned them to taking either a placebo or a 1-gram capsule of omega-3s. At the end of 3 years, there were over 14 percent fewer deaths in the omega-3 group (sudden deaths cut by 50%) and fewer second heart attacks and strokes.

So now that you've heard how terrible trans-fats are for you and how healthy unsaturated fats are for you would you like to know what the draft Food Guide had to say on the matter?

Dr. Willett, on reviewing the draft Food Guide had this to say on the Guide's fat recommendations,

"Like the US Guidelines, the draft Canadian document is still fat phobic. There is suggestion to use a very limited amount of vegetable oils, but there are recommendations to reduce or avoid fat in general, when it really trans fat in partially hydrogenated foods that should be totally avoided and saturated fat that should be limited. The main message should be to replace trans and saturated fat with unsaturated fats."
The words trans fat do not appear even once in the draft Food Guide, this despite the ridiculously large amount of evidence pointing to the need for their elimination. Health Canada's own Trans-Fat Task Force report recommends we eliminate them from our diet and Health Canada's own labeling laws required trans-fat to be listed on our food labels. Why then don't they point us in the Food Guide to look for and steer clear of trans fats?

Regarding healthy fats, the words unsaturated fats do appear twice. There's a statement that tells use to use vegetable oils high in unsaturated fats "most of the time", and then there's a statement to aim for a small amount of unsaturated oils or soft margarine each day. There's no mention of the healthy fats found in fish and the only call to action on fish is buried on page 6 where it says consume fish once a week. There's also no recommendation to try to replace some of the saturated fats in our diet with unsaturated fats (remember, replace 5% of one with the other and the risk of heart attack and death goes down by 40%).

So just as with the data supporting the preferential consumption of whole grains over refined grains, the preferential consumption of unsaturated fat over saturated fat and the elimination of trans fats from our diets are as black and white as things get in medicine.

Unfortunately our Food Guide seems hopelessly mired in gray.

Tomorrow: All Meat is Good, and Please Eat More of it - Beef farmers rejoice, Health Canada recommends Canadians eat more beef and still doesn't tell us fish is a healthier choice.

Yesterday: Please Eat White Bread - Why Wonder Bread's more in touch with the evidence on whole wheat than Health Canada.