Friday, February 15, 2013

Is a Low-Fat Diet Healthiest?

In the last two blogs I tried to correct the (dangerous) misunderstanding many Americans have regarding high-protein diets.  Today I focus on the confusion many people have about low-fat diets.

Americans have focused ad nauseam on low-fat diets.  Now overwhelming evidence indicates that it is the type of fat that matters, not the amount.  Traditional Greeks, arguably the healthiest people on the planet measured by low rates of premature mortality, ate a 40% fat diet based predominantly on olive oil.  Americans are shocked to hear that such a “high” fat diet actually lowers triglycerides.  In recent years the American Heart Association has “tweaked” its recommendation upwards from 20 to 30% fat.  The National Cholesterol Education Program’s cholesterol-lowering diet (p. V-2) has been revised to 25-35% fat with an emphasis on plant fat.

Yet due to decades of low-fat recommendations based on nutrition research which at first glance seemed to indicate that a low-fat diet would prevent cardiovascular disease, and due to the plethora of low-fat products which subsequently flooded the market with their “nutrition education” influence on the American public, many Americans still think that eating a low-fat diet is the “healthiest” way to live.  However, overwhelming evidence indicates that a moderate fat diet is much healthier.  Actually, a diet that would be considered high-fat (40%) in comparison to previous recommendations (20%) actually reduces the incidence of cardiovascular disease.  The 7 Countries Study performed way back in the 1960’s by T. Ancel Keys found that the diet eaten by the Greeks on the island of Crete was one of the highest fat diets at 40% fat, low in saturated (or animal) fat and high in monounsaturated fat (from plants), but the Greeks eating it came out with some of the lowest rates of cardiovascular disease and all-cause mortality and had the longest life expectancies in the world at that time.  The diet, now fondly called the “Mediterranean Diet” is high in vegetables (about 2-3 cups/day), especially green leafy types, high in fruits (2-3 /day), high in wholegrain carbohydrates (equivalent to 8 servings/day), high in legumes and nuts, moderate in fish and alcohol, low in meat and fermented milk products.  The diet is also low in animal and saturated fat but high in total fat (40%) with 4 Tbsp. olive oil/day. 

So how was it that American nutrition experts originally came to the low-fat conclusion? 

As with any research, initial studies often reveal part(s) of the answer(s), but the longer researchers study a question the more the big picture is revealed.  Additionally, just because a low-fat diet has a positive effect on some of the risk factors for cardiovascular disease does not necessarily mean that lowering some risk factors translates to lower mortality.  That is a huge seemingly reasonable leap of logic which does not always pan out to be true.  Some examples:  weight-loss is not always healthy, half of all heart attacks occur in people with low cholesterol, and just because a certain amount of a nutrient is good for you does not mean that more is better.

The reason that the low-fat diet recommendation resulted in some positive effect is that the Standard American Diet (S.A.D), is high in animal fat--the cholesterol-raising, artery-clogging saturated fat.  The recommendation to cut fat in an American diet would therefore automatically cut mostly animal/saturated fat in the diet, leading to some improvement and the assumption that a lower fat diet is healthier.  However, in recommending the low-fat diet, the improvements were inconsistent, to say the least.  While reducing the intake of excessive animal fat is beneficial, reducing the intake of all fat is not.  As is the way of research, a longer and broader look into the issue began to show the distinction of saturated fat vs. other fats, and that a low-fat diet is not necessarily healthy.  It soon became evident that half of all heart attacks occur in people with low LDL-cholesterol and that there must be more to this story.  In fact we now know that cardiovascular disease is a multi-factorial disease and is basically a disease of inflammation of the blood vessels. 

So a low-fat diet has proven to be a very ineffective way to prevent heart attacks and strokes.  The American Heart Association has adjusted its recommendations accordingly, continually “tweaking” its fat recommendations in recent years along with accumulating research.  Originally the AHA recommended a diet based on 20% or less fat, then 30% or less, and presently “no more than 30% fat”.  The National Cholesterol Education Program recommends 25-35% fat for a cholesterol-lowering diet, and the Syndrome X diet to treat the metabolic syndrome which places 1 out of every 3 American adults at increased risk for cardiovascular disease is based on 40% fat, similar to the traditional diet of healthy Greeks and the highly recommended Mediterranean Diet.  Prominent scientists in the field of nutrition report that a high plant fat diet actually lowers triglycerides, one of the major players in cardiovascular disease, and does not lower the good HDL-cholesterol like low-fat diets do.   Many experts now recommend diets consisting of up to 40% calories from fat, with an emphasis on monounsaturated fats.  Monounsaturated fats reduce the risk of heart disease when they replace saturated fats and aren’t just added. 

The take-home message is this—the type of fat is clearly more important than the amount.  A higher amount of good fat may actually be healthier as monounsaturated fats replace excessive refined carbohydrates and animal protein in the diet.  Both refined carbohydrates and animal protein stimulate insulin secretion (exacerbating “hyperinsulinemia”, which is the root problem of the metabolic syndrome) whereas monounsaturated fats do not.  Unfortunately, the average American diet provides 37-42% fat, mostly LDL-and triglyceride-raising animal/saturated fat. 

Now I could tell you all about the types of fat as we group them into monounsaturated fats, polyunsaturated fats, and saturated fats, as well as trans fatty acids.  And I could tell you about how saturated fats usually raise LDL “bad” cholesterol, but not always, or how monounsaturated fats sometimes lower LDL cholesterol and do not lower good HDL cholesterol, and how polyunsaturated fats lower LDL cholesterol but have been found to be inflammatory to our blood vessels in the amounts we eat them in the Standard American Diet (SAD).  But it is a lot simpler, and the evidence is bearing it out to be more completely correct, to simply adhere to the paradigm which has never been proven wrong and is continually being proven correct, and that is to eat less animal and processed food, and more plant food.  If we follow the same pattern with fat--avoid animal and processed fat and focus on vegetable fat--it will have a positive effect on our LDL cholesterol, HDL cholesterol, and triglycerides.

So a low-fat diet is not optimal, and I haven’t even mentioned the fact that our bodies need a consistent intake of “essential fatty acids”, and that another function of fat is lubrication (anti-constipation!)  Instead, a diet based primarily on plant fat (especially olive oil, nuts, seeds), with moderate intake of fish (omega 3 fatty acids also found in flax and walnuts), and low in animal and processed (trans) fat supports optimal health.

What has always been a healthy diet, still is, and always will be.  

Enjoy the blessing of food,

Diane Preves, M.S., R.D. 

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1 comment:

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