High fat diet increases insulin resistance?

Thursday, September 3, 2009 17:47
Comments Off on High fat diet increases insulin resistance?

I was just re-reading Tara Parker Pope's article in the NY Times on the now-famous rat study which found that high-fat meals impaired cognitive and athletic performance. Predictably, the study was dissed and dismissed by the low-carb and pro-fat bloggerati.

(By the way, for those who dismissed the study because it involved rodents, data from a parallel human study are still being analyzed but appear to line up with the original findings.)

Whatever the merits and implications of this particular study, I was struck by the following quote from Pope's article:

It’s not clear why fatty foods would cause a short-term decline in
cognitive function. One theory is that a high-fat diet can trigger
insulin resistance
, which means the body becomes less efficient at
using the glucose, or blood sugar, so important to brain function.

This, of course, is exactly the opposite of what low-carb/high-fat advocates are always telling us The story is that a high carbohydrate diet is the culprit (and a low-carb diet is the cure) for insulin resistance.

Specifically, ingestion of carbohydrates (especially high glycemic carbs) sends blood sugar soaring, which triggers insulin secretion. Over time, cells become less sensitive to the effects of all that insulin and blood sugar levels creep dangerously higher.  Next stop: obesity, Type 2 Diabetes, and heart disease. Cutting down on carbs reverses the whole cycle.

So what's all this about a high-fat diet triggering insulin resistance? 

In a long discussion, Mark Jenkins, MD, suggests that while carbohydrates may raise insulin levels, high insulin levels do not cause cells to become insulin resistant. Further, he suggests that obesity leads to insulin resistance and not the other way around.

Here are a few of his observations, which some may find surprising:

  • High fat stores [in obese individuals] down-regulate insulin receptors and cause a
    resistance to circulating insulin.
  • It has been repeatedly shown in the
    medical literature that…insulin sensitization is accomplished by aerobic
    exercise, low-fat / high-carbohydrate diet, and reduction of excessive
    body fat. Conversely, obesity and high fat diets have been shown to
    induce insulin resistance. 
  • It is important that the high carbohydrate
    diet have predominantly complex carbohydrates and also have a high
    fiber content.  Overly refined, simple sugars do not appear to have the
    same effect as complex carbos. 

Please see Jenkins' entire discussion here and selected references here.

Maybe the problem is not the fat in our foods but the fat in our bodies

Jenkins' arguments don't separate the effects of diet
composition from the effects of body weight or weight loss. In the studies he cites, those with insulin resistance aren't just eating a high fat diet; they're also obese. Those who see increased insulin sensitivity aren't just eating a low-fat diet, they're also exercising and losing weight. One wonders: Does a high fat diet lead to
insulin resistance in normal weight people? Does a low-fat diet improve
insulin resistance if the subjects don't lose weight? What if they lose
weight on a high fat diet?

The epidemiological argument?

I find it interesting that both sides of this debate invoke epidemiological evidence. The pro-fat folks (the Weston Price gang, for example) claim that atherosclerosis and diabetes were "unheard of" in traditional cultures which had high fat, grain-free diets.  Jenkins, on the other hand, says:

If one looks at epidemiological data,
the traditional diet of many third world countries consists of high
complex carbohydrate content, very low fat, and high fiber.
Atherosclerotic disease was virtually unheard of until the introduction
of the high fat Western diet. 

Obviously the ratio of fats to carbohydrates does not tell the whole story.  Jenkin's observation about the difference between complex and simple carbohydrates is one key.

Maybe we can't blame the modern epidemic of obesity, heart disease, and diabetes on fat OR carbohydrates–but on a toxic combination of fat AND refined carbohydrates (with over-consumption and sedentary lifestyles playing significant supporting roles).

Your thoughts?

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