When humans consume more carbohydrates than can be stored, the excess carbohydrate energy is converted to fat by the liver. This process may maintain blood sugar control and prevent diabetes in the short-term, however it may also increase triglyceride concentrations, which may increase the risk of cardiovascular disease.

In the last decade, researchers established that fat production by the liver varies depending on dietary habits and health status.

The typical Western diet has a high fat content, which means that only a limited amount of carbohydrates are available for liver fat production, and liver fat production tends to be very low among individuals who eat this type of diet. However, when too many carbohydrates were consumed, both liver fat and sugar production were increased.

A very low-fat (10 percent of energy) and very high-carbohydrate (75 percent of energy) diet also leads to increased liver fat production, with the increase being even more pronounced when more than half of the carbohydrate was consumed as simple sugars. This points to the importance of carbohydrate quality, as another study using 68 percent of energy from complex carbohydrate resulted in minimal liver fat production.

However, it was found that obese individuals with high insulin levels who consume a high-fat (40 percent of energy) diet had a liver fat production rate three to four times higher than that of lean individuals with normal insulin levels. But, both normal and high insulin groups had lower liver fat production on the high-fat diet than on a low-fat, high-carbohydrate diet.

Moreover, the low-fat, high-carbohydrate diet caused an increase in triglyceride concentrations, a risk factor for coronary heart disease, which was associated with the liver fat production in both normal and high-insulin individuals.

Researchers concluded that the low-fat, high-carbohydrate diet might not be ideal, as it can induce liver fat production and insulin resistance. This is especially true when most of the carbohydrate is in the form of simple sugars.

American Journal Clinical Nutrition January 2003 77: 43-50 (Free Full Text Journal)

Dr. Mercola's Comments:

Many people are still convinced that a low-fat diet is the way one treats high cholesterol or triglyceride levels. It is still part of the traditional dogma and two months ago the Canadian Medical Journal published a review that continues to promote the low-fat diet. They did electronically publish my rebuttal to that review, however, and will publish it in the hard copy in the near future. The above study illustrates quite clearly that our bodies can only use a very small amount of sugar, and the liver is forced to convert any extra that we can’t use by converting it to fat, either in the form of cholesterol or triglycerides. What the study also makes very clear is that there is a difference in the way one responds depending on their insulin levels. Those with high insulin levels, which are most people who are overweight, or have diabetes, high cholesterol or high blood pressure, will respond negatively to increased carbohydrate content. If you have low insulin levels this is less likely to occur. Not many Americans have low insulin levels, however, only about 10 percent to 15 percent by my estimate, and those who do would mostly be normal weight individuals who regularly exercise. It is these individuals that can tolerate more grain carbohydrates. Whole unrefined grains, as the study suggests, are nearly always preferable to refined grains. What the study does not review, largely because they are unaware of it, is that your metabolic type, just like their insulin level, controls how readily one converts excess carbohydrate to fat. Those who are "carb" types can tolerate far more grains than "protein" types, nearly all of who will benefit from a near exclusion of grains, even whole grains. If you haven’t read The Metabolic Typing Diet, I would strongly encourage you to do so. It has become one of the foundations of the nutritional therapy that we provide in our office. Related Articles: Scientist Questions Benefits of Low Fat Diets Fructose is Not an Acceptable Sugar Killer Sugar! Suicide With A Spoon