Wednesday, May 24, 2006

Does Saturated Fat Increase Health Risks?

MSNBC carried the column of registered dietian Karen Collins last week - Saturated Fats are Worse than You Think - that set out to convince readers that consuming saturated fat increases the risk of cancer, diabetes, infertility and heart disease. On her list of foods to avoid or strictly limit - the usual suspects: red meat, full-fat dairy products and butter.

While Ms. Collins states this is based on recent findings that saturated fat increases risk, and claims it as fact, she offers no references to published studies. In her article she writes "Now research suggests that too much saturated fat may be problematic, even if your cholesterol isn’t high, because of its possible effects on insulin functions, potentially raising the risk of diabetes, cancer, ovarian disorders and other health problems."

She continues later with "One of the new studies that links saturated fat consumption with problems in proper functioning of insulin suggests that initially too much saturated fat might decrease the pancreas’s secretion of insulin. Less insulin might then cause a chain of events that leads to over-production of insulin, resistance to its functioning and ultimately to the most common form of diabetes."

I wondered, what new data was published investigating the effect of saturated fat on insulin in healthy individuals with normal cholesterol?

A quick search in was all it took to find the study that seems a likely fit with what Ms. Collins wrote. Differential effects of monounsaturated, polyunsaturated and saturated fat ingestion on glucose-stimulated insulin secretion, sensitivity and clearance in overweight and obese, non-diabetic humans is published in the June issue of Diabetologia.

An interesting study indeed, but it seems Ms. Collins committed the ultimate faux pax of many in the popular press who write about research studies - she took the study abstract and ran with it rather than take the time to read the full-text and data published to understand where the conclusions in the abstract came from.

The conclusion in the abstract stated "Oral ingestion of fats with differing degrees of saturation resulted in different effects on insulin secretion and action. PUFA ingestion resulted in an absolute reduction in insulin secretion and SFA ingestion induced insulin resistance. Failure of insulin secretion to compensate for insulin resistance implies impaired beta cell function in the SFA study."

A pretty powerful conclusion. The question begs - did the study design provide the power to extrapolate the findings to a wide population reading Ms. Collins colum?

In a word - no.

There are a number of profound limitations with the study - the study included just seven individuals; the macronutrient mix of the test beverages was insanely high in fat content providing 89% of calories (238g of fat over 24-hours) and bankrupt for protein with a mere 1.74% of calories (just 10g) consumed over the test period; one specific type of fat - palm oil - tested as the saturated fat; and each of the fat types tested - monounsaturated, polyunsaturated and saturated - had negative impacts on risk markers which were neglected in the conclusions but included in the full-text.

That doesn't mean the study doesn't have merit. In fact, there are a number of questions left unanswered that should be pursued in the future to understand the results from this study. For example:
  • did the type of saturated fat - palm oil - influence the results?
  • would butter, coconut oil or lard result in similar findings?
  • did the short-term deficiency in essential amino acids influence the results?
  • would longer-term testing find different effects with time for metabolic homeostasis?
  • would a different macronutrient mix, while remaining high in fat but adequate for essential amino acids, result in similar findings?

The researchers in this study sought to understand the effect of different fat types on metabolic markers. While tightly controlled, the sample size and number of potential confounding variables make it too small with too many questions to be a source to write a column stating that eating saturated fat will raise your risk "for diabetes, cancer, ovarian disorders and other health problems."

Simply put - the data in this study has no weight to make such an interpretation, especially when there are numerous other studies finding the exact opposite effect. Let's not forget the recent study A High Fat Diet in Obese Patients Induces Weight Loss, Leads to Improved Insulin Resistance, and Lowers Systolic Blood Pressure Despite Marked Increase in Dietary Sodium I wrote about in Researching Diet and Saturated Fats Impact on Blood Pressure and Heart Disease earlier this month!


  1. of course, the subjects in this study we not restricting their CHO intake, so all bets are off. we have to consider the possibility that SFA may induce insulin resistance when consumed in combination with a high-carb (i.e. standard american) diet.

  2. But if 89% of calories came from fat and 1.4% from protein, wouldn't carbs make up the rest? And wouldn't 10% of total calories be pretty low-carb?

  3. these people were eating their normal diets and then consumed the 89%-fat diets over a 24-hour period. this could hardly be termed a low-carb diet...