Do Saturated Fats and Trans Fats Cause Type-2 Diabetes?

Question: I am having a very difficult time defending the benefits of a diet rich in saturated fat. I attend Bastyr University, a naturopathic medical school, and through all my nutriton classes, saturated fat has been deemed unhealthy and detrimental to one’s health. For instance, my Diet and Nutrient Therapy class professor cites a 2002 article in the British Journal of Nutrition, “Acute effects of a meal fatty acid composition on insulin sensitivity in healthy post-menopausal women”1 as showing that saturated fat reduces insulin sensitivity, thereby contributing to type-2 diabetes. He also cited a 2002 study in Diabetologia, “Substituting dietary saturated fat with polyunsaturated fat changes abdominal fat distribution and improves insulin sensitivy.”2 I would be very interested in your comments on these studies and your views on saturated fat and diabetes.

Answer: Insulin insensitivity has been postulated to be the underlying factor for type-2 diabetes; that is, a condition in which the receptors for insulin on the cell membranes do not work very well. In type-2 diabetes, the pancreas secretes insulin, but since the receptors don’t work, the bloodstream contains chronic high levels of insulin and glucose, while little gets into the cell where it is needed.

In the first study cited by your professor, four groups of subjects were fed a breakfast of rice krispies, banana, skimmed milk, “Nesquik” (presumably a chocolate drink) and something called “Marvel,” along with 40 grams of fat. The first group got mostly saturated fat from palm oil, the second group got mostly monounsaturated fat from olive oil, the third group got mostly omega-6 fatty acids from safflower oil and the fourth group got mostly omega-3 fatty acids from a combination of safflower oil and fish oil.

Levels of insulin and glucose in the blood were measured at intervals after breakfast and also after a so-called low-fat lunch consisting of cheese pizza (said to contain only 5.4 grams of fat), lettuce, cucumber and tomatoes. Those given the mostly saturated palm oil had higher insulin levels at about one hour after breakfast and lunch compared to the other three groups. However, insulin levels were the same as the other groups two hours after each meal. Blood glucose levels followed a similar curve for all four groups.

This is a very poor study to justify a recommendation against saturated fat. All four groups were on a very unnatural diet high in processed foods, and the fats used do not reflect the type of fatty acid profiles that we consume in normal diets. Furthermore, the levels of insulin in the subjects were not chronically high, as one finds in type-2 diabetes, and the glucose curves were normal for all groups. The study tells us nothing about what happens in real life with people eating real food.

The second study looked at a small group of subjects—a total of 17—who were told to follow a diet rich in saturated (by using more dairy products) or polyunsaturated fatty acids (by using more oils and spreads) for five weeks. When on the saturated fat diet, the subjects had a slightly lower measure of insulin sensitivity but glucose levels and body mass indices were virtually identical.

Again, this study has little to do with real life. The actual amount of saturated or polyunsaturated fat (or trans fat) in each diet was not measured and the number of subjects was too small to be meaningful.

Neither of these studies tells us what happens in real life in subjects who eat a diet high in natural saturated fats compared to those whose diets contain a lot of vegetable oils. The fact that the researchers are strong in their condemnation of saturated fats after such trivial findings is strong evidence of bias.

The real problem is that recommendations to avoid saturated fats almost invariably result in people consuming more trans fats. There is no question but that the trans fats have been shown to have a detrimental effect on the incidence and treatment of type-2 diabetes. The saturated fats, on the other hand, have no effect when appropriate comparisons are made.3
Very good studies indicate that trans fats interfere with insulin receptors and therefore with insulin resistance. The saturated fats do not.4

The recommendations regarding dietary saturated fats intake versus trans fats intake for the past number of years have been very confusing to the public, and judging from the articles, also confusing to the researchers. Trans fats are mistaken by many of the health professionals for saturated fats although they are not similar in their effects on the human body, just similar in the manner of stability in the baking or cooking realm.

“So Many Nutrition Recommendations Contradictory or Compatible?” written by a major dietitian from the American Dietetic Association lists the amounts of fat and different fats that are acceptable. According to their recommendations, total fats could represent 20-35 percent of the calories in the diets of individuals as listed in the Dietary Reference Intakes, 25-35 percent as called for by the National Cholesterol Education Program, but the American Diabetes Association says that fat intake should be individualized (expert consensus). However, recommendations for the type of fat mixes the saturated fats and the trans fats, as do almost all of the writers in these organizations. The report notes that a diet with only 5 percent of the total energy from saturated fats is adequate; and yet research shows that the normal level of saturated fats in the tissues is much higher.5

Another example of inappropriate conclusions drawn from a research project comes from Colorado State University, where researchers decided that a “saturated fat byproduct” was a potential contributor to type-2 diabetes. This so-called saturated fat metabolite is ceramide. Ceramide is a lipid molecule made in the body from something called sphingosine and a fatty acid (which could be oleic acid, a so-called good fatty acid). This molecule is used to make sphingomyelin, which is one of the structural elements in the lipid bilayer, as well as being a cellular signal molecule. Sphingomyelin is one of the lipid building blocks of the myelin sheath so important for nerves.

Ceramides are interesting molecules currently being studied for a role in programmed cell death, and substances known to induce ceramide production are components such as endotoxins and chemotherapeutic agents more likely to be from the stress of trans fats than from the normal saturated fats, which are such important building blocks of our tissues. The saturated fat in the study was based on in vitro measures of free fatty acids and therefore does not represent a diet intake.6

In summary, the studies cited by your professor and others do not represent what happens in the real world with people eating real food. Think of it this way: type-2 diabetes is a new disease, one that has now reached epidemic proportions. Type-2 diabetes did not exist 100 years ago when our diets were very rich in saturated fats. Type-2 diabetes appeared when trans fats came into the diet, and has become epidemic as people are eating more and more foods containing trans fats. And since we know that trans fats interfere with insulin receptors in the cells, it is clear that the blame lies with new industrial fats, not traditional saturated fats.

REFERENCES

  1. Robertson MD and others. Acute effects of meal fatty acid composition on insulin sensitivity in healthy post-menopausal women. British Journal of Nutrition 2002 88, 635-640.
  2. Summers LK and others. Diabetologia 2002 mar;45(3):369-77.
  3. Hu FB and others. Diet lifestyle and the risk of type 2 diabetes mellitus in women. New England Journal of Medicine 2001, 345: 790-7; American Journal of Clinical Nutrition June 2001, 73: 1001-1002, 019-1020.)
  4. Research by Barnard, Dennis, University of Maryland and USDA.
  5. Marion J, Franz, MS,RD,LD,CDAE, Task Force Chair, ADA.
  6. Chavez JA and others. Acid ceramidase overexpression prevents the inhibitory effects of saturated fatty acids on insulin signaling. Journal of Biological Chemistry 2005 280:20148-53.

This article appeared in Wise Traditions in Food, Farming and the Healing Arts, the quarterly magazine of the Weston A. Price Foundation, Summer 2006.

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